Structure, magnetic properties, and exchange coupling in thermally processed NdDyFeCoB/α-Fe nanoscale multilayer magnets

Authors

W. Liu, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
Xingzhong Li, University of Nebraska-LincolnFollow
Y. C. Sui, University of Nebraska - Lincoln
J. Zhou, University of Nebraska - Lincoln
W. J. Ren, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
Z. D. Zhang, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
David J. Sellmyer, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2-7-2008

Comments

Published in JOURNAL OF APPLIED PHYSICS 103, 07E130 (2008). Copyright 2008 American Institute of Physics. Used by permission.

Abstract

The structure and magnetic properties of multilayer magnets with a hard phase (HP1 =NdM_13.5Dy_1.5Fe₆₈Co₁₀₇ or HP2=Nd₁₄Dy₁Fe₆₈Co₁₀B₇) and soft phase Fe, prepared by sputtering and subsequent heat treatment, have been investigated. For Si/Ti(20 nm)/[HP1(2.0 nm)/Fe(0.5 nm)] x 200/Ti(10 nm) multilayer film, transmission electron microscopy results show that Fe disperses in amorphous NdDyFeCoB alloy. After annealing at 575 °C for 5 min, the hard Nd₂Fe₁₄B phase typically with grains of about 50 nm and some amount of α-Fe coexist in the film. The grain size of the hard and soft phases can be controlled by the proper thickness of the layer and the period. A coercivity of 7.7 kOe and a ratio M_r/M_s of 0.74 are achieved in the multilayer Si/Ti(20 nm) /&#;[HP2(2 nm) /Fe(0.5 nm)]x200/Ti(10 nm). A good squareness of the hysteresis loop (measured even at 200 K) is observed, due to the effective exchange coupling between the magnetically soft and hard nanograins in the film. A pinning-type mechanism dominates the magnetization reversal process. In addition, the effect of the effective anisotropy, the grain size, and interfaces between the magnetically hard and soft phases on the exchange coupling is discussed.