Longitudinal Magnetoimpedance Research Articles

Directional Field-Dependence of Magnetoimpedance Effect on Integrated YIG/Pt-Stripline System.

We investigated the magnetization dynamics through the magnetoimpedance effect in an integrated YIG/Pt-stripline system in the frequency range of 0.5 up to 2.0 GHz. Specifically, we explore the dependence of the dynamic magnetic behavior on the field orientation by analyzing beyond the traditional longitudinal magnetoimpedance effect of the transverse and perpendicular setups. We disclose here the strong dependence of the effective damping parameter on the field orientation, as well as verification of the very-low damping parameter values for the longitudinal and transverse configurations. We find considerable sensitivity results, bringing to light the facilities to integrate ferrimagnetic insulators in current and future technological applications.

Magnetoimpedance and magnetooptical properties of electrodeposited NiFeMo ribbons

We produced NiFeMo ribbons by electrodeposition technique under applied currents ranging from 40 to 240 mA. The SEM analysis showed a uniform and crack-free coating. Then, we measured the transverse and longitudinal magnetoimpedance of ribbons. We also obtained the hysteresis loops of the ribbons by means of magnetooptical Kerr effect to investigate their magnetic properties. The result showed that the increase in deposition current density caused a decline in the magnetic softness of the ribbons so that some of the ribbons exhibited an exchange spring effect. The magnetic hardening also caused a reduction in the magnetoimpedance response. We also theoretically calculated the susceptibility of a ribbon by considering the random magnetic anisotropy. The multi-peak behavior of susceptibility is in agreement with the multi-peak behavior of magnetoimpedance.

Magnetoimpedance effect at the high frequency range for the thin film geometry: Numerical calculation and experiment

The magnetoimpedance effect is a versatile tool to investigate ferromagnetic materials, revealing aspects on the fundamental physics associated to magnetization dynamics, broadband magnetic properties, important issues for current and emerging technological applications for magnetic sensors, as well as insights on ferromagnetic resonance effect at saturated and even unsaturated samples. Here, we perform a theoretical and experimental investigation of the magnetoimpedance effect for the thin film geometry at the high frequency range. We calculate the longitudinal magnetoimpedance for single layered, multilayered, or exchange biased systems from an approach that considers a magnetic permeability model for planar geometry and the appropriate magnetic free energy density for each structure. From numerical calculations and experimental results found in literature, we analyze the magnetoimpedance behavior and discuss the main features and advantages of each structure. To test the robustness of the approach, we directly compare theoretical results with experimental magnetoimpedance measurements obtained at the range of high frequencies for an exchange biased multilayered film. Thus, we provide experimental evidence to confirm the validity of the theoretical approach employed to describe the magnetoimpedance in ferromagnetic films, revealed by the good agreement between numerical calculations and experimental results.

Magnetoimpedance hysteresis in amorphous microwires induced by core–shell interaction

We report on magneto-impedance (MI) hysteresis at MHz and GHz frequencies in amorphous microwires subject to a sufficiently high applied axial magnetic field HE. We show that this hysteresis originates from the magnetic hysteresis of the inner core which biases the outer shell causing a shift of the MI curve along the HE axis. Combined experiments (longitudinal and off-diagonal MI Z(HE), hysteresis loops M(HE) by vibrating sample magnetometer, and induction method) reveal the details of the magnetization reversal process in these microwires: Partial field dependencies Z(HE) and M(HE) are shown to be practically anhysteretic but shifted to the left or to the right about the origin by a residual magnetic field of the inner core HC. This shift can vary in the range from −35 to +35 A/m, depending on the magnetic history of the sample. We demonstrate that the hysteresis can be suppressed by application of a high enough axial magnetic field that saturates the magnetization of the inner core. A potential application of this hysteresis for memory devices is also proposed.

Expanding the longitudinal magnetoimpedance sensor range by direct bias current

We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range.

Manipulating the magnetoimpedance by dc bias current in amorphous microwire

We have studied the effect of the internal circumferential magnetic field HB created by the dc bias current IB on longitudinal and off-diagonal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that by changing the dc current IB it is possible to considerably change the MI dependencies. The bias current applied to such microwire transforms the symmetric and hysteretic MI curve to asymmetrical and anhysteretic. The minimum of longitudinal MI curve shifts from the zero-field point. Reversing the bias current causes reversal of the bias field direction and results in a mirroring of the MI curves. It is proposed to apply a cross-checking of two MI curves with IB of different polarity for magnetic field sensing. In particular, this method allows to overcome the drawbacks usually associated with longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. Moreover, the operating range of the longitudinal MI sensor, in contrast to the off-diagonal one, can be much extended as it exhibits a quite high sensitivity in the field range up to one order of magnitude higher than the anisotropy field.

Symmetry breaking effect of dc bias current on magnetoimpedance in microwire with helical anisotropy: Application to magnetic sensors

We have investigated the effect of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that, by changing the dc current IB, it is possible to considerably affect the MI dependence. We propose to use this effect in developing a longitudinal MI sensor that overcomes the drawbacks usually associated with the longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. We demonstrate that a set of two measurements of longitudinal wire impedance with properly selected bias current IB allows determination of both the magnitude and direction of the magnetic field HE over an extended range, much higher than the sample anisotropy field. Additional features of the proposed method are the increased sensitivity and the detection of exceeding the operating range.

Correlation of surface domain structure and magneto-impedance in amorphous microwires

The correlation between surface domain structure (SDS) and high frequency magneto-impedance (MI) in amorphous microwires has been systematically studied. First, we applied the magneto-optical polarizing microscopy to determine the SDS and found that it is considerably different in unstressed microwire and in microwires to which tensile and torsional stress were applied. Then, we measured the longitudinal and off-diagonal MI in these microwires and also observed quite different MI dependencies. We analyzed the experimental MI curves and their dependence on the SDS with the help of a simple model that nevertheless yields good qualitative agreement with experiment. We have demonstrated that the analysis of the MI dependencies, especially the off-diagonal one, can reveal the SDS in the microwires. The obtained results can also be useful for magnetic and stress sensing applications.

