Magnetoimpedance Measurements Research Articles

Detailed investigation on structural, optical, dielectric and magneto-dielectric properties with enhanced magneto-impedance characteristic of NdFeO3 nanoparticles

NdFeO3 (NFO) was synthesized using sol-gel citrate method and subsequent calcination at 1023 K. Utilizing Rietveld refinement analysis of the XRD pattern, it has been verified that NFO exhibits an orthorhombic crystal structure, with space group Pbnm. NFO grains were seen to be strongly agglomerated in a SEM image, despite their irregular shapes. The analysis of optical properties revealed a transmittance range of ∼20%–∼50% and an optical band gap of 2.15 eV for the NFO material. The dielectric properties of NFO were analyzed with respect to their dependence on frequency and temperature, while the ac electrical conductivity was studied in terms of its frequency variation. The dielectric dispersion behavior of NFO is explained by Maxwell Wagner-type polarization. A negative magneto-dielectric (MD) coupling of −19% and −35% was measured for ε and tanδ at 1 kHz for NFO. Magneto-impedance measurements on NFO showed positive magneto-resistance and both positive and negative magneto-capacitance, suggesting that the grain effect had a substantial role in the material's magnetic properties. These results suggest that NFO is an excellent choice for memory-based electronic devices with an appropriate band gap for optoelectronic applications having a large MD effect.

Response of the magneto-impedance to the martensitic transformation of the Ni46Mn22Ga24Co4Cu4 shape memory microwire

Based on the frequency dependence and the sensitivity of magneto-impedance to anisotropy, temperature, frequency, and magnetic field were able to co-regulated the impedance signals. In this paper, we used the magneto-impedance technique to characterize the martensitic transformation of Ni46Mn22Ga24Co4Cu4 shape memory microwire. The phase transformation from martensite to austenite at 345–368 K was accompanied by the magnetic transition. There was a significant difference in the magneto-impedance between the two phases that was strongly dependent on the range of the excitation current frequency. Higher magneto-impedance was acquired in martensite with high anisotropy indicating its higher sensitivity to the magnetic field. Additionally, the structure of the martensite variants caused hysteresis in the magneto-impedance and the maximum magneto-impedance ratio of the two phases was obtained at a high frequency (50 MHz). The results of this indicate the potential applicability of magneto-impedance measurement in analyzing phase transformations.

Magneto-Impedance measurements in thin films of the Spin-Glass Cu100-xMnxAu13.5 (x = 6.75 and 13.5) alloys

Magneto-impedance measurements (MI) were carried out on thin-films of Cu100-xMnxAu13.5 (x = 6.75 and 13.5). The sample with × = 6.75 (13.5) undergoes a phase transition to a spin-glass state below a glass temperature of about TG = 31 K (55 K). The MI measurements were carried out for temperatures (T) from 300 K down to 5 K in applied magnetic fields in the range of ± 3.5 kOe and for an ac electric current with frequency of 9.0 MHz. Short-range interaction and spin-fluctuations yielded non-vanishing values for the MI data for all values of T. The transverse magnetic permeability (μT) was obtained for both sample compositions demonstrating that MI is a suitable technique to study canonical spin-glasses in the MHz regime. Moreover, it was observed that the spin-fluctuations in very short time scale (∼10−7 s) are important down to the lowest temperature investigated of 5 K. The transverse magnetic susceptibility, μT, showed a minimum near the freezing temperature.

Broad-energy oxygen ion implantation controlled magnetization dynamics in CoFeTaZr

