Magnetomechanical damping in a nanocrystalline two-phase composite

The magnetomechanical coupling in a nanocrystalline Nd2Fe14B + 0.18 vol alp ha Fe composite is investigated using mechanical spectroscopy technics. The internal friction and the elastic modulus are simultaneously measured betw een 4 and 300 K (800 Hz, epsilon less than or equal to 10(-4)). The composi te magnetization is also measured as a function of temperature in the same range. The experiments are performed in the same sample exhibiting two diff erent magnetic states. The state I is thermally demagnetized and-domain wal ls are found in both phases. The state II, in which alpha Fe is saturated a nd the Nd2Fe14B rains are single domains, is attained by applying a de magn etic field of 4.5 kOe during measurements. The elastic modulus increases du ring heating and in both states this recovering is correlated with the irre versible changes in the composite magnetization. The internal damping in th e 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 i nvestigated. Large contributions to the mechanical dissipation are related to irreversible changes in the magnetization by a nucleation mechanism in t he Nd2Fe14B grains. [S0163-1829(99)06541-8].