High tunability of synthetic antiferromagnets applied in magnetic field sensing and memory devices

We investigated magnetic configurations in synthetic antiferromagnets (SAFs) of CoFeB/Ta/CoFeB by tuning interlayer exchange coupling (IEC, the energy density is denoted by J_ex) and perpendicular magnetic anisotropy (PMA, K_u). Two magnetic layers are either ferromagnetic or antiferromagnetic coupling, depending on both the non-magnetic layer thickness (d_NM) and the ferromagnetic layer thickness. Besides spin-flip transitions in SAFs with large PMA, we observed the canted magnetic configurations and spin-flop transitions when K_u < J_ex/d_NM. Most interestingly, the transfer curve of anomalous Hall resistance (magnetizations) becomes linear when tuning IEC and PMA to moderate values. This allows for applications in anomalous Hall effect (AHE) sensors with ultrahigh magnetic field detectability. Noise spectra reveal the magnetic field detectability reaches 100 nT/√Hz (at 1 Hz) at room temperature and decreases to sub-µT/√Hz (at 1 Hz) at 150 K. The studies indicate that the synthetic antiferromagnets are good candidates for both the magnetic memory devices and ultra-detectable magnetic field sensors with high thermal stability.