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Inverse photoemission and photoemission spectroscopic studies on sputter-annealed Ni–Mn–Sn and Ni–Mn–In surfaces
Accepted Manuscript Title: Inverse photoemission and photoemission spectroscopic studieson sputter-annealed Ni-Mn-Sn and Ni-Mn-In surfaces Author: M. Maniraj S.W. D’Souza Sandeep Singh C. Biswas S. Majumdar S.R. Barman PII: DOI: Reference:
S0368-2048(14)00227-8 http://dx.doi.org/doi:10.1016/j.elspec.2014.10.006 ELSPEC 46357
To appear in:
Journal of Electron Spectroscopy and Related Phenomena
Received date: Revised date: Accepted date:
14-7-2014 18-9-2014 13-10-2014
Please cite this article as: M. Maniraj, S.W. D’Souza, Sandeep Singh, C. Biswas, S. Majumdar, S.R. Barman, Inverse photoemission and photoemission spectroscopic studieson sputter-annealed Ni-Mn-Sn and Ni-MnIn surfaces, Journal of Electron Spectroscopy and Related Phenomena (2014), http://dx.doi.org/10.1016/j.elspec.2014.10.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights
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Comparison of inverse photoemission spectra and Korringa–Kohn–Rostoker method calculation show dominant feature is related to Mn 3d-like states. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization.
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Rigid band shift between Ni2MnIn and Ni2MnSn is observed because of band filling, due to increase in the number of 5p electrons from In to Sn.
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Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.
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*Manuscript
Inverse photoemission and photoemission spectroscopic studies on sputter-annealed Ni-Mn-Sn and Ni-Mn-In surfaces M. Maniraja,∗, S. W. D′ Souzaa , Sandeep Singhb , C. Biswasb , S. Majumdarc , S. R. Barmana a UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore, 452001, Madhya Pradesh, India of Condensed Matter Physics and Materials Science, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata, 700098 West Bengal, India c Indian Association for the Cultivation of Science, Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
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Abstract
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The electronic structure of nearly stoichiometric Ni-Mn-Sn and Ni-Mn-In surface is investigated by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated inverse photoemission spectra shows that the dominant feature is related to Mn 3d-like states. The overall shape and peak position of the theoretically obtained spectra show good agreement with the experimental ultraviolet photoemission valence band spectra. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization. Both inverse photoemission and ultraviolet photoemission study show a rigid band shift between Ni2 MnIn and Ni2 MnSn because of band filling, due to increase in the number of 5p electrons from In to Sn. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.
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Keywords: Inverse photoemission spectroscopy, Photoemission spectroscopy, Full Heusler alloy, Korriga- Kohn-Rostoker method. 1. Introduction
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The interest in ferromagnetic ternary intermetallic Heusler compounds such as Ni-Mn-X (X=Sn and In) has grown enormously in recent times because these alloys exhibit a diverse range of functional properties such as the shape memory effect, inverse magnetocaloric effect, large magnetoresistance and magnetic superelasticity.[1, 2, 3, 4, 5, 6] This has prompted many groups to study the electronic structure of these materials. Ahuja et al.[7] studied the band structure of Ni2 MnIn using the full potential linearized augmented plane wave (FPLAPW) method. They found that in the case of majority-spin states, the 3d bands of Ni and Mn atoms overlap with each other and are mostly occupied; whereas for the minority-spin states, the main contribution arises from the Ni 3d states, while the Mn 3d states have hardly any contribution. The minority-spin Mn 3d states appear above the Fermi level (E F ) with the peak around 1.2 eV. Deb et al.[8] have studied the band structure of Ni2 MnSn using FPLAPW method and found that the Ni 3d states and majority spin the Mn 3d states are mainly confined to the 0−6 eV region of the valence band. On the other hand, the minority spin Mn 3d states dominate the lower region of the conduction band at up to about 3 eV above E F . Imada et al.[9] have performed the ultraviolet photoemission spectroscopy (UPS) studies on Ni2 MnX (X= Ga, Sn, and In). Significant changes in the spectral shape were reported between Ni2 MnGa and Ni2 MnIn, that are interpreted in terms of ∗ Corresponding
author Email address: [email protected] (M. Maniraj)
Preprint submitted to Journal of Electron Spectroscopy and Related Phenomena
the increase of the hybridization between the neighboring transition metal 3d states. An increase of the band filling has been found from Ni2 MnIn to Ni2 MnSn, which is interpreted by the increase in the number of 5p electrons from In to Sn.[9] Relatively recently, Ye et al.[10] have studied the Ni-Mn-Sn using hard x-ray photoemission and their study showed spectral weight transfer in the valence band upon the martensite phase transition. It has been reported that the Ni 3d eg states in the cubic phase systematically shift towards the Fermi energy with an increase in the number of Mn atoms substituted in the Sn sites. Furthermore, an abrupt decrease of the intensity of the Ni 3d eg states upon martensite phase transition has been observed in the vicinity of E F . Plogmann et al.[11] have studied Ni-Mn-Sn, Ni-Mn-In and many other Heusler alloys using x-ray photoelectron spectroscopy (XPS). They experimentally found that the exchange splitting in the Mn 2p3/2 spectra is related to the local magnetic moment at the Mn site. From the spin polarized density of states (DOS) calculations and Mn and Ni Lα resonant x-ray emission spectra, Yablonskikh et al.[12] reported that the spin splitting in Mn 3d shell is larger than in Ni 3d shell. Technological applications of multi-elemental systems are intimately connected with a detailed understanding of the electronic structure of the surface and its properties such as segregation, termination, relaxation and reconstruction, etc. Specifically for the multi-element system, the surface composition is highly sensitive to the surface treatment, and as a consequence the properties can be considerably different from the bulk. In our earlier studies, the surface preparation of Ni-Mn-Ga polySeptember 18, 2014
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crystalline sample was studied using sputtering and annealing method.[13, 14] Bulk composition was attained at the surface after annealing at appropriate temperature, although sputtering changes surface composition. The well known 6 eV satellite of Ni metal[14] has been observed in the valence band of Ni2 MnGa, but its intensity was found to be lower than the Ni metal. The decreased intensity of the satellite feature has been explained to be due to decrease in the number of holes in the d band of Ni2 MnGa, which results in the better screening of the core-hole. In the present work, we report the effect of sputtering and annealing on the surface composition of Ni2 Mn1.4 Sn0.6 and Ni2 Mn1.3 In0.7 polycrystalline samples using XPS. Inverse photoemission spectroscopy (IPES) and UPS have been used to study the electronic structure above and below E F , respectively.
Ni 3p
Sn 4d
(a)
TA(K)
Mn 3p
intensity (arb. units)
673 623 573 523
423 373
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(b)
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2. Experimental Method
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The experiments were carried out in a µ-metal shielded stainless steel chamber at a base pressure of 5×10−11 mbar. XPS was performed using Mg Kα x-ray source (hν= 1253.6 eV) and a commercial electron energy analyzer with an overall energy resolution was about 0.8 eV. He I radiation (hν= 21.2 eV) was used for UPS measurement with an overall energy resolution of about 0.12 eV. Samples were cleaned in situ by cycles of 1.5 keV Ar+ ions sputtering at normal incidence geometry and subsequent annealing at various temperatures for 1−2 hrs. Resistive heating method was used for annealing the samples using the sample holder that is specifically designed to study the complex metals.[15] The surface composition was determined using XPS by measuring the following core-levels: Ni 3p, Mn 3p, Sn 4d, and In 4d appropriately. Since, the shallow core-level binding energies are in the same order of energy, the mean-freepath of the photoelectrons and analyzer transmission function are close to one another. The core level intensities were determined after subtracting the Mg Kα3,4 x-ray satellites[13, 16] and Tougard inelastic background.[17] IPES in the isochromat mode was performed by use of a Stoffel-Johnson design electron source and a CaF2 /acetone photon detector. The details of the IPES spectrometer are provided in Refs. [18, 19, 20, 21, 22]. The total energy resolution was about 0.5 eV. IPES spectrum is obtained by normalizing the measured counts by the sample current at each energy step as in our previous work.[23, 24, 25, 26] The polycrystalline samples with bulk composition of Ni2 Mn1.4 Sn0.6 and Ni2 Mn1.3 In0.7 were prepared by arc furnace melting. The details of the preparation and characterization of these specimens can be found elsewhere.[27, 28] The Ni-Mn-Sn sample used for this measurement showed about 5% Mo 3d signal compared to Ni 3p. This impurity Mo 3d peak appears at around 36 eV binding energy in Fig. 1(a), but its intensity is too less to affect the measurements presented herein. The calculations were performed using the Korriga-KohnRostoker (KKR) method.[29] The details of the calculations can be found in Refs. [30, 31]. The experimental spectra are compared with the theory following the procedures, described below. In case of UPS and XPS, all PDOS were added after multiplying with the corresponding atomic photoemission cross-
VB
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Ni Mn Sn
1.0
300
400
500
600
TA (K) Figure 1: (a) Ni 3p, Mn 3p, and Sn 4d core-level spectra and (b) variation in the surface composition of Ni-Mn-Sn as a function of annealing temperature (TA ). The bottom spectrum in (a) has been recorded after sputtering at 1.5 keV Ar+ ions at room temperature without further annealing. The spectra in (a) are staggered along the vertical axis for the clarity of presentation.
