Magnetic Layer Thickness Research Articles

Effect of magnetic layer thickness on magnetic properties of Ce-Fe-B thin films

The Ce2Fe14B thin films with a notable out-of-plane c-axis texture were prepared by DC magnetron sputtering on a Ta buffer layer. The morphological and magnetic properties were investigated. The thickness of the magnetic layer had a dramatic effect on the formation of Ce2Fe14B phase, and excellent magnetic properties (Hci ≈ 4.25 kOe, Mr/Ms ≈ 0.81) were observed for the Ce-Fe-B film with the thickness dm = 200 nm. The results of the hysteresis loops for Ce-Fe-B film (dm = 200 nm) at various measured temperatures show that a decoupling between the hard and the soft phases is observed at low temperatures, which is due to the regions with quite low anisotropy provided by the α-Fe. Moreover, it is clear that significantly various magnetization behaviors between the films with dm = 200 and 300 nm were observed with a similar trend due to the existence of the α-Fe soft phase.

Spin-valve Josephson junctions for cryogenic memory

Josephson junctions containing two ferromagnetic layers are being considered for use in cryogenic memory. Our group recently demonstrated that the ground-state phase difference across such a junction with carefully chosen layer thicknesses could be controllably toggled between zero and $\ensuremath{\pi}$ by switching the relative magnetization directions of the two layers between the antiparallel and parallel configurations. However, several technological issues must be addressed before those junctions can be used in a large-scale memory. Many of these issues can be more easily studied in single junctions, rather than in the superconducting quantum interference device (SQUID) used for phase-sensitive measurements. In this work, we report a comprehensive study of spin-valve junctions containing a Ni layer with a fixed thickness of 2.0 nm and a NiFe layer of thickness varying between 1.1 and 1.8 nm in steps of 0.1 nm. We extract the field shift of the Fraunhofer patterns and the critical currents of the junctions in the parallel and antiparallel magnetic states, as well as the switching fields of both magnetic layers. We also report a partial study of similar junctions containing a slightly thinner Ni layer of 1.6 nm and the same range of NiFe thicknesses. These results represent the first step toward mapping out a ``phase diagram'' for phase-controllable spin-valve Josephson junctions as a function of the two magnetic layer thicknesses.

Fabrication of package embedded spiral inductors with two magnetic layers for flexible SIP point of load converters in Internet of Everything devices

Inductive DC-DC converters are key elements in power delivery units for the development of Internet of Everything (IoE) architectures made of interconnected networks of smart devices, self-powered from different energy sources. The ultra-low power levels involved in IoE devices in addition to cost reduction of final products requires the development of new technologies for the miniaturization of all the active and passive components. In this paper, a low temperature, cheap and simple two-steps fabrication process of embedded planar inductors with two magnetic layers on a very thin, flexible and lightweight FR4 organic substrate is demonstrated for flexible System in package (SIP) based point of load DC-DC converters in IoE devices. The process uses standard printed wiring board (PWB) copper etching to define the square geometry of the planar inductors and trenches underneath the inductor copper traces. Very thick top and bottom magnetic layers are deposited using stencil printing of an FR4 compatible epoxy-NiZn ferrite composite magnetic material on top of the copper traces and into the trenches. At 30MHz, the permittivity is 3.4 and 6.23 while the dielectric loss tangent is 0.014 and 0.009 for the epoxy and composite magnetic material respectively. The composite material has a permeability of 8.46, a loss tangent value of 0.1 at a frequency of 30MHz and saturates around 0.13 Tesla. The DC resistance varies from 136mΩ to 386mΩ while at 30MHz the AC resistance varies from 1.9Ω to 10.1Ω for an inductance value from 180nH to 715nH, corresponding to an inductance density between 5.69nH/mm2 and 12.47nH/mm2 and a quality factor between 13 and 17. Flexibility and its effect on the electrical parameters of the fabricated inductors is demonstrated through bending tests. A variation of <3% for the DC resistance is obtained for 5mm bend radius. At 30MHz and for a bend radius (both upward and downward) from 3.7mm to 5mm, the flat state (unbent) AC resistance and inductance values (1.9Ω to 10.1Ω for 180nH to 715nH) decrease by 6.5% to 18% and by 2% to 4.4% respectively which increase the self-resonant frequency by 3% to 3.4% and the quality factor by 2.2% to 20%. The characterized inductors are modeled in ANSYS HFSS electromagnetic simulator and simulation results show a good correspondence with the measured inductances and quality factors, which allows a reliable prediction of the inductors behavior for DC-DC converter design and implementation for IoE devices.

