Complete sets of elastic constants of rare-earth bismuth iron garnet (111) films containing Pb were determined by resonantultrasound spectroscopy. Resonant-ultrasound spectroscopy can be used to determine all independent elastic constants from one specimen by measuring the resonance frequencies of free vibrations. For accurate measurement of the resonance frequencies, we used a tripod transducer, and the vibration modes of each resonance frequency were identified by laser-Doppler interferometry. Rare-earth bismuth-iron garnet belongs to the space group Ia 3 3d, and shows cubic symmetry. However, it was nearly elastically isotropic; 2C 44 =ðC 11 À C 12 Þ ¼ 0:99. Their elastic constants were almost independent of the Pb content; C 11 ¼ 242:9 AE 4:4 GPa, C 12 ¼ 99:1 AE 2:0 GPa, and C 44 ¼ 71:1 AE 0:8 GPa. The observed isotropic elasticity corresponds to that of the other garnet group crystals.
A micromagnetostrictive vibrator using a U-shaped core made of iron-gallium alloy (Galfenol) was investigated. The vibrator consists of a Galfenol core, with a 1mm2 cross section, a length of 5.8mm, and a 0.3mm separation between the prongs of the “U,” driving coils, and an iron yoke to close the magnetic loop. The Galfenol vibrator is superior to the PZT type in its high mechanical strength, low drive voltage requirements, and wide temperature operating range, and compared to our previous cylindrical type vibrator has a simpler construction and higher bandwidth. A displacement of 1.2μm (220ppm) was verified for the prototype with a 5.8mm long Galfenol core; the high magnetostriction >200ppm is inherited from the stress-annealed Galfenol. The displacement was also maintained under a 21MPa tensile stress (1.5kg hanging weight). Incorporation of a Nd–B–Fe magnet into the magnetic circuit successfully shifted the operating point to the linear portion of the magnetostrictive curves. This biasing effect is useful in reducing the drive voltage.
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