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Abstract:
Within the huge family of Heusler compounds only a few quaternary
derivatives are known that crystallize in the F (4) over bar 3m space
group. In this work, the yet unreported compounds CoRhMnZ (Z = Ga, Sn,
Sb) and the alloy Co0.5Rh1.5MnSb were investigated in detail by
experimental techniques and theoretical methods. The ab initio
calculations predict the CoRhMnZ compounds to be half-metallic
ferromagnets or to be close to the half-metallic ferromagnetic state.
Calculations of the elastic constants show that the cubic structure is
stable in compounds containing Mn. Both calculations and experiment
reveal that Mn cannot be exchanged by Fe (CoRhFeGa). The low temperature
magnetization of the compounds is in the range of 3.4-5.5 mu B depending
on the composition. The best agreement between experiment and
calculation has been achieved for CoRhMnSn (5 mu B). The other compounds
are also cubic but tend to anti-site disorder. Compared to Co2MnSn it is
interesting to note that the magnetic properties and half-metallicity
are preserved when replacing one of the 'magnetic' Co atoms by a
'non-magnetic' Rh atom. This allows us to increase the spin-orbit
interaction at one of the lattice sites while keeping the properties as
a precondition for applications and physical effects relying on a large
spin-orbit interaction. The Curie temperatures were determined from
measurements in induction fields of up to 1 T by applying molecular
field fits respecting the applied field. The highest Curie temperature
was found for CoRhMnSn (620 K) that makes it, together with the other
well defined properties, attractive for above room temperature
spintronic applications.
