Double exchange in CrxMn1−xas compounds1)

Abstract

The magnetic moment M and the specific resistivity ϱ of CrxMn1−xAs polycrystals are measured for temperatures between 5 and 300 K and for eight different compositions. Structures in the ϱ(T) and M(T) curves define characteristic temperatures which are used to construct a magnetic phase diagram. The large number of magnetic phases between ferromagnetic MnAs and antiferromagnetic CrAs are explained on the basis of two competing superexchange–double exchange magnetic couplings.

Thermal and Magnetic Properties of CrxMn1−xAs Compounds

“…In addition we confirm and extend the magnetic phase diagram, as proposed recently by Wohl et al [2].…”

“…Polycrystalline samples of CrzMnl,As were prepared as described earlier [2]. Lattice parameters a t 300 K have been determined for these compounds and no indication of two-phase regions have been found [2, 81.…”

“…Until recently only one model has been presented to explain the variety of magnetic phases of Cr,Mnl-,As [2]. This model takes into consideration the resonant states as discussed above.…”

“…For the closely related classical LazCal-,Mn03 DE-SE system, in order to determine the magnetic moment a t T = 0, the percolation probability P of the Mn3+ and Mn4+ pairs must be calculated. Correspondingly, for Cr,Mnl-,As the percolation probabilities of the corresponding triangles have to be calculated (see [2] and Fig. 1).…”

Pressure dependence of the magnetic order in CrAs: A neutron diffraction investigation

“…CrAs is set aside from other recently discovered superconductors, since its superconducting state emerges from a metallic antiferromagnet and not from a spin/charge density wave. Though the exchange mechanism to stabilize the magnetic spiral order remains quantitatively unresolved 12 , it can be qualitatively argued and with consideration of the closeness of the propagation vector to 1/3, that the helical state might be stabilized by ferromagnetic third nearest neighbor exchange interaction 13 , while the exchange interaction between the four spirals might be a weak indirect exchange interaction through the polarization of the conduction electrons, basically RKKY-type. While we do not want to speculate on the pairing mechanism in CrAs, the properties in the region of co-existing antiferromagnetism and superconductivity indicate a explicit dependendance on the electron density of states for both ordering phenomena.…”