New model to predict thermomagnetic properties of nanostructured magnetic compounds

Abstract

The development of new materials showing the magneto-caloric effect (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, $$\Delta S_\textrm{M}$$ Δ S M , the magnetization-related change of the specific heat, $$\Delta C_{P,H}$$ Δ C P , H , and the relative cooling power, RCP) via calculation from magnetization measurements as a function of temperature, M(T). However, fitting the M(T) data is difficult 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 different approach enabling proper fitting 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 fits to M(T) curves of polycrystalline, bulk $$\hbox {La}_{0.67}\hbox {Ba}_{0.33}\hbox {MnO}_3$$ La 0.67 Ba 0.33 MnO 3 as well as $$\hbox {La}_{1-x}\hbox {Sr}_{x}\hbox {MnO}_3$$ La 1 - x Sr x MnO 3 ($$x=$$ x = 0.2, 0.3, 0.4) and $$\hbox {La}_{0.7}\hbox {Ca}_{0.3}\hbox {MnO}_3$$ La 0.7 Ca 0.3 MnO 3 nanostructured materials from various authors.