Influence of the Size and Structural Factors on the Magnetism of Multilayer Films Based on 3d and 4f Metals

This work has presented some data on the layer structuring of films of 3d and 4f metals and their alloys, which have potential for practical use in magnetic sensors. The decrease in the thickness of magnetic layers with this structuring entails natural worsening of the crystallinity and leads to a degradation of magnetic ordering. However, the manifestation of these tendencies depends to a great extent on the conditions of preparation, the composition, and the sequence of the deposition of the contacting layers in the multilayer structures. The combination of these factors makes it possible to realize an optimum composition and optimum structural states of the films, which in a number of cases lead to the appearance of new combinations of functional properties.

Observation of carbon impurity flow in the edge stochastic magnetic field layer of Large Helical Device and its impact on the edge impurity control

The parallel flow of carbon impurity in a thick stochastic magnetic field layer called the ‘ergodic layer’ located at the edge plasma of the Large Helical Device (LHD) is studied by space-resolved vacuum ultraviolet (VUV) spectroscopy, using a 3 m normal incidence spectrometer. A full vertical profile of C3+ impurity flow is evaluated from the Doppler shift of the second order of CIV line emission (2 × 1548.20 Å) at a horizontally-elongated plasma position of LHD. The carbon flow at the top and bottom edges in the ergodic layer has the same direction toward the outboard side along the major radius direction. The observed flow quantitatively agrees with the simulation results calculated with a 3D simulation code, EMC3-EIRENE. It experimentally verifies the validity of edge parallel flow driving the impurity screening.

Tailoring the magnetization states in 2D arrays of multiresponse ferromagnetic nanomagnets

We have fabricated nanomagnet arrays as a function of several geometrical parameters like the spacing between nanostructures, the aspect ratio and the layers thicknesses. The nanomagnets consist in two magnetic layers, separated by a non magnetic interlayer, that interact through magnetostatic coupling. They present a multiresponse hysteresis loops with two different switching fields. We have performed micromagnetic simulations to discern the role play by the different interactions. The spacing in the array strongly modifies the saturating field along the short axis and the magnetization reversal mechanisms from coherent rotation to domain wall nucleation. A small asymmetry between the two magnetic layers favors a magnetization reversal mechanism along the long axis with two different switching fields. These fields can be tailored through the thickness of the layers or the inter-element spacing in the array. In trilayers with the same magnetic layer thicknesses, the asymmetry can be induced by growing the two magnetic layers with a different anisotropy. The well-defined reversal fields make these nanomagnets potentially useful for magnetic tagging.

Magnetoelastic Properties of Epitaxially Grown Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5Heusler Alloys Thin Films

The out-of-plane magnetocrystalline anisotropy and magnetoelastic properties of series of epitaxially grown layers of Co2Fe0.4Mn0.6Si (CFMS) and Co2FeGa0.5Ge0.5 (CFGG) Heusler alloys thin films deposited on MgO with chromium buffer layer were investigated by means of the ferromagnetic resonance (FMR), SQUID magnetometer, and by the strain modulated FMR technique. The magnitude of the magnetocrystalline anisotropy constant was found to decrease with increasing layer thickness. The change of the anisotropy is caused mainly by the surface effects. However, for some of the samples series, the change of chemical ordering with the change of the magnetic layer thickness was also observed. An additional silver buffer layer influence on the properties of the magnetic layer was also investigated. For all three of the investigated series of the Heusler alloys, i.e., CFMS without Ag, CFMS with Ag, and CFGG, the experimentally observed magnitude of the magnetoelastic constant increases with the increase of the magnetic layer thickness.

A finite element correction method for sub-20 nm nanoindentation considering tip bluntness

Due to substrate effects and inherent tip bluntness, using current state-of-the-art nanoindentation instrumentation, it is difficult to directly measure mechanical properties of thin films less than 20 nm thick. With the aid of Finite Element Analysis (FEA), we obtain the mechanical properties by correlating simulated force-displacement responses with those from nanoindentation experiments. For shallow indentation experiments that is required for very thin films, it is found that an indenter model with a blunt tip is more realistic and leads to accurate characterization of mechanical properties. The proposed blunt tip model is validated with experiments on a standard fused quartz sample, and then applied to measure the nanomechanical properties of a 90 nm thick metal alloy layer and a 14 nm thick magnetic layer sandwiched between a carbon overcoat and a metal alloy. The magnetic layer properties are found to be 180 GPa for the reduced modulus and 2.9 GPa for the yield strength.

