A change of magnetic moment of Cr ion with the magnetic phase transition in CuCr2Se4

In order to obtain information about the magnetic moment of CuCr2Se4 and the changes in the Curie point, we have investigated the magnetic structure and the temperature dependance of the magnetic susceptibility. Neutron diffraction experiments were done on the powder of a CuCr2Se4, sample both at 10 K and at 295 K. The magnetic measurements were done in the temperature range 295-720 K. CuCr2Se4. which crystallizes in the normal spinel structure, is a collinear ferromagnetic. The obtained magnetic moment mu(Cr) = 2.81 mu(B) (at 10 K) and the interatomic distances indicate that in the ferromagnetic phase chromium is in the oxidation state between + 3 and + 4. On the other hand, the effective magnetic moment mu(eff)(Cr) = 4.4 mu(B), obtained from the susceptibility measurements in the paramagnetic phase, corresponds to chromium in an oxidation state between +2 and + 3. The spin value. assuming a quenched moment, is S = 1.40 and S = 1.75 in the ferromagnetic and in the paramagnetic phase, respectively. At the Curie point; T-c = 450 K, the phase transition of the first order with the change of magnetic moment and valence of the chromium ion rakes place. (c) 1998 Elsevier Science B.V. All rights reserved