Spin reorientation by Ni doping in Cu1−Ni Cr2O4 spinels with  x = 0 and 0.1, and evidence for canted magnetic Cr order above the onset of a ferromagnetic Cu

Abstract

In ferrimagnetic spinels AB2O4 the magnetic structure is strongly influenced by lattice distortions, geometric frustration and the electronic properties of the cations at the A and B sites.Here, we report a comprehensive study on the temperature dependence of the magnetic structure of CuCr2O4 and Cu0.9Ni0.1Cr2O4 using neutron diffraction. CuCr2O4 undergoes a first continuous magnetic transition around 155 K into a canted long-range spin order on the Cr sublattice established by an antiferromagnetic and a ferromagnetic mode. Below 130 K a second transition occurs into a ferromagnetic order on the Cu sublattice resulting in a ferrimagnetic spin arrangement. Correlations between the appearance of magnetic modes and changes in the lattice geometry at different temperatures are discussed giving insight to magnetoelastic coupling. The occurrence of a ferromagnetic Cr mode above 130 K questions the common interpretation that a strong antiferromagnetic coupling between A and B spins in ferrimagnetic AB2O4 spinels is responsible for spin canting. From our neutron diffraction measurements of Cu1−xNixCr2O4 we identify a spin reorientation for the ferromagnetic modes with a nickel content between x = 0 and 0.1. I. INTRODUCTIONCurrent interest in functional materials has initiated many studies on spin, lattice, and orbital degrees of freedom, especially focusing on their mutual interactions. Magnetic oxides like spinels with the general formula AB2O4, belong to this class of materials. Spinels show many types of spin arrangements due to a large variety in the magnetic interactions, magnetoelastic and magnetodielectric effects, geometrical frustration etc. [1]. Normal spinels