INFLUENCE OF THE DEFECTIVENESS OF THE CRYSTAL LATTICE ON THE METAMAGNETIC PHASE TRANSITIONS IN Cd_1-xCu_xCr₂S₄ (WHERE x <= 0.2) AND ZnCr_2-In_xSe₄ (WHERE x<= 0.14). J. Warczewski, J. Krok-Kowalski, T. Grón, Universily of Silesia, Institute of Physics, ul. Uniwersytecka 4, PL-40-(007 Katowice, Poland

The stability of spinel crystal structures decreases with the increase of the anion radius. It is connected with the increase of the anion covalency [1] and the vacancy concentration [2] in the sequence: O,S,Se and Te.

High structure defectiveness of the spinels under investigation is confirmed by the x-ray studies [3] and the vacancy model [2]. Mixed valence of chromium ions (Cr²⁺-Cr³⁺) resulting from the defectiveness mentioned above is the main cause of the metamagnetic phase transition in Cd_1-xCu_xCr₂S₄, where as in the case of

ZnCr_2-xIn_xSe₄ it contributes to this effect by the increase of the values of the critical magnetic fields.

References:

[1] H. Von Philipsborn, Z. Kristallogr., 133 (1971), 464.

[2] T. Gron, Phil. Mag. B, 70 (1994), 121.

[3] H. Rej, J. Warczewski and I. Okonska-Kozlowska, Materials Science Forum, Vol. 133-136 (1993), 733.