Magnetism of III–V crystals doped with rare-earth elements
Abstract
The procedure of measuring static magnetic susceptibility is used for the study of local ordering in III–V crystals containing rare-earth dopants. The dependences of the static magnetic susceptibility on the temperature and magnetic field show a slight paramagnetism at high temperatures due to quasi-molecular Ln 2O3-type centers present in the III–V(Ln) crystals. In such centers, the pairs of Ln 3+ ions are antiferromagnetically ordered by an exchange interaction via the oxygen valence electrons. At low temperatures, the crucial role is played by localization of electrons at shallow donors. Due to the s-f exchange interaction, such localization results either in paramagnetism of the crystals, due to transformation of the Ln 2O3 molecules from the antiferromagnetically ordered state to an ferromagnetically ordered state, or in superparamagnetism, due the formation of bound spin polarons. In this case, the constants of the s-f exchange interaction determined from the temperature dependences of the static magnetic susceptibility are anomalously large. This circumstance probably results from the efficient compensation of spin correlations by the electron-vibration interaction.