Investigation of spin and orbital moments of L1 FePtRh thin films

Abstract

Fe50Pt50−xRhx films have attracted much interest recently due to their potential usage in heat assisted magnetic recording media and the ferromagnetic (FM) to antiferromagnetic (AFM) transition as Rh concentration is increased. In this study, we present an investigation of the spin moment (ms) and orbital moment (ml) of Fe in Fe50Pt50−xRhx films using x-ray magnetic circular dichroism. The measurements were made in the soft x-ray region along the film normal, which corresponds to the easy axis of the (001) textured L10 FePt with uni-axial magnetic anisotropy. They show that the magnetic moment of Fe mainly contributes to the whole magnetization of the films. The decrease of ml with Rh doping concentration implies a decrease of magneto-crystalline anisotropy, whereas the significant decrease of ms is consistent with the FM to AFM transition at above 15 at. % of Rh.

Orbital moment anisotropy in ultrathin FePt layers

“…We should note that the calculations of Ravindran et al [13] and Daalderop et al [11] (Table I) The agreement still holds if we take into account the dipolar correction (7m T ) to m eff s , of the order of 2% [19] to 20% [23]. We should note that this m o /m eff s (⊥) ratio is smaller by a factor around 2 with respect to most of the experimental ratios reported in the literature for FePt [20][21][22] and slightly smaller than the value reported by Imada et al [8] ( Table I).…”

“…This is the case of Soares et al [10], where a reevaluation of the data showed the presence of a nonlinear background that overestimated m o . In the case of Xu et al [20], a reduced integration range (up to 735 eV) may cause an overestimation of m o /m eff s by 65%, according to the inset of Fig. 3.…”

“…The experimental values previously reported were given for nanoparticles [22] or for thicker films with similar [8,21] or higher [20] order parameters. This could explain part of the discrepancy with our experiments.…”

“…In addition, there is a serious discrepancy between most experimental determinations of Fe m o deduced from XMCD sum rules [10,[20][21][22] (0.2-0.3μ B ) and those obtained from ab initio calculations [6,[11][12][13]23] (0.06-0.13μ B ). The large experimental values for m o reported in the literature can be interpreted as due to the enhancement of the orbital moment in the ordered FePt alloy and the source of MAE [10,22].…”

“…The large experimental values for m o reported in the literature can be interpreted as due to the enhancement of the orbital moment in the ordered FePt alloy and the source of MAE [10,22]. Nevertheless, such measurements have been performed for randomly oriented nanoparticles [22] or normally to the films [20,21] and angle dependent measurements are missing.…”