Magnetic energy distribution in polycrystalline sputtered CoCr magnetic thin films

¹ Center for Nanomaterials Research, Rutgers University, Busch Campus, Piscataway, New Jersey 08854, USA
² Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37234, USA
³ Komag Incorporated, 1710 Automation parkway, San Jose, CA 95131, USA
⁴ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6064,USA

Corresponding author: jafarhan@rci.rutgers.edu

Received: 3 May 2007
Accepted: 7 February 2008
Published online: 29 April 2008

Abstract

Magnetic thin films of Co₈₀Cr₁₆Ta₄ were sputtered onto identical CrMo seed-layers at –200 V bias and 3 different substrate temperatures (150, 200, and 250 °C). Energy-filtered transmission electron microscopy (EFTEM) was performed to analyze Cr levels at the grain boundaries as well as inside the grains. These quantitative Cr measurements were used to estimate the local values of magnetocrystalline anisotropy (K_u) and, together with grain size distributions, calculate the product of K_u and the grain volume (K_uV), a quantity which is a measure of thermal stability. The results show that the coercivity as well as the fraction of stable grains increased with increasing substrate temperature. The increase in the fraction of stable grains is produced by the enhancement in the K_u value due to Cr depletion of the grain interiors and the magnetic decoupling between the grains from Cr grain-boundary segregation.