Effects of external heat upon ferromagnetic resonance characteristics of TMR heads

Abstract

        Thermal stability of magnetic recording heads is an important issue; and most analysis was carried out in macro-magnetic state as a whole which leaving out the micro-magnetic analysis state particularly in the layer-level state of TMRs. This work focuses on the analysis of thermal stability of TMR heads in layer-level state; free layer (FL), reference layer (RL) and pinned layer (PL) using ferromagnetic resonance (FMR) during 0.2GHz – 10 GHz range of frequency. Heat energy was transferred to TMR heads through hot air; and the results were compared with TMR heads without heat transfer which operating at room temperature. The experiments were conducted under two conditions; (I) External magnetic field of 750 Oe – 1,200 Oe was applied to TMR heads in the direction of hard bias field (HB) (II) External magnetic field of ? 520 Oe was applied to TMR heads in the direction of reference layer (RL). The conclusions are: Condition (I) TMR heads with heat transfer through hot air had 2-3 times higher peak amplitude of noise than that of TMR heads without heat transfer through hot air at the approximate resonance frequency of 9 GHz. This indicated the magnetic fluctuation caused by heat and resulted in lowering the exchange bias field, HEB while the normal TMR heads showed no peak amplitude of noise over testing frequency; hence higher stability. Condition (II) TMR heads with heat transfer through hot air had differential peak amplitude of noise voltage is 4.14 times of normal TMR. This indicates asymmetry caused by the degradation of HB field due to thermal energy from heat transfer through hot air.