Magnetic properties of small Pt-capped Fe, Co and Ni clusters: A density functional theory study

TL;DR

This study uses density functional theory to analyze the magnetic anisotropy and moments of small Fe, Co, Ni, and Pt-capped Fe clusters, revealing size and composition-dependent magnetic properties that differ significantly from bulk materials.

Contribution

It provides detailed DFT calculations of magnetic properties for various small clusters, including the effect of Pt capping, which is a novel insight into nanoscale magnetism.

Findings

MAE varies significantly among clusters, with some exceeding bulk values.

Pt capping enhances the magnetic anisotropy energy of Fe clusters.

Ni clusters show much smaller MAE compared to bulk Ni.

Abstract

Theoretical studies on M$_{13}$ (M = Fe, Co, Ni) and M$_{13}$Pt$_n$ (for $n$ = 3, 4, 5, 20) clusters including the spin-orbit coupling are done using density functional theory. The magnetic anisotropy energy (MAE) along with the spin and orbital moments are calculated for M$_{13}$ icosahedral clusters. The angle-dependent energy differences are modelled using an extended classical Heisenberg model with local anisotropies. From our studies, the MAE for Jahn-Teller distorted Fe$_{13}$, Mackay distorted Fe$_{13}$ and nearly undistorted Co$_{13}$ clusters are found to be 322, 60 and 5 $\mu$eV/atom, respectively, and are large relative to the corresponding bulk values, (which are 1.4 and 1.3 $\mu$eV/atom for bcc Fe and fcc Co, respectively.) However, for Ni$_{13}$ (which practically does not show relaxation tendencies), the calculated value of MAE is found to be 0.64 $\mu$eV/atom, which is approximately four times smaller compared to the bulk fcc Ni (2.7 $\mu$eV/atom). In addition, MAE of the capped cluster (Fe$_{13}$Pt$_4$) is enhanced compared to the uncapped Jahn-Teller distorted Fe$_{13}$ cluster.