Composition-dependent induced spin and orbital magnetic moments of Ir in Co-Ir alloys from x-ray magnetic circular dichroism

Abstract

X-ray magnetic circular dichroism measurements with the photon helicity modulation technique at Ir ${L}_{2,3}$ absorption edges and sum rule analysis show that Ir develops a composition-dependent induced spin and orbital magnetic moments in hcp ${\mathrm{Co}}_{100\ensuremath{-}x}{\mathrm{Ir}}_{x}$ $(x=5,17,25,32)$ alloys. The total moment per Ir is found to be in the range of $0.39{\ensuremath{\mu}}_{B}--0.1{\ensuremath{\mu}}_{B}$---i.e., decreasing with the increase of $x$. The spin and orbital moments of Ir in the alloys are found to be aligned antiparallel, showing the violation of the third Hund's rule at these compositions. Electronic structure calculations of Co and Ir magnetic moments in ${\mathrm{Co}}_{100\ensuremath{-}x}{\mathrm{Ir}}_{x}$ at $x=25$ within the local spin density approximation illustrate that significant $3d\text{\ensuremath{-}}5d$ hybridization results in the formation of an induced moments at the Ir sites, with the spin moments on the order of $0.2{\ensuremath{\mu}}_{B}--0.3{\ensuremath{\mu}}_{B}$ that are antiparallel to the Ir orbital moment concomitant with a reduced moment on the neighboring Co sites.