- Email: [email protected]
Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy
Accepted Manuscript Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy
T.T. Lin, X.F. Dai, X.M. Zhang, H.P. Zhang, G.F. Chen, G.D. Liu PII:
S0749-6036(18)31118-2
DOI:
10.1016/j.spmi.2018.06.064
Reference:
YSPMI 5799
To appear in:
Superlattices and Microstructures
Received Date:
26 May 2018
Accepted Date:
28 June 2018
Please cite this article as: T.T. Lin, X.F. Dai, X.M. Zhang, H.P. Zhang, G.F. Chen, G.D. Liu, Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy, Superlattices and Microstructures (2018), doi: 10.1016/j.spmi.2018.06.064
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.
ACCEPTED MANUSCRIPT
Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy T.T. Lina,b, X.F. Daia, X.M. Zhanga, H.P. Zhanga, G.F. Chena, G.D. Liua,b,* a
School of Material Sciences and Engineering, Hebei University of Technology,
Tianjin, P. R. China. b
School of Physics and Electronic Engineering, Chongqing Normal University,
Chongqing, P. R. China. *Corresponding authors. Email address: [email protected] (G. D. Liu), Address for correspondence: Building 8, 1st Road, DingZiGu Hongqiao zone, Tianjin, P. R. China. Abstract The CoFeTiAl1-xSix (x=3.125%) compound with Heusler structure was studied by theory and experiment. An unexpected diluted magnetism is found with a Curie temperature of 100 K. The calculated electronic structures show that the spin-splitting of DOS only occurs in p-like the states achieved by p-d hybridization near Fermi level and leads to the ferromagnetism when the Si content is lower than 6%. The magnetic moment is not localized on any atom but distributed in a region with the doped Si atom as the center. An anomalous hall effect is observed, which confirms the ferromagnetism in Si-doped CoFeTiAl alloy. A magnetoresistance of 0.375% for CoFeTiAl1-xSix is observed at 2 K.
Keywords: Magnetic materials; Crystal structure; Heusler alloy; Semiconductor
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1. Introduction Diluted magnetic semiconductors (DMSs) are believed to pave the way to develop both the spin and the charge of carriers [1,2]. In DMSs, there is mostly p-d exchange interaction between the itinerant carriers and the local magnetic ions. DMSs are sensitive to magnetic field, so their physical properties can be controlled by changing the intensity of magnetic field. In the current, there has been a rapidly growing interest in the field of DMSs, due to their potential applications in electronic devices. The magnetism in most of DMSs is achieved by doping magnetic elements, therefore magnetism is mostly localized around magnetic ions. Beside doping magnetic elements, introducing vacancies has been another way to achieve DMSs [3-7], for example, the DMS in oxygen-vacancied ZnO [3]. Zhu et al. investigated the effect of vacancies in half-Heusler semiconductors NiTiSn and CoTiSb [4] and found that magnetism is localized around vacancies. In 2016, we reported the anti-site-induced diluted magnetism in CoFeTiAl Heusler alloy, where magnetism also is localized at the anti-site atoms [8]. To our best knowledge, the magnetism of known DMSs is local, and occurs around doped elements. In this paper, we investigate the diluted magnetic properties of nonmagnetic Si doped semiconductor CoFeTiAl alloy. We find that the diluted magnetism, which is induced by the doped Si element, has a strong p-state itinerant character, instead of the localization around magnetic ions. Based on the itinerant magnetism model, the p carriers are easier to be controlled by applying magnetic field, which is desirable for the
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magnetic control in DMS-based devices. 2. Computational details and experimental methods The arc-melt method was used to prepare CoFeTiAl1-xSix (x=0 and 3.125%). Then, precursor ingots were encapsulated under Ar in quartz glass tubes and annealed at 1273 K for 8 days. The structure of all the samples was determined using powder x-ray diffraction (XRD). The magnetization curves and transport properties were measured using a Physical Property Measurement System. The electronic structures and magnetic properties of CoFeTiAl1-xSix (x=0 and 3.125%) compounds were calculated using the CASTEP package [9]. The interaction between ions and electrons was described by ultrasoft pseudopotentials [10]. The electronic exchange-correlation energy was treated under the generalized-gradient approximation (GGA) [11,12]. For the quaternary Heusler structure, Co atoms occupy the A(0,0,0) site, Fe atoms occupy the C(1/ 2,1/2,1/2) site, Ti atoms occupy the B(1/4,1/4,1/4) site and Al atoms occupy the D(3/4,3/4,3/4) site. We use 2×2×2 supercells containing 32 primitive cells to simulate the dilute limit of the magnetic system. 216 k-points were used in the irreducible Brillouin and the cut-off energy was chosen as 400 eV. 3. Results and discussion Fig.1 shows the XRD patterns of the CoFeTiAl1-xSix compounds with x=0 and 3.125%. The (111) and (200) peaks indicate that a highly-ordered quaternary Heusler structure can be clearly observed. The lattice parameters are 5.8561 Å and 5.8551 Å for
