Iulian Teliban

Giant magnetoelectric effect in vacuum

Magnetoelectric (ME) thin film cantilever type sensors made of AlN and FeCoSiB are operated in vacuum, reducing air damping and thus increasing the ME coefficient and improving the limit of detection (LOD) for ac-magnetic fields. Depending on the sensor geometry, the response is increased by a factor of 5 resulting in a ME coefficient of 20 kV/cmOe at 152 Hz and by a factor of 11 with 12 kV/cmOe at 4.7 kHz and an improvement in LOD by an order of magnitude. Modelling these cantilevers reveals dominant contributions of viscoelastic and molecular damping above and intrinsic damping below 10−2 mbar, respectively.

Magnetoelectric thin film composites with interdigital electrodes

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.

Exchange biased magnetoelectric composites for magnetic field sensor application by frequency conversion

A comparison is presented between magnetoelectric composite sensors based on AlN and FeCoSiB with and without exchange bias coupling. All layer stacks were fabricated by thin film deposition on Si substrates. Whereas sensors without exchange bias exhibit a low limit of detection in the 1 pT/√Hz regime for resonant AC fields, such sensors fail at the detection of low frequency signals. Accordingly, their detection limit increases to about 10 nT/√Hz for alternating magnetic fields with 10 Hz frequency and an integration time equal to 3 s. A frequency conversion technique based on magnetic modulation of the sensors improves their detection limit by about one order of magnitude. However, frequency conversion can be applied more effectively to magnetoelectric sensors with exchange biased multilayers as a magnetostrictive phase. As a result, their limit of detection is about 180 pT/√Hz for 10 Hz signals and an integration time of 1 s. This is in contrast to the magnetoelectric coefficient αME of the two types o...

Magnetic domain control and voltage response of exchange biased magnetoelectric composites

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 whic...

Origin of hysteretic magnetoelastic behavior in magnetoelectric 2-2 composites

The local magnetization behavior of the magnetostrictive phase of ferromagnetic/piezoelectric magnetoelectric composites is compared to the hysteretic response using advanced magneto-optical imaging. Local magnetoelastic relaxation leads to the formation of magnetization modulated branched domain structures in the magnetic phase. This results in a complex field response governed by interlocking domain processes. An interrelation of magnetic domain formation and the piezomagnetic response is derived, revealing the origin of the hysteretic magnetoelectric response. As a result, domain wall induced effects lead to a reduction of magnetoelectric signal. Controlling the magnetic domain formation processes is the foundation for reversible magnetoelectric behavior.

An experiment for the investigation of forces on microparticles in ion beams

A novel experiment for the study of forces on microparticles in ion beams is presented. A broad beam ion source provides a vertically upward directed beam wherein 100 microm hollow glass spheres are injected. The particles are illuminated by a diode laser and recorded with a charge-coupled device camera. From the trajectories the acceleration and the net force on the particles are determined. Information on energetic neutral atoms is achieved, which is not accessible by electrostatic methods.

Adaptive Acoustic Noise Cancellation for Magnetoelectric Sensors

Sensors based on the magnetoelectric (ME) effect have the potential to be genuine alternatives for measuring bio-magnetic signals. Unfortunately, the sensor structure usually inhibits the problem that several non-magnetic types of noise couple mechanically into the sensor: in this contribution, we will focus on undesired acoustic coupling. Therefore, an adaptive cancellation approach based on a computationally efficient gradient estimation algorithm with a pseudo-optimally control scheme is proposed. The approach is using a microphone as a noise reference sensor and is implemented in real time. An evaluation in terms of measurements is performed inside a magnetically shielded chamber. For a particular scenario, which is characterized by double excitation, an algorithm with binary control-scheme improves the signal-to-noise ratio (SNR) only by around 4dB. If the proposed control scheme is used instead, an improvement of the SNR of around 13dB is achieved.

Magnetic moment investigation by frequency mixing techniques

Gas turbines and other large industrial equipment are subjected to high-temperature oxidation and corrosion. Research and development of efficient protective coatings is the main task in the field. Also, knowledge about the depletion state of the coating during the operation time is important. To date, practical nondestructive methods for the measurement of the depletion state do not exist. By integrating magnetic phases into the coating, the condition of the coating can be determined by measuring its magnetic properties. In this paper, a new technique using frequency mixing is proposed to investigate the thickness of the coatings based on their magnetic properties. A sensor system is designed and tested on specific magnetic coatings. New approaches are proposed to overcome the dependency of the measurement on the distance between coil and sample that all noncontact techniques face. The novelty is a low cost sensor with high sensibility and selectivity which can provide very high signal-to-noise ratios. Prospects and limitations are discussed for future use of the sensor in industrial applications.

Reconstruction of Magnetization Curve Using Magnetic Spectroscopy

A new measurement principle based on the frequency mixing technique for investigating the shape of the magnetization curve of soft non-hysteretic magnetic materials is introduced. Based on Taylor expansion of the magnetization curve and spectral investigation of an inductively detected signal, a mathematical model for the reconstruction of M(H) is proposed, [7]. Here, the model is experimentally verified using a nanocrystalline soft magnetic material with defined properties. It is shown that the magnetization curve can be reconstructed very accurately and the influence of an additional parameter, i.e. strain, can be investigated in detail as well.