Magnetic structure of Cu0.3Zn0.7Cr2Se4

Ferromagnetic spinel system Cu1-xZnxCr2Se4 has been studied by neutron diffraction, NMR and magnetization measurements on both polycrystalline and single crystal samples. The magnetic state are discussed mainly for x = 0.7: At low temperature, the system is essentially in the conically ordered state, and the uniform magnetization M and the modulation vector Q(m) are along <100> in zero magnetic field but not necessarily parallel to each other. All Cr moments within a plane perpendicular to Q(m) are parallel, where the conical angle theta(c) of the Cr moment is similar to50degrees and the pitch deltaphi of the azimuthal angles phi is estimated to be similar to38degrees. The width of the random distribution of deltaphi around the average value increases rather significantly with increasing temperature T, while the correlation length of the ferromagnetic component does not exhibit significant change up to room temperature. When the external magnetic field is applied, the conical axis of each domain rotates toward the field direction without changing the modulation vector Q(m). Brief discussion on the relationship between the non-trivial magnetic structure and the behavior of the anomalous Hall resistivity is also given.