In this paper, a novel pulsed broad energy spectrum ion-implantation technique, using the dense plasma focus device (DPF), for uniform oxygen-ion doping along the thickness of a ~250 nm thick magnetic CoFeTaZr layer is investigated. A new operational regime of the dense plasma focus – the off-focus mode – is explored to avoid the surface damage of the exposed sample by the high energy plasma streams/jets and instability accelerated ions, typically observed in conventional efficient-focus mode operation. The faraday cup measurements shows the increase in ion fluence from 3.83 × 1013 ion/cm2 for efficient-focus mode to 8.76 × 1013 ion/cm2 for off-focused mode operation in the broad-ion-energy range of 1–100 keV. The x-ray photoelectron spectroscopy (XPS) of the unexposed sample shows the presence of Co in Co0, Co2+ and Co3+, Fe in Fe0, Fe2+ and Fe3+, and Ta in Ta0 and Ta2+ oxidation states while Zr was observed with only metallic Zr binding energy peaks indicating the surface oxidation of the unexposed sample. The exposure to oxygen plasma in DPF device led to the increase in the higher oxidation states of Co, Fe and Ta with reduction in metallic binding energy peak and the deconvolution of oxygen XPS spectrum confirmed the bonding of oxygen to Co, Fe and Ta. The magnetization dynamics of unexposed and oxygen-ion doped samples was studied using magnetoimpedance measurements in the 1–2.5 GHz frequency range. Gilbert’s damping factor, in-plane anisotropy and effective magnetization of the magnetic substrate were calculated and it is found that these properties can be modulated with a lighter ion dosage using this novel pulsed broad-energy-ion implantation technique. It is concluded that the off-focus mode DPF operation can provide the ions of required energy and fluence to implant oxygen ions across the thickness of the CoFeTaZr magnetic thin film to modulate its magnetic properties.

Magnetoimpedance effect in amorphous Co-rich ferromagnetic microwires and its application as low-field sensor

The magnetoimpedance in amorphous microwires with a nominal composition of Co67Fe4Si14B15 has been investigated. The measurements were carried out with an Agilent 4395A network analyzer in the frequency range from 100 kHz to 60 MHz. The experimental setup for magnetoimpedance measurements and the analysis of the results are presented. Our results show that an optimum frequency exists, where the magnetoimpedance ratio is maximum for all studied frequencies. In this frequency, the amorphous microwire is very sensitive to variations of the dc magnetic field. Therefore, we propose a possible application as a low dc field sensor.

Exchange bias training effect in IrMn-layer/ferromagnetic-ribbon heterostructures probed with magnetoimpedance

The exchange-bias training effect in IrMn-layer/ferromagnetic-ribbon heterostructure is studied by performing magnetoimpedance (MI) measurements. Asymmetric, hysteretic and single peak behavior of the MI response and a shift in the MI peak to zero fields accompanied by 52% increase in MI has been detected as the signature of the exchange bias (EB) and training effect (TE), respectively. Also, during the consecutive filed sweep of MI response, both EB field and the degree of asymmetry of MI decrease that is another reason for existence of TE in our sample. The analysis of the magneto-optical Kerr effect (MOKE) and MI behavior establish that Hoffmann s model (Phys. Rev. Lett. 93, 097203 (2004)) is a good description of our experimental data, due to the existence of a strong single cycle TE in our IrMn-layer/ferromagnetic-ribbon system.

High-frequency magnetoimpedance effect in meander-line trilayered films

We report a systematic study of structural properties and quasi-static and dynamical magnetization behavior of trilayered systems produced in the meander-line geometry. Our samples consist of NiFe/Cr/NiFe layers produced by the magnetron sputtering technique. Here we grow samples with NiFe and Cr layers in a wide thickness range, keeping constant the total thickness of the trilayer. The structural properties and the quasi-static magnetic behavior were characterized by X-ray diffraction and magnetization curves, respectively. The magnetization dynamics was investigated through the magnetoimpedance effect at the high-frequency regime. The sample geometry, as well as the configuration of the magnetic fields, employed in the magnetoimpedance measurements, enabled us to modify the frequency limits in which the distinct mechanisms are acting on the magnetoimpedance response. Hence, we are able to modify/tailor the impedance as a function of both the magnetic field and probe frequency. Our results pave the way for the exploration the meander-line geometry at the high-frequency regime in samples with low dimensionalities.

Effect of multilayer structure parameters on magnetoimpedance ratio with low frequency measurements

The magneto-impedance of the NiFe thin films is experimentally dependent on their structure. The multilayer structures of [NiFe/Cu]<sub>4</sub> and [NiFe/Cu]<sub>2</sub>/Cu/[NiFe/Cu]<sub>2</sub> on the <em>meander structure</em> PCB Cu substrate in this study were deposited using the electrodeposition method. The frequency was varied in order to determine its effect on the magneto-impedance ratio. The results of the magneto-impedance characterization measurement showed that the maximum MI ratio in the multilayer [NiFe/Cu]<sub>4</sub> structure was 6.82% while in [NiFe/Cu]<sub>2</sub>/Cu/[NiFe/Cu]<sub>2</sub> was 3.08% with a frequency of 100 kHz. The increase in the MI ratio in the low frequency range indicates that the MI ratio depends on the structure of the layer which is affected by the permeability of the magnetic material.

