Transition from helimagnetism to ferromagnetism in Cu_xZn_1-xCr₂Se₄

Abstract

We present detailed results concerning temperature and field dependences of magnetization, paramagnetic susceptibility, magnetic anisotropy and neutron diffraction for Cu_xZn_1-xCr₂Se₄ spinels. Particular emphasis is put on the gradual transition from helimagnetism to ferromagnetism as a function of concentration x. The transition takes place through an intermediate structure for 0.05 ≤ x ≤ 0.8 with the ferromagnetic component growing with concentration. It is suggested that a double exchange mechanism predominates as x increases and this can be regarded as the origin of the transition.