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CoFeTiAl and CoFeTiAl1-xSix, respectively. Note, the CoFeTiAl alloy with Heusler structure was previously synthesized by Basit et al. [13] and Lin et al. [14], which has been characterized as a semiconductor phase. Our XRD results of CoFeTiAl agree well with previous experiments. Fig.2(a) shows the M-H and M-T results for the CoFeTiAl1-xSix (x=3.125%) compound. In Fig.2(a), we use the original CoFeTiAl composition as the background of the measured M-H curve of CoFeTiAl1–xSix compound, so that the obtained M-H curve can reflect the net magnetization induced by Si element. The saturation magnetization is found to be 0.031µB/f.m. for CoFeTiAl1–xSix compound. Inset of Fig.2(a) shows that the hysteresis of CoFeTiAl1–xSix compound at 2 K is about 494.53 Oe, indicating a soft ferromagnetic ordering. Fig.2 (b) shows the M-T curve of CoFeTiAl1–xSix compound. One observes that the Curie temperature is 100 K for CoFeTiAl1–xSix. Anomalous Hall effect is a unique characteristic of ferromagnetic materials and DMSs. Fig.2(c) shows the Hall effect curves at different temperatures for CoFeTiAl1–x Six (x=3.125%) compound. From Fig.2(c), the nonlinear dependent between Hall resistance and magnetic field is clearly observed in low magnetic field when the temperature is lower than Curie temperature. This is another confirmation of ferromagnetism. In high magnetic field, the Hall effect is linearly dependent on the magnetic field. When the temperature is higher than Curie temperature, the CoFeTiAl1–xSix (x=3.125%) compound only shows a normal linear behavior of the Hall resistance regardless. The separated net anomalous and normal Hall effect are shown in the insets of Fig.2(c). It is
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clear that electrons are the carriers in the compound. Fig.2(d) shows the magnetoresistance behavior of CoFeTiAl1–xSix (x=3.125%) compound. A negative magnetoresistance of 0.375% is observed at 2 K for CoFeTiAl1–xSix compound. The negative magnetoresistance decreases with increasing temperature below the Curie temperature. Such magnetoresistance behavior is a typical signature of the ferromagnetic state. When the temperature is above the Curie temperature, the magnetoresistance becomes positive and linearly increases with the increasing of magnetic field, which is a typical normal magnetoresistance behavior of nonmagnetic materials. In order to illustrate the origin of the ferromagnetism, we have calculated the electronic structures of CoFeTiAl1–xSix (x=3.125%) compound, with the band structures and electronic density of states (DOS) are shown in Fig.3(b) and (d), respectively. For comparison, the band structures and DOS of the original CoFeTiAl composition are also provided, as shown in Fig.3(a) and (c). After the Si doping, one can observe that: 1) the energy gap decreases from 0.088 eV to 0.047 eV; 2) The Fermi level shifts upon and cut the valence bands in both spin channels; 3) A spin-splitting occurs near the Fermi level. The band structures indicate that CoFeTiAl1–xSix (x=3.125%) compound is ferromagnetic and the carriers are electrons, which are consistent with our experimental results. From the atomic-projected PDOS, we find that the spin-splitting mainly originates from p-d hybridization. Considering Si atom possesses one more valence electron than Al atom, so when Si replace Al in CoFeTiAl compound, the Fermi level
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would shift upon the valence bands. Furthermore, the electron number in spin-up and spin-down channels are calculated using integrated DOS. It is found that all the extra electrons from the silicon element fill in the spin-up channel, which leads to the spin-splitting. The magnetization for each supercell containing one Si atom is 1µB. So, the value of total magnetic moment per CoFeTiAl1–xSix formula unit is 0.03125µB/f.u., which is consistent with our experimental results. 4. Conclusions In summary, we investigated the diluted magnetism in CoFeTiAl1-xSix alloy both theoretically and experimentally. The CoFeTiAl1-xSix alloy crystallized in a quaternary Heusler structure, with DMS signature. The saturation magnetization is found to be 0.031µB/f.u., and the Curie temperature is 100 K. Based on computation results, it is found that the magnetization in CoFeTiAl1-xSix alloy originates from the spin splitting induced by extra p electrons provided by the non-magnetic Si element, quite different from previous DMSs. Acknowledgements This work was supported by Chongqing City Funds for Distinguished Young Scientists (No. cstc2014jcyjjq50003), the Program for Leading Talents in Science and Technology Innovation of Chongqing City (No. CSTCKJCXLJRC19), Natural Science Foundation of Tianjin City (No.16JCYBJC17200).
