Temperature dependence of the magnetomechanical effect in metal-bonded cobalt ferrite composites under torsional strain

Metal-bonded cobalt ferrite composites are promising candidates for torque sensors and other magnetostrictive sensing and actuating applications. In the present study, the temperature dependence of the magnetomechanical effect in a ring-shape cobalt ferrite composite under torsional strain has been investigated in the temperature range of -37 to 90 degrees C. The changes of external axial magnetic field were measured as a function of applied torque. Magnetomechanical sensitivity of Delta H-ext/Delta tau=65 A N-1 m(-2) was observed with a magnetomechanical hysteresis of Delta tau=+/- 0.62 N m at room temperature (22 degrees C). These were then measured as a function of temperature. Both decreased as the temperature increased throughout the entire range. The magnetomechanical hysteresis became negligible at temperatures higher than 60 degrees C, above which there was a linear change in external magnetic field with applied torque. These temperature dependences are explained by the changes of magnetostriction, anisotropy, spontaneous magnetization, and pinning of domain walls caused by the availability of increased thermal energy. (C) 2000 American Institute of Physics. [S0021- 8979(00)94408-6].