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Fluctuations of the Molecular Field in the Two‐Ion Model for Temperature‐Induced Metamagnets
Author(s) -
Rudziński W.,
Onyszkiewicz Z.
Publication year - 1991
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221630127
Subject(s) - quartic function , ion , gaussian , dipole , magnetization , mean field theory , metamagnetism , field (mathematics) , physics , condensed matter physics , statistical physics , magnetic field , quantum mechanics , mathematics , pure mathematics
A special quartic spin model of spontaneous metamagnetism, proposed by Onyszkiewicz is considered involving dipole‐octopole interaction between two neighbouring ions. The thermodynamic properties of this model are investigated, using the high‐density expansion method in the approximation including Gaussian fluctuations of the molecular field. The free energy, the magnetization, the octopole parameter as well as mean squares of fluctuations are calculated for A → F metamagnets. The results are then compared with those obtained by the molecular field approximation. Moreover, a comparison of the results with those obtained earlier for the so called four‐ion model confirm effectiveness of the two‐ion model also in such refined procedure as the Gaussian fluctuation approximation.