section and then multiplied with the Fermi function. Thereafter, it was convoluted with a Voigt function: the full width at half maximum (FWHM) of the Gaussian component, which represents the instrumental resolution. The FWHM of the energy dependent Lorentzian that represents the life-time broadening was taken as 0.3E, where E is the energy with respect to the EF .[32] In the case of IPES, procedure is the same and we have considered cross-section as unity, due to lack of availability of values. Furthermore, we have not considered the inelastic background and the matrix element effect in any of these cases. 3. Results and Discussion As discussed in the previous section, we have treated the surface by repeated cycles of sputtering and annealing with the aim of obtaining a stoichiometric surface even though the 2
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Ni-Mn-Sn
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Mn:Ni 0.6
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Ni Mn In
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total Mn 3d Ni 3d
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0.5 300
500
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600 650 TA(K)
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Figure 2: Variation in the surface composition of Ni-Mn-In as a function of TA determined from Ni 3p, Mn 3p, and In 4d core-level spectra.
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Figure 3: IPES spectra measured at room temperature for different surface compositions of Ni-Mn-Sn as indicated by Mn:Ni ratio. The convoluted total DOS and PDOS are also shown. The convoluted total DOS and PDOS are also shown.
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bulk is non-stoichiometric. The surface composition of NiMn-Sn as a function of annealing temperature (TA ) is shown in Fig. 1. After sputtering with Ar+ ions of 1.5 keV, the surface became Ni-rich.[33] The sputtering yield of Mn and Sn is higher than Ni in Ni-Mn-Sn and hence the sputtered surface is Ni-rich.[33] This result is very similar to Ni2 MnGa and Mn2 NiGa, discussed in Ref. [34]. However, when the sputtered surface is annealed to high temperature, Mn segregates to the surface that results in the near stoichiometric composition. The measured XPS core-level spectra as a function of TA are shown in Fig. 1(a) and it clearly depicts that when TA is increased, the Ni 3p peak intensity decreases, whereas Sn 3d and Mn 3p peak intensities increase. The trend of relative composition change is clearly observable in Fig. 1(b), which shows the surface composition as a function of TA . We found that TA of about 580 K is sufficient to obtain the near stoichiometric surface composition (Fig. 1(b)).[33] For TA > 600 K, the composition remains nearly unchanged and the Mn excess composition is not attained. This behavior is contrary to what has been observed for Ni2 MnGa(100), which showed Mn excess surface composition for TA higher than that required to achieve the stoichiometric surface.[35] Similar experiment performed on Ni-Mn-In show that TA of about 500−700 K is sufficient to attain the stoichiometric composition (Fig. 2). For higher TA , Ni-Mn-In also behaves similar to Ni-Mn-Sn i.e. Mn excess bulk composition is not achieved. The possible reason for not attaining the Mn excess bulk composition in case of both Ni-Mn-Sn and Ni-MnIn is possibly related to evaporative loss of Mn at the surface for higher TA , since these alloys contain excess Mn in the bulk. The IPES spectra measured as a function of Ni-Mn-Sn surface composition are shown in Fig. 3. For Mn:Ni= 0.6, the spectrum exhibits a broad peak centered at about 2 eV above E F (tick mark in Fig. 3). On the other hand, for Mn:Ni= 0.5, the spectral shape becomes nearly flat. The calculated spectrum based on the DOS from Ref. [31] shows a clear step like Fermi edge that originates due to similar contributions from Ni 3d and
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Mn 3d states (Fig. 3). On the other hand, the peak observed at 1 eV above E F is mainly dominated by the Mn 3d minority spin states. A comparison between the calculated and experimental spectra show that the broad peak observed around 2 eV in the experimental IPES spectrum can be related to the Mn 3d dominated peak at 1 eV in the calculated spectrum. Similar amount of peak shift between the experiment and calculated spectra have been noticed in Ni-Mn-Ga.[36] As discussed in Ref. [36], a possible reason for this shift is electron-electron correlation effect that is accounted for only in an average way by the theory. Figure 4 shows the composition dependent experimental IPES spectra of Ni-Mn-In and the calculated IPES spectrum along with contribution from Mn and Ni 3d partial DOS (PDOS) from Ref. [30]. The spectral shape of the experimental IPES spectra for Mn:Ni= 0.4 to 0.5 is nearly flat and are nearly identical to one another (Fig. 4). The spectral shape is not remarkably different compared to Ni-Mn-Sn (compare Figs. 3 and 4) because at this photon energy the valence band is dominated by Ni and Mn 3d states. The calculated spectra show that the main peak is dominated by the Mn 3d minority states[7], whereas the near Fermi edge has similar contributions from Ni 3d and Mn 3d states. Interestingly, the peak position observed in the calculated spectra of Ni2 MnIn (shown by an arrow in Fig. 4) is located at around 1.2 eV above E F , which is about 0.2 eV higher compared to that of peak position (1 eV) observed for Ni2 MnSn (Fig. 3). Such peak shift between Ni2 MnIn and Ni2 MnSn can be related to rigid band effect since the outer shell configuration of In is 5s2 5p1 and Sn is 5s2 5p2 . Thus, the extra 5p electron in the valence band causes a shift of E F and thus the peak observed for Ni2 MnSn appears at lower energy than that of Ni2 MnIn when their E F are aligned. A way to examine
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Ni2MnSn Mn:Ni 0.49 0.52 0.57
total Mn 3d Ni 3d
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1 2 energy (eV; EF=0)
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DOS total Ni 3d Mn 3d
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intensity (arb. units)
intensity (arb. units)
Ni-Mn-In
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Figure 4: IPES spectra measured at room temperature for different surface compositions of Ni-Mn-In, as indicated by the Mn:Ni ratio. The convoluted total DOS and PDOS are also shown.
Ni2MnIn Mn:Ni 0.42 0.43 0.47
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whether the shift is indeed related to the rigid band effect is to study the occupied states. If same amount of shift is also observed for the occupied peaks, it would confirm the rigid band shift. A comparison of the experimental UPS spectra of Ni2 MnSn and Ni2 MnIn measured at room temperature austenite phase is shown in Fig. 5. The experimental spectra are compared with the calculated valence band based on the calculated DOS from Refs. [30, 31]. For calculating the valence band, we have considered the Ni 3d and Mn 3d PDOS. This is because the atomic photoemission cross-sections for these states at excitation energy of hν= 21.2 eV (He I) is 3.98 and 5.34 Mb for Ni 3d and Mn 3d, respectively and these values are much larger compared to Ni 4s, Mn 4s, and Sn and In 4s, p and d states.[37] The UPS valence band spectrum for Ni-Mn-Sn and NiMn-In exhibits a broad main peak centered at around 1.4 eV (tick) and -1.2 eV (arrow), respectively (Fig. 5). The position of this peak as well as the spectral shape are in good agreement with previous work reported in the literature[9], where stoichiometric Ni2 MnSn and Ni2 MnIn bulk specimens were studied. Since the UPS spectral shape depends sensitively on composition as evidenced in Ni-Mn-Ga[35], this agreement shows that the present surface (Mn:Ni ≈ 0.5) is indeed stoichiometric. For both Ni2 MnSn and Ni2 MnIn, the peak position and spectral shape of the calculated spectrum show excellent agreement with the experimental UPS spectrum. The calculated PDOS[30, 31] shows that the UPS valence band is largely dominated by Ni 3d related states with peaks at -1.5 and -0.4 eV for Ni2 MnSn and -1.25 and -0.2 eV for Ni2 MnIn (Fig. 5). The Mn 3d states exhibit a peak at -1.25 and -1.1 eV for Ni2 MnSn and Ni2 MnIn, respectively. Thus, the main peak in the UPS spectrum arises due to Ni 3d−Mn 3d hybridized states. This is evident from
-3
-2.5
-2 -1.5 -1 -0.5 binding energy (eV; EF=0)
0
0.5
Figure 5: He I UPS valence band spectra measured for different surface compositions of Ni-Mn-Sn and Ni-Mn-In, as indicated by the Mn:Ni ratio. The calculated valence band for Ni2 MnSn and Ni2 MnIn and Ni 3d and Mn 3d contributions to the calculated valence band are shown.
