RESUMO
The temperature dependence of the magnetic specific heat of the semimagnetic semiconductor Pb(1-x)Gd(x)Te for x = 0.033 and 0.054, over the temperature range from 0.5 to 10 K, in magnetic fields up to 2 T, has been measured and analyzed theoretically. The maxima of the magnetic specific heat in nonzero magnetic fields are shifted to lower temperatures in comparison with theoretical predictions based on the simple cluster model. We propose a mechanism which explains these shifts. According to our model, they are caused by strong hybridization of the 5d shell of gadolinium with band states of the crystal.
RESUMO
We report on the magnetic properties of thoroughly characterized Zn(1-x)Co(x)O epitaxial thin films, with low Co concentration, x = 0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials.
