In this work, we demonstrate that interlayer exchange-coupled magnetic thin films can be employed to fabricate ultrasensitive and thermally stable magnetic sensors, taking advantage of the linear anomalous Hall effect via tuning the interlayer exchange coupling and magnetic anisotropy. We investigate the magnetotransport and noise properties of these anomalous Hall sensors. The magnetic field detectability reaches $126.1\mathrm{nT/}\sqrt{\mathrm{Hz}}$ at 1 Hz and $4.5\mathrm{nT/}\sqrt{\mathrm{Hz}}$ at 1 kHz, at room temperature. Meanwhile, the achieved dynamic reserve is 103.0 dB. The magnetic field detectability shows a good temperature stability in the 200 to 300 K range. Within the temperature range, the temperature coefficient of sensitivity is determined to be 530 ppm/K. The high temperature stability is attributed to the interlayer exchange coupling, which also improves the stability against in-plane magnetic fields, beneficial for perpendicular magnetic field sensing. The interlayer exchange-coupled magnetic thin-film-based anomalous Hall sensors solve the trade-off between the sensor size, sensing capability, and stability, which are desirable for microimaging and biomedical applications.

We took advantage of the large anomalous Hall effect (AHE) in Fe–Pt ferromagnetic alloys and fabricated magnetic sensors for low-frequency applications. We characterized the low-frequency electronic noise and the field detectability of the Fe_xPt_100-x system with various thin film thicknesses and Fe concentrations. The noise source consisted of 1/f and Johnson noise. A large current density increased the 1/f noise but not the Johnson noise. We found that the field detectability of the optimized Fe–Pt thin film offers much better low-frequency performance than a highly sensitive commercial semiconductor Hall sensor. Anomalous Hall effect sensors are, therefore, good candidates for magnetic sensing applications.

Multiple geometrical conditions for different magnetic vortex states to appear in micrometer-sized magnetic tunnel junctions (MTJs) are investigated in experiment and simulation. Both results match up well, providing clear images of vortex behaviors. We pattern a compact array of single-vortex MTJ elements and perform magnetotransport and noise measurements. This sensor features nonhysteretic behavior, a small size of 0.5 × 0.5 ${\mathrm{mm}}^2$, a low normalized noise of ${10}^{-13}{\mathrm{Hz}}^{-1}$, a detectability of $18nT/\sqrt{Hz}$ at 1 Hz, and a large dynamic range of 100 Oe. Its 115 dB broad dynamic reserve and superior stability against temperature and environmental stray fields are ideally suited for magnetic sensing applications.

We have performed magnetotransport and noise characterization studies of ultrasensitive anomalous Hall effect (AHE) sensors based on the Ta/Co₄₀Fe₄₀B₂₀/MgO multilayer structure. The magnetization is near spin reorientation transition. This greatly reduces the saturation field with improvement of the magnetic sensing performance. We have performed temperature-dependent measurements to investigate the effect of tunable magnetic anisotropy. Both 1/f noise and sensitivity have a strong temperature dependence. Moreover, the scaling relations between 1/f noise and sensitivity change dramatically as temperature changes, showing different noise originations depending on magnetic anisotropies. With a small sensing area of $20\times 20\hspace{0.17em}\mu {\mathrm{m}}^2$ , the best magnetic field detectability reaches $76\hspace{0.17em}\mathrm{nT}/\sqrt{\text{Hz}}$ at 1 Hz and $2\hspace{0.17em}\mathrm{nT}/\sqrt{\text{Hz}}$ at 10 kHz. AHE sensors with compensated magnetic anisotropies are, thus, suitable for ultrasensitive magnetic field sensing applications.

In this work, we fabricate and characterize an energy-efficient anomalous Hall sensor based on soft-magnetic Fe_xPt_1−x thin films with a large anomalous Hall angle. By varying the composition of the Fe_xPt_1−x alloy, its layer thickness and interfacial materials, the magnetization is tuned to be near the spin transition between the perpendicular and in-plane reorientations. We performed magneto-transport and noise characterizations on anomalous Hall sensors with a small sensing area of 20 × 20 µm² in the 180 to 350 K temperature range. We found the best performance in a 1.25-nm-thick Fe_0.48Pt_0.52 sandwiched by two 1.6-nm-thick MgO layers at room temperature. The sensor has a large anomalous Hall angle of 1.95%. Moreover, it has the best field detectability of 237.5 nT/√Hz at 1 Hz and 15.3 nT/√Hz at 10 kHz, as well as a high dynamic reserve of 112.0 dB. These results suggest that the Fe_xPt_1−x alloy system is suitable for energy-efficient anomalous Hall sensors, particularly in micro-sensing applications.