On the Mechanisms of Obtaining the Spin-Glass State in the Spinels with Chromium.

Four mechanisms of obtaining the spin-glass state in the spinels with chromium, namely: 1. the competition of the already existing antiferromagnetic (via superexchange) and the partially developed ferromagnetic (via double exchange) interactions, 2. competition of the already existing antiferromagnetic (via superexchange) and the partially destroyed ferromagnetic (via double exchange) interactions, 3. the competition of the ferromagnetic (via superexchange) and ferromagnetic (via double exchange) interactions and 4. local competition of both the superexchange ferromagnetic and antiferromagnetic interactions, have been discussed. The first two items are based on the earlier results of the authors concerning Zn1-xCuxCr2Se4 and CuCr2-xSbxS4, respectively, whereas the second two bring new results concerning both the single crystals of HgCr2Se4 doped with copper (7%), gold (2%) and gallium (8%) and the single crystals of HgCr2Se4 with and without vacancies. A theoretical approach based on the assumption of the random distribution of either dopants or defects (below the percolation threshold) is given to explain and confirm the creation of spin-glass states in all the four cases. [ABSTRACT FROM AUTHOR]