the composition dependent spectra of Ni-Mn-Sn, which show peak broading and intensity increase at about 0.4 eV with decreasing Mn:Ni ratio, due to increasing Ni concentration. Moreover, in both Ni-Mn-Sn and Ni-Mn-In at the vicinity of E F , spectral intensity systematically increases with decreasing Mn:Ni ratio due to changes in Ni and Mn concentration and consequent change in hybridization of Ni 3d and Mn 3d states (Fig. 5). A shift of about 0.2 eV in the main peak towards higher binding energy is observed between Ni2 MnSn (1.4 eV) and Ni2 MnIn (1.2 eV). A similar shift of the main peak between the calculated IPES spectra of Ni2 MnSn (Fig. 3) and Ni2 MnIn (Fig. 4) is observed. This confirms that this effect is due to the rigid band shift, as discussed above. The experimental XPS valence band spectra of Ni2 MnSn and Ni2 MnIn and the calculated XPS valence band spectra based on DOS from Refs. [30, 31] are shown in Fig. 6. In the calculation of the XPS valence band, we have considered only the PDOS of Ni 3d and Mn 3d. This is because the atomic photoemission cross-sections of Ni 3d (0.01 Mb), Mn 3d (0.003 Mb) for excitation energy of 1253.6 eV is higher than the other states such as Sn 5s (0.001 Mb) and In 5s (0.001 Mb).[37] Moreover, the PDOS of Sn and In is small compared to Ni 3d and Mn 4
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Mn 2p3/2
Ni2MnSn
Ni2MnIn
Ni2MnIn - 644
-8
-6 -4 -2 binding energy (eV; EF=0)
0
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- 636
Figure 7: Mn 2p3/2 core-level peak of Ni2 MnSn and Ni2 MnIn recorded by using hν= 1253.6 eV.
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intensity (arb. units)
expt. total Ni 3d Mn 3d
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pared to Ni2 MnIn. A previous XPS study performed for many Heusler alloys shows the exchange splitting of the Mn 2p3/2 that varies for different alloys.[11, 12, 40] The exchange splitting has been shown to be linearly related to the the local magnetic moment of Mn.[11] Mn 2p3/2 peak of Ni2 MnSn and Ni2 MnIn are shown in Fig. 7. In both the cases, the peak is broad and is asymmetric toward the higher binding energy side. The spectra have been acquired using the best possible energy resolution by setting the pass energy of the analyzer to 10 eV. However, although there is a hint of the exchange splitting as shown by the ticks, the exchange split peaks are not clearly resolved possibly due to limited energy resolution of XPS that is typically 0.8 eV. For Ni2 MnZ (Z= Ga, Sn, and In) Heusler alloys, it is known that localized magnetic moment is associated with the Mn atom. Therefore, the exchange splitting of Ni2 MnGa is expected to be similar to Ni2 MnIn or Ni2 MnSn. The comparison of the Mn 2p3/2 core-level spectra of Ni2 MnSn and Ni2 MnIn with Mn 2p3/2 core-level spectra of Ni2 MnGa (not shown) recorded with high resolution (0.3 eV) hard x-ray photoemission spectroscopy[41] shows clear evidence of exchange splitting with ∆ex of about 1 eV, and the resolved exchange split peaks coincide in binding energy with those of Ni2 MnIn and Ni2 MnSn (shown by ticks in Fig. 7). This confirms that the exchange splitting exists in both Ni2 MnSn and Ni2 MnIn and it is of the same order as Ni2 MnGa. This is because the calculated magnetic moments at Mn site for Ni2 MnZ, Z= Ga, Sn, and In is 3.6, 3.45, and 3.44 µB , respectively.[12, 42] This result is in agreement with Yablonskikh et al.[12] who have calculated the exchange splitting of Mn 2p3/2 for Ni2 MnSn and Ni2 MnIn and reported that magnitude of the exchange splitting is nearly same for both the samples. Further, they show experimentally that the shape of the Mn 2p3/2 peak for Ni2 MnSn and Ni2 MnIn is nearly same and has exchange splitting of about 1 eV which in good agreement with present results. The exchange splitting of the Mn 3s core level also pro-
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Figure 6: XPS valence band of Ni2 MnSn and Ni2 MnIn measured at room temperature in the austenite phase. The calculated total DOS and PDOS are also shown.
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3d. Thus the contribution from Sn and In related states at the valence band for excitation energy of 1253.6 eV is negligible. A single broad peak centered at -1.4 and -1.2 eV below E F is observed in the XPS valence band for Ni2 MnSn and Ni2 MnIn, respectively (Fig. 6). The calculated spectrum (Fig. 6) is dominated by Ni 3d contribution, since it has an order of magnitude larger cross-section than Mn 3d states. In both the cases, the Mn 3d states consist of two main features located at around 1 and -3 eV. In case of Ni2 MnIn, a broad feature appears at around 6 eV (tick in Fig. 6). The calculated spectra show that in this energy range, no peak is expected and this is not associated with Sn PDOS. Thus, this feature might be related to the well known 6 eV Ni satellite.[14, 38, 39] This satellite feature has been also observed for Ni-Mn-Ga.[14] The origin of the 6 eV satellite in the Ni 2p core-level photoemission spectra has been explained by considering interaction of 3d states with 4s conduction states. The ground state of Ni is 3d9 4s. When a photo-hole is created, the Coulomb interaction pulls down the conduction band due to screening. As a consequence, there is a possibility of adding charge into the 3d band by the transfer of an electron from the 4s conduction band. This transfer results in 2p5 3d10 configuration. If 4s band produce the screening rather than the 3d band i.e. 4s conduction electron transfer does not occur, then the final state has two holes, one at core level by photoemission and another at the d band. This results in 2p5 3d9 configuration. The latter configuration is the excited state and produces the satellite. The excitation energy of this state is 6 eV higher than the main line. In the case of valence band, the main feature arises due to the 3d9 4s configuration, whereas the satellite arises due to the 3d8 4s2 configuration.[39] However, the 6 eV satellite is almost absent in Ni2 MnSn (Fig. 6) which indicates presence of more efficient screening in Ni2 MnSn com-
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a rigid band shift between Ni2 MnSn and Ni2 MnIn because of band filling, due to increase in the number of 5p electrons from In to Sn. This observation is supported by our theoretical calculations. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting.
Ni2MnSn
Acknowledgment
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Aparna Chakrabarti is thanked for useful discussions and suggestions. This work has been funded by the Department of Science and Technology Project SP/S2/M-06/99. M.M. and S.W.D. is thankful to Council of Scientific and Industrial Research, India for research fellowship.
