Thursday, June 27, 2013

1306.6236 (K. Kn\'ıžek et al.)

Effect of rare-earth ions on magnetic properties of

K. Kn\'ıžek, Z. Jirák, J. Hejtmánek, M. Veverka, O. Kaman, M. Maryško, G. André
The crystal and magnetic structure of La$_{0.6}$Tb$_{0.2}$Ca$_{0.2}$CoO$_3$ perovskite has been determined from the powder neutron diffraction measured at the temperatures from 1.8 to 300 K. Enhancement of the diffraction peaks due to ferromagnetic or cluster glass ordering is observed below $T_C=55$ K. The moments evolve at first on Co sites, and ordering of Ising-type Tb$^{3+}$ moments is induced at lower temperatures by a molecular field due to Co ions. The final magnetic configuration is collinear F$_x$ for cobalt subsystem, while it is canted F$_x$C$_y$ for terbium ions. The rare-earth moments align along local Ising axes within \textit{ab}-plane of the orthorhombic $Pbnm$ structure. The behavior in external fields up to 70-90 kOe has been probed by the magnetization and heat capacity measurements. The presence of rare earths contributes to significant coercivity and remanence that both steeply increase with decreasing temperature. A remarkable manifestation of the Tb$^{3+}$ Ising character is the observation of a low-temperature region of anomalously large linear term of heat capacity and its field dependence.
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