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 t he present study, the temperature dependence of the magnetomechanical effec t 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 o f external axial magnetic field were measured as a function of applied torq ue. Magnetomechanical sensitivity of Delta H-ext/Delta tau=65 A N-1 m(-2) w as observed with a magnetomechanical hysteresis of Delta tau=+/- 0.62 N m a t room temperature (22 degrees C). These were then measured as a function o f temperature. Both decreased as the temperature increased throughout the e ntire range. The magnetomechanical hysteresis became negligible at temperat ures higher than 60 degrees C, above which there was a linear change in ext ernal magnetic field with applied torque. These temperature dependences are explained by the changes of magnetostriction, anisotropy, spontaneous magn etization, and pinning of domain walls caused by the availability of increa sed thermal energy. (C) 2000 American Institute of Physics. [S0021- 8979(00 )94408-6].