Hall resistivities ρ H , the magnetizations M and the magnetoresistances Δρ have been measured as functions of the applied magnetic field H in the wide temperature range for ferromagnetic systems of CuCr 2 S 4 , Cu 0.5 Zn 0.5 Cr 2 Se 4 and Cr 3 Te 4 , which are considered to have non-trivial spin structures below the temperature T m . For CuCr 2 S 4 and Cr 3 Te 4 , the Hall resistivities have been found to deviate from the ordinary expression ρ H = R 0 H +4π R s M below T m , where R 0 and R s are the ordinary and anomalous Hall coefficients, respectively. The sign change of R s with T has also been observed for all the systems. These behaviors are discussed in relation to their possibly non-trivial magnetic structures.

Unusual Anomalous Hall Resistivities of CuCr2S4, Cu0.5Zn0.5Cr2Se4 and Cr3Te4

Antiferromagnetism of Zn1−xGa2x3Cr2Se4 (for 0.0⩽x⩽0.5)+

Structural properties of normal-type spinel ZnCr 2 Se 4 have been studied as a function of temperature by means of neutron diffraction. It is found that the structural phase transition (T C ) from a cubic to orthorhombic symmetry simultaneously occurs at the antiferromagnetic phase transition temperature (T N ∼21 K), where the cubic and orthorhombic symmetry is 7 O h -Fd3m and 24 D 2h -Fddd, respectively. The structural phase transition is mainly characterized by the cooperative displacements of Se 2- ions, which are induced by a magnetostriction resulting from the magnetic interaction of Cr 3+ ions in CrSe 4 chains along [110]. The antiferromagnetic magnetic structure below T N is made by a spiral magnetic coupling between the ferromagnetic CrSe 4 chains around crystallographic screw axes, which are parallel to an orthorhombic C axis. The spiral long-range order of the spins of Cr 3+ is incommensurate and its periodicity of q along a reciprocal lattice axis C * shows temperature dependence from about 0.47 (2.5 K) to 0.43 (18 K). The spiral periodicity of the spin order along the C axis shows a first order transition at about 21 K.

Correlation between the structural and antiferromagnetic phase transitions in ZnCr2Se4

The magnetization, the susceptibility and the magnetic anisotropy field of Cu x Zn1−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 CuxZn1−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, Okonska-Kozlowska, Broda, Warczewski, Byszewski, 1981) and the neutron diffraction studies a modification of the simple spin spiral forced by a strong m...

Helimagnetism of CuxZn1−xCr2Se4 (for 0.0 ≤ × ≤ 0.1)

Double exchange magnetic interaction and giant negative magnetoresistivity in the spin glass state of the new compound CuCr1.6Sb0.4S4

We present detailed results concerning temperature and field dependences of magnetization, paramagnetic susceptibility, magnetic anisotropy and neutron diffraction for CuxZn1-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.

W. Szamraj

Papers

Transition from helimagnetism to ferromagnetism in CuxZn1-xCr2Se4

Helimagnetism of CuxZn1−xCr2Se4 (for 0.0 ≤ × ≤ 0.1)