New model to predict thermomagnetic properties of nanostructured magnetic compounds

Abstract

The development of new materials showing the magneto-caloric efect (MCE) requires fast and reliable characterization methods. For this purpose, a phenomenological model developed by M. A. Hamad has proven to be a useful tool to predict the magnetocaloric properties (the isothermal magnetic entropy change, ΔSM, the magnetization-related change of the specifc heat, ΔCP,H, and the relative cooling power, RCP) via calculation from magnetization measurements as a function of temperature, M(T). However, ftting the M(T) data is difcult for broad, smoothed-out transition curves which are often observed for material systems such as core-shell nanoparticles, nanowires, nanowire fabrics or nanoparticle hybrid materials. Thus, in this contribution we present a diferent approach enabling proper ftting of such magnetization data via the use of an asymmetric Boltzmann sigmoid function, which provides a clear physical background and enables to properly describe the broad and smoothed out transitions of nanomaterials. As examples for our procedure, we present fts to M(T) curves of polycrystalline, bulk La0.67Ba0.33MnO3 as well as La1−xSrxMnO3 (x = 0.2, 0.3, 0.4) and La0.7Ca0.3MnO3 nanostructured materials from various authors.