Helimagnetism of Cu_xZn_1−xCr₂Se₄ (for 0.0 ≤ × ≤ 0.1)

Abstract

The magnetization, the susceptibility and the magnetic anisotropy field of Cu _x Zn_1−xCr₂Se₄ compounds have been studied at low temperatures (down to 2.9 K) in: high magnetic stationary fields (up to 14 T), high pulsed magnetic fields (up to 25 T), medium magnetic stationary fields (up to 0.6 T). The magnetic structure of these spinels was studied by neutron powder diffraction.

The magnetic properties of Cu_xZn_1−xCr₂Se₄ are explained in terms of the molecular field approximation assuming the existence of 90° exchange interactions, ferromagnetic for Cr-Se-Cr between the nearest Cr ions and antiferromagnetic for Cr-Se-Se-Cr between the second-nearest Cr ions. The exchange parameters and integrals for the whole series under consideration are calculated. Taking into account the three magnetic phase transitions observed in these spinels (Juszczyk, Krok, Okońska-Kozłowska, Broda, Warczewski, Byszewski, 1981) and the neutron diffraction studies a modification of the simple spin spiral forced by a strong magnetic field is described.