Modulation of the magnetoimpedance effect of ZnO:Ag/NiFe heterostructures by thermal annealing

The magnetization dynamics in ZnO:Ag/NiFe heterostructures has been investigated through magnetoimpedance measurements. By annealing the ZnO:Ag layer during the production process of the samples, structural and magnetic features of the whole heterostructure are modified, showing that the dynamical magnetic response of the heterostructure is strongly dependent on the annealing temperature. The magnetoimpedance results are discussed in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges and in terms of the evolution of the ZnO:Ag layer with annealing. The presented results open new roads for technological application of semiconductor/ferromagnetic heterostructures.

Crystal field deformation by Ce3+ doping in spinel Mn-Cr ferrite

We investigated the doping of the spinel structure Mn-Cr ferrite with cations of the rare-earth Ce. The material was characterized by X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy and saturation magnetization. The magneto-impedance showed a step-like drop in impedance that ranges from 10% to 45% at the highest and lowest biased electric field, respectively. There was no crystal structure deformation detected in the diffraction patterns, but rather the deformation of the crystal field was seen in the Raman spectra. We can conclude that doping a large rare-earth cation in a closed packed spinel structure results more in a distortion in the crystal field of the material rather than in its crystal structure. This crystal field distortion results in non-symmetric splitting of the energy states of the doping cations in octahedral and tetrahedral sites, for which Raman scattering shift is very sensitive, and can be seen also in magneto-impedance measurements.

Enhanced magnetic and room temperature intrinsic magnetodielectric effect in Mn modified Ba2Mg2Fe12O22 Y-type hexaferrite

We have reported a systematic investigation on structural, magnetic, magnetodielectric and magnetoimpedance characteristics of Y-type Ba2Mg2(Fe1−xMnx)12O22 (0 ⩽ x ⩽ 0.12) hexaferrite synthesized by solid-state reaction route. Rietveld refinement of x-ray diffraction pattern confirms the phase purity of all the samples with rhombohedral crystal structure. The Mn dopant modulates not only superexchange angle near to the boundary of magnetic blocks but also magnetic transition temperature. Temperature-dependent magnetization data suggests that due to Mn doping at Fe sites, ferrimagnetic to proper screw transition temperature (TII) increases from 190 K to 208 K, while there is a decrease in proper screw to longitudinal conical spin transition temperature (TI) from 35 K to 25 K. We observe remarkable decrease in the magnetic field from 20 kOe to 12 kOe to produce intermediate spin ordering from ferrimagnetic ordering which can be understood because of modification of superexchange angle due to Mn doping. The value of loss tangent decreases with increasing doping concentration at 300K, i.e. ~60% and 180% in BMFM4 (x = 0.04) and BMFM8 (x = 0.08) respectively as compared to BMF, suggesting the evolution of intrinsic feature in the doped samples. Magnetodielectric (MD) effect shows that in the low-frequency regime, the robust MD effect is because of Maxwell–Wagner interfacial polarization, whereas in the high-frequency regime intrinsic effect dominates. Further, magnetoimpedance measurement confirms the presence of substantial intrinsic MD% (~6%) at 1.3 T applied field at 300 K for 4% Mn-doped sample. Finally, the nature and strength of magnetoelectric coupling in BMFM4 and BMFM8 samples at 300 K is found to be biquadratic (P2M2) and maximum strength of coupling is 3.09 × 10−4 emu2 g−2 and 2.34 × 10−4 emu2 g−2, respectively.

Detection of electron paramagnetic resonance in La0.6Ca0.4MnO3 using a copper stripcoil

