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Magnetic phase diagram of Heuselr alloys Pd2Mn1+xSn1−x
Accepted Manuscript Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x Y. Chieda, T. Kanomata, R.Y. Umetsu, H. Okada, H. Nishihara, A. Kimura, M. Nagasako, R. Kainuma, K.R.A. Ziebeck PII: DOI: Reference:
S0925-8388(12)02192-5 http://dx.doi.org/10.1016/j.jallcom.2012.11.175 JALCOM 27411
To appear in: Received Date: Revised Date: Accepted Date:
27 October 2012 26 November 2012 28 November 2012
Please cite this article as: Y. Chieda, T. Kanomata, R.Y. Umetsu, H. Okada, H. Nishihara, A. Kimura, M. Nagasako, R. Kainuma, K.R.A. Ziebeck, Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x, (2012), doi: http:// dx.doi.org/10.1016/j.jallcom.2012.11.175
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Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x
Y. Chieda,a T. Kanomata,b,c R.Y. Umetsu,d,* H. Okada,a H. Nishihara,e A. Kimura,f M. Nagasako,c R. Kainumac, K.R.A. Ziebeckg
a
Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
b
Research Institute for Engineering and Technology, Tohoku Gakuin University, Tagajo 985-8537,
Japan c
Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai
980-8579, Japan d
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
e
f
Faculty of Science and Technology, Ryukoku University, Otsu 520-2194, Japan
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
g
Department of Physics, Cavendish Laboratory, University of Cambridge, CB3 0HE, UK
*Corresponding author. Tel.: +81 22 215 2492; fax: +81 22 215 2381; e-mail: [email protected]
1
Abstract Permeability, magnetization and differential scanning calorimetry measurements are carried out on Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined.
The
determined phase diagram is spanned by a paramagnetic austenite phase (P-A), a paramagnetic martensite phase (P-M), a ferrimagnetic austenite phase (F-A) and a martensite phase (F-M) with a small spontaneous magnetization.
It is found that
Pd2Mn1+xSn1-x has the characteristics of the phase diagrams of Ni2Mn1+xZ1-x (Z = In, Sn) metamagnetic shape memory alloys.
Keywords: Heusler alloy, Magnetic phase diagram, Martensitic transition, Magnetic moment
2
1. Introduction Magnetic shape memory alloys (MSMAs) have attracted much attention due to their potential application as functional materials such as magneto-mechanical actuators. Ullakko et al. first reported a large magnetic field-indused strain by the rearrangement of twin variants in the martensite phase of the stoichiometric Heusler alloy Ni2MnGa [1]. Subsequently, in the orthorhombic seven-layered martensite phase of Ni-Mn-Ga alloys, a magnetic field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less 10 kOe [2].
Furthermore, a large magnetocaloric effect due to
the magnetic field-induced martensitic transition in the Ni-Mn-based Heusler-type MSMAs was reported on Ni-rich Ni2+xMn1-xGa [3, 4].
This phenomenon originates
from the magnetostructural transition, i.e., a direct transition between a paramagnetic austenite phase and a ferromagnetic martensite phase, which can be seen in the phase diagram of Ni2+xMn1-xGa (0 ≤ x ≤ 0.36) [5-8].
Recently, a large magnetocaloric effect
and a similar phase transition have also been found in Ni2Mn1-xCuxGa [9-13].
It
should be noted that the characteristics of the phase diagram of Ni2+xMn1-xGa (0 ≤ x ≤ 0.36) are closely similar to that of Ni2Mn1-xCuxGa (0 ≤ x ≤ 0.4) [14]. Recently, Ni2Mn1+xZ1-x (Z = In, Sn) with the Heusler-type L21-type structure have also attracted much attention due to their potential application as functional materials because these alloys undergo a magnetic field-induced reverse martensitic transition from a paramagnetic martensite phase to a ferromagnetic austenite phase [15-20]. These alloy systems open up to the possibility of utilizing the magnetic field-induced shape memory effect.
The large magnetocaloric effect has also been observed in the
Mn rich Ni2Mn1+xZ1-x (Z = In, Sn) [16,21,22].
More recently, a new magnetic alloy
Pd2Mn1.46Sn0.54 with the L21-type structure at room temperature, which shows 3
martensitic transition during cooling, has been synthesized [23]. It was confirmed from the low temperature X-ray diffraction measurements that the martensite phase of Pd2Mn1.46Sn0.54 has an orthorhombic four-layered structure. The magnetization versus temperature curve of Pd2Mn1.46Sn0.54 is very similar to those of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn) [19,20].
In this paper, the magnetic and structural properties of
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are examined experimentally by measuring the permeability, magnetization and differential scanning calorimetry measurements.
The
phase diagram obtained for this alloy system is compared with the already reported phase diagrams of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn) [24-26].
Furthermore, the
concentration dependence of the magnetic moment per formula unit at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) is reported. Preliminary results of the magnetic properties for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) have been reported previously by some of authors in this paper [27].
