Grout and March utilized the exact solution of the two-dimensional Ising model to relate the internal energy E(T) to the magnetization M(T). These authors then used Bloch spin-wave theory to relate E and M at low temperatures for both insulating and metallic ferromagnets in three dimensions.
Ayuela and March, very recently, have used experimental data on the specific heat and the magnetization to show that for metallic Fe and Ni the E – M data collapse on to a single curve. A model with long-range exchange interactions is presented to allow insight to be gained into this feature. Reference is also made briefly to the ferromagnetism of the electron-doped In2 O3:Cr system.
Two antiferromagnetically ordered materials are next considered, though now more qualitatively than for the ferromagnets. The first is the spin −1/2 kagome antiferromagnet ZnCu3(OH)6 Cl2, and the second is the κ-phase layered material (BEDT-TTF)2 Cu[N(CN)2]Cl. Anomalous low-temperature specific heat Cv (T) is emphasized, with an enhancement that is reduced by application of a magnetic field. Further work is proposed, both experiment and theory, to understand the precise nature of the low-lying magnetic excitations in the latter κ-phase material. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009