Macrospin resonance and giant magnetoimpedance effect in Fe3O4 nanoparticles observed at high frequency and low magnetic field

In the present work we report the spin resonance and giant magnetoimpedance(GMI) effect in cold pressed Fe3O4 measured with a copper stripcoil at high frequency and low magnetic fields. The AC magnetoresistance of bulk Fe3O4 was measured at room temperature using an impedance analyzer by applying frequencies of the order of 100 Hz to 5.5 MHz. The high frequency AC magnetoresistance and magnetic field derivative of the electromagnetic power absorbed (dP/dH) were measured indirectly via the stripcoil for frequencies from 10 kHz to 18 GHz, as the DC magnetic field was swept from 0 to 500 G. A giant low-field AC positive magnetoresistance (~44%) was found in a magnetic field of 105 G at 1.5 GHz. The investigation inferred that magnetic field dependence of the electrical resistance in cold pressed Fe3O4 is due to spin current driven effects. An abrupt increase in the value of MR was observed at a particular applied DC magnetic field and a shift in position of the resonance field of the stripcoil indicated the generation of spin current, established by Kittle’s theory of spin wave propagation. These observations provide a basis to develop a low field high frequency spinwave devices using the Fe3O4 nanoparticles.