Magnetomechanical damping in a nanocrystalline two-phase composite

S. E. URRETA; H. SALVA; A. GHILARDUCCI; O. BILLONI; L. FABIETTI; H. BERTORELLO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 1999 p. 14565 - 14568

0163-1829

The magnetomechanical coupling in a nanocrystalline Nd2Fe14B+0.18 vol α Fe composite is investigated using mechanical spectroscopy technics. The internal friction and the elastic modulus are simultaneously measured between 4 and 300 K (800 Hz, ε<~10-4). The composite magnetization is also measured as a function of temperature in the same range. The experiments are performed in the same sample exhibiting two different magnetic states. The state I is thermally demagnetized and domain walls are found in both phases. The state II, in which α Fe is saturated and the Nd2Fe14B grains are single domains, is attained by applying a dc magnetic field of 4.5 kOe during measurements. The elastic modulus increases during heating and in both states this recovering is correlated with the irreversible changes in the composite magnetization. The internal damping in the sample with a single domain configuration (state II) is higher than that found when both phases have multidomain grains (state I) in all the range investigated. Large contributions to the mechanical dissipation are related to irreversible changes in the magnetization by a nucleation mechanism in the Nd2Fe14B grains.