High-frequency magnetic properties and their thermal stability in diluted IrMn–Al2O3/FeCo exchange-biased multilayers

• Al2O3 doped FeCo/IrMn–Al2O3 exchange bias multilayer were prepared.
• High frequency magnetic properties at high temperature were studied.
• Exchange bias and resonant frequency decrease with increasing temperature.
• Rotatable anisotropy field show different thermal behavior for Al2O3 doped sample.
• Conversion among three type AF grains results in the thermal and magnetic behavior.

In this work, we prepare and characterize FeCo/IrMn–Al2O3 multilayers using magnetron sputtering method with various doping concentrations in order to study the doping effect of the antiferromagnetic layer in exchange-biased films on their high frequency magnetic properties and their thermal stability for fundamental research as well as for application. The influences of the nonmagnetic Al2O3 doping in the antiferromagnetic layers on the high frequency magnetic properties from 1 GHz up to 8 GHz and their thermal stability of the FeCo/IrMn exchange-biased multilayer have been investigated in the temperature range from room temperature up to 420 K. The temperature behavior of exchange bias, static magnetic anisotropy field, dynamic magnetic anisotropy field, rotatable magnetic anisotropy field, resonant frequency and damping of the samples are presented and interpreted by classifying the antiferromagnet grains into random spin grains, frozen spin grains and rotatable spin grains. In particular, the roles and changes of each grain type with the doping amount and with temperature are discussed in conjunction with the variations of the magnetic and microwave parameters.