Recently, we had reported the detection of electron paramagnetic resonance (EPR) from magnetoimpedance (MI) measurements in bulk La0.60Ca0.40MnO3 (LCMO) samples using radio frequency (rf) currents [U. Chaudhuri and R. Mahendiran, Appl. Phys. Lett. 115, 092405 (2019)]. Here, we report an alternative method which involves measuring the effective MI changes of a copper stripcoil that encloses the LCMO sample. Magnetoresistance (∆R/R0) and magnetoreactance (∆X/X0) of the sample were measured indirectly via the stripcoil for frequencies of current from f = 0.5 to 2.5 GHz. During the field sweep, ∆R/R0 shows an abrupt increase that is accompanied by a dip in ΔX/X0 at a critical value of dc magnetic field (Hc) when f ≥ 0.9 GHz. Hc increased linearly with frequency (f) of the current in the stripcoil, satisfying the EPR relation fr = (γ/2π)Hdc, where γ is the gyromagnetic ratio and fr is the resonance frequency. The same stripcoil and the sample were also used to measure microwave power absorption using a vector network analyzer. The features observed in both these techniques were strikingly similar to the results obtained from the direct MI measurement in LCMO, which confirms the electrical detection of EPR.

Detection of electron spin resonance via magnetoimpedance in La1−xCaxMnO3

We demonstrate a method to detect the spin resonance of Mn electrons at room temperature in paramagnetic samples of La1−xCaxMnO3 with x = 0.35, 0.40, and 0.45 using a simple magnetoimpedance (MI) measurement. The magnetic field dependent “ac” resistance and reactance were simultaneously measured at 300 K using a single-port impedance analyzer by passing a current of frequency f = 500 MHz–3 GHz directly through the sample. The magnetoresistance of each sample increased abruptly at a critical value of the applied magnetic field while the magnetoreactance displayed a dip. Both these features shifted linearly toward higher “dc” magnetic fields with increasing frequency of the current. We suggest that these anomalies in MI are imprints of spin resonance from the Mn electrons. Our results were also verified using a conventional broadband spectrometer (f = 2–10 GHz). Thus, the electrical detection of paramagnetic resonance using a low-cost impedance analyzer, as demonstrated here, can provide an alternate method to investigate magnetic resonances in various materials.

Magnetoimpedance study of nickel incorporated diamond like carbon thin films

The present work aims to investigate the magnetoimpedance (MI) behaviour of electrodeposited nickel incorporated carbon (Ni–C) composite thin films of varying nickel content. Ni–C thin films were synthesized by electrodeposition method at room temperature with low voltage. Low nickel content thin films exhibited diamond-like carbon (Ni–DLC) phase. Considering the variation of magnetoimpedance due to change in transverse magnetic permeability of Ni–C thin films, magnetoimpedance measurements were performed with frequency by applying dc magnetic field in the plane of the film in the range of −1000 Oe < H < 1000 Oe. MI measurements were carried out, by passing alternating current of 1 mA through the samples perpendicular to the magnetic field, at room temperature within a low excitation frequency (up to 100 kHz) range. Magnetoimpedance peaks were observed at 9 kHz in each thin film. Variations in the intensity of MI peaks with magnetic field were also observed. Maximum MI ratio achieved for our samples was 123%, while Ni–DLC thin film showed an MI of 110%. The values of maximum magnetoimpedance of the films were found to change with nickel content in the Ni–C thin films.

Broad band magnetotransport at room temperature in La0.7Sr0.3−Ca MnO3: Electrically detected magnetic resonances

Abstract We report the room temperature magnetoimpedance in bulk samples of La0.7Sr0.3−xCaxMnO3 (0 ≤ x ≤ 1) subjected to ac current excitation of frequency f = 1 MHz to 3 GHz and dc magnetic fields (−5 kOe 700 MHz. A plot of Hdc corresponding to the double peak/critical field versus frequency suggest that the curves are linear for PM samples and non-linear for FM samples. We suggest that the observed anomalies in the ac magnetoresistance are due to electron paramagnetic resonance for x ≥ 0.24 and ferromagnetic resonance for x ≤ 0.20. Thus, we are able to electrically detect paramagnetic and ferromagnetic resonances in these conducing magnetic oxides through a simple magnetoimpedance measurement.

Exploring the magnetization dynamics, damping and anisotropy in engineered CoFeB/(Ag, Pt) multilayer films grown onto amorphous substrate

Abstract We investigate the magnetization dynamics in CoFeB/(Ag, Pt) multilayer films grown onto amorphous substrate engineered to have in-plane magnetic anisotropy and distinct effective damping parameter. We go beyond quasi-static magnetic properties and characterize the dynamic magnetic response by employing ferromagnetic resonance and magnetoimpedance measurements. The link between magnetic features and dynamic magnetic behavior allows us to identify the role of the effective damping parameter and of the magnetic anisotropy on the magnetoimpedance effect in multilayer films. In addition, we consider a theoretical approach to interpret the experimental data and also predict the magnetization dynamics in wider ranges of the explored parameters. From our results, we provide insights to tune the damping parameter and magnetic anisotropy in engineered multilayer films grown onto amorphous substrates.