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References [1] P. Sharma, A. Gupta, K.V. Rao, F.J. Owens, R. Sharmaa, R. Ahuja, J.M.O. Guillen, B. Johansson, G.A. Gehring, Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO, Nat. Mater. 2 (2003) 673. [2] H. Ohno, Making nonmagnetic semiconductors ferromagnetic, Science 281 (1998) 951. [3] J.B. Yi, C.C. Lim, G.Z. Xing, H.M. Fan, L.H. Van, S.L. Huang, K.S. Yang, X.L. Huang, X.B. Qin, B.Y. Wang, T. Wu, L. Wang, H.T. Zhang, X.Y. Gao, T. Liu, A.T.S. Wee, Y.P. Feng and J. Ding, Ferromagnetism in dilute magnetic semiconductors through defect engineering: Li-doped ZnO, Phys. Rev. Lett. 104 (2010) 137201. [4] Z.Y. Zhu, Y.C. Cheng and U. Schwingenschlӧgl, Vacancy induced half-metallicity in half-Heusler semiconductors, Phys. Rev. B 84 (2011) 113201. [5] H. Gu, Y.Z. Jiang, Y.B. Xu and M. Yan, Evidence of the defect-induced ferromagnetism in Na and Co codoped ZnO, Appl. Phys. Lett. 98 (2011) 012502. [6] H. S. Saini, M. Singh, A. H. Reshak and M. K. Kashyap, Accounting oxygen vacancy for half-metallicity and magnetism in Fe-doped CeO2 dilute magnetic oxide, Comp. Mater. Sci. 74 (2013) 114-118. [7] X.G. Gao, B.Y. Man, C. Zhang, J.C. Leng, Y.L. Xu, Q. Wang, M. Zhang and Y. Meng, The important role of Ga vacancies in the ferromagnetic GaN thin films, J. Alloy. Compd. 699 (2017) 596-600.
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[8] T.T. Lin, X.F. Dai, L.Y. Wang, X.F. Liu, Y.T. Cui and G.D. Liu, Anti-site-induced diluted magnetism in semiconductive CoFeTiAl alloy, J. Alloy. Compd. 657 (2016) 519-525. [9] M.C. Payne, M.P. Teter, D.C. Allan, T.A. A.rias, and J.D. Joannopoolous, Iterative minimization techniques for ab initio total-energy calculations: molecular dynamics and conjugate gradients, Rev. Mod. Phys. 64 (1992) 1065. [10] D. Vanderbilt, Soft self-consistent pseudopotentials in a generalized eigenvalue formalism, Phys. Rev. B 41 (1990) 7892. [11] E. Wimmer, H. Krakauer, M. Weinert, A.J. Freeman, Full-potential self-consistent linearized-augmented-plane-wave method for calculating the electronic structure of molecules and surfaces: O2 molecule, Phys. Rev. B 24 (1981) 864. [12] J.P. Perdew, Y. Wang, Density-functional approximation for the correlation energy of the inhomogeneous electron gas, Phys. Rev. B 33 (1986) 8800. [13] L. Basit, Gerhard H. Fecher, S. Chadov, B. Balke and C. Felser, Eur. Quaternary Heusler compounds without inversion symmetry: CoFe1+xTi1-xAl and CoMn1+xV1-xAl, J. Inorg. Chem. 26 (2011) 3950-3954. [14] T.T. Lin, X.F. Dai, J.X. Zhao, L.W. Wang, X.T. Wang, Y.T. Cui and G.D. Liu, The structural, electronic and magnetic properties for the transition process between nonmagnetic and magnetic states in CoFe1+xTi1-xAl, J. Alloy. J. Alloy. Compd. 684 (2016) 143-150.
