Magnetic and Magnetoelastic Properties of Highly Magnetostrictive Amorphous Films with TbFe-FeB-TbFe Sandwich Structure
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T. Igari, S. Ishii, M. Inoue and T. Fujii Dept. of Electrical and Electronic Engng., Toyohashi University of Technology Tempaku, Toyohashi, Aichi 441, Japan
ABSTRACT Amorphous Tb40Fe60-FesoB 20-Tb40Fe60 sandwich films were prepared by multitarget rf magnetron co-sputtering. Their magnetization and magnetostriction were studied to examine whether magnetic softening of the amorphous TbFe films could be achieved without loosing their giant magnetostriction by introducing the simple sandwich structure. The results revealed that a considerably soft in-plane magnetization (coercive force Hct 60e and the squareness ratio Mr/MsA 0.8) and a huge magnetostriction ( . >500ppm) could be obtained in the sandwich films at room temperature, provided that the thickness of the FeB interlayer was within the range of 10% to 40% of the total film thickness (1 pm).
INTRODUCTION Cubic Laves phase TbFe 2 intermetallic compound is a very attractive material for magnetomechanical applications because of its ultra-high magnetostriction that exceeds 1700ppm') at room temperature. The huge saturation magnetostriction is, however, realized only when a considerably large magnetic field of more than lOkOe is applied due to the large magnetocrystalline anisotropy of the alloy.
Thus far, many efforts 2-9) have been made to reduce the magnetocrystalline anisotropy of the alloy and to increase its effective magnetomechanical coupling constant k.. Among them, the most successful anisotropy reduction was achieved in the pseudobinary alloy of T0.2 7 1Dyo.73Fe 2 (so-called Terfenol-D) having a k. of about 0.75. This k,2 value is still unsatisfactorily small especially when one applies the alloy to integrated magnetomechanical applications, such as micro-magnetic actuators and/or sensors. Recently, we'°) have shown that the coercive force Hc of the amorphous TbFe film can be reduced greatly by inserting amorphous FeB layers between the TbFe films. The reduction of Hc occurs via ferromagnetic and magnetostatic interactions between magnetic layers which reduce the energy of magnetic domain walls. However, the magnetostrictive stress S which is proportional to the magnetostriction ý is also reduced in association with the increasing number of FeB interlayers. This was because all multilayer films investigated were subject to the oxide contamination at each interfaces. In this work, we prepared the contamination free amorphous TbFe-FeB-TbFe sandwich films and studied their fundamental magnetic and magnetoelastic properties. The results suggest that, by controlling the thickness of the FeB interlayer, the simple sandwich film can possess both the ultra-high magnetostriction and considerably soft in-plane magnetization.
347 Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
FeB layer
0\•.
.''"
'TbFe layer
lass substrate~\ Fig. 1 Sandwich structure of the sample.
EXPERIMENTAL As illustrated in Fig. 1, the TbFe-FeB-TbFe sandwich films were fabricated onto soft glass substrates held at room temperature using the co-sputtering techniqu
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