Phase transitions in Ni2MnX (X=In, Sn, Sb) Heusler alloys with inversion of exchange interaction

Vasiliy D. Buchelnikov 1Sergey V. Taskaev 1Mikhail A. Zagrebin 1Peter Entel 2

1. Chelyabinsk State University (ChelSU), Br. Kashirinykh Str, 129, Chelyabinsk 454021, Russian Federation
2. University of Duisburg Essen, Campus Duisburg, Department of Theoretical Physics, Lotharstrasse 1, Duisburg 47048, Germany

Abstract

In ferromagnetic (FM) Heusler alloys the structural transition from high temperature cubic phase to low temperature tetragonal one takes place. The experiments show that in Ni2MnX (X=In, Sn, Sb) alloys the next sequence of phase transitions occurs: paramagnetic (PM) cubic phase → FM cubic one → PM tetragonal one → FM tetragonal one [1]. This magnetic behavior can be explained by the existence in these alloys the inversion of exchange interaction [2]. In this work with the help of the Ginzburg-Landau theory the phase diagrams of Heusler alloys with inversion of exchange interaction are theoretically investigated. We used the expression for the Ginzburg-Landau functional from works [2,3]

Fm2/2+βm2cosφ/2-γm4cosφ/4+δ1m4cos2φ/4+δ2m4/4-ω1m2(e22+ e32)/2-

ω2m2(e22+ e32)cosφ/2+a(e22+ e32)/2+be3(e32-3e22)/3+c(e22+ e32)2/4 (1)



where m is the normalized magnetization; φ is the angle between the magnetizations of two ferromagnetic sublattices; e2,3 are the linear combinations of the strain tensor; α, β, δ1, δ2, γ are the exchange interaction parameters; ω1, ω2 are the magnetoelastic constants; a, b, c are the linear combinations of the 2nd-, 3rd-, and 4th-order elastic moduli. After minimization energy with respect to the order parameters m, φ, e2,3 we constructed the phase diagrams on the (β-a) plane. The analysis shows that in general case twelve phases exist: three paramagnetic, three ferromagnetic and six antiferromagnetic phases. At certain values of functional parameters (1) we obtained the same sequence of phase transitions as in experimental work [1].

This work was supported by grants RF and CRDF Y2-P-05-19, RFBR 05-08-50341, 06-02-16266, 07-02-96029-r-ural, 06-02-39030-NNSF, 05-02-19935-YaF_a RFBR and JSPS, RF President MK-5658.2006.2 and Human Capital Foundation.

1. T. Krenke, M. Acet, E.F. Wasserman et al., Phys. Rev. B 72 (2005) 014412.
2. C. Kittel, Phys. Rev. 120 (1960) 335.
3. M.A. Fradkin, Phys. Rev. B 50 (1994) 16326.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Vasiliy D. Buchelnikov
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-11 10:12
Revised:   2009-06-07 00:44