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High sensitivity magnetoelectric (ME) thin film composite sensors, which enable the detection of picotesla magnetic fields, are improved in terms of magnetic noise performance by the elimination of magnetic domain (MD) activity. Using an antiparallel (AP) exchange biasing scheme, suppression of magnetic noise is obtained. Postsetting of AP biased ferromagnetic/antiferromagnetic multilayers is accomplished by magnetic field free annealing with in-situ MD control. Overcoming the shape and demagnetization effects, stable single MD configurations in the magnetic sensing layers of magnetic multilayers are formed. Magnetic noise contributions are undetectable. The achieved single domain field stability opens the path to ultralow noise ME sensor applications. The demonstrated AP biasing scheme is applicable to other magnetic layer-based field sensing devices.High sensitivity magnetoelectric (ME) thin film composite sensors, which enable the detection of picotesla magnetic fields, are improved in terms of magnetic noise performance by the elimination of magnetic domain (MD) activity. Using an antiparallel (AP) exchange biasing scheme, suppression of magnetic noise is obtained. Postsetting of AP biased ferromagnetic/antiferromagnetic multilayers is accomplished by magnetic field free annealing with in-situ MD control. Overcoming the shape and demagnetization effects, stable single MD configurations in the magnetic sensing layers of magnetic multilayers are formed. Magnetic noise contributions are undetectable. The achieved single domain field stability opens the path to ultralow noise ME sensor applications. The demonstrated AP biasing scheme is applicable to other magnetic layer-based field sensing devices.

We present a fully integrated microelectromechanical magnetic field sensor based on the ΔE effect. The vacuum encapsulated sensor extends our previous approach [B. Gojdka et al., Appl. Phys. Lett. 99, 223502 (2011); Nature 480, 155 (2011)] and now involves an intermediate piezoelectric AlN layer between a SiO2 cantilever and a magnetostrictive FeCoBSi top layer. The AlN layer serves two functions: It drives the resonator, and it is used for electrical read out. The limit of detection was strongly enhanced to 12 nT/ Hz at 10 Hz.

Self-biased magnetoelectric composites, which are realized with the exchange bias effect, hold an increased total anisotropy field compared to systems without exchange bias. Thus, small exchange bias fields are favorable because of a minor reduction of magnetic permeability and magneto-electric voltage coefficient. However, weakly biased magnetoelectric composites lose their self-biasing properties and possibly show an increase of discontinuities in magnetization reversal due to the formation of magnetic domains. By a thickness variation of the ferromagnetic layer, a maximum voltage coefficient αME ≈ 430 V/cm Oe was found for a magnetostrictive multilayer of 3 × (5 nm Ta/3 nm Cu/8 nm Mn-Ir/333 nm Fe-Co-Si-B). Yet, a stable single domain state indicating a well defined magnetization reversal by coherent magnetization rotation was achieved for layer thicknesses up to 100 nm Fe-Co-Si-B with αME ≈ 340 V/cm Oe. This slight reduction is overcompensated by the improved control of the magnetic domain pattern which is highly beneficial for magnetic field sensing applications and of special importance, when frequency conversion techniques are applied.

Magnetoelectric (ME) thin film composites on silicon cantilevers are fabricated using Pb(Zr0.52Ti0.45)O3 (PZT) films with interdigital transducer electrodes on the top side and FeCoSiB amorphous magnetostrictive thin films on the backside. These composites without any direct interface between the piezoelectric and magnetostrictive phase are superior to conventional plate capacitor-type thin film ME composites. A limit of detection of 2.6 pT/Hz1/2 at the mechanical resonance is determined which corresponds to an improvement of a factor of approximately 2.8 compared to the best plate type sensor using AlN as the piezoelectric phase and even a factor of approximately 4 for a PZT plate capacitor.