Sintering effect and magnetodielectric studies on nanostructured BiFe0.95Co0.05O3

Abstract Multiferroic nanoparticles of BiFe0.95Co0.05O3 (BFCO) with different sizes were prepared by low temperature acetate precursor based modified sol–gel method. X–ray diffraction (XRD) measurement revealed rhombohedral phase of nanoparticles. Crystallite size increases from ∼41.05 nm (700 °C) to ∼ 48.42 nm (800 °C). The dielectric constant and loss tangent were studied as a function of temperature at different frequencies. The appearance of dielectric anomalies around antiferromagnetic transition temperature prove the existence of possible magnetoelectric (ME) coupling. Possible present ME coupling has been studied by performing magnetodielectric (MD) measurements at room temperature. The strong variation in dielectric constant and loss has been found under the influence of magnetic field at room temperature. The magnetoimpedance (MI) measurement was studied to separate out intrinsic and extrinsic MD effect. Spin spiral suppression at nanoscale with crystallite size less than ∼62 nm and lattice strain, arises due to Cobalt doping, play an important role in controlling multiferroic properties.

De-embedding zero-field signal in high-frequency magneto-impedance measurements of soft ferromagnetic materials

Abstract Devices based on soft ferromagnetic materials are promising for high-frequency flexible electronics. Especially, wide-range tunable ferromagnetic resonance response of ferromagnetic microwires and ribbons can be functionalized in the form of magneto-impedance sensors in stretchable, bendable and twistable environments. A vector network analyzer calibrated by standard techniques is required to characterize the high-frequency properties of such devices. However, most of the calibration techniques necessitate calculations, computer simulations, and/or fabricating calibration kits in the shape of various test fixtures. Here, we employ a fixture calibration method for high-frequency (up to 4 GHz) impedance measurements of CoFeSiB microwires and melt-spun ribbons taking zero applied magnetic field as the reference. This method is based on a virtual de-embedding procedure, in which a reference signal is subtracted from all the subsequent measurements, which reduces the time for the total calibration procedure down to few minutes. Applications of the method are not limited to the cases where applied magnetic field varies. Any external parameter (strain, temperature, pressure etc.) that can change the impedance is allowed by this method.

Dipolar interaction in multiple FINEMET ribbons

Abstract The dipolar interaction between FINEMET ribbons was investigated using giant magneto-impedance (GMI) measurement. It can be clearly revealed via the GMI response of a probe ribbon surrounding by nanocrystalline ribbons, which exhibited a plateau in the lower field region and double-peak in higher region. The plateau was gradually broadened with increasing the number of the surrounding ribbons or decreasing its length and the peak position shifted to higher field at the meantime. The frequency also affects the shift of the GMI peak field of the probe ribbon at high driving frequency, but has slight influence on the plateau in the measurement frequency range. Furthermore, the dipolar field between one surrounding ribbon and the probe ribbon and the geometric factor of ribbons are calculated using dipolar magnetization model to explicate the variation of dipolar interaction with number and length of ribbons. Thus, the GMI response of a probe ribbon can be employed as a novel tool to investigate the dipolar interaction in FINEMET ribbons.

Study of dipolar interaction in amorphous microwires using longitudinally driven magneto-impedance effect

The long-range dipole-dipole interaction in an array of Co57.3Fe7.6Cr1.7C33.4 amorphous microwires with axial bistability has been studied through magnetic hysteresis and longitudinally driven magneto-impedance (LDMI) measurements in this paper. Hysteresis loops performed for an array of microwires exhibit jumps and plateaux on the demagnetization curves. For LDMI curves, the multi-peak characteristic is presented as the number of microwires changes from 1 to 4. Each step in the hysteresis loops or each peak in the LDMI curves is correspondent to the magnetization reversal of an individual wire. To analysis the difference between the switching field of hysteresis loops and the peak field of LDMI curves, we further studied the dependence of the peak field on the driving current. The results showed that the ac magnetic field has a compensatory effect on the magnetization reversal of an individual wire.