2. Experimental Polycrystalline samples of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) were prepared by the repeated melting of the appropriate quantities of constituent elements, namely 99.9% pure Pd, 99.99% pure Mn and 99.999% pure Sn, in an argon arc furnace. To obtain homogeneous samples with 0 ≤ x ≤ 0.40, the reaction products were sealed in evacuated double silica tubes, heated at 1123 K for 3 days and then quenched into water. For the samples with x = 0.41, 0.42, 0.44 and 0.47, the reaction products after the repeated arc melting were heated at 1373 K for 2 days because the melting temperature is higher than that of the sample with 0 ≤ x ≤ 0.40. To achieve high crystalline perfection, the reaction products were annealed at 673 K for 1 day and subsequently 573 K for 3 days, 4
and lastly quenched into water. The 2-step annealing was treated because the degree of the order for the specimen annealed at 673 K was not enough because the order-disorder phase transformation temperature was comparatively low.
For the
samples with x = 0.45 and 0.46, the reaction products were heated at 1373 K for 3 days and then annealed at 673 K for 1 days and lastly quenched into water. The phase characterization of the samples was carried out by X-ray powder diffraction measurements using Cu Kα radiation.
The magnetization measurements were carried
out using a commercial superconducting interference device (SQUID) magnetometer. The magnetic and martensitic transition temperatures were determined by measuring the temperature dependence of the magnetization and an initial permeability, where the initial permeability was measured by using an ac transformer method.
Thermal
analysis was carried out by differential scanning calorimetric (DSC) measurement, where the heating and cooling temperature rate was 10 K/min.
3. Results and discussion The stoichiometric compound Pd2MnSn crystallizes in the Heusler-type (L21-type) structure.
The unit cell of the L21-type structure is comprised of four interpenetrating
fcc sublattices A, B, C and D. The Pd atoms occupy the corner (A and C) sites of the bcc structure, while the Mn and Sn atoms occupy alternate body center (B and D, respectively) sites. Recently, Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) were shown to crystallize in the L21-type structure at room temperature [27].
The lattice parameter a of
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) at room temperature decreased linearly with increasing the concentration x, which was attributed to the difference in the atomic radii of Mn and Sn atom.
A similar concentration dependence of the lattice parameter was observed in 5
Ni2Mn1+xSn1-x (0 ≤ x ≤ 0.46) [24,28] and Ni2Mn1+xIn1-x (0 ≤ x ≤ 0.40) with the L21-type structure [25]. Furthermore, the profile refinement of X-ray diffraction pattern using the standard Rietvelt technique showed that the excess Mn atoms in Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) preferentially occupy the vacant Sn site (D site).
High-resolution neutron
powder diffraction measurements on Ni2Mn1.44Sn0.56 also made clear that the excess Mn atoms preferentially occupy the vacant Sn site [18].
It should be noted that
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) do not exhibit the martensitic transition in the temperature range from 5 K to 300 K [27]. In this study, all samples of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are shown to crystallize in the L21-type structure at room temperature by X-ray powder diffraction measurements.
Fig. 1 shows the concentration dependence of the
lattice parameter a for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50).
Though the lattice parameter
decreases linearly with increasing x as shown in Fig. 1, the lattice parameter decreases steeply with increasing x in the concentration range above x ≈ 0.32. Now, it is not clear for the origin of this anomaly on the lattice parameter versus concentration curve of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). More recently, some of the authors investigated the crystal structure of the martensitic phase for Pd2Mn1.46Sn0.54 (x = 046) using the low temperature X-ray diffraction measurement [23].
Most of main reflections on the
X-ray powder diffraction pattern of Pd2Mn1.46Sn0.54 were indexed as the 4-layered orthorhombic (4O) structure as mentioned above.
The crystal structure of the
martensite phase and the austenite phase for Pd2Mn1.46Sn0.54 is similar to those of Ni2Mn1.44Sn0.56 [15,18]. Fig. 2(a) shows the temperature dependence of the magnetization M at H = 1 kOe for Pd2Mn1.40Sn0.60 (x = 0.40). In a zero-field-cooled process (ZFC), a sample was first cooled to 5 K from room temperature under zero magnetic field; at this temperature the 6
magnetic field H (= 1 kOe) was applied and the magnetization was measured at this constant field with increasing temperature up to 375 K. Then, without removing the external magnetic field, the magnetization measurement was made with decreasing temperature, i.e., field-cooled (FC). The behavior of M(T) for Pd2Mn1.40Sn0.60 is that of typical ferri- or ferromagnets. Even in the external magnetic field of 1 kOe, the splitting of the ZFC and FC curves appears as shown in Fig. 2(a). This may be attributed to the pinning effect of the domain wall.
The inset in Fig. 2(a) shows the
temperature dependence of the permeability μ for Pd2Mn1.40Sn0.60. Abrupt changes in μ are observed around 210 K in cooling and heating processes. variations of μ are similar to those of Pd2MnSn (x = 0) [27].
These temperature
Therefore, the abrupt
changes of μ are thought to correspond to a transition from the ferrimagnetic state to the paramagnetic state. Recently, Kanomata et al. showed that the magnetic moment of the Mn atoms substituted onto Sn sites in Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) is antiferromagnetically coupled to the magnetic moment of the Mn atoms on Mn sites [27], indicating that the magnetic structure of Pd2Mn1+xSn1-x (0 < x ≤ 0.30) is collinear ferrimagnetic.
