The effect of Cu additions in FePt–BN–SiO₂ heat-assisted magnetic recording media

Abstract

Structural and chemical order impact magnetic properties of solids, which are governed by spin–orbit coupling and exchange interaction. The ordered L10 phase of FePt is a key material to heat-assisted magnetic recording; to enable high storage density, a solid understanding is needed of structural and chemical disorder at small length scales, as well as associated modifications of the electronic band structure. Here, we investigate the effect of boron and copper additions (≲6 mol% Cu) on structural and magnetic properties of L10 FePt granular media. Two copper-driven mechanisms, although competing, can lead to improvements in both structural and magnetic properties. In particular, the Cu substitution on the Fe-site leads to a degradation of magnetic properties due to the delocalized electron orbitals originating from a larger Cu d-orbital occupancy. At the same time, Cu substitution leads to an enhanced crystallographic order and consequently magneto-crystalline anisotropy, which offsets the former effect to a large extent. Our study is based on magnetometry, x-ray absorption spectroscopy, ab-initio calculations and a phenomenological theory of disordered FePt granular media. We do not observe a sizable modification to Fe moments and electronic configuration; Cu reveals two different resonances associated with the presence and absence of Cu–B bonds that vary with total Cu concentration.

Chiral Spin Textures in Amorphous Iron–Germanium Thick Films

“…A high degree of orbital alignment manifests a large orbital moment as reported in L 1 0 FePt. [ 53,54 ] We observe a significant drop of the orbital‐to‐spin‐moment ratio both as a function of Fe concentration ( x ≲ 0.61) and temperature, for example, near 140 K for x = 0.52 (Figure 1d). As shown below, the suppression of the orbital moment coincides with the emergence of non‐collinear helical spin textures.…”

Electronic structure of cobalt valence tautomeric molecules in different environments

“…The binding energies are referenced to the carbon 1s peak at 284.7 eV to compensate for charging effects. Owing to negligible contributions from inelastic scattering of excited electrons, the commonly used product functions consisting of an asymmetric Lorentzian and Gaussian 74,75 to fit XAS and IPES spectra can be simplified to a finite set of symmetric Gaussians. The corresponding resonances are assigned to groups of orbital levels derived from density functional theory.…”

Ejection of boron from L10 phase for sputtered FePt-BN granular films by post-annealing

“…2) For HAMR media, it is necessary to have magnetically isolated fine FePt grains to prevent magnetization reversal due to exchange coupling, and highly ordered columnar FePt grains with cplane sheet texture. In order to achieve these requirements, many studies to add grain boundary materials (GBMs), such as TiO 2 , [3][4][5] C, [6][7][8] MgO, 9) Ta 2 O 5 , 10) B 2 O 3 11) SiO 2 , 12-16) Al 2 O 3 , [17][18][19] Cr 2 O 3 , 20) MnO, 21) WO 3 , 22) AlN, 23) TiN, 24) TaN, 25) ZrO 2 , 26) BN 27,28) into FePt magnetic thin films to separate neighboring magnetic grains and promote the exchange decoupling have been done. According to our previous report, saturation magnetization (M s ) of the granular film depends on the melting point of the GBMs.…”