2002 Volume 43 Issue 5 Pages 1254-1257
The GMR effect in nanogranular Ag72Co28 films made by rf sputtering has been investigated in order to apply to the sensors in brushless DC motors. In a Ag72Co28 film having the MR ratio of 9.5%, the Co particle size decomposed from a Ag matrix was estimated to be about 20 nm. The temperature dependence of resistivity linearly increases up to 573 K, whereas the MR ratio linearly decreases up to 573 K, that is, 12% at room temperature and 4% at 573 K. These behaviors are to the advantage of compensation both the temperature dependences of the film sensor. In addition, the thermal stability of the MR effect is excellent. Accordingly, the nanogranular Ag72Co28 film sensors have a potential to replace with conventional Hall sensors restricted below about 400 K in brushless DC motors. The nanogranular Ag72Co28 film sensors attached to the bias permanent magnets set in a brushless motor are able to detect the rotating angle of the rotor together with the distinction between the polarity from the quiescent state and the rotating state. Consequently, the nanogranular GMR Ag72Co28 thin films have excellent properties for rotating angle sensors at high temperatures in brushless motors.