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Figure captions: Fig. 1. X-ray diffraction patterns of CoFeTiAl1-xSix (x=0 and 3.125%) compounds. Fig. 2. (a) The M-H curves measured at 2K and (b) M-T curve in an induction field of 100Oe for the CoFeTiAl1-xSix (x=3.125%). The inset shows the hysteresis on an enlarged scale. (c) Hall resistivity as a function of magnetic field measured at different temperatures for CoFeTiAl1-xSix. The insets are the separated net anomalous and normal Hall effect. (d) Magnetoresistivity measured at different temperatures for CoFeTiAl1xSix.
Fig. 3. The calculated band structures of the (a) CoFeTiAl and (b) CoFeTiAl1-xSix (x=3.125%). Spin-resolved density states (DOS) of (c) CoFeTiAl and (d) CoFeTiAl1xSix (x=3.125%).
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Highlights (for review) • The CoFeTiAl1-xSix (x=3.125%) compound with Heusler structure was synthesized at 300 K. • The diluted magnetism in the compound can be achieved by doping nonmagnetic Si atom. • The magnetism is not localized on any atom but distributed in a region with the doped Si atom as the center. • An anomalous Hall effect is observed, which confirms the ferromagnetism in Si-doped CoFeTiAl alloy.
T.T. Lin, X.F. Dai, X.M. Zhang, H.P. Zhang, G.F. Chen, G.D. Liu PII:
S0749-6036(18)31118-2
DOI:
10.1016/j.spmi.2018.06.064
Reference:
YSPMI 5799
To appear in:
Superlattices and Microstructures
Received Date:
26 May 2018
Accepted Date:
28 June 2018
Please cite this article as: T.T. Lin, X.F. Dai, X.M. Zhang, H.P. Zhang, G.F. Chen, G.D. Liu, Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy, Superlattices and Microstructures (2018), doi: 10.1016/j.spmi.2018.06.064
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.
ACCEPTED MANUSCRIPT
Nonmagnetic element induced novel ferromagnetism in CoFeTiAl quaternary Heusler alloy T.T. Lina,b, X.F. Daia, X.M. Zhanga, H.P. Zhanga, G.F. Chena, G.D. Liua,b,* a
School of Material Sciences and Engineering, Hebei University of Technology,
Tianjin, P. R. China. b
School of Physics and Electronic Engineering, Chongqing Normal University,
Chongqing, P. R. China. *Corresponding authors. Email address: [email protected] (G. D. Liu), Address for correspondence: Building 8, 1st Road, DingZiGu Hongqiao zone, Tianjin, P. R. China. Abstract The CoFeTiAl1-xSix (x=3.125%) compound with Heusler structure was studied by theory and experiment. An unexpected diluted magnetism is found with a Curie temperature of 100 K. The calculated electronic structures show that the spin-splitting of DOS only occurs in p-like the states achieved by p-d hybridization near Fermi level and leads to the ferromagnetism when the Si content is lower than 6%. The magnetic moment is not localized on any atom but distributed in a region with the doped Si atom as the center. An anomalous hall effect is observed, which confirms the ferromagnetism in Si-doped CoFeTiAl alloy. A magnetoresistance of 0.375% for CoFeTiAl1-xSix is observed at 2 K.
