Ultrasonic Attenuation in Magnetic Single Crystals

A striking connection has been found between the magnetic properties and the ultrasonic attenuation properties of a nickel single crystal. The magnetic anisotropy has been detected by measuring the attenuation as a function of applied field intensity. Information about the vibrations of Bloch walls and the number of vibrating walls per unit length has also been obtained. The dependence of the attenuation on magnetic induction for 5-100 mc shear and longitudinal waves propagated in the [110] direction was the same for $B$ parallel to both the [111] and [001] directions. The shear modes induce much greater losses than the longitudinal mode.

Similar measurements on a 3.8 percent Si-Fe crystal showed that the walls in this alloy are not as easily vibrated, i.e., there is a small difference in attenuation between the magnetized and unmagnetized states. At these frequencies this indicates that there is a direct connection between the magnetostrictive constants and the dynamic behavior of Bloch walls.

The elastic constants were computed from velocity measurements, but no $\Delta E$ effect was observed.

Pulsed ultrasonic techniques as described by Roderick and Truell (see reference 4) were used in taking the measurements. The single crystals used were grown from the melt in a hydrogen atmosphere and then oriented so that pure modes of vibration could be propagated.