Behavior of Magnetization in Magnetic Oxide Compact Sintered by Magnetic and Electric Field of Microwave Irradiation

The samples had been heated by magnetic or electric field of microwave. During microwave heating by magnetic field, the samples were heated to the sintering temperature of 1000°C for 12 min followed by 70 min soak time. In initial heating step during the first 30 min, the sample temperature was dramatically changed. Thereafter, the sample temperatures settled and microwave power was lowered as 270 watt. In case of electric field heating of microwave, the samples were heated to the sintering temperature of 1000°C for 2 min followed by 100 min soak time. The heating mechanism was electric loss, because the heating rate was not correlative with Curie temperature. As a result, the microstructures were very different in sintered samples obtained by magnetic field and electric field heating under microwave irradiation. The sample heated in the magnetic field exhibited the presence of randomly oriented nano-crystalline domains. The domain sizes of this sample were approximately 10 nm in average. On the other hands, the sintered sample in electric field showed rather large grain growth.