Abstract
We have performed ab initio electronic structure calculations and Monte Carlo simulations of frustrated ferroic materials where complex magnetic configurations and chemical disorder lead to rich phase diagrams. With lowering of temperature, we find a ferromagnetic phase which transforms to an antiferromagnetic phase at the magnetostructural (martensitic) phase transition and to a cluster spin glass at still lower temperatures. The Heusler alloys Ni-(Co)-Mn-(Cr)-(Ga, Al, In, Sn, Sb) are of particular interest because of their large inverse magnetocaloric effect associated with the magnetostructural transition and the influence of Co/Cr doping. Besides spin glass features, strain glass behavior has been observed in Ni-Co-Mn-In. The numerical simulations allow a complete characterization of the frustrated ferroic materials including the Fe-Rh-Pd alloys.
Highlights
The widely used intermetallics Ti-Ni have attracted much interest over decades because of their martensitic transformation, superelasticity and excellent shape memory behavior [1] and new glass phases [2]
With magnetism as additional degree of freedom, magnetic shape memory Heusler alloys have been found with large reversible deformations under the application or removal of a magnetic field [3]
The strong coupling between magnetism and structure leads to a first order magnetostructural transition with different magnetization of austenite and martensite because of different magnetocrystalline anisotropy and different magnetic exchange coupling constants
Summary
The widely used intermetallics Ti-Ni have attracted much interest over decades because of their martensitic transformation, superelasticity and excellent shape memory behavior [1] and new glass phases [2]. With magnetism as additional degree of freedom, magnetic shape memory Heusler alloys have been found with large reversible deformations under the application or removal of a magnetic field [3]. The stronger anisotropy of the martensitic phase allows rotation of the martensitic variants under the application of a magnetic field, leading to the magnetic shape memory effect [4]. Spin-glass [15] and strain-glass [16] In this short communication, we compare the structural and magnetic behavior and magnetocaloric properties of cubic Heusler alloys shown in Fig. 1 with some of the giant magnetocaloric materials known before like Gd5(Si2Ge) (monoclinic crystal structure) [17], La(Fe13-xSix) (cubic NaZn13 D23-type structure) [18], and Fe-Rh (cubic CsCl-type structure) [19]. The comparison shows remarkable similarities associated with the inverse magnetocaloric effect emerging from the magnetostructural transition in the magnetic Heusler alloys with the corresponding magnetostructural transition and caloric effect of the Gd based and Fe-Rh-Pd based compounds as discussed below
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