Abstract
The spiral antiferromagnetic phase of polycrystalline dysprosium between 140 K and the Néel temperature at 178 K and its domain wall (DW) dynamics were investigated using high-resolution ultrasonic spectroscopy. Two kinetic processes of quasi-static DW motion occur under non-isothermal and isothermal conditions. A “fast” process is proportional to the rate of the temperature change and results in a new category of anelastic phenomena: magnetic transient ultrasonic internal friction (IF). This IF, related to fast moving magnetic DWs, decays rapidly after interruptions of cooling/heating cycles. A second, “slow” kinetic process is seen as logarithmic IF relaxation under isothermal conditions. This second process is glass-like and results in memory and temperature chaos effects. Low-frequency thermal fluctuations of DWs, previously detected by X-ray photon correlation spectroscopy, are related to critical fluctuations with Brownian motion-like dynamics of DWs.
Highlights
A Young’s modulus minimum concomitant with an internal friction (IF) peak at TN = 178 K is typical for an AFM transition[24,25]
The IF spectra were registered under constant cooling/heating rate and differ notably below TN from the IF behaviour under isothermal conditions dT /dt = 024,25
Broad maxima of the IF below TN in Dy for longitudinal and especially for transverse waves were observed under non-isothermal conditions in[26] but were not commented upon
Summary
Young’s modulus, E, were measured by piezoelectric ultrasonic composite oscillator technique[22] over a temperature range 80–210 K at frequencies near 90 kHz, which is determined by the type of the quartz transducer used. Temperature spectra of the internal friction and Youngs modulus were taken either in a continuous mode (uninterrupted scans) or in interrupted mode with isothermal holdings of 40 min. The samples from the first series were spark-cut from 1 mm thick rolled plate, supplied by Sigma Aldrich (99.9% purity). The second series (as cast samples) was cut from an ingot produced by arc melting from 99.0% purity (99.9% purity with respect to rare earth elements) raw material purchased from Suzhou Chemical Co, China. Samples from the first series were studied in as received (rolled) state and after vacuum annealing at 920 K for 2 hours. The data are presented for the as-cast samples
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