Developmental Research of Ferromagnetic Thin Films for Surface Acoustic Wave with Field-Induced Giant Attenuation

蒸发镍膜声表面波延迟线在平行于膜面的磁场中有一个衰减峰，它强烈地依赖于膜厚和磁场。对于200埃厚的镍膜，在20 Oe（= H_c）处，磁场引起的最大衰减约为40 dB/cm。为了得到具有更大衰减效果的声表面波器件，我们制备了多层Ni/W薄膜声表面波器件。结果发现，场致衰减与Ni层的数量成正比地增强。这些结果表明，采用多层Ni/W膜的声表面波器件具有很大的衰减，这是单层Ni膜所不能达到的。本文<1-x><85><15>用交流等离子体溅射法在微晶玻璃和石英衬底上制备了（Fe_ Co_x）_ Zr_（1-x）非晶薄膜，研究了薄膜的磁滞回线和交流磁化率随电场的变化关系。当在氩气气氛下以小于1 × 10 ~（-6）Torr的压力通过溅射制备非晶膜时<-3>，发现膜具有小于1 Oe的矫顽力，在该矫顽力下，与单层Ni膜相比，交流磁化率显示出非常大的峰值。其次，我们设计了一种新型的声表面波器件，它是由钽酸锂（LiTaO_3）制成的，其机电耦合系数比石英晶体大。我们制备了四种尺寸为10 mm × 5 mm的SAW器件，它们分别可以产生200、500、700和900 MHz的SAW（SAW器件由FUJITSU LIMITED的代理处提供）。上述非晶（Fe_<1-x>Co_x）_<85>Zr_<15>x薄膜声表面波器件的测试正在进行中。

SAW delay line with evaporated nickel films shows an attenuation peak in a magnetic field parallel to the film plane which strongly depends on film thickness and magnetic fields. The maximum attenuation induced by fields was found to become about 40 dB/cm at 20 Oe (= H_c) for 200 A^^ﾟ thick Ni film. In order to get a SAW device having much larger attenuation effect, we have prepared the SAW devices with multi-layered Ni/W films. It was found that the field-induced attenuation was enhanced in proportion to the number of Ni layers. These results indicate that a SAW device with multi-layered Ni/W films gives a very large attenuation which can not be obtained with the single layered Ni film.In this term of project(1989), we firstly tried to get the SAW device which can control the attenuation by a small bias magnetic field. We have prepared amorphous thin films of (Fe_<1-x>Co_x)_<85>Zr_<15> on the substrates of Foto-ceram and quartz by ac plasma sputtering and studied the hysteresis loop and the field dependence of ac susceptibility. When the amorphous films are made by sputtering under an argon gas atmosphere with pressure less than 1 X 10^<-3> Torr, the films were found to have coercive force less than 1 Oe, at which the ac susceptibility shows a very large peak compared with that of a single layered Ni film. Then we have got one of the most suitable films for the SAW device which will show very large field-induced attenuation by a small magnetic field.Secondly, we designed the new SAW device made of lithium tantalate (LiTaO_3) with larger electromechanical coupling factor than that of crystalline quartz. We prepared the four kinds of SAW devices of 10 mm x 5 mm dimension which can generate SAW of 200, 500, 700 and 900 MHz,' respectively (the SAW devices were offered by the good offices of FUJITSU LIMITED). Testings of the above SAW devices with amorphous (Fe_<1-x>Co_x)_<85>Zr_<15> films are now in progress.