Keywords: Magnetic materials; Crystal structure; Heusler alloy; Semiconductor
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1. Introduction Diluted magnetic semiconductors (DMSs) are believed to pave the way to develop both the spin and the charge of carriers [1,2]. In DMSs, there is mostly p-d exchange interaction between the itinerant carriers and the local magnetic ions. DMSs are sensitive to magnetic field, so their physical properties can be controlled by changing the intensity of magnetic field. In the current, there has been a rapidly growing interest in the field of DMSs, due to their potential applications in electronic devices. The magnetism in most of DMSs is achieved by doping magnetic elements, therefore magnetism is mostly localized around magnetic ions. Beside doping magnetic elements, introducing vacancies has been another way to achieve DMSs [3-7], for example, the DMS in oxygen-vacancied ZnO [3]. Zhu et al. investigated the effect of vacancies in half-Heusler semiconductors NiTiSn and CoTiSb [4] and found that magnetism is localized around vacancies. In 2016, we reported the anti-site-induced diluted magnetism in CoFeTiAl Heusler alloy, where magnetism also is localized at the anti-site atoms [8]. To our best knowledge, the magnetism of known DMSs is local, and occurs around doped elements. In this paper, we investigate the diluted magnetic properties of nonmagnetic Si doped semiconductor CoFeTiAl alloy. We find that the diluted magnetism, which is induced by the doped Si element, has a strong p-state itinerant character, instead of the localization around magnetic ions. Based on the itinerant magnetism model, the p carriers are easier to be controlled by applying magnetic field, which is desirable for the
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magnetic control in DMS-based devices. 2. Computational details and experimental methods The arc-melt method was used to prepare CoFeTiAl1-xSix (x=0 and 3.125%). Then, precursor ingots were encapsulated under Ar in quartz glass tubes and annealed at 1273 K for 8 days. The structure of all the samples was determined using powder x-ray diffraction (XRD). The magnetization curves and transport properties were measured using a Physical Property Measurement System. The electronic structures and magnetic properties of CoFeTiAl1-xSix (x=0 and 3.125%) compounds were calculated using the CASTEP package [9]. The interaction between ions and electrons was described by ultrasoft pseudopotentials [10]. The electronic exchange-correlation energy was treated under the generalized-gradient approximation (GGA) [11,12]. For the quaternary Heusler structure, Co atoms occupy the A(0,0,0) site, Fe atoms occupy the C(1/ 2,1/2,1/2) site, Ti atoms occupy the B(1/4,1/4,1/4) site and Al atoms occupy the D(3/4,3/4,3/4) site. We use 2×2×2 supercells containing 32 primitive cells to simulate the dilute limit of the magnetic system. 216 k-points were used in the irreducible Brillouin and the cut-off energy was chosen as 400 eV. 3. Results and discussion Fig.1 shows the XRD patterns of the CoFeTiAl1-xSix compounds with x=0 and 3.125%. The (111) and (200) peaks indicate that a highly-ordered quaternary Heusler structure can be clearly observed. The lattice parameters are 5.8561 Å and 5.8551 Å for
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CoFeTiAl and CoFeTiAl1-xSix, respectively. Note, the CoFeTiAl alloy with Heusler structure was previously synthesized by Basit et al. [13] and Lin et al. [14], which has been characterized as a semiconductor phase. Our XRD results of CoFeTiAl agree well with previous experiments. Fig.2(a) shows the M-H and M-T results for the CoFeTiAl1-xSix (x=3.125%) compound. In Fig.2(a), we use the original CoFeTiAl composition as the background of the measured M-H curve of CoFeTiAl1–xSix compound, so that the obtained M-H curve can reflect the net magnetization induced by Si element. The saturation magnetization is found to be 0.031µB/f.m. for CoFeTiAl1–xSix compound. Inset of Fig.2(a) shows that the hysteresis of CoFeTiAl1–xSix compound at 2 K is about 494.53 Oe, indicating a soft ferromagnetic ordering. Fig.2 (b) shows the M-T curve of CoFeTiAl1–xSix compound. One observes that the Curie temperature is 100 K for CoFeTiAl1–xSix. Anomalous Hall effect is a unique characteristic of ferromagnetic materials and DMSs. Fig.2(c) shows the Hall effect curves at different temperatures for CoFeTiAl1–x Six (x=3.125%) compound. From Fig.2(c), the nonlinear dependent between Hall resistance and magnetic field is clearly observed in low magnetic field when the temperature is lower than Curie temperature. This is another confirmation of ferromagnetism. In high magnetic field, the Hall effect is linearly dependent on the magnetic field. When the temperature is higher than Curie temperature, the CoFeTiAl1–xSix (x=3.125%) compound only shows a normal linear behavior of the Hall resistance regardless. The separated net anomalous and normal Hall effect are shown in the insets of Fig.2(c). It is