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References
[1] Y. Sutou, Y. Imano, N. Koeda, T. Omori, R. Kainuma, K. Ishida, and K. Oikawa, Appl. Phys. Lett. 85, 4358 (2004). [2] T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya, I. Ma˜nosa and A. Planes, Nature Mater. 4, 450 (2005). [3] S. Y. Yu, Z. H. Liu, G. D. Liu, J. L. Chen, Z. X. Cao, G. H. Wu, B. Zhang, and X. X. Zhang, Appl. Phys . Lett. 89, 162503 (2006). [4] K. Koyama, H. Okada, K. Watanabe, T. Kanomata, R. Kainuma, W. Ito, K. Oikawa, and K. Ishida, Appl. Phys. Lett. 89, 182510 (2006). [5] T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya, L. Manosa, A. Planes, E. Suard, and B. Ouladdiaf, Phys. Rev. B 75, 104414 (2007). [6] S. Singh and C. Biswas, Appl. Phys. Lett. 98, 212101 (2011). [7] B. L. Ahuja, A. Dashora, N. L. Heda, K. R. Priolkar, L. Vadkhiya, M. Itou, N. Lobo, Y. Sakurai, A. Chakrabarti, S. Singh and S. R. Barman, J. Phys.: Condens. Matter 22, 446001 (2010). [8] A. Deb, N. Hiraoka, M. Itou, Y. Sakurai, M. Onodera, and N. Sakai, Phys. Rev. B 63, 205115 (2001). [9] S. Imada, A. Yamasaki, K. Kusuda, A. Higashiya, A. Irizawa, A. Sekiyama, T. Kanomata, and S. Suga, J. Elec. Spec. Rel. Phen. 156-158 433 (2007). [10] M. Ye, A. Kimura, Y. Miura, M. Shirai, Y. T. Cui, K. Shimada, H. Namatame, M. Taniguchi, S. Ueda, K. Kobayashi, R. Kainuma, T. Shishido, K. Fukushima, and T. Kanomata, Phys. Rev. Lett. 104, 176401 (2010). [11] S. Plogmann, T. Schlath¨olter, J. Braun, M. Neumann, Yu. M. Yarmoshenko, M. V. Yablonskikh, E. I. Shreder, E. Z. Kurmaev, A. Wrona ´ and A. Slebarski, Phys. Rev. B 60, 6428 (1999). [12] M. V. Yablonskikh, J. Braun, M. T. Kuchel, A. V. Postnikov, J. D. Denlinger, E. I. Shreder, Y. M. Yarmoshenko, M. Neumann, and A. Moewes, Phys. Rev. B 74, 085103 (2006). [13] C. Biswas and S. R. Barman, Appl. Surf. Sci. 252, 3380 (2006). [14] C. Biswas, S. Banik, A. K. Shukla, R. S. Dhaka, V. Ganesan, and S. R. Barman, Surf. Sci. 600, 3749 (2006). [15] R. S. Dhaka, A. K. Shukla, M. Maniraj, S. W. D’Souza, J. Nayak, and S. R. Barman, Rev. Sci. Instrum. 81, 043907 (2010). [16] M. Cardona, L. Ley, Photoemission in Solids, Springer-Verlag, Berlin, 1978. [17] S. Tougaard, Surf. Sci. 216, 343 (1989). [18] S. Banik, A. K. Shukla, and S. R. Barman, Rev. Sci. Instrum. 76, 066102 (2005). [19] A. K. Shukla, S. Banik, and S. R. Barman, Current Science 90, 490 (2006). [20] M. Maniraj, S. W. D’Souza, J. Nayak, A. Rai, S. Singh, B. N. Raja Sekhar, and S. R. Barman, Rev. Sci. Instrum. 82, 093901 (2011). [21] M. Maniraj, B. N. Raja Sekhar, and S. R. Barman, Rev. Sci. Instrum. 83, 046107 (2012). [22] M. Maniraj and S. R. Barman, Rev. Sci. Instrum. 85, 033301 (2014). [23] R. Kundu, P. Mishra, B. R. Sekhar, M. Maniraj, and S. R. Barman, Phys. B 407, 827 (2012). [24] S. K. Pandey, A. Kumar, S. Banik, A. K. Shukla, S. R. Barman, and A. V. Pimpale, Phys. Rev. B 77, 113104 (2008). [25] R. S. Dhaka, S. Banik, A. K. Shukla, V. Vyas, A. Chakrabarti, S. R. Barman, B. L. Ahuja, and B. K. Sharma, Phys. Rev. B 78, 073107 (2008).
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Figure 8: Mn 3s XPS core-level spectrum of Ni2 MnSn and Ni2 MnIn. The exchange splitting i.e. the separation between 7 S and 5 S peaks is indicated by ticks.
cr
intensity (arb. units)
Mn 3s
Ac ce pt e
d
M
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vides a quantitative estimate of the average local magnetic moment of Mn atoms. The Mn 3s peak is split into two components due to the exchange interaction between the 3s core hole and the unpaired electrons in the 3d orbital.[43, 44] This means that when an electron is emitted by photoemission, the 3s level is left with spin of s= ±1/2. This electron couples in either parallel or anti-parallel orientation with the total unpaired electron spin in the valence 3d orbital. This interaction gives rise to the exchange splitting and leads to two final states, referred as 7 S and 5 S. The energy difference between these two states is the exchange splitting and is good measure of the d band moment. The experimentally measured Mn 3s spectrum for Ni2 MnSn and Ni2 MnIn are shown in Fig. 8. The separation of 7 S and 5 S is about 4.6 eV and 5.4 eV for Ni2 MnSn and Ni2 MnIn, respectively. From the high resolution Mn 3s XPS core-level study carried out for various Mn based samples, McFeely et al.[45] reported a linear relation between the exchange splitting and local moment of Mn. From that relation, they reported that the exchange splitting of 4.08 eV corresponds to the local moment of 2.5 µB for α-Mn.[45] Using the same relation, for exchange splitting of about 4.6 eV and 5.4 eV for Ni2 MnSn and Ni2 MnIn, we obtain about 3 µB and 3.8 µB as the Mn local moment, respectively. This approximate estimate is in good agreement with the Mn magnetic moment calculated for Ni2 MnSn (3.45 µB ) and Ni2 MnIn (3.44 µB ). 4. Conclusion
We report the electronic structure of stoichiometric Ni2 MnSn and Ni2 MnIn surface by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated IPES spectra shows that the dominant feature is the Mn 3d states. The spectral shape and peak position of the calculated valence band show good agreement with the experimental UPS valence band. The observed changes in the composition dependent UPS are related to changes in hybridization between Ni and Mn d states. Both IPES and UPS study show 6
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[26] M. K. Dalai, P. Pal, R. Kundu, B. R. Sekhar, S. Banik, A. K. Shukla, S. R. Barman and C. Martin, Physica B 405, 186 (2010). [27] S. Chatterjee, S. Giri, S. K. De, and S. Majumdar, Phys. Rev. B 79, 092410 (2009). [28] S. Singh, I. Glavatskyy, C. Biswas, J. Alloys Compd., (accepted). [29] Ebert H et al., the Munich SPRKKR package, version 5.4, http://olymp.cup.uni-muenchen.de/ak/ebert/SPRKKR. [30] K. R. Priolkar, P. A. Bhobe, D. N. Lobo, S. W. D’Souza, S. R. Barman, A. Chakrabarti, and S. Emura, Phys. Rev. B 87, 144412 (2013). [31] S. W. D’Souza et al., (unpublished). [32] D. D. Sarma, N. Shanthi, S. R. Barman, N. Hamada, H. Sawada and K. Terakura, Phys. Rev. Lett., 75 1126 (1995); A. Fujimori and A. Minami, Phys. Rev. B, 30 957 (1984); S. R. Barman and D. D. Sarma, Phys. Rev. B, 51 4007(1995). [33] M. Maniraj, S. W. D’Souza, S. Majumdar, A. Chakrabarti, and S. R. Barman, AIP Conf. Proc. 1447, 819 (2012). [34] R. S. Dhaka, S. W. D’Souza, M. Maniraj, A. Chakrabarti, D. L. Schlagel, T. A. Lograsso, and S. R. Barman, Surf. Sci. 603, 1999 (2009). [35] S. W. D’Souza, J. Nayak, M. Maniraj, Abhishek Rai, R. S. Dhaka, S. R. Barman, D. L. Schlagel, T. A. Lograsso, and Aparna Chakrabarti, Surf. Sci. 606, 130 (2012). [36] S. Banik, A. Chakrabarti, U. Kumar, P. K. Mukhopadhyay, A. M. Awasthi, R. Ranjan, J. Schneider, B. L. Ahuja, and S. R. Barman, Phys. Rev. B 74, 085110 (2006). [37] J. J. Yeh, I. Lindau, Atomic Data Nucl. Data Tables 32, 1 (1985). [38] A. Bosch, H. Feil, G. A. Sawatzky, N. Martensson, Solid State Commun. 41, 355 (1982). [39] S. Hufner, Photoelectron Spectroscopy Principles and Application, 3rd Edition, Springer-Verlag, Berlin, 2003. [40] Y. M. Yarmoshenko, M. I. Katsnelson, E. I. Shreder, E. Z. Kurmaev, A. Slebarski, S. Plogmann, T. Schlatholter, J. Braun, and M. Neumann, Eur. Phys. J. B 2, 1 (1998). [41] S. Singh et al., unpublished. [42] P. J. Webster, K. R. A. Ziebeck, S. L. Town, and M. S. Peak, Philos. Mag. B 49, 295 (1984). [43] C. S. Fadley, D. A. Shirley, A. J. Freeman, P. S. Bagus, and J. V. Mallow, Phys. Rev. Lett. 23, 1397 (1969). [44] C. S. Fadley and D. A. Shirley, Phys. Rev. A 2, 1109 (1970). [45] F. R. McFeely, S. P. Kowalczyk, L. Ley and D. Shirley, Solid State Commun. 15, 1051 (1974).
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S0368-2048(14)00227-8 http://dx.doi.org/doi:10.1016/j.elspec.2014.10.006 ELSPEC 46357
To appear in:
Journal of Electron Spectroscopy and Related Phenomena
Received date: Revised date: Accepted date:
14-7-2014 18-9-2014 13-10-2014
Please cite this article as: M. Maniraj, S.W. D’Souza, Sandeep Singh, C. Biswas, S. Majumdar, S.R. Barman, Inverse photoemission and photoemission spectroscopic studieson sputter-annealed Ni-Mn-Sn and Ni-MnIn surfaces, Journal of Electron Spectroscopy and Related Phenomena (2014), http://dx.doi.org/10.1016/j.elspec.2014.10.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights
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Comparison of inverse photoemission spectra and Korringa–Kohn–Rostoker method calculation show dominant feature is related to Mn 3d-like states. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization.