The Curie temperature TCA was defined as the cross point of the linear
extrapolation lines from higher and lower temperature ranges on the μ versus T curve. The TCA is found to be 210.4 K for the sample with x = 0.40, which is somewhat higher than that (= 183.9 K) of Pd2MnSn [27]. The TCA determined from the M versus T curve is very close to the value of 210.4 K. Fig. 2(b) shows the temperature dependence of the magnetization M at H = 1 kOe for Pd2Mn1.42Sn0.58 (x = 0.42). The changes of M with a large temperature hysteresis of about 38 K are observed around 100 K for ZFC and FC processes. This temperature variations of M are similar to those of the MSMA Ni2Mn1.44Sn0.56 [18]. Therefore, the abrupt changes of M are thought to correspond to 7
a transition between the martensitic phase and the austenite phase. It should be noted that the temperature hysteresis appeared in Pd2Mn1.42Sn0.58 is very wide compared to that of Ni2Mn1.42Sn0.58. Both austenite and the martensite phases of Pd2Mn1.42Sn0.58 have the spontaneous magnetization. The martensitic transition starting and finishing temperatures TMs and TMf and the reverse martensitic transition starting and finishing temperatures TAs and TAf were also defined as the points of the intersection of the linear extrapolation of both the higher and lower temperature ranges on the M versus T curves as shown in Fig. 2(b). The TCA of Pd2Mn1.42Sn0.58 is found to be 203.1 K. Fig. 2(c) shows the temperature dependence of M of Pd2Mn1.47Sn0.53 (x = 0.47) measured in an applied magnetic field of 1.0 kOe. The abrupt changes of M around 180 K with decreasing temperature are thought to correspond to the transition from the ferrimagnetic austenite phase to a paramagnetic martensite phase. More recently, similar magnetic behavior was observed on Pd2Mn1.46Sn0.54 (x = 0.46) [23]. Recently, some of present authors carried out Mössbauer measurements to investigate the magnetic properties of Ni2Mn1.4657Fe0.02Sn0.52 [19] and Ni50Mn34.357Fe0.5In15.2 [20].
These alloys
and Pd2Mn1+xSn1-x (x = 0.46 and 0.47) exhibit very similar M versus T curves. According to the results of the Mössbauer measurements, the spectra just below the martensitic transition temperature and above the Curie temperature are composed of a singlet with a narrow line width, indicating that the magnetic state just below the martensitic transition temperature is paramagnetic. With increasing temperature, M decreases abruptly around 200 K. This change of M corresponds to the transition from the ferrimagnetic state to the paramagnetic state in the austenite phase. The TCA of Pd2Mn1.47Sn0.53 (x = 0.47) is found to be 198.2 K.
At low temperature in the
martensite phase, the M of Pd2Mn1.47Sn0.53 increases, suggesting that the transition to a 8
ferri- or ferromagnetic state with the small magnetization occurs at the Curie temperature TCM(= 94 K) of the martensite phase.
Fig. 3 shows the DSC curves of
Pd2Mn1.50Sn0.50 (x = 0.50) for the heating and cooling processes.
TMs, TMf, TAs and TAf
were determined by using the intersections of the baseline and the tangent lines with the largest slopes of the DSC peaks as shown in Fig. 3.
The small hump on the left side of
the main exothermic peak may be due to the inhomogeneity of the alloy.
The
magnetization measurements were carried out at 5 K for the samples with 0 ≤ x ≤ 0.47. The magnetization of all the samples is not saturated in a field of 50 kOe. The spontaneous magnetization at 5 K for Pd2Mn1+xSn1-x was determined by the linear extrapolation to H/M = 0 of the M2 versus H/M curve. The magnetic moments per formula unit, μs, of the samples with 0 ≤ x ≤ 0.47 at 5 K were deduced from the values of the spontaneous magnetization.
The concentration dependence of the magnetic
moments at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) are shown in Fig. 4, where the data of the μs at 5 K at the samples with 0 ≤ x ≤ 0.30 were taken from the reference [27]. Though the μs at 5 K decreases with increasing x, the μs decreases steeply with increasing x from x ≈ 0.32.
As mentioned above, the concentration dependence of the
lattice parameter at room temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) also shows the anomaly at x ≈ 0.32. The experimental T versus x phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50), which was constructed from the measurements of the temperature dependence of μ and M, and DSC measurement, is shown in Fig. 5. This phase diagram is very similar to those of Ni2Mn1+xSn1-x (0 ≤ x ≤ 0.46) [24] and Ni2Mn1+xIn1-x (0 ≤ x ≤ 0.40) alloys [25]. As shown in Fig. 4, the Curie temperature TCA of the austenite phase makes a broad maximum around x ≈ 0.35. The martensitic transition increases with increasing x, 9
where TM was defined as TM = (TMs+TAf)/2. The paramagnetic phase (P-M) and the ferromagnetic phase (F-M) with the small spontaneous magnetization appear below TM. On the other hand, the Curie temperature TCM of the martensite phase decreases with increasing x.