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clear that electrons are the carriers in the compound. Fig.2(d) shows the magnetoresistance behavior of CoFeTiAl1–xSix (x=3.125%) compound. A negative magnetoresistance of 0.375% is observed at 2 K for CoFeTiAl1–xSix compound. The negative magnetoresistance decreases with increasing temperature below the Curie temperature. Such magnetoresistance behavior is a typical signature of the ferromagnetic state. When the temperature is above the Curie temperature, the magnetoresistance becomes positive and linearly increases with the increasing of magnetic field, which is a typical normal magnetoresistance behavior of nonmagnetic materials. In order to illustrate the origin of the ferromagnetism, we have calculated the electronic structures of CoFeTiAl1–xSix (x=3.125%) compound, with the band structures and electronic density of states (DOS) are shown in Fig.3(b) and (d), respectively. For comparison, the band structures and DOS of the original CoFeTiAl composition are also provided, as shown in Fig.3(a) and (c). After the Si doping, one can observe that: 1) the energy gap decreases from 0.088 eV to 0.047 eV; 2) The Fermi level shifts upon and cut the valence bands in both spin channels; 3) A spin-splitting occurs near the Fermi level. The band structures indicate that CoFeTiAl1–xSix (x=3.125%) compound is ferromagnetic and the carriers are electrons, which are consistent with our experimental results. From the atomic-projected PDOS, we find that the spin-splitting mainly originates from p-d hybridization. Considering Si atom possesses one more valence electron than Al atom, so when Si replace Al in CoFeTiAl compound, the Fermi level
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would shift upon the valence bands. Furthermore, the electron number in spin-up and spin-down channels are calculated using integrated DOS. It is found that all the extra electrons from the silicon element fill in the spin-up channel, which leads to the spin-splitting. The magnetization for each supercell containing one Si atom is 1µB. So, the value of total magnetic moment per CoFeTiAl1–xSix formula unit is 0.03125µB/f.u., which is consistent with our experimental results. 4. Conclusions In summary, we investigated the diluted magnetism in CoFeTiAl1-xSix alloy both theoretically and experimentally. The CoFeTiAl1-xSix alloy crystallized in a quaternary Heusler structure, with DMS signature. The saturation magnetization is found to be 0.031µB/f.u., and the Curie temperature is 100 K. Based on computation results, it is found that the magnetization in CoFeTiAl1-xSix alloy originates from the spin splitting induced by extra p electrons provided by the non-magnetic Si element, quite different from previous DMSs. Acknowledgements This work was supported by Chongqing City Funds for Distinguished Young Scientists (No. cstc2014jcyjjq50003), the Program for Leading Talents in Science and Technology Innovation of Chongqing City (No. CSTCKJCXLJRC19), Natural Science Foundation of Tianjin City (No.16JCYBJC17200).
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References [1] P. Sharma, A. Gupta, K.V. Rao, F.J. Owens, R. Sharmaa, R. Ahuja, J.M.O. Guillen, B. Johansson, G.A. Gehring, Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO, Nat. Mater. 2 (2003) 673. [2] H. Ohno, Making nonmagnetic semiconductors ferromagnetic, Science 281 (1998) 951. [3] J.B. Yi, C.C. Lim, G.Z. Xing, H.M. Fan, L.H. Van, S.L. Huang, K.S. Yang, X.L. Huang, X.B. Qin, B.Y. Wang, T. Wu, L. Wang, H.T. Zhang, X.Y. Gao, T. Liu, A.T.S. Wee, Y.P. Feng and J. Ding, Ferromagnetism in dilute magnetic semiconductors through defect engineering: Li-doped ZnO, Phys. Rev. Lett. 104 (2010) 137201. [4] Z.Y. Zhu, Y.C. Cheng and U. Schwingenschlӧgl, Vacancy induced half-metallicity in half-Heusler semiconductors, Phys. Rev. B 84 (2011) 113201. [5] H. Gu, Y.Z. Jiang, Y.B. Xu and M. Yan, Evidence of the defect-induced ferromagnetism in Na and Co codoped ZnO, Appl. Phys. Lett. 98 (2011) 012502. [6] H. S. Saini, M. Singh, A. H. Reshak and M. K. Kashyap, Accounting oxygen vacancy for half-metallicity and magnetism in Fe-doped CeO2 dilute magnetic oxide, Comp. Mater. Sci. 74 (2013) 114-118. [7] X.G. Gao, B.Y. Man, C. Zhang, J.C. Leng, Y.L. Xu, Q. Wang, M. Zhang and Y. Meng, The important role of Ga vacancies in the ferromagnetic GaN thin films, J. Alloy. Compd. 699 (2017) 596-600.
