Formal approach to various properties of antiferromagnets

Journal Article · Thu Dec 01 00:00:00 EST 1977 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00661549· OSTI ID:5240017

Goldstein, L; Goldstein, J C

The formal representation of thermal and magnetic properties of moderately anisotropic antiferromagnets in the presence and absence of a constant, uniform external magnetic field is discussed both in selective ordered configurations and in the paramagnetic phase. The mean-field-theoretical formalism is shown to give a satisfactory account of the magnetic properties of a class of two-sublattice antiferromagnets in those ordered configurations where the applied magnetic field is at a right angle to the direction of the spontaneously evolving sublattice magnetic moments. Predictions of mean-field theory on the linearity of the magnetic moment in the applied field strength and the attendant invariant molar susceptibility throughout the relevant portions of the configuration phase diagrams, phase-boundary lines included, are seen to be well satisfied. This is verified in detail on the typical antiferromagnet MnCl/sub 2/x4H/sub 2/O, where the Mn/sup 2 +/ ions in their /sup 6/S/sub 5/2/ ground state determine the magnetic properties and fwhich numerous magnetic and thermal measurements have been accumulated in both the ordered and paramagnetic phases. In contrast with the magnetic properties, mean-field theory is less successful in accounting for the thermal properties of antiferromagnets, but its qualitative predictions agree well with the observations. In the paramagnetic phase, the isotropic nearest-neighbor exchange-coupled model system is used. Here the formal approach corresponds to a series expansion of the various properties in ascending powers of J/kT, in the absence of magnetic field, with an additional magnetic-field-exchange double series in the presence of an external field. In those temperature and field-strength regions where convergence is satisfactory, the above approach is shown to give a good account of the observed thermal properties of the manganese compound in the absence of magnetic field, as well as of the low-field paramagnetic susceptibility

• Research Organization: University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico
• OSTI ID: 5240017
• Journal Information: J. Low Temp. Phys.; (United States), Vol. 29:5
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANTIFERROMAGNETISM
SPECIFIC HEAT
MAGNETIC MOMENTS
MAGNETIC SUSCEPTIBILITY
PARAMAGNETISM
PHASE DIAGRAMS
TEMPERATURE DEPENDENCE
DIAGRAMS
MAGNETIC PROPERTIES
MAGNETISM
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
656000* - Condensed Matter Physics
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