It is not possible to determine from the present data the exact magnetic
structures of the F-M state. A neutron powder diffraction measurement is in progress to determine the magnetic structures and the magnetic properties of the sample with x = 0.46.
The magnetic moments at 5 K of Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 are found
to be 0.54 μB/f.u. [23] and 0.50 μB/f.u., respectively. The values of the magnetic moment at 5 K for MSMAs Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60 were reported to be 1.46 μB/f.u. [24] and 1.27 μB/f.u. [25], respectively. The magnetic moments per formula unit at 5 K for Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 are about three times smaller than those of Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60. magnetic moment on the Pd atoms.
This may be attributed to a very small
As mentioned above, it should be noted that the
temperature dependence of M for Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 is very similar to those of Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60.
The values of TC for Pd2Mn1+xSn1-x (x =
0.46 and 0.47) are found to be 201.1 K and 198.2 K, respectively. These values are much lower than TC (= 310 K) of Ni2Mn1.48Sn0.52 [24] and (= 302.8 K) of Ni2Mn1.40In0.60 [25]. This may be also attributed to a very small magnetic moment on the Pd sites. Ye et al. revealed the underlying mechanism of the martensitic transition for MSMAs Ni2Mn1+xSn1-x by the combination of a bulk-sensitive hard X-ray photoemission spectroscopy and a first-principles density-functional calculation [31]. They made clear that a strong hybridization takes place between the Ni3d eg states and the 3d states of excess Mn atoms at the Sn sites. This hybridization is believed to be the main reason causing the martensitic transition in MSMAs Ni2Mn1+xSn1-x. 10
An
investigation of the bulk-sensitive hard X-ray photoemission spectroscopy and the first-principles density-functional calculation will be necessary to make clear the mechanism of the martensitic transition of Pd2Mn1+xSn1-x system.
However, from the
similarity of the phase diagram and the magnetic properties between Pd2Mn1+xSn1-x and Ni2Mn1+xZ1-x (Z = In and Sn), it is expected that Pd2Mn1+xSn1-x alloys also show the metamagnetic behavior and the field-induced shape memory effect.
4. Conclusion Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) crystallizes in the L21-type structure at room temperature.
Though the lattice parameter a decreases linearly with increasing x, the a
decreases steeply above x ≈ 0.32.
Permeability, magnetization and differential
scanning calorimetry measurements are carried out on Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). On
the
basis
of
the
experimental
results,
temperature-concentration plane is determined. exhibit the martensitic transition.
the
phase
diagram
in
the
The samples with 0.42 ≤ x ≤ 0.50
The determined phase diagram is spanned by the
paramagnetic austenite phase (P-A), the paramagnetic martensite phase (P-M), ferrimagnetic (ferromagnetic for the sample with x = 0) austenite phase (F-M) and the martensite phase (F-M) with the small spontaneous magnetization.
It is found that the
phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) is similar to the phase diagrams of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn). However, the values of the Curie temperature and the martensitic transition temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are appreciably lower than those of Ni2Mn1+xZ1-x (Z = In, Sn). The magnetic moments per formula unit at 5 K of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) are also lower compared to those of Ni2Mn1+xZ1-x (Z = In, Sn). These may be attributed to the small magnetic moment on the Pd sites. 11
Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (C) (No. 21560693) and (S) (No. 22226011) from the Japan Society for the Promotion of Science (JSPS).
12
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Figure captions Fig. 1
Concentration dependence of the lattice parameter a at room temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50).
Fig. 2
Temperature dependence of the magnetization M at 1 kOe for Pd2Mn1.40Sn0.60 (a), Pd2Mn1.42Sn0.58 (b) and Pd2Mn1.47Sn0.53(c). The arrows with ZFC and FC along the curves show the zero-field-cooling and field-cooling processes, respectively. The inset in Fig. 2(a) shows the permeability μ versus T curve for Pd2Mn1.40Sn0.60.
Fig. 3
DSC curves of Pd2Mn1.50Sn0.50.
The arrows along the curves show the
cooling and heating processes. Fig. 4
Concentration dependence of the magnetic moment per formula unit, μs, at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47).
The data of the samples with 0 ≤ x ≤ 0.30
were taken from the reference [27]. Fig. 5
The solid line is a guide for the eyes.
Phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). P and F mean the paramagnetic state and the state with the spontaneous magnetization, respectively. A and M represent the austenite and martensite phases, respectively. TCA and TCM are the Curie temperature of the austenite phase and the martensite phase, respectively. TM means the martensitic transition temperature. The data of the samples with 0 ≤ x ≤ 0.30 were taken from the reference [27]. in the figure are a guide for the eyes.
16
Solid lines
Figure(s) 1
Figure(s) 2
Figure(s) 3
Figure(s) 4
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Highlights of the manuscript entitled “Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x” by Chieda et al.
1. Magnetic phase diagram was first established in Pd2Mn1+xSn1-x alloy system. 2. The magnetic phase diagram of Pd2Mn1+xSn1-x is similar to that of Ni2Mn1+xSn1-x shape memory alloys. 3. It was suggested that Pd2Mn1+xSn1-x system has a possibility to be metamagnetic shape memory alloys.
