High Temperature Magneto-Acoustic Anomalies in Active Material for Parametric Phase Conjugation
R.V.Klopotov, L.M.Krutyansky, V.L.Preobrazhensky (Wave Research Center of the General Physics Institute RAS)
The results of measurements of the temperature dependence of sound velocities in magnetostrictive ceramics based on Ni Fe2O4 composition are presented. This kind of magnetic material is used as an active element of the supercritical ultrasonic wave phase conjugator . The measurements were made for longitudinal and shear waves by the resonance method in the interval 300- 740 K at several values of external magnetic field strength. Anomalous temperature dependence of the resonance frequencies, increase of magneto-elastic coupling coefficient and enhancement of acoustic nonlinearity were observed near 630 K. Bistability of the resonance excitations and auto-modulation phenomena are detected in this temperature region. Observed magneto-acoustic behavior is typical for magnetic materials in the vicinity of spin reorientation instability . Possibilities to use high temperature anomaly for improvement of efficiency of supercritical phase conjugation in magnetic ceramics are discussed. References: 1. A.P.Brysev, L.M.Krutyansky, V.L.Preobrazhensky. Uspekhi Phys. Nauk, v.168, p.877 (1998). 2. V.I.Ozhogin, V.L.Preobrazhensky. Journ. Magn. & Magn. Materials, v.100, p.544 (1991).
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