Low-temperature dislocation and magnetomechanical acoustic effects in high purity Fe single crystals

Abstract

The effect of preliminary plastic deformation εpl<3% and an external magnetic field H⩽3.35 kOe on linear and nonlinear acoustic properties of high purity Fe single crystals is studied. Measurements were made at frequencies ∼90 kHz in the temperature interval 5.5–300 K using the two-component composite oscillator technique. The wave vector of the longitudinal standing wave and the magnetic field direction coincide with the crystallographic axis 〈731〉. In the linear range, the main attention is paid to the influence of the deformation level and subsequent low-temperature recovery on parameters of the relaxation α-peak near 50 K. The increase in εpl leads to a considerable rise in the height of the peak, while the height and temperature of the peak are considerably lowered in the recovery process. An increase in the amplitude ε0 of the ultrasonic deformation beyond a certain threshold ε0c is accompanied by the emergence of strong amplitude dependences of acoustic parameters of the crystals under investigation. As a result of plastic deformation, the amplitude dependences of the decrement and the Young’s modulus are displaced towards lower amplitudes. Magnetoacoustic effects in a saturating external field are practically independent of the amplitude and display a weak monotonic dependence on temperature in the region of the α-peak. It is concluded that the amplitude dependences as well as the α-peak are of the dislocation nature. Possible microscopic mechanisms of the observed effects are discussed.