17
S0925-8388(12)02192-5 http://dx.doi.org/10.1016/j.jallcom.2012.11.175 JALCOM 27411
To appear in: Received Date: Revised Date: Accepted Date:
27 October 2012 26 November 2012 28 November 2012
Please cite this article as: Y. Chieda, T. Kanomata, R.Y. Umetsu, H. Okada, H. Nishihara, A. Kimura, M. Nagasako, R. Kainuma, K.R.A. Ziebeck, Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x, (2012), doi: http:// dx.doi.org/10.1016/j.jallcom.2012.11.175
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Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x
Y. Chieda,a T. Kanomata,b,c R.Y. Umetsu,d,* H. Okada,a H. Nishihara,e A. Kimura,f M. Nagasako,c R. Kainumac, K.R.A. Ziebeckg
a
Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
b
Research Institute for Engineering and Technology, Tohoku Gakuin University, Tagajo 985-8537,
Japan c
Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai
980-8579, Japan d
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
e
f
Faculty of Science and Technology, Ryukoku University, Otsu 520-2194, Japan
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
g
Department of Physics, Cavendish Laboratory, University of Cambridge, CB3 0HE, UK
*Corresponding author. Tel.: +81 22 215 2492; fax: +81 22 215 2381; e-mail: [email protected]
1
Abstract Permeability, magnetization and differential scanning calorimetry measurements are carried out on Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined.
The
determined phase diagram is spanned by a paramagnetic austenite phase (P-A), a paramagnetic martensite phase (P-M), a ferrimagnetic austenite phase (F-A) and a martensite phase (F-M) with a small spontaneous magnetization.
It is found that
Pd2Mn1+xSn1-x has the characteristics of the phase diagrams of Ni2Mn1+xZ1-x (Z = In, Sn) metamagnetic shape memory alloys.
Keywords: Heusler alloy, Magnetic phase diagram, Martensitic transition, Magnetic moment
2
1. Introduction Magnetic shape memory alloys (MSMAs) have attracted much attention due to their potential application as functional materials such as magneto-mechanical actuators. Ullakko et al. first reported a large magnetic field-indused strain by the rearrangement of twin variants in the martensite phase of the stoichiometric Heusler alloy Ni2MnGa [1]. Subsequently, in the orthorhombic seven-layered martensite phase of Ni-Mn-Ga alloys, a magnetic field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less 10 kOe [2].
Furthermore, a large magnetocaloric effect due to
the magnetic field-induced martensitic transition in the Ni-Mn-based Heusler-type MSMAs was reported on Ni-rich Ni2+xMn1-xGa [3, 4].
This phenomenon originates
from the magnetostructural transition, i.e., a direct transition between a paramagnetic austenite phase and a ferromagnetic martensite phase, which can be seen in the phase diagram of Ni2+xMn1-xGa (0 ≤ x ≤ 0.36) [5-8].
Recently, a large magnetocaloric effect
and a similar phase transition have also been found in Ni2Mn1-xCuxGa [9-13].
It
should be noted that the characteristics of the phase diagram of Ni2+xMn1-xGa (0 ≤ x ≤ 0.36) are closely similar to that of Ni2Mn1-xCuxGa (0 ≤ x ≤ 0.4) [14]. Recently, Ni2Mn1+xZ1-x (Z = In, Sn) with the Heusler-type L21-type structure have also attracted much attention due to their potential application as functional materials because these alloys undergo a magnetic field-induced reverse martensitic transition from a paramagnetic martensite phase to a ferromagnetic austenite phase [15-20]. These alloy systems open up to the possibility of utilizing the magnetic field-induced shape memory effect.
The large magnetocaloric effect has also been observed in the
Mn rich Ni2Mn1+xZ1-x (Z = In, Sn) [16,21,22].
More recently, a new magnetic alloy
Pd2Mn1.46Sn0.54 with the L21-type structure at room temperature, which shows 3
martensitic transition during cooling, has been synthesized [23]. It was confirmed from the low temperature X-ray diffraction measurements that the martensite phase of Pd2Mn1.46Sn0.54 has an orthorhombic four-layered structure. The magnetization versus temperature curve of Pd2Mn1.46Sn0.54 is very similar to those of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn) [19,20].
In this paper, the magnetic and structural properties of
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are examined experimentally by measuring the permeability, magnetization and differential scanning calorimetry measurements.
The
phase diagram obtained for this alloy system is compared with the already reported phase diagrams of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn) [24-26].
Furthermore, the
concentration dependence of the magnetic moment per formula unit at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) is reported. Preliminary results of the magnetic properties for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) have been reported previously by some of authors in this paper [27].
2. Experimental Polycrystalline samples of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) were prepared by the repeated melting of the appropriate quantities of constituent elements, namely 99.9% pure Pd, 99.99% pure Mn and 99.999% pure Sn, in an argon arc furnace. To obtain homogeneous samples with 0 ≤ x ≤ 0.40, the reaction products were sealed in evacuated double silica tubes, heated at 1123 K for 3 days and then quenched into water. For the samples with x = 0.41, 0.42, 0.44 and 0.47, the reaction products after the repeated arc melting were heated at 1373 K for 2 days because the melting temperature is higher than that of the sample with 0 ≤ x ≤ 0.40. To achieve high crystalline perfection, the reaction products were annealed at 673 K for 1 day and subsequently 573 K for 3 days, 4
and lastly quenched into water. The 2-step annealing was treated because the degree of the order for the specimen annealed at 673 K was not enough because the order-disorder phase transformation temperature was comparatively low.
