Magnetic entropy changes in nanogranular Fe:Ni61Cu39

Steven A. Michalski, University of Nebraska-Lincoln
Ralph Skomski, University of Nebraska-Lincoln
T. Mukherjee, University of Nebraska-Lincoln
X. Z. Li, University of Nebraska-Lincoln
Christian Binek, University of Nebraska-Lincoln
David J. Sellmyer, University of Nebraska-Lincoln

Document Type Article

Copyright 2011 American Institute of Physics

Abstract

Artificial environment-friendly Gd-free magnetic nanostructures for magnetic cooling are investigated by temperature-dependent magnetic measurements. We consider two-phase nanocomposites where nanoclusters (Fe) are embedded in a Ni₆₁Cu₃₉ matrix. Several composite films are produced by cluster deposition. The average Fe cluster size depends on the deposition conditions and can be tuned by varying the deposition conditions. The quasiequilibrium Curie temperature of the Fe particles is high, but slightly lower than that of bulk Fe due to finite-size effects. Our experiments have focused on ensembles of 7.7 nm Fe clusters in a matrix with a composition close to Ni₆₁Cu₃₉, which has a T_C of 180 K. The materials are magnetically soft, with coercivities of order 16 Oe even at relatively low temperature of 100 K. The entropy changes are modest, -DS¼0.05 J/kg K in a field change of 1 T and 0.30 J/kg K in a field change of 7 T at a temperature of 180 K, which should improve if the cluster size is reduced.