D. Lenz

Magnetoelastic effects in La1−xCexB6

Abstract The elastic constants of La 1− x Ce x B 6 (x = 0.00, 0.01, 0.03) single crystals were determined by ultrasonic measurements. The temperature dependence of the elastic symmetry modes c 44 and (c 11 − c 12 )/2 is explained on the basis of the crystalline-electric-field level scheme of CeB 6 by taking the magnetoelastic interaction into account. An influence of the Kondo effect on the elastic constants could not be detected.

Effect of Kondo Resonance Scattering on Magnetoacoustic Quantum Oscillations

Magnetoacoustic quantum oscillations in dilute (La, Ce)B6 have been found. They are caused by a very small Fermi surface extremal area with F 6.5 T. Unlike in pure LaB6 the temperature dependence of the oscillatory amplitude is not described by the standard Lifshitz-Kosevich formula. We show that La, Ce)B6 is one of the rare cases where the energy dependence of conduction electron lifetime is important for the temperature dependence of the amplitude. This is due to Kondo resonance scattering of conduction electrons near the Fermi level.

Temperature and Magnetic Field Dependence of Elastic Constants in (La, Ce)B6 Single Crystals

Measurements of the sound velocity in dilute (La1-xCex)B6 (x=0.01,0.03,0.1) crystals were used to determine the temperature and magnetic field dependence of elastic constants c44 and (c11-c12)/2. Their softening below 4.2 K is explained on the basis of a single ion magnetoelastic interaction. From this we conclude that the majority of Ce-ions has static splitting (2.2 K) of the ?8 ground state into two doublets. From the observed magnetoacoustic quantum oscillations in very dilute (La,Ce)B6 Fermi surface cross sections, effective Dingle temperatures and their T-dependence were determined.

Effect of magnetic field on ultrasonic attenuation in nickel single crystals

Abstract The attenuation of ultrasound in nickel single crystals was studied as a function of the external magnetic field along [ 1 11], [ 1 10] or [001] for the three pure wave modes propagating along [110] at frequencies between 10 and 250 MHz. Due to magnetoelastic interactions the attenuation includes a contribution changing with the magnetic state of the sample. The most striking feature is a sharp peak of the attenuation of the longitudinal and of the transversal mode T2 especially when the external field H a is parallel to [001]. Turning of H a out of this direction induces the decrease of the height of the maximum but to a far smaller extend as one expects if the maximum were caused by ferroacoustic resonance. In the case of H a being parallel to one of the directions the magnetic contribution to the attenuation decreases monotonously. Other combinations of the directions of magnetizing field and the stress of the applied ultrasound wave produce some types of intermediate behaviour. The magnetic contribution to sound attenuation vanishes between 0.58 and 0.82 B s ( B s saturation induction) dependent on the mutual orientation of the stress tensor and the external field. The hysteresis observed on the attenuation as a function of the magnetic induction corresponds to the hysteresis of the magnetic configuration. The new experimental results allow some conclusions concerning the explanation of these complex effects.

Theorien der untersuchten Absorptionsmechanismen

Wenn ein Schallstrahl beim Durchdringen einer Schicht der Dicke dx den Bruchteil α dx seiner Amplitude und damit den Bruchteil 2α dx seiner Intensitat I (d.h. seiner sekundlich einfallenden Energie) verliert, so erhalt man

Untersuchung der Versetzungsabsorption in schwach verformten Einkristallen

- \frac{{dI}}{I} = 2\alpha dx;I = {I_O}\exp ( - 2\alpha dx)

Elastic constants and quadrupolar interactions in the (LaCe) B6 series

(1) α wird Extinktions- oder Absorptionskoeffizient genannt und besitzt die Einheit cm−1, die auch als Neper/cm (= Np/cm) bezeichnet wird. fur die Diskussion spezieller Absorptionsmechanismen werden auch die als logarithmisches Dekrement δ bzw. Dampfung δ/π oder reziproke Gute Q−1 bezeichneten dimensionslosen Grosen benutzt, wobei