For the
samples with x = 0.45 and 0.46, the reaction products were heated at 1373 K for 3 days and then annealed at 673 K for 1 days and lastly quenched into water. The phase characterization of the samples was carried out by X-ray powder diffraction measurements using Cu Kα radiation.
The magnetization measurements were carried
out using a commercial superconducting interference device (SQUID) magnetometer. The magnetic and martensitic transition temperatures were determined by measuring the temperature dependence of the magnetization and an initial permeability, where the initial permeability was measured by using an ac transformer method.
Thermal
analysis was carried out by differential scanning calorimetric (DSC) measurement, where the heating and cooling temperature rate was 10 K/min.
3. Results and discussion The stoichiometric compound Pd2MnSn crystallizes in the Heusler-type (L21-type) structure.
The unit cell of the L21-type structure is comprised of four interpenetrating
fcc sublattices A, B, C and D. The Pd atoms occupy the corner (A and C) sites of the bcc structure, while the Mn and Sn atoms occupy alternate body center (B and D, respectively) sites. Recently, Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) were shown to crystallize in the L21-type structure at room temperature [27].
The lattice parameter a of
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) at room temperature decreased linearly with increasing the concentration x, which was attributed to the difference in the atomic radii of Mn and Sn atom.
A similar concentration dependence of the lattice parameter was observed in 5
Ni2Mn1+xSn1-x (0 ≤ x ≤ 0.46) [24,28] and Ni2Mn1+xIn1-x (0 ≤ x ≤ 0.40) with the L21-type structure [25]. Furthermore, the profile refinement of X-ray diffraction pattern using the standard Rietvelt technique showed that the excess Mn atoms in Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) preferentially occupy the vacant Sn site (D site).
High-resolution neutron
powder diffraction measurements on Ni2Mn1.44Sn0.56 also made clear that the excess Mn atoms preferentially occupy the vacant Sn site [18].
It should be noted that
Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) do not exhibit the martensitic transition in the temperature range from 5 K to 300 K [27]. In this study, all samples of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are shown to crystallize in the L21-type structure at room temperature by X-ray powder diffraction measurements.
Fig. 1 shows the concentration dependence of the
lattice parameter a for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50).
Though the lattice parameter
decreases linearly with increasing x as shown in Fig. 1, the lattice parameter decreases steeply with increasing x in the concentration range above x ≈ 0.32. Now, it is not clear for the origin of this anomaly on the lattice parameter versus concentration curve of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). More recently, some of the authors investigated the crystal structure of the martensitic phase for Pd2Mn1.46Sn0.54 (x = 046) using the low temperature X-ray diffraction measurement [23].
Most of main reflections on the
X-ray powder diffraction pattern of Pd2Mn1.46Sn0.54 were indexed as the 4-layered orthorhombic (4O) structure as mentioned above.
The crystal structure of the
martensite phase and the austenite phase for Pd2Mn1.46Sn0.54 is similar to those of Ni2Mn1.44Sn0.56 [15,18]. Fig. 2(a) shows the temperature dependence of the magnetization M at H = 1 kOe for Pd2Mn1.40Sn0.60 (x = 0.40). In a zero-field-cooled process (ZFC), a sample was first cooled to 5 K from room temperature under zero magnetic field; at this temperature the 6
magnetic field H (= 1 kOe) was applied and the magnetization was measured at this constant field with increasing temperature up to 375 K. Then, without removing the external magnetic field, the magnetization measurement was made with decreasing temperature, i.e., field-cooled (FC). The behavior of M(T) for Pd2Mn1.40Sn0.60 is that of typical ferri- or ferromagnets. Even in the external magnetic field of 1 kOe, the splitting of the ZFC and FC curves appears as shown in Fig. 2(a). This may be attributed to the pinning effect of the domain wall.
The inset in Fig. 2(a) shows the
temperature dependence of the permeability μ for Pd2Mn1.40Sn0.60. Abrupt changes in μ are observed around 210 K in cooling and heating processes. variations of μ are similar to those of Pd2MnSn (x = 0) [27].
These temperature
Therefore, the abrupt
changes of μ are thought to correspond to a transition from the ferrimagnetic state to the paramagnetic state. Recently, Kanomata et al. showed that the magnetic moment of the Mn atoms substituted onto Sn sites in Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.30) is antiferromagnetically coupled to the magnetic moment of the Mn atoms on Mn sites [27], indicating that the magnetic structure of Pd2Mn1+xSn1-x (0 < x ≤ 0.30) is collinear ferrimagnetic.