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Rigid band shift between Ni2MnIn and Ni2MnSn is observed because of band filling, due to increase in the number of 5p electrons from In to Sn.
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Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.
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*Manuscript
Inverse photoemission and photoemission spectroscopic studies on sputter-annealed Ni-Mn-Sn and Ni-Mn-In surfaces M. Maniraja,∗, S. W. D′ Souzaa , Sandeep Singhb , C. Biswasb , S. Majumdarc , S. R. Barmana a UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore, 452001, Madhya Pradesh, India of Condensed Matter Physics and Materials Science, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata, 700098 West Bengal, India c Indian Association for the Cultivation of Science, Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
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Abstract
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The electronic structure of nearly stoichiometric Ni-Mn-Sn and Ni-Mn-In surface is investigated by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated inverse photoemission spectra shows that the dominant feature is related to Mn 3d-like states. The overall shape and peak position of the theoretically obtained spectra show good agreement with the experimental ultraviolet photoemission valence band spectra. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization. Both inverse photoemission and ultraviolet photoemission study show a rigid band shift between Ni2 MnIn and Ni2 MnSn because of band filling, due to increase in the number of 5p electrons from In to Sn. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.
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Keywords: Inverse photoemission spectroscopy, Photoemission spectroscopy, Full Heusler alloy, Korriga- Kohn-Rostoker method. 1. Introduction
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The interest in ferromagnetic ternary intermetallic Heusler compounds such as Ni-Mn-X (X=Sn and In) has grown enormously in recent times because these alloys exhibit a diverse range of functional properties such as the shape memory effect, inverse magnetocaloric effect, large magnetoresistance and magnetic superelasticity.[1, 2, 3, 4, 5, 6] This has prompted many groups to study the electronic structure of these materials. Ahuja et al.[7] studied the band structure of Ni2 MnIn using the full potential linearized augmented plane wave (FPLAPW) method. They found that in the case of majority-spin states, the 3d bands of Ni and Mn atoms overlap with each other and are mostly occupied; whereas for the minority-spin states, the main contribution arises from the Ni 3d states, while the Mn 3d states have hardly any contribution. The minority-spin Mn 3d states appear above the Fermi level (E F ) with the peak around 1.2 eV. Deb et al.[8] have studied the band structure of Ni2 MnSn using FPLAPW method and found that the Ni 3d states and majority spin the Mn 3d states are mainly confined to the 0−6 eV region of the valence band. On the other hand, the minority spin Mn 3d states dominate the lower region of the conduction band at up to about 3 eV above E F . Imada et al.[9] have performed the ultraviolet photoemission spectroscopy (UPS) studies on Ni2 MnX (X= Ga, Sn, and In). Significant changes in the spectral shape were reported between Ni2 MnGa and Ni2 MnIn, that are interpreted in terms of ∗ Corresponding
author Email address: [email protected] (M. Maniraj)
Preprint submitted to Journal of Electron Spectroscopy and Related Phenomena
the increase of the hybridization between the neighboring transition metal 3d states. An increase of the band filling has been found from Ni2 MnIn to Ni2 MnSn, which is interpreted by the increase in the number of 5p electrons from In to Sn.[9] Relatively recently, Ye et al.[10] have studied the Ni-Mn-Sn using hard x-ray photoemission and their study showed spectral weight transfer in the valence band upon the martensite phase transition. It has been reported that the Ni 3d eg states in the cubic phase systematically shift towards the Fermi energy with an increase in the number of Mn atoms substituted in the Sn sites. Furthermore, an abrupt decrease of the intensity of the Ni 3d eg states upon martensite phase transition has been observed in the vicinity of E F . Plogmann et al.[11] have studied Ni-Mn-Sn, Ni-Mn-In and many other Heusler alloys using x-ray photoelectron spectroscopy (XPS). They experimentally found that the exchange splitting in the Mn 2p3/2 spectra is related to the local magnetic moment at the Mn site. From the spin polarized density of states (DOS) calculations and Mn and Ni Lα resonant x-ray emission spectra, Yablonskikh et al.[12] reported that the spin splitting in Mn 3d shell is larger than in Ni 3d shell. Technological applications of multi-elemental systems are intimately connected with a detailed understanding of the electronic structure of the surface and its properties such as segregation, termination, relaxation and reconstruction, etc. Specifically for the multi-element system, the surface composition is highly sensitive to the surface treatment, and as a consequence the properties can be considerably different from the bulk. In our earlier studies, the surface preparation of Ni-Mn-Ga polySeptember 18, 2014
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crystalline sample was studied using sputtering and annealing method.[13, 14] Bulk composition was attained at the surface after annealing at appropriate temperature, although sputtering changes surface composition. The well known 6 eV satellite of Ni metal[14] has been observed in the valence band of Ni2 MnGa, but its intensity was found to be lower than the Ni metal. The decreased intensity of the satellite feature has been explained to be due to decrease in the number of holes in the d band of Ni2 MnGa, which results in the better screening of the core-hole. In the present work, we report the effect of sputtering and annealing on the surface composition of Ni2 Mn1.4 Sn0.6 and Ni2 Mn1.3 In0.7 polycrystalline samples using XPS. Inverse photoemission spectroscopy (IPES) and UPS have been used to study the electronic structure above and below E F , respectively.
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The experiments were carried out in a µ-metal shielded stainless steel chamber at a base pressure of 5×10−11 mbar. XPS was performed using Mg Kα x-ray source (hν= 1253.6 eV) and a commercial electron energy analyzer with an overall energy resolution was about 0.8 eV. He I radiation (hν= 21.2 eV) was used for UPS measurement with an overall energy resolution of about 0.12 eV. Samples were cleaned in situ by cycles of 1.5 keV Ar+ ions sputtering at normal incidence geometry and subsequent annealing at various temperatures for 1−2 hrs. Resistive heating method was used for annealing the samples using the sample holder that is specifically designed to study the complex metals.[15] The surface composition was determined using XPS by measuring the following core-levels: Ni 3p, Mn 3p, Sn 4d, and In 4d appropriately. Since, the shallow core-level binding energies are in the same order of energy, the mean-freepath of the photoelectrons and analyzer transmission function are close to one another. The core level intensities were determined after subtracting the Mg Kα3,4 x-ray satellites[13, 16] and Tougard inelastic background.[17] IPES in the isochromat mode was performed by use of a Stoffel-Johnson design electron source and a CaF2 /acetone photon detector. The details of the IPES spectrometer are provided in Refs. [18, 19, 20, 21, 22]. The total energy resolution was about 0.5 eV. IPES spectrum is obtained by normalizing the measured counts by the sample current at each energy step as in our previous work.[23, 24, 25, 26] The polycrystalline samples with bulk composition of Ni2 Mn1.4 Sn0.6 and Ni2 Mn1.3 In0.7 were prepared by arc furnace melting. The details of the preparation and characterization of these specimens can be found elsewhere.[27, 28] The Ni-Mn-Sn sample used for this measurement showed about 5% Mo 3d signal compared to Ni 3p. This impurity Mo 3d peak appears at around 36 eV binding energy in Fig. 1(a), but its intensity is too less to affect the measurements presented herein. The calculations were performed using the Korriga-KohnRostoker (KKR) method.[29] The details of the calculations can be found in Refs. [30, 31]. The experimental spectra are compared with the theory following the procedures, described below. In case of UPS and XPS, all PDOS were added after multiplying with the corresponding atomic photoemission cross-
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TA (K) Figure 1: (a) Ni 3p, Mn 3p, and Sn 4d core-level spectra and (b) variation in the surface composition of Ni-Mn-Sn as a function of annealing temperature (TA ). The bottom spectrum in (a) has been recorded after sputtering at 1.5 keV Ar+ ions at room temperature without further annealing. The spectra in (a) are staggered along the vertical axis for the clarity of presentation.
section and then multiplied with the Fermi function. Thereafter, it was convoluted with a Voigt function: the full width at half maximum (FWHM) of the Gaussian component, which represents the instrumental resolution. The FWHM of the energy dependent Lorentzian that represents the life-time broadening was taken as 0.3E, where E is the energy with respect to the EF .[32] In the case of IPES, procedure is the same and we have considered cross-section as unity, due to lack of availability of values. Furthermore, we have not considered the inelastic background and the matrix element effect in any of these cases. 3. Results and Discussion As discussed in the previous section, we have treated the surface by repeated cycles of sputtering and annealing with the aim of obtaining a stoichiometric surface even though the 2
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Figure 2: Variation in the surface composition of Ni-Mn-In as a function of TA determined from Ni 3p, Mn 3p, and In 4d core-level spectra.
