Effects of ion-beam irradiation on the L1₀ phase transformation and their magnetic properties of FePt and PtMn films (Invited)

Authors

Chih-Huang Lai, National Tsing Hua University, 300, HsinChu, Taiwan
Sheng-Huang Huang, National Tsing Hua University, 300, HsinChu, Taiwan
Cheng-Han Yang, National Tsing Hua University, 300, HsinChu, Taiwan
C.C. Chiang, National Tsing Hua University, 300, HsinChu, Taiwan
Sy_Hwang Liou, University of Nebraska-LincolnFollow
David J. Sellmyer, University of Nebraska-LincolnFollow
M. L. Yan, University of Nebraska-LincolnFollow
L. Yuan, University of Nebraska-Lincoln
T. Yokata, Department of Environmental Engineering of Materials, Nagoya institute of Technology, Nagoya, Japan

Date of this Version

2006

Comments

Published in Mater. Res. Soc. Symp. Proc. Vol. 887. Copyright © 2006 Materials Research Society. Used by permission.

Abstract

In this paper, we illustrate how to modify the structure and magnetic properties of L1₀ FePt and PtMn films using ion-beam irradiation. Highly ordered L1₀ FePt and PtMn phases were achieved directly by using 2 MeV He-ion irradiation without conventional post-annealing. A high ion-beam current density (~μA/cm² ) was used to achieve direct beam heating on samples. This irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered L1₀ phase. In-plane coercivity of FePt films greater than 5700 Oe could be obtained after disordered FePt films were irradiated with a He-ion dose of 2.4x10¹⁶ ions/cm². The direct ordering of FePt took place by using ion-irradiation heating at a temperature as low as 230 ℃. In PtMn-based spin valves, an L1₀ PtMn phase, a large exchange field and a high giant magnetoresistance (GMR) ratio (11%) were simultaneously obtained by using He-ion irradiation. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and the GMR of PtMn-based spin valves, respectively.