P Entel et al 2006 J. Phys. D: Appl. Phys. 39 865 doi:10.1088/0022-3727/39/5/S13
Modelling the phase diagram of magnetic shape memory Heusler alloys
P Entel1,6, V D Buchelnikov2, V V Khovailo3, A T Zayak4, W A Adeagbo1,5, M E Gruner1, H C Herper1 and E F Wassermann1
Show affiliationsWe have modelled the phase diagram of magnetic shape memory alloys of the Heusler type by using the phenomenological Ginzburg–Landau theory. When fixing the parameters by realistic values taken from experiment we are able to reproduce most details of, for example, the phase diagram of Ni2+xMn1−xGa in the (T, x) plane. We present the results of ab initio calculations of the electronic and phonon properties of several ferromagnetic Heusler alloys, which allow one to characterize the structural changes associated with the martensitic instability leading to the modulated and tetragonal phases. From the ab initio investigations emerges a complex pattern of the interplay of magic valence electron per atom numbers (Hume–Rothery rules for magnetic ternary alloys), Fermi surface nesting and phonon instability. As the main result, we find that the driving force for structural transformations is considerably enhanced by the extremely low lying optical modes of Ni in the Ni-based Heusler alloys, which interfere with the acoustical modes enhancing phonon softening of the TA2 mode. In contrast, the ferromagnetic Co-based Heusler alloys show no tendency for phonon softening.
- PACS
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75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.)
71.20.Lp Intermetallic compounds
81.30.Bx Phase diagrams of metals and alloys
- Subjects
- Dates
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Issue 5 (7 March 2006)
Received 25 October 2005, in final form 16 December 2005
Published 17 February 2006
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Modelling the phase diagram of magnetic shape memory Heusler alloys
P Entel et al 2006 J. Phys. D: Appl. Phys. 39 865
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