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Figure 3: IPES spectra measured at room temperature for different surface compositions of Ni-Mn-Sn as indicated by Mn:Ni ratio. The convoluted total DOS and PDOS are also shown. The convoluted total DOS and PDOS are also shown.
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bulk is non-stoichiometric. The surface composition of NiMn-Sn as a function of annealing temperature (TA ) is shown in Fig. 1. After sputtering with Ar+ ions of 1.5 keV, the surface became Ni-rich.[33] The sputtering yield of Mn and Sn is higher than Ni in Ni-Mn-Sn and hence the sputtered surface is Ni-rich.[33] This result is very similar to Ni2 MnGa and Mn2 NiGa, discussed in Ref. [34]. However, when the sputtered surface is annealed to high temperature, Mn segregates to the surface that results in the near stoichiometric composition. The measured XPS core-level spectra as a function of TA are shown in Fig. 1(a) and it clearly depicts that when TA is increased, the Ni 3p peak intensity decreases, whereas Sn 3d and Mn 3p peak intensities increase. The trend of relative composition change is clearly observable in Fig. 1(b), which shows the surface composition as a function of TA . We found that TA of about 580 K is sufficient to obtain the near stoichiometric surface composition (Fig. 1(b)).[33] For TA > 600 K, the composition remains nearly unchanged and the Mn excess composition is not attained. This behavior is contrary to what has been observed for Ni2 MnGa(100), which showed Mn excess surface composition for TA higher than that required to achieve the stoichiometric surface.[35] Similar experiment performed on Ni-Mn-In show that TA of about 500−700 K is sufficient to attain the stoichiometric composition (Fig. 2). For higher TA , Ni-Mn-In also behaves similar to Ni-Mn-Sn i.e. Mn excess bulk composition is not achieved. The possible reason for not attaining the Mn excess bulk composition in case of both Ni-Mn-Sn and Ni-MnIn is possibly related to evaporative loss of Mn at the surface for higher TA , since these alloys contain excess Mn in the bulk. The IPES spectra measured as a function of Ni-Mn-Sn surface composition are shown in Fig. 3. For Mn:Ni= 0.6, the spectrum exhibits a broad peak centered at about 2 eV above E F (tick mark in Fig. 3). On the other hand, for Mn:Ni= 0.5, the spectral shape becomes nearly flat. The calculated spectrum based on the DOS from Ref. [31] shows a clear step like Fermi edge that originates due to similar contributions from Ni 3d and
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Mn 3d states (Fig. 3). On the other hand, the peak observed at 1 eV above E F is mainly dominated by the Mn 3d minority spin states. A comparison between the calculated and experimental spectra show that the broad peak observed around 2 eV in the experimental IPES spectrum can be related to the Mn 3d dominated peak at 1 eV in the calculated spectrum. Similar amount of peak shift between the experiment and calculated spectra have been noticed in Ni-Mn-Ga.[36] As discussed in Ref. [36], a possible reason for this shift is electron-electron correlation effect that is accounted for only in an average way by the theory. Figure 4 shows the composition dependent experimental IPES spectra of Ni-Mn-In and the calculated IPES spectrum along with contribution from Mn and Ni 3d partial DOS (PDOS) from Ref. [30]. The spectral shape of the experimental IPES spectra for Mn:Ni= 0.4 to 0.5 is nearly flat and are nearly identical to one another (Fig. 4). The spectral shape is not remarkably different compared to Ni-Mn-Sn (compare Figs. 3 and 4) because at this photon energy the valence band is dominated by Ni and Mn 3d states. The calculated spectra show that the main peak is dominated by the Mn 3d minority states[7], whereas the near Fermi edge has similar contributions from Ni 3d and Mn 3d states. Interestingly, the peak position observed in the calculated spectra of Ni2 MnIn (shown by an arrow in Fig. 4) is located at around 1.2 eV above E F , which is about 0.2 eV higher compared to that of peak position (1 eV) observed for Ni2 MnSn (Fig. 3). Such peak shift between Ni2 MnIn and Ni2 MnSn can be related to rigid band effect since the outer shell configuration of In is 5s2 5p1 and Sn is 5s2 5p2 . Thus, the extra 5p electron in the valence band causes a shift of E F and thus the peak observed for Ni2 MnSn appears at lower energy than that of Ni2 MnIn when their E F are aligned. A way to examine
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Figure 4: IPES spectra measured at room temperature for different surface compositions of Ni-Mn-In, as indicated by the Mn:Ni ratio. The convoluted total DOS and PDOS are also shown.
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whether the shift is indeed related to the rigid band effect is to study the occupied states. If same amount of shift is also observed for the occupied peaks, it would confirm the rigid band shift. A comparison of the experimental UPS spectra of Ni2 MnSn and Ni2 MnIn measured at room temperature austenite phase is shown in Fig. 5. The experimental spectra are compared with the calculated valence band based on the calculated DOS from Refs. [30, 31]. For calculating the valence band, we have considered the Ni 3d and Mn 3d PDOS. This is because the atomic photoemission cross-sections for these states at excitation energy of hν= 21.2 eV (He I) is 3.98 and 5.34 Mb for Ni 3d and Mn 3d, respectively and these values are much larger compared to Ni 4s, Mn 4s, and Sn and In 4s, p and d states.[37] The UPS valence band spectrum for Ni-Mn-Sn and NiMn-In exhibits a broad main peak centered at around 1.4 eV (tick) and -1.2 eV (arrow), respectively (Fig. 5). The position of this peak as well as the spectral shape are in good agreement with previous work reported in the literature[9], where stoichiometric Ni2 MnSn and Ni2 MnIn bulk specimens were studied. Since the UPS spectral shape depends sensitively on composition as evidenced in Ni-Mn-Ga[35], this agreement shows that the present surface (Mn:Ni ≈ 0.5) is indeed stoichiometric. For both Ni2 MnSn and Ni2 MnIn, the peak position and spectral shape of the calculated spectrum show excellent agreement with the experimental UPS spectrum. The calculated PDOS[30, 31] shows that the UPS valence band is largely dominated by Ni 3d related states with peaks at -1.5 and -0.4 eV for Ni2 MnSn and -1.25 and -0.2 eV for Ni2 MnIn (Fig. 5). The Mn 3d states exhibit a peak at -1.25 and -1.1 eV for Ni2 MnSn and Ni2 MnIn, respectively. Thus, the main peak in the UPS spectrum arises due to Ni 3d−Mn 3d hybridized states. This is evident from
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Figure 5: He I UPS valence band spectra measured for different surface compositions of Ni-Mn-Sn and Ni-Mn-In, as indicated by the Mn:Ni ratio. The calculated valence band for Ni2 MnSn and Ni2 MnIn and Ni 3d and Mn 3d contributions to the calculated valence band are shown.
the composition dependent spectra of Ni-Mn-Sn, which show peak broading and intensity increase at about 0.4 eV with decreasing Mn:Ni ratio, due to increasing Ni concentration. Moreover, in both Ni-Mn-Sn and Ni-Mn-In at the vicinity of E F , spectral intensity systematically increases with decreasing Mn:Ni ratio due to changes in Ni and Mn concentration and consequent change in hybridization of Ni 3d and Mn 3d states (Fig. 5). A shift of about 0.2 eV in the main peak towards higher binding energy is observed between Ni2 MnSn (1.4 eV) and Ni2 MnIn (1.2 eV). A similar shift of the main peak between the calculated IPES spectra of Ni2 MnSn (Fig. 3) and Ni2 MnIn (Fig. 4) is observed. This confirms that this effect is due to the rigid band shift, as discussed above. The experimental XPS valence band spectra of Ni2 MnSn and Ni2 MnIn and the calculated XPS valence band spectra based on DOS from Refs. [30, 31] are shown in Fig. 6. In the calculation of the XPS valence band, we have considered only the PDOS of Ni 3d and Mn 3d. This is because the atomic photoemission cross-sections of Ni 3d (0.01 Mb), Mn 3d (0.003 Mb) for excitation energy of 1253.6 eV is higher than the other states such as Sn 5s (0.001 Mb) and In 5s (0.001 Mb).[37] Moreover, the PDOS of Sn and In is small compared to Ni 3d and Mn 4
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Figure 7: Mn 2p3/2 core-level peak of Ni2 MnSn and Ni2 MnIn recorded by using hν= 1253.6 eV.
