Temperature- and field-induced entropy changes in nanomagnets

Authors

Ralph Skomski, University of Nebraska-LincolnFollow
Christian Binek, University of Nebraska, LincolnFollow
Tathagata Mukherjee, University of Nebraska-LincolnFollow
Sarbeswar SahooFollow
David J. Sellmyer, University of Nebraska-LincolnFollow

Date of this Version

2-28-2008

Comments

Published in JOURNAL OF APPLIED PHYSICS 103, 07B329 (2008). Copyright © 2008 American Institute of Physics. Used by permission.

Abstract

Room-temperature magnetic-entropy changes in nanostructures for magnetic refrigeration are investigated by model calculations. Using a mean-field approach, the magnetic entropy is calculated as a function of temperature, magnetic field, particle size, anisotropy, and interaction strength. Both isotropic (Heisenberg) and uniaxial (Ising and XY) anisotropies are considered. The nanoparticle entropy strongly depends on the character of the anisotropy, in contrast to atomic ferromagnetism, where the anisotropy energy is much smaller than the interaction energy. Most promising are isotropic particles and particles with weak easy axis anisotropy, as well as easy-plane particle with the field in the plane. The optimum nanoparticle size is not much larger than 1 nm, because the relative magnetization direction in a nanoparticle is usually frozen and do not contribute to the entropy change.