Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy

Abstract

We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlOx and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlOx, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlOx, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures.

Spin–Orbit Effects in CoFeB/MgO Heterostructures with Heavy Metal Underlayers

“…Note that M/V di®ers from the saturation magnetization ðM S Þ when a magnetic dead layer [53][54][55] forms within the magnetic (CoFeB) layer or when proximity induced magnetization (PIM) appears in the neighboring layer. [56][57][58] For the¯lms studied here, we¯nd evidence of nonzero magnetic dead layer thickness in many¯lm structures but no indication of the PIM.…”

“…53 To obtain a large K I in CoFeB/MgO based structures, it is considered important to remove the boron from the CoFeB/ MgO interface and promote the Fe-oxygen bonding that is essential for establishing perpendicular magnetic anisotropy. 58,[68][69][70] The HM underlayer has to enable boron di®usion from the CoFeB layer; however too much di®usion may promote intermixing of HM and CoFeB, which will result in an increase of t D (and possible degradation of M S Þ. We infer that Ta 48 N 52 (Q $ 0.7%) is at the right balance of promoting boron di®usion and simultaneously limiting the intermixing.…”

Magnetocrystalline anisotropy of FePt: A detailed view

“…We used E max =100 Ry, meaning that all eigen-states were included. Even though the formula was originally derived for systems with only one atomic type, the relation between the MCA energy and the anisotropy of orbital magnetic moments has been frequently applied also for multicomponent systems [12,[53][54][55][56][57]. In such a case an estimate of E MCA can be made by evaluating (cf.…”

Copper dusting effects on perpendicular magnetic anisotropy in Pt/Co/Pt tri-layers

“…This results in an anti-symmetric exchange like Dzyaloshinskii-Moriya interactions 6 which can stabilize new phases like skyrmions. 7 Extensive research work has been carried out in recent times in the investigation of physical properties such as magnetization, 8 anisotropic constant 2 and the effect of introducing ultra-thin films of Cu, Ta etc. 9 (known as dusting) in proximity with Co layer in Pt/Co/Pt thin films.…”