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expt. total Ni 3d Mn 3d
2
pared to Ni2 MnIn. A previous XPS study performed for many Heusler alloys shows the exchange splitting of the Mn 2p3/2 that varies for different alloys.[11, 12, 40] The exchange splitting has been shown to be linearly related to the the local magnetic moment of Mn.[11] Mn 2p3/2 peak of Ni2 MnSn and Ni2 MnIn are shown in Fig. 7. In both the cases, the peak is broad and is asymmetric toward the higher binding energy side. The spectra have been acquired using the best possible energy resolution by setting the pass energy of the analyzer to 10 eV. However, although there is a hint of the exchange splitting as shown by the ticks, the exchange split peaks are not clearly resolved possibly due to limited energy resolution of XPS that is typically 0.8 eV. For Ni2 MnZ (Z= Ga, Sn, and In) Heusler alloys, it is known that localized magnetic moment is associated with the Mn atom. Therefore, the exchange splitting of Ni2 MnGa is expected to be similar to Ni2 MnIn or Ni2 MnSn. The comparison of the Mn 2p3/2 core-level spectra of Ni2 MnSn and Ni2 MnIn with Mn 2p3/2 core-level spectra of Ni2 MnGa (not shown) recorded with high resolution (0.3 eV) hard x-ray photoemission spectroscopy[41] shows clear evidence of exchange splitting with ∆ex of about 1 eV, and the resolved exchange split peaks coincide in binding energy with those of Ni2 MnIn and Ni2 MnSn (shown by ticks in Fig. 7). This confirms that the exchange splitting exists in both Ni2 MnSn and Ni2 MnIn and it is of the same order as Ni2 MnGa. This is because the calculated magnetic moments at Mn site for Ni2 MnZ, Z= Ga, Sn, and In is 3.6, 3.45, and 3.44 µB , respectively.[12, 42] This result is in agreement with Yablonskikh et al.[12] who have calculated the exchange splitting of Mn 2p3/2 for Ni2 MnSn and Ni2 MnIn and reported that magnitude of the exchange splitting is nearly same for both the samples. Further, they show experimentally that the shape of the Mn 2p3/2 peak for Ni2 MnSn and Ni2 MnIn is nearly same and has exchange splitting of about 1 eV which in good agreement with present results. The exchange splitting of the Mn 3s core level also pro-
an
Figure 6: XPS valence band of Ni2 MnSn and Ni2 MnIn measured at room temperature in the austenite phase. The calculated total DOS and PDOS are also shown.
Ac ce pt e
d
M
3d. Thus the contribution from Sn and In related states at the valence band for excitation energy of 1253.6 eV is negligible. A single broad peak centered at -1.4 and -1.2 eV below E F is observed in the XPS valence band for Ni2 MnSn and Ni2 MnIn, respectively (Fig. 6). The calculated spectrum (Fig. 6) is dominated by Ni 3d contribution, since it has an order of magnitude larger cross-section than Mn 3d states. In both the cases, the Mn 3d states consist of two main features located at around 1 and -3 eV. In case of Ni2 MnIn, a broad feature appears at around 6 eV (tick in Fig. 6). The calculated spectra show that in this energy range, no peak is expected and this is not associated with Sn PDOS. Thus, this feature might be related to the well known 6 eV Ni satellite.[14, 38, 39] This satellite feature has been also observed for Ni-Mn-Ga.[14] The origin of the 6 eV satellite in the Ni 2p core-level photoemission spectra has been explained by considering interaction of 3d states with 4s conduction states. The ground state of Ni is 3d9 4s. When a photo-hole is created, the Coulomb interaction pulls down the conduction band due to screening. As a consequence, there is a possibility of adding charge into the 3d band by the transfer of an electron from the 4s conduction band. This transfer results in 2p5 3d10 configuration. If 4s band produce the screening rather than the 3d band i.e. 4s conduction electron transfer does not occur, then the final state has two holes, one at core level by photoemission and another at the d band. This results in 2p5 3d9 configuration. The latter configuration is the excited state and produces the satellite. The excitation energy of this state is 6 eV higher than the main line. In the case of valence band, the main feature arises due to the 3d9 4s configuration, whereas the satellite arises due to the 3d8 4s2 configuration.[39] However, the 6 eV satellite is almost absent in Ni2 MnSn (Fig. 6) which indicates presence of more efficient screening in Ni2 MnSn com-
5
Page 6 of 16
a rigid band shift between Ni2 MnSn and Ni2 MnIn because of band filling, due to increase in the number of 5p electrons from In to Sn. This observation is supported by our theoretical calculations. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting.
Ni2MnSn
Acknowledgment
7
S
- 95
- 90
Aparna Chakrabarti is thanked for useful discussions and suggestions. This work has been funded by the Department of Science and Technology Project SP/S2/M-06/99. M.M. and S.W.D. is thankful to Council of Scientific and Industrial Research, India for research fellowship.
5
ip t
Ni2MnIn
S - 85
- 80
-75
binding energy (eV)
References
[1] Y. Sutou, Y. Imano, N. Koeda, T. Omori, R. Kainuma, K. Ishida, and K. Oikawa, Appl. Phys. Lett. 85, 4358 (2004). [2] T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya, I. Ma˜nosa and A. Planes, Nature Mater. 4, 450 (2005). [3] S. Y. Yu, Z. H. Liu, G. D. Liu, J. L. Chen, Z. X. Cao, G. H. Wu, B. Zhang, and X. X. Zhang, Appl. Phys . Lett. 89, 162503 (2006). [4] K. Koyama, H. Okada, K. Watanabe, T. Kanomata, R. Kainuma, W. Ito, K. Oikawa, and K. Ishida, Appl. Phys. Lett. 89, 182510 (2006). [5] T. Krenke, E. Duman, M. Acet, E. F. Wassermann, X. Moya, L. Manosa, A. Planes, E. Suard, and B. Ouladdiaf, Phys. Rev. B 75, 104414 (2007). [6] S. Singh and C. Biswas, Appl. Phys. Lett. 98, 212101 (2011). [7] B. L. Ahuja, A. Dashora, N. L. Heda, K. R. Priolkar, L. Vadkhiya, M. Itou, N. Lobo, Y. Sakurai, A. Chakrabarti, S. Singh and S. R. Barman, J. Phys.: Condens. Matter 22, 446001 (2010). [8] A. Deb, N. Hiraoka, M. Itou, Y. Sakurai, M. Onodera, and N. Sakai, Phys. Rev. B 63, 205115 (2001). [9] S. Imada, A. Yamasaki, K. Kusuda, A. Higashiya, A. Irizawa, A. Sekiyama, T. Kanomata, and S. Suga, J. Elec. Spec. Rel. Phen. 156-158 433 (2007). [10] M. Ye, A. Kimura, Y. Miura, M. Shirai, Y. T. Cui, K. Shimada, H. Namatame, M. Taniguchi, S. Ueda, K. Kobayashi, R. Kainuma, T. Shishido, K. Fukushima, and T. Kanomata, Phys. Rev. Lett. 104, 176401 (2010). [11] S. Plogmann, T. Schlath¨olter, J. Braun, M. Neumann, Yu. M. Yarmoshenko, M. V. Yablonskikh, E. I. Shreder, E. Z. Kurmaev, A. Wrona ´ and A. Slebarski, Phys. Rev. B 60, 6428 (1999). [12] M. V. Yablonskikh, J. Braun, M. T. Kuchel, A. V. Postnikov, J. D. Denlinger, E. I. Shreder, Y. M. Yarmoshenko, M. Neumann, and A. Moewes, Phys. Rev. B 74, 085103 (2006). [13] C. Biswas and S. R. Barman, Appl. Surf. Sci. 252, 3380 (2006). [14] C. Biswas, S. Banik, A. K. Shukla, R. S. Dhaka, V. Ganesan, and S. R. Barman, Surf. Sci. 600, 3749 (2006). [15] R. S. Dhaka, A. K. Shukla, M. Maniraj, S. W. D’Souza, J. Nayak, and S. R. Barman, Rev. Sci. Instrum. 81, 043907 (2010). [16] M. Cardona, L. Ley, Photoemission in Solids, Springer-Verlag, Berlin, 1978. [17] S. Tougaard, Surf. Sci. 216, 343 (1989). [18] S. Banik, A. K. Shukla, and S. R. Barman, Rev. Sci. Instrum. 76, 066102 (2005). [19] A. K. Shukla, S. Banik, and S. R. Barman, Current Science 90, 490 (2006). [20] M. Maniraj, S. W. D’Souza, J. Nayak, A. Rai, S. Singh, B. N. Raja Sekhar, and S. R. Barman, Rev. Sci. Instrum. 82, 093901 (2011). [21] M. Maniraj, B. N. Raja Sekhar, and S. R. Barman, Rev. Sci. Instrum. 83, 046107 (2012). [22] M. Maniraj and S. R. Barman, Rev. Sci. Instrum. 85, 033301 (2014). [23] R. Kundu, P. Mishra, B. R. Sekhar, M. Maniraj, and S. R. Barman, Phys. B 407, 827 (2012). [24] S. K. Pandey, A. Kumar, S. Banik, A. K. Shukla, S. R. Barman, and A. V. Pimpale, Phys. Rev. B 77, 113104 (2008). [25] R. S. Dhaka, S. Banik, A. K. Shukla, V. Vyas, A. Chakrabarti, S. R. Barman, B. L. Ahuja, and B. K. Sharma, Phys. Rev. B 78, 073107 (2008).
