Temperature dependence of magnetic anisotropy for single domain L10 FePd crystal and role of the ordering defects

TLDR: In this article, the authors present results of the magnetic measurements for a single variant highly ordered L1 0 FePd crystals, known for its significantly lower ordering temperature (950 vs. 1910 K) and somewhat smaller MAE K 1 of about 2'107 erg/cc.

Abstract: The ordered alloys of Fe with nominally non-magnetic 4d/5d (Rh, Pd, Pt) elements demonstrate an array of an attractive magnetic properties. The high magnetic anisotropy energy (MAE) of the ordered L1 0 FePt is considered as particularly important property for achieving small thermally stable magnetic grains [1]. Recent progress in fabrication and characterization of nano-granular and nano-particulate FePt films puts emphasize on understanding of the temperature dependence of MAE [2]. Theoretical framework for the temperature dependence of the MAE was summarized by Callen and Callen [3]. This theory predicts universal parametric dependence between K 1 (T) and M S (T) which for the uniaxial magnet simply given by the K 1 (M S (T)) ∼ M S 3 in the low temperature region. Measurements on epitaxial FePt films, however, demonstrate K(T) ∼ M S 2 scaling in the wide temperature range [2]. The origin of this behavior was found to be in the magnetic interactions mediated by the Pt induced spin moment [4]. In FePt anisotropic exchange mediated by the induced Pt spin moment appears to be dominating over the Fe contribution and thus leading to the K 1 ∼ M s 2.1 low temperature scaling behavior [4]. In this work we present results of the magnetic measurements for a single variant highly ordered L1 0 FePd crystals. This chemical analog of the FePt is known for its significantly lower ordering temperature (950 vs. 1910 K) and somewhat smaller MAE K 1 of about 2'107 erg/cc. We present results of K 1 (T) measurements on single ordering domain FePd samples which clearly demonstrate different than reported for the FePt thin films scaling behavior K(T) ∼ M3.8. We discuss initial theoretical interpretation provided on the basis of recently measured ordering defects in the form of intermediate disordered phase [5,6].