Effect of Cu Impurities on ${\rm K}_{\rm AF}$ in IrMn$_{1 - {x}}$Cu$_{x}$/CoFe Exchange Bias System

Abstract

We report on the effect of introducing non-magnetic Cu as an impurity in IrMn in IrMn/CoFe exchange bias systems. Films were prepared by sputtering from a specially designed target. Thermal activation measurements and determination of the grain size distribution from TEM analysis of these samples allowed the anisotropy constant (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AF</sub> ) of the IrMn to be determined. The level of Cu impurity in the IrMn was varied from 0.0% to 17.7% at.% Cu. The anisotropy constant initially rose from (10 plusmn 1) times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> erg/cc at 0.0 at.% Cu to (13 plusmn 2) times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> erg/cc at 1.8 at.% Cu and reduced with increasing Cu concentration to (4.7 plusmn 1) times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> erg/cc at 17.7 at.% Cu. The change in K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AF</sub> is explained by the effect of the Cu on the stoichiometry of the IrMn which in turn affected the ordering of the L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> phase causing the variation in K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AF</sub> . The exchange bias (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex</sub> ) of these samples was reduced ~40% with only 1 at.% Cu in the IrMn, and continued to reduce exponentially down to 5 Oe with 17.7 at.% Cu.