The Curie temperature TCA was defined as the cross point of the linear
extrapolation lines from higher and lower temperature ranges on the μ versus T curve. The TCA is found to be 210.4 K for the sample with x = 0.40, which is somewhat higher than that (= 183.9 K) of Pd2MnSn [27]. The TCA determined from the M versus T curve is very close to the value of 210.4 K. Fig. 2(b) shows the temperature dependence of the magnetization M at H = 1 kOe for Pd2Mn1.42Sn0.58 (x = 0.42). The changes of M with a large temperature hysteresis of about 38 K are observed around 100 K for ZFC and FC processes. This temperature variations of M are similar to those of the MSMA Ni2Mn1.44Sn0.56 [18]. Therefore, the abrupt changes of M are thought to correspond to 7
a transition between the martensitic phase and the austenite phase. It should be noted that the temperature hysteresis appeared in Pd2Mn1.42Sn0.58 is very wide compared to that of Ni2Mn1.42Sn0.58. Both austenite and the martensite phases of Pd2Mn1.42Sn0.58 have the spontaneous magnetization. The martensitic transition starting and finishing temperatures TMs and TMf and the reverse martensitic transition starting and finishing temperatures TAs and TAf were also defined as the points of the intersection of the linear extrapolation of both the higher and lower temperature ranges on the M versus T curves as shown in Fig. 2(b). The TCA of Pd2Mn1.42Sn0.58 is found to be 203.1 K. Fig. 2(c) shows the temperature dependence of M of Pd2Mn1.47Sn0.53 (x = 0.47) measured in an applied magnetic field of 1.0 kOe. The abrupt changes of M around 180 K with decreasing temperature are thought to correspond to the transition from the ferrimagnetic austenite phase to a paramagnetic martensite phase. More recently, similar magnetic behavior was observed on Pd2Mn1.46Sn0.54 (x = 0.46) [23]. Recently, some of present authors carried out Mössbauer measurements to investigate the magnetic properties of Ni2Mn1.4657Fe0.02Sn0.52 [19] and Ni50Mn34.357Fe0.5In15.2 [20].
These alloys
and Pd2Mn1+xSn1-x (x = 0.46 and 0.47) exhibit very similar M versus T curves. According to the results of the Mössbauer measurements, the spectra just below the martensitic transition temperature and above the Curie temperature are composed of a singlet with a narrow line width, indicating that the magnetic state just below the martensitic transition temperature is paramagnetic. With increasing temperature, M decreases abruptly around 200 K. This change of M corresponds to the transition from the ferrimagnetic state to the paramagnetic state in the austenite phase. The TCA of Pd2Mn1.47Sn0.53 (x = 0.47) is found to be 198.2 K.
At low temperature in the
martensite phase, the M of Pd2Mn1.47Sn0.53 increases, suggesting that the transition to a 8
ferri- or ferromagnetic state with the small magnetization occurs at the Curie temperature TCM(= 94 K) of the martensite phase.
Fig. 3 shows the DSC curves of
Pd2Mn1.50Sn0.50 (x = 0.50) for the heating and cooling processes.
TMs, TMf, TAs and TAf
were determined by using the intersections of the baseline and the tangent lines with the largest slopes of the DSC peaks as shown in Fig. 3.
The small hump on the left side of
the main exothermic peak may be due to the inhomogeneity of the alloy.
The
magnetization measurements were carried out at 5 K for the samples with 0 ≤ x ≤ 0.47. The magnetization of all the samples is not saturated in a field of 50 kOe. The spontaneous magnetization at 5 K for Pd2Mn1+xSn1-x was determined by the linear extrapolation to H/M = 0 of the M2 versus H/M curve. The magnetic moments per formula unit, μs, of the samples with 0 ≤ x ≤ 0.47 at 5 K were deduced from the values of the spontaneous magnetization.
The concentration dependence of the magnetic
moments at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) are shown in Fig. 4, where the data of the μs at 5 K at the samples with 0 ≤ x ≤ 0.30 were taken from the reference [27]. Though the μs at 5 K decreases with increasing x, the μs decreases steeply with increasing x from x ≈ 0.32.
As mentioned above, the concentration dependence of the
lattice parameter at room temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) also shows the anomaly at x ≈ 0.32. The experimental T versus x phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50), which was constructed from the measurements of the temperature dependence of μ and M, and DSC measurement, is shown in Fig. 5. This phase diagram is very similar to those of Ni2Mn1+xSn1-x (0 ≤ x ≤ 0.46) [24] and Ni2Mn1+xIn1-x (0 ≤ x ≤ 0.40) alloys [25]. As shown in Fig. 4, the Curie temperature TCA of the austenite phase makes a broad maximum around x ≈ 0.35. The martensitic transition increases with increasing x, 9
where TM was defined as TM = (TMs+TAf)/2. The paramagnetic phase (P-M) and the ferromagnetic phase (F-M) with the small spontaneous magnetization appear below TM. On the other hand, the Curie temperature TCM of the martensite phase decreases with increasing x.
It is not possible to determine from the present data the exact magnetic
structures of the F-M state. A neutron powder diffraction measurement is in progress to determine the magnetic structures and the magnetic properties of the sample with x = 0.46.
The magnetic moments at 5 K of Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 are found
to be 0.54 μB/f.u. [23] and 0.50 μB/f.u., respectively. The values of the magnetic moment at 5 K for MSMAs Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60 were reported to be 1.46 μB/f.u. [24] and 1.27 μB/f.u. [25], respectively. The magnetic moments per formula unit at 5 K for Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 are about three times smaller than those of Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60. magnetic moment on the Pd atoms.
