Theoretical predictions of interface anisotropy in the presence of interdiffusion (invited)

Abstract

The first ab initio electronic structure calculations of the magnetocrystalline anisotropy of superlattices with imperfect interfaces are presented. Specifically the possibility of an interdiffusion between the layers at the interface in Co/Pd and Co/Pt superlattices is considered. The electronic structure calculations use the local spin-density formalism as implemented with the layer Korringa–Kohn–Rostoker method. Interdiffusion at the interface is modeled in two distinct ways. In the first approach a diffuse interface is represented by ordered arrangement of substitutions, while in the second approach interdiffusion is assumed to produce a substitutionally disordered random alloy on the layers at the interface, which is solved using the coherent potential approximation. The calculated interface anisotropies for superlattices with perfect and imperfect interfaces are, on average, modeled accurately by a simple Néel-type model. This model always predicts a reduction in magnetic anisotropy resulting from the presence of defects.

Role of orbital polarization in calculations of the magnetic anisotropy

“…3 Attempts are under way to include the effects of interface disorder, surface steps, and other imperfections. 4,5 But questions remain even for ideal systems like bulk Fe and Ni. For Ni in particular it is not clear at all at this point if the LSDA leads to the correct easy axis.…”

Anisotropic short-range structure of Co0.16Pd0.84 alloy films having perpendicular magnetic anisotropy

“…[1][2][3][4][5] Co-Pd and Co-Pt alloy films were since found to exhibit PMA, and relationships between alloy composition, preparation conditions, microstructure, and magnetic properties have been established. [6][7][8][9][10][11] Weller et al 7,9 reported that Co-Pt and Co-Pd alloys have PMA, 100% remanence, and high coercivity comparable to those in their multilayer systems.…”

“…A polarized extended x-ray absorption fine structure ͑EXAFS͒ study of Co-Pt alloy films concludes its origin is likely to be clustering ͑ordering͒ of Co atoms in surface normal ͑111͒ planes yielding internal interfaces 12 based on a model of intermixing at the interface of superlattice. 4 As for the Co-Pd alloy, the origin of its PMA was speculated to be a similar compositional anisotropy of Co atoms in the Pd matrix 10 without direct evidence. The origin of PMA in the alloys has remained unclear because of limited direct structural information and lack of theoretical study while the PMA in multilayers has been explained by the interfacial, magnetocrystalline, and magnetoelastic anisotropy ͑MEA͒ originating from the uniaxial asymmetry.…”

“…The origin of PMA in the alloys has remained unclear because of limited direct structural information and lack of theoretical study while the PMA in multilayers has been explained by the interfacial, magnetocrystalline, and magnetoelastic anisotropy ͑MEA͒ originating from the uniaxial asymmetry. [1][2][3][4] To investigate the short range structure of Co-Pd alloy films, we analyzed polarized EXAFS's which provide direct short range information about the average Co environment. Polarized EXAFS was chosen because of its ability to provide both directional-and chemical-specific nearest-neighbor information around Co absorbers.…”

Geometric and magnetic properties of Co/Pd system

“…On the other hand, it acts to reduce magnetocrystalline anisotropy (MCA) [10]. Defects from interdiffusion also reduce magnetic anisotropy [11]. Hence, depending on the strength of each contribution, PMA may be enhanced or reduced by the surface roughness.…”