Analysis of the Thermal Magnetic Noise Spectrum of TMR Heads by Micromagnetic Simulation

We studied the thermal magnetic noise of TMR heads by using micromagnetic simulation, which considers an effective random thermal field corresponding to the thermal fluctuation. In this paper, we report the relationships between the thermal magnetic noise spectrum and the TMR head parameters. The free layer and the synthetic ferrimagnetic (SF)-pinned layer have individual magnetic resonant peak frequencies which depend on the internal magnetic fields, such as the permanent magnetic biasing field or the unidirectional exchange coupling field, between the pinned layer and the antiferromagnetic layer. The magnitude of the thermal magnetic noise increases with a decrease in either resonant peak frequency. Moreover, the magnetic resonant peak frequency depends on the TMR sensor aspect ratio, namely the ratio of width to height. Two peaks appear in the thermal magnetic noise spectrum if the individual resonant frequencies of the free and SF-pinned layers, which depend on the internal field strength, are markedly different.