Magnetic Field Dependence of Thermodynamic Properties of Antiferromagnets; Adiabatic Magnetization

Abstract

The thermodynamic properties of cubic or uniaxial antiferromagnets are examined using spin wave theory. The specific heat, magnetization, and parallel susceptibility are shown to be exponentially increasing functions of applied field for values of H Q less than the critical spin-flopping field. Since this field dependence suggests that an antiferromagnet can be cooled by the adiabatic application of a magnetic field, the theory of adiabatic magnetization is investigated. Field-dependent nuclear spin effects are evaluated on an effective field model by perturbation theory and are included in the analysis. It is found that when spin wave effects are dominant, cooling should be observed; at lower temperatures, when nuclear effects are non-negligible, either cooling or heating may be observed, depending on the initial temperature and final value of the magnetic field. The dependence of the cooling on the physical parameters of the antiferromagnet is discussed and detailed calculations are made for MnF 2 .

Isofield low-temperature specific heat of single-crystalHo1−xYxNi2Massalami1, Takeya2, Chaves3 2004Phys. Rev. B

“…Equation (6) is equivalent to Eq. (25) of Joenk 22 and, moreover, does reproduce our earlier reported zero-field limit. 23 The magnetic entropy in this range of field and temperature is given as…”

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

“…5 It has been known for a long time that the isothermal reduction of a magnetic field gives rise to a decrease in entropy in some antiferromagnetic and ferrimagnetic systems. 6,7 This inverse magnetocaloric phenomenon was supposed to produce small effects and has been largely ignored. Recently, however, it has been shown that in some ferromagnetic 8 and metamagnetic 9 systems, inverse MCE can have an amplitude comparable to the conventional effect detected in giant magnetocaloric intermetallic materials.…”

Magnetocaloric effect of the (Pr,Ca)MnO3 manganite at low temperatures

“…Usually, the desired temperature for maximum magnetocaloric values are obtained by different stoichiometric sample composition or by sample doping, in order to shift the magnetic transition temperature. Up to now, the literature has not explored systems where antiferromagnetic [10] and ferromagnetic phases coexistence [11] are involved, as well as the behavior of MCE when metamagnetic transitions occurs. For this reason, there is no satisfactory explanation for the behavior observed for DS mag ; which turns to be positive or negative in a given temperature range [12].…”