Tailoring Magnetic Anisotropy Gradient Kai Liu, University of California-Davis, DMR 1008791

1. Tailoring Magnetic Anisotropy GradientKai Liu, University of California-Davis, DMR 1008791 Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. Typically, the anisotropy gradient has been achieved by changing the sample growth conditions. We have demonstrated a new approach of using post-deposition Ar ion irradiation to create an anisotropy gradient in Co/Pd multilayer films, as shown in Fig. 1. As the irradiation energy increases, and so does the ion penetration depth, structural damage propagates downwards. The destruction of the surface anisotropy causes the local magnetic easy axis to fall into the plane of the film. In addition, we have achieved graded media made of (001)-oriented FePt by using a PtMn underlayer. It is promising that using a combination of these degrees of freedom (irradiation, underlayer, composition, layer thickness, sputtering pressure, etc) one can dial up the desired magnetic anisotropy gradient. Work done in collaboration with HZDR (Germany), National Tsing Hua University (Taiwan), and NIST. Fig. 1: Hysteresis loops of Ar+ irradiated Co/Pd films, with field applied (a) perpendicular and (b) parallel to film plane, exhibit a magnetic anisotropy gradient along the film depth.

2. Tailoring Magnetic Anisotropy Gradient Kai Liu, University of California-Davis, DMR 1008791 • Materials World Network • UCD graduate student Peter Greene visited NTHU (Taiwan) for 2 months during July-August, 2012 as a NSF EAPSI fellow • UCD graduate student Dustin Gilbert attended the 2012 IEEE Magnetics Society Summer School at SRM University, India • Collaboration with NIST on neutron scattering, SEMPA, and HRTEM • New collaboration with HZDR (Germany) on ion irradiation experiments • Collaboration with Univ. Complutense (Spain) onflux pinning in superconducting-nanomagnet hybrids • PI co-organized the 2011 Spintronics Workshop at the Univ. of Delaware in Sept. (over 100 participants) • PI organized UCD-Nanjing University (China) workshop on Condensed Matter Physics at UCD in March 2012 (~50 participants) • PI proposed and organized a symposium on “Effect of Electric Field on Magnetism” at the 2012 International Magnetics Conference in Vancouver, Canada UCD graduate student Dustin Gilbert (highlighted) attending the IEEE Magnetics Society Summer School in Chennai, India in July 2012. (Left) Spintronics Workshop at the University of Delaware in Sept. 2011. (Right) 1st UCD-NJU Workshop on Condensed Matter Physics in March 2012.