us
Figure 8: Mn 3s XPS core-level spectrum of Ni2 MnSn and Ni2 MnIn. The exchange splitting i.e. the separation between 7 S and 5 S peaks is indicated by ticks.
cr
intensity (arb. units)
Mn 3s
Ac ce pt e
d
M
an
vides a quantitative estimate of the average local magnetic moment of Mn atoms. The Mn 3s peak is split into two components due to the exchange interaction between the 3s core hole and the unpaired electrons in the 3d orbital.[43, 44] This means that when an electron is emitted by photoemission, the 3s level is left with spin of s= ±1/2. This electron couples in either parallel or anti-parallel orientation with the total unpaired electron spin in the valence 3d orbital. This interaction gives rise to the exchange splitting and leads to two final states, referred as 7 S and 5 S. The energy difference between these two states is the exchange splitting and is good measure of the d band moment. The experimentally measured Mn 3s spectrum for Ni2 MnSn and Ni2 MnIn are shown in Fig. 8. The separation of 7 S and 5 S is about 4.6 eV and 5.4 eV for Ni2 MnSn and Ni2 MnIn, respectively. From the high resolution Mn 3s XPS core-level study carried out for various Mn based samples, McFeely et al.[45] reported a linear relation between the exchange splitting and local moment of Mn. From that relation, they reported that the exchange splitting of 4.08 eV corresponds to the local moment of 2.5 µB for α-Mn.[45] Using the same relation, for exchange splitting of about 4.6 eV and 5.4 eV for Ni2 MnSn and Ni2 MnIn, we obtain about 3 µB and 3.8 µB as the Mn local moment, respectively. This approximate estimate is in good agreement with the Mn magnetic moment calculated for Ni2 MnSn (3.45 µB ) and Ni2 MnIn (3.44 µB ). 4. Conclusion
We report the electronic structure of stoichiometric Ni2 MnSn and Ni2 MnIn surface by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated IPES spectra shows that the dominant feature is the Mn 3d states. The spectral shape and peak position of the calculated valence band show good agreement with the experimental UPS valence band. The observed changes in the composition dependent UPS are related to changes in hybridization between Ni and Mn d states. Both IPES and UPS study show 6
Page 7 of 16
Ac ce pt e
d
M
an
us
cr
ip t
[26] M. K. Dalai, P. Pal, R. Kundu, B. R. Sekhar, S. Banik, A. K. Shukla, S. R. Barman and C. Martin, Physica B 405, 186 (2010). [27] S. Chatterjee, S. Giri, S. K. De, and S. Majumdar, Phys. Rev. B 79, 092410 (2009). [28] S. Singh, I. Glavatskyy, C. Biswas, J. Alloys Compd., (accepted). [29] Ebert H et al., the Munich SPRKKR package, version 5.4, http://olymp.cup.uni-muenchen.de/ak/ebert/SPRKKR. [30] K. R. Priolkar, P. A. Bhobe, D. N. Lobo, S. W. D’Souza, S. R. Barman, A. Chakrabarti, and S. Emura, Phys. Rev. B 87, 144412 (2013). [31] S. W. D’Souza et al., (unpublished). [32] D. D. Sarma, N. Shanthi, S. R. Barman, N. Hamada, H. Sawada and K. Terakura, Phys. Rev. Lett., 75 1126 (1995); A. Fujimori and A. Minami, Phys. Rev. B, 30 957 (1984); S. R. Barman and D. D. Sarma, Phys. Rev. B, 51 4007(1995). [33] M. Maniraj, S. W. D’Souza, S. Majumdar, A. Chakrabarti, and S. R. Barman, AIP Conf. Proc. 1447, 819 (2012). [34] R. S. Dhaka, S. W. D’Souza, M. Maniraj, A. Chakrabarti, D. L. Schlagel, T. A. Lograsso, and S. R. Barman, Surf. Sci. 603, 1999 (2009). [35] S. W. D’Souza, J. Nayak, M. Maniraj, Abhishek Rai, R. S. Dhaka, S. R. Barman, D. L. Schlagel, T. A. Lograsso, and Aparna Chakrabarti, Surf. Sci. 606, 130 (2012). [36] S. Banik, A. Chakrabarti, U. Kumar, P. K. Mukhopadhyay, A. M. Awasthi, R. Ranjan, J. Schneider, B. L. Ahuja, and S. R. Barman, Phys. Rev. B 74, 085110 (2006). [37] J. J. Yeh, I. Lindau, Atomic Data Nucl. Data Tables 32, 1 (1985). [38] A. Bosch, H. Feil, G. A. Sawatzky, N. Martensson, Solid State Commun. 41, 355 (1982). [39] S. Hufner, Photoelectron Spectroscopy Principles and Application, 3rd Edition, Springer-Verlag, Berlin, 2003. [40] Y. M. Yarmoshenko, M. I. Katsnelson, E. I. Shreder, E. Z. Kurmaev, A. Slebarski, S. Plogmann, T. Schlatholter, J. Braun, and M. Neumann, Eur. Phys. J. B 2, 1 (1998). [41] S. Singh et al., unpublished. [42] P. J. Webster, K. R. A. Ziebeck, S. L. Town, and M. S. Peak, Philos. Mag. B 49, 295 (1984). [43] C. S. Fadley, D. A. Shirley, A. J. Freeman, P. S. Bagus, and J. V. Mallow, Phys. Rev. Lett. 23, 1397 (1969). [44] C. S. Fadley and D. A. Shirley, Phys. Rev. A 2, 1109 (1970). [45] F. R. McFeely, S. P. Kowalczyk, L. Ley and D. Shirley, Solid State Commun. 15, 1051 (1974).
7
Page 8 of 16
Figure
Ni 3p
Sn 4d
(a)
TA(K)
Mn 3p
intensity (arb. units)
673
VB
623
ip t
573 523
cr
473
us
423
an
373
- 40 -20 binding energy (eV)
2.5 2.0 1.5
d
0
(b)
Ac ce p
surface composition
te
- 60
M
1.5 keV
Ni Mn Sn
1.0
300
400
500
600 Page 9 of 16
TA (K)
an
us
cr
ip t
Figure
1.5 1.0
M d te
2.0
Ac ce p
surface composition
2.5
Ni Mn In
0.5 300
500
550
600 650 TA(K)
700 Page 10 of 16
Ni-Mn-Sn
an M d te
Mn:Ni 0.6
Ac ce p
intensity (arb. units)
us
cr
ip t
Figure
0.52
total Mn 3d Ni 3d
0.5 theory -1
0
1 2 3 energy (eV; EF=0)
4 Page 11 of 16
Ni-Mn-In
an M d te
Mn:Ni
Ac ce p
intensity (arb. units)
us
cr
ip t
Figure
0.5
total Mn 3d Ni 3d
0.45 0.4
theory -1
0
1 2 energy (eV; EF=0)
3
4 Page 12 of 16
Figure
d te
Ac ce p
DOS total Ni 3d Mn 3d
M
an
intensity (arb. units)
us
cr
ip t
Ni2MnSn Mn:Ni 0.49 0.52 0.57
-3
-2.5
-2 -1.5 -1 -0.5 binding energy (eV; EF=0)
Ni2MnIn Mn:Ni 0.42 0.43 0.47
0
0.5
Page 13 of 16
ip t
Figure
cr us an te
d
M
Ni2MnSn
Ac ce p
intensity (arb. units)
expt. total Ni 3d Mn 3d
Ni2MnIn
-10
-8
-6 -4 -2 binding energy (eV; EF=0)
0
2 Page 14 of 16
Mn 2p3/2
d te
Ni2MnSn
Ac ce p
intensity (arb. units)
M
an
us
cr
ip t
Figure
Ni2MnIn
- 644
- 642 - 640 - 638 binding energy (eV)
- 636 Page 15 of 16
Ni2MnIn
- 95
- 90
d
Mn 3s
te
Ni2MnSn
Ac ce p
intensity (arb. units)
M
an
us
cr
ip t
Figure
7
S
5
S - 85
- 80
-75 Page 16 of 16
binding energy (eV)