Interpretation of the Magnetic Properties of the Rare Earth Chromites and the Rare Earth Manganites

Abstract

The magnetostatic properties of the rare earth chromites, RCrO3, and those of the rare earth manganites, RMnO3, have been studied between 1.6° and 1500°K, in fields up to 28 000 Oe. These compounds are antiferromagnetic; they present two Néel points. For the rare earth chromites, the first Néel point varies between 112°K for LuCrO3 and 282°K for LaCrO3; it corresponds to the ordering of the spins of the Cr3+ ions; below this transition temperature, a ferromagnetism is superimposed upon the antiferromagnetism. The second Néel point is situated in the neighborhood of the temperature of liquid helium; it corresponds to the ordering of the moments of the rare earth ions. These properties are interpreted in terms of a molecular-field model. The lattice of the Cr3+ ions and that of the R3+ ions are decomposed into two identical sublattices. The Cr-Cr exchange interaction is negative; it is dominant; it defines principally the first Néel point. The R-R interaction is negative and weaker; it defines the second Néel point. The R-Cr interaction can be positive or negative, and its magnitude is small. The configuration of the moments of the chromium ions can be weakly ferromagnetic; this would induce a ferromagnetic polarization of the rare earth ion, and can give rise to a compensation temperature. With the perovskite rare earth manganites, the first Néel point is between 45°K for EuMnO3 and approximatively 131°K for LaMnO3; a ferromagnetism is superimposed upon the antiferromagnetism. These substances behave like the rare earth chromites. With the hexagonal rare earth manganites, the first Néel point is characterized only by a change in the slope of the susceptibility curve; there is no superimposed ferromagnetism. Near 10°K, it appears a ferromagnetic term which can be induced by the ordering of the spins of the rare earth ions. The rare earth-manganese interaction is determined in the molecular-field approximation. The interpretation of the magnetic properties of the rare earth chromites has been published in the “Compt. Rend, 262, 799, 866 (1966); a full report on the interpretation of the magnetic properties of the rare earth maganites will be published in “J. Phys.”.