Magnetoelastic Effects in Nickel Single Crystals Studied by Ultrasonic Attenuation and Velocity

Sound attenuation and velocity in nickel single crystals have been studied as function of frequency (10 to 250 MHz), temperature, strength and direction of external magnetic field along , (110> and , for the three pure wave modes propagating along . The observed effects are found to be specific for each combination of sound mode and field direction, and especially interesting for the field along (100, which is the hard magnetization direction in Ni. The measured frequency, field, and temperature effects on sound attenuation and velocity can be rationalized in terms of field induced changes of the domain structure. Earlier studies of magnetoelastic damping in nickel single crystals refer to effects of frequency 11-8/, magnetic field /1,3,5-13/ and temperature /8,9,11,13-15/. The frequency dependence (mainly studied between 10-100 MHz) has been explained by micro-eddy currents-generated by ultrasound set up by magnetoelastically induced changes of magnetization /1,4,5,7,10,13/. The effect of field strength and direction seems more controversial; the pronounced attenuation peaks observed for some combinations of wave mode and field direction have been attributed to the ferroacoustic resonance /8,9,11,12/, magnetoelastic coupling /5,7/ and to internal stress effects /lo/. The decrease in attenuation in zero field with decreasing temperature has been explained by the change in spontaneous magnetization due to the strongly increasing anisotropy energy /16/. The frequency /17-19/, magnetic field /2,18/ and temperature 116/ dependences of wave velocity have also been explained by magnetoelastically induced oscillations of domain walls or magnetic moments inside domains. The present work intends to contribute to the understanding of the magnetoelastic effects in nickel single crystals by combining measurements of field, frequency and temperature dependence of sound attenuation and velocity on a high purity Ni single crystal. ("on leave from the Herchant marine Academy. Gdynia. Poland ("11. Physikelisches Institut. Universtitet zu K&ln.; F.R.G. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987871