Critical behaviour of the mean-field ferromagnet Cu1.02[Cr 1.77Ti0.24]Se4

Magnetization, M, and susceptibility, , measurements showed both strong lowering of magnetic moment in comparison with CuCr2Se4 matrix and zero- eld-cooling eld-cooling susceptibility splitting characteristic for the spin-glass behaviour. Isothermal magnetization curves, M(H), easy saturate and large values both of the Curie TC = 253 K and Curie Weiss = 283:5 K temperatures indicate the ferromagnetic order which coexists with the spin-glass state. The critical behaviour investigated around the paramagnetic ferromagnetic phase transition revealed that the values of critical exponents are close to those predicted by the mean eld model for long-range magnetic interactions

Influence of Cu, Ga and Au dopants and technology conditions on the magnetic interactions in HgCr2Se4 single crystals

For single crystals HgCr2Se4 doped by nonmagnetic Cu+, Au2+ and Ga3+ ions and single crystals of HgCr2Se4 matrix growing in different synthesis conditions both the dc and ac magnetic susceptibility as well as the magnetization have been measured. As it follows from the analysis of the obtained results, paradoxically, the dopants strengthen the long range magnetic interactions of the ferromagnetically ordered single crystals under study, evidenced by the higher values of the ordering temperature in comparison with those ones for pure matrix. An influence of the technological processes connected with deficiency and/or excess of Hg on the long range magnetic interactions was not observed