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[8] T.T. Lin, X.F. Dai, L.Y. Wang, X.F. Liu, Y.T. Cui and G.D. Liu, Anti-site-induced diluted magnetism in semiconductive CoFeTiAl alloy, J. Alloy. Compd. 657 (2016) 519-525. [9] M.C. Payne, M.P. Teter, D.C. Allan, T.A. A.rias, and J.D. Joannopoolous, Iterative minimization techniques for ab initio total-energy calculations: molecular dynamics and conjugate gradients, Rev. Mod. Phys. 64 (1992) 1065. [10] D. Vanderbilt, Soft self-consistent pseudopotentials in a generalized eigenvalue formalism, Phys. Rev. B 41 (1990) 7892. [11] E. Wimmer, H. Krakauer, M. Weinert, A.J. Freeman, Full-potential self-consistent linearized-augmented-plane-wave method for calculating the electronic structure of molecules and surfaces: O2 molecule, Phys. Rev. B 24 (1981) 864. [12] J.P. Perdew, Y. Wang, Density-functional approximation for the correlation energy of the inhomogeneous electron gas, Phys. Rev. B 33 (1986) 8800. [13] L. Basit, Gerhard H. Fecher, S. Chadov, B. Balke and C. Felser, Eur. Quaternary Heusler compounds without inversion symmetry: CoFe1+xTi1-xAl and CoMn1+xV1-xAl, J. Inorg. Chem. 26 (2011) 3950-3954. [14] T.T. Lin, X.F. Dai, J.X. Zhao, L.W. Wang, X.T. Wang, Y.T. Cui and G.D. Liu, The structural, electronic and magnetic properties for the transition process between nonmagnetic and magnetic states in CoFe1+xTi1-xAl, J. Alloy. J. Alloy. Compd. 684 (2016) 143-150.
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Figure captions: Fig. 1. X-ray diffraction patterns of CoFeTiAl1-xSix (x=0 and 3.125%) compounds. Fig. 2. (a) The M-H curves measured at 2K and (b) M-T curve in an induction field of 100Oe for the CoFeTiAl1-xSix (x=3.125%). The inset shows the hysteresis on an enlarged scale. (c) Hall resistivity as a function of magnetic field measured at different temperatures for CoFeTiAl1-xSix. The insets are the separated net anomalous and normal Hall effect. (d) Magnetoresistivity measured at different temperatures for CoFeTiAl1xSix.
Fig. 3. The calculated band structures of the (a) CoFeTiAl and (b) CoFeTiAl1-xSix (x=3.125%). Spin-resolved density states (DOS) of (c) CoFeTiAl and (d) CoFeTiAl1xSix (x=3.125%).
Relative Intensity(a.u.)
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(111) 24
(200)
28
CoFeTiAl
(220)
32
(422) (400)
(111) (200)
CoFeTiAl1-xSix 24
20
28
30
(x=3.125%)
32
40
50
60
70
80
90
2(degree)
Fig. 1. T.T. Lin et al for Superlattices and Microstructures
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1.0
(a)
0.02
Normalized moment
CoFeTiAl1-xSix x=3.125%
0.00 0.02
M(B)
Magnetic moment(B)
0.04
-0.02
0.01 0.00
-0.01 -0.02 -600 -300
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x=3.125%
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(d)
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H(Oe)
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2K 10K
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MR()/%
xycm
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100000
-0.2
15 2K 10K 150K
10
-2
xycm
xycm
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50
Temperature(K)
Magnetic Field(Oe) 6
CoFeTiAl1-xSix
0.0
300 600
H(Oe)
-0.04
(b)
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-4
5
2K 10k 250k
-0.3
0 -5 -10 -15 -100000 -50000
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H(Oe)
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H(Oe)
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H(Oe)
Fig. 2. T.T. Lin et al for Superlattices and Microstructures
100000
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(a)
0.4
(b)
Spin up Spin down
E(eV)
0.2 0.0 -0.2 -0.4 -0.6 -0.8
X (c)
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M
G
300
R X
150 0
DOS(states/eV atom spin)
M
G
R Total Total-s Total-p Total-d
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-300 Fe1-s Co1-s Ti1-s Al-s
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Fe1-s Co1-s Ti1-s Al-s Si-s
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Fe1-p Co1-p Ti1-p Al-p Si-p
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Energy(eV)
Fig. 3. T.T. Lin et al for Superlattices and Microstructures
1
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Highlights (for review) • The CoFeTiAl1-xSix (x=3.125%) compound with Heusler structure was synthesized at 300 K. • The diluted magnetism in the compound can be achieved by doping nonmagnetic Si atom. • The magnetism is not localized on any atom but distributed in a region with the doped Si atom as the center. • An anomalous Hall effect is observed, which confirms the ferromagnetism in Si-doped CoFeTiAl alloy.