This may be attributed to a very small
As mentioned above, it should be noted that the
temperature dependence of M for Pd2Mn1.46Sn0.54 and Pd2Mn1.47Sn0.53 is very similar to those of Ni2Mn1.48Sn0.52 and Ni2Mn1.40In0.60.
The values of TC for Pd2Mn1+xSn1-x (x =
0.46 and 0.47) are found to be 201.1 K and 198.2 K, respectively. These values are much lower than TC (= 310 K) of Ni2Mn1.48Sn0.52 [24] and (= 302.8 K) of Ni2Mn1.40In0.60 [25]. This may be also attributed to a very small magnetic moment on the Pd sites. Ye et al. revealed the underlying mechanism of the martensitic transition for MSMAs Ni2Mn1+xSn1-x by the combination of a bulk-sensitive hard X-ray photoemission spectroscopy and a first-principles density-functional calculation [31]. They made clear that a strong hybridization takes place between the Ni3d eg states and the 3d states of excess Mn atoms at the Sn sites. This hybridization is believed to be the main reason causing the martensitic transition in MSMAs Ni2Mn1+xSn1-x. 10
An
investigation of the bulk-sensitive hard X-ray photoemission spectroscopy and the first-principles density-functional calculation will be necessary to make clear the mechanism of the martensitic transition of Pd2Mn1+xSn1-x system.
However, from the
similarity of the phase diagram and the magnetic properties between Pd2Mn1+xSn1-x and Ni2Mn1+xZ1-x (Z = In and Sn), it is expected that Pd2Mn1+xSn1-x alloys also show the metamagnetic behavior and the field-induced shape memory effect.
4. Conclusion Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) crystallizes in the L21-type structure at room temperature.
Though the lattice parameter a decreases linearly with increasing x, the a
decreases steeply above x ≈ 0.32.
Permeability, magnetization and differential
scanning calorimetry measurements are carried out on Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). On
the
basis
of
the
experimental
results,
temperature-concentration plane is determined. exhibit the martensitic transition.
the
phase
diagram
in
the
The samples with 0.42 ≤ x ≤ 0.50
The determined phase diagram is spanned by the
paramagnetic austenite phase (P-A), the paramagnetic martensite phase (P-M), ferrimagnetic (ferromagnetic for the sample with x = 0) austenite phase (F-M) and the martensite phase (F-M) with the small spontaneous magnetization.
It is found that the
phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) is similar to the phase diagrams of MSMAs Ni2Mn1+xZ1-x (Z = In, Sn). However, the values of the Curie temperature and the martensitic transition temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50) are appreciably lower than those of Ni2Mn1+xZ1-x (Z = In, Sn). The magnetic moments per formula unit at 5 K of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47) are also lower compared to those of Ni2Mn1+xZ1-x (Z = In, Sn). These may be attributed to the small magnetic moment on the Pd sites. 11
Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (C) (No. 21560693) and (S) (No. 22226011) from the Japan Society for the Promotion of Science (JSPS).
12
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Figure captions Fig. 1
Concentration dependence of the lattice parameter a at room temperature for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50).
Fig. 2
Temperature dependence of the magnetization M at 1 kOe for Pd2Mn1.40Sn0.60 (a), Pd2Mn1.42Sn0.58 (b) and Pd2Mn1.47Sn0.53(c). The arrows with ZFC and FC along the curves show the zero-field-cooling and field-cooling processes, respectively. The inset in Fig. 2(a) shows the permeability μ versus T curve for Pd2Mn1.40Sn0.60.
Fig. 3
DSC curves of Pd2Mn1.50Sn0.50.
The arrows along the curves show the
cooling and heating processes. Fig. 4
Concentration dependence of the magnetic moment per formula unit, μs, at 5 K for Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.47).
The data of the samples with 0 ≤ x ≤ 0.30
were taken from the reference [27]. Fig. 5
The solid line is a guide for the eyes.
Phase diagram of Pd2Mn1+xSn1-x (0 ≤ x ≤ 0.50). P and F mean the paramagnetic state and the state with the spontaneous magnetization, respectively. A and M represent the austenite and martensite phases, respectively. TCA and TCM are the Curie temperature of the austenite phase and the martensite phase, respectively. TM means the martensitic transition temperature. The data of the samples with 0 ≤ x ≤ 0.30 were taken from the reference [27]. in the figure are a guide for the eyes.
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Solid lines
Figure(s) 1
Figure(s) 2
Figure(s) 3
Figure(s) 4
Figure(s) 5
Highlights of the manuscript entitled “Magnetic Phase diagram of Heuselr alloys Pd2Mn1+xSn1-x” by Chieda et al.
1. Magnetic phase diagram was first established in Pd2Mn1+xSn1-x alloy system. 2. The magnetic phase diagram of Pd2Mn1+xSn1-x is similar to that of Ni2Mn1+xSn1-x shape memory alloys. 3. It was suggested that Pd2Mn1+xSn1-x system has a possibility to be metamagnetic shape memory alloys.
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