Longitudinal and Transverse Magnetoimpedance in FeNi/Cu/FeNi Multilayers With Longitudinal and Transverse Anisotropy

Longitudinal and transverse magnetoimpedance is studied for Fe19Ni81 (150 nm)/Cu(500 nm)/Fe19Ni81 (150 nm) multilayered structures with exactly the same geometry, having either longitudinal or transverse magnetic anisotropy, at frequencies up to 500 MHz, convenient enough for technological applications. The highest sensitivity was observed for longitudinal magnetoimpedance of the structures with transverse magnetic anisotropy. Transverse magnetoimpedance ratio for structures with transverse magnetic anisotropy was small but transverse magnetoimpedance and its sensitivity for the structures with longitudinal magnetic anisotropy was quite high. Relatively high values of transverse and longitudinal magnetoimpedance for the structures with longitudinal anisotropy lead to the possibility to design a single sensitive element detector for the control of the magnetic fields, parallel and perpendicular to the element.

Performances of a high sensitive trilayer F/Cu/F GMI sensor

We have selected stress-annealed nanocrystalline FeSiBCuNb ribbons for trilayer ferromagnetic/copper/ferromagnetic sensors exhibiting high magneto-impedance (MI) ratio. Longitudinal MI δZ reaches 450% at 60kHz. Measurements of responses of the GMI sensor on the small amplitude ac fields displays sensitivity of 60V/T up to a few 100Hz. The noise equivalent magnetic induction is equal to 13nT/Hz+1/2, limited to the added noise from electronics.

Giant magneto-impedance in stress-annealed finemet/copper/finemet-based trilayer structures

The resistive and reactive components of magneto-impedance (MI) for finemet/copper/finemet sandwiched structures based on stress-annealed nanocrystalline Fe 75Si 15B 6Cu 1Nb 3 ribbons as functions of different fields (longitudinal and perpendicular) and frequencies have been measured and analyzed. Maximum changes of 700% and 450% in the resistive and inductive components of MI, respectively, have been obtained in 30–600 kHz frequency range. These large changes in MI are a direct consequence of the large effective relative permeability due to the closed magnetic flux path in the trilayer structure. The influence of perpendicular bias fields ( H per) in the longitudinal MI (LMI) configuration greatly improves the MI ratios and sensitivities. The maximum MI ratio for the resistive component increases to as large as 2500% for H per∼1 Oe. The sensitivity of the field dependence of resistive component of MI increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of H per∼30 Oe. Such high increase in MI ratios and sensitivities with perpendicular bias fields are due to the formation the favorable (transverse) domain structures.

Enhancement of Magnetoimpedance in Fe74.5−xCuxNb3Si13.5B9 As Cast Ribbons

With increasing Cu content x in Fe74.5−xCuxNb3Si13.5B9 as cast ribbons, an enhancement of magnetoimpedance can be observed. The magnetoimpedance (Z(H) − Z(0))/Z(0) for Fe72Cu2.5Nb3Si13.5B9 as cast ribbon reaches −35% under a dc field H = 7162 A/m at a frequency ƒ = 1 MHz. The longitudinal magnetoimpedance effect in Fe74.5−xCuxNb3Si13.5B9 as cast ribbons is connected with the variation of transverse permeability. The grain size of α-Fe(Si) in Fe72Cu2.5Nb3Si13.5B9 as cast ribbon was estimated as about 7—10 nm. This revealed that soft magnetic nanocrystalline materials with giant magnetoimpedance effect can be obtained directly from the melt - spinning technique without additional annealing processes.

Magnetoimpedance effect in a NiFeMoMn supermalloy ribbon

The magnetoimpedance (MI) effect in NiFeMoMn supermalloy ribbon, as well as the magnetoresistance and magnetoreactance, are investigated as the functions of the dc magnetic field and ac driving current frequency. The longitudinal MI reaches 44% in 65 Oe at 0.2 MHz but the transverse effect is small (<2%). The MI effect is discussed in terms of the magnetic permeability.

Enhanced GMI in ribbons of Co 70.4Fe 4.6Si 15B 10 alloy

We show that the longitudinal magnetoimpedance (GMI) in ribbons of amorphous alloys can be highly enhanced by varying the sample length, the annealing temperature, and the magnitude of the AC electrical current.

Giant transversal magnetoimpedance and Hall-effect measurements in Co70.4Fe4.6Si15B10

We report room-temperature transversal magnetoimpedance (TMI) and Hall-effect measurements performed in ribbons of the zero-magnetostriction soft-ferromagnet Co70.4Fe4.6Si15B10 alloy annealed at 587 K for 15 min at a dc magnetic field of 2 kOe. The annealing showed little effect on the magnetostriction of the samples. The frequency f and the amplitude Iac of the current used in the measurements, and the measuring magnetic field H were varied in the intervals 10≤f≤105 Hz, 2.5≤Iac≤25 mA, and −15≤H≤15 kOe, respectively. The magnetic field dependence of the TMI shows a peak which is strongly dependent on f and on Iac. It reaches the giant value of 28% at H=350 Oe for f=100 kHz and Iac=25 mA. This TMI giant value is of the same order of the giant longitudinal magnetoimpedance (GLMI) but its peak is positioned in a magnetic field two orders of magnitude larger than the value obtained for the GLMI. The Hall effect yielded a value of RS=0.43 μΩ cm kOe−1. Peaks which are also frequency dependent were observed at the Hall voltage.