Giant magnetoresistance (GMR) behavior of electrodeposited NiFe/Cu multilayers: Dependence of non-magnetic and magnetic layer thicknesses

Giant magnetoresistance (GMR) behavior in electrodeposited NiFe/Cu multilayers was investigated as a function of non-magnetic (Cu) and ferromagnetic (NiFe) layer thicknesses, respectively. Prior to the GMR analysis, structural and magnetic analyses of the multilayers were also studied. The elemental analysis of the multilayers indicated that the Cu and Ni content in the multilayers increase with increasing Cu and NiFe layer thickness, respectively. The structural studies by X-ray diffraction revealed that all multilayers have face centred cubic structure with preferred (110) crystal orientation as their substrates. The magnetic properties studied with the vibrating sample magnetometer showed that the magnetizations of the samples are significantly affected by the layer thicknesses. Saturation magnetisation, Ms increases from 45 to 225emu/cm3 with increasing NiFe layer thickness. The increase in the Ni content of the multilayers with a small Fe content causes an increase in the Ms. And, the coercivities ranging from 2 to 24 Oe are between the soft and hard magnetic properties. Also, the magnetic easy axis of the multilayers was found to be in the film plane. Magnetoresistance measurements showed that all multilayers exhibited the GMR behavior. The GMR magnitude increases with increasing Cu layer thickness and reaches its maximum value of 10% at the Cu layer thickness of 1nm, then it decreases. And similarly, the GMR magnitude increases and reaches highest value of pure GMR (10%) for the NiFe layer thickness of 3nm, and beyond this point GMR decreases with increasing NiFe layer thickness. Some small component of the anisotropic magnetoresistance was also observed at thin Cu and thick NiFe layer thicknesses. It is seen that the highest GMR values up to 10% were obtained in electrodeposited NiFe/Cu multilayers up to now. The structural, magnetic and magnetoresistance properties of the NiFe/Cu were reported via the variations of the thicknesses of Cu and NiFe layers with stressing the role of layer thicknesses on the high GMR behavior.

Magnetic properties and simulated structure of granular nanothickness in magnetic films in a pre-percolation area

Multilayered (CoFeB)m(SiO2)100−m nanogranular film composites are probed via ferromagnetic resonance (FMR) spectroscopy. When the layer thickness is 1.0 to 2.6 nm and magnetic phase concentrations remain in the percolation range, the FMR field in these nanosystems reveals no dependence on the magnetic composite layer thickness. The observed phenomena are explained in the context of the FMR theory, and the relationship between the magnetic granule shape and absorbed electromagnetic radiation is established as well.

AC and DC-shielding properties for the Ni80Fe20/Cu film structures

Multilayered Ni80Fe20/Cu film shields were obtained via electrochemistry method with different thickness and number of partial magnetic layers. Magnetic properties and shielding characteristics were investigated as well as function of thickness and number of layers. Difference in magnetic properties for Ni80Fe20 films with different thickness is due to formation of defect layers on the top and bottom film surfaces during electrodeposition processes. These layers can be characterized as layers with high density defects (as a result poor iron content). Main deviation in magnetic properties is typical for thinner films. It was measured DC and AC shielding and results discussed. Maximal value of DC-shielding effectiveness was observed for multilayered samples with small number magnetic layers with large thickness (80–400μm). The minimal value of DC-shielding effectiveness was observed for the multilayered sample with the minimum thickness of the magnetic layer (5μm) and maximal number of the layers (80 layers). It is in good agreement with shunting mechanism. In low frequency range maximal values of AC-shielding effectiveness were observed like in case of DC-shielding for samples with small number magnetic layers with large thickness. With frequency increasing the situation was radically changed and AC-shielding effectiveness was higher for samples with maximal number of layers. In the frequency range above 40kHz AC-shielding effectiveness was sharply decreased due to sharply decreasing of permeability value. As a result it leads to decrease of absorption loses (SEabs.). It was discussed the main shielding mechanisms for multilayered Ni80Fe20/Cu film samples under different external influences. Main contribution in electromagnetic shielding in the range 300Hz–20kHz is absorption and reflection processes. In the range 20kHz–50kHz main shielding mechanisms are reflection and re-reflection. For 300Hz–50kHz frequency range most appropriate to use multilayered structures with large number of thin layers with cardinally different values of magnetic permeability and electrical conductivity.

Annealing temperature dependence of magnetic properties of CoFeB/MgO stacks on different buffer layers

We investigate the annealing temperature dependence of the magnetic properties of CoFeB/MgO stacks with different buffer materials (Mo, Ta, and W). For Mo and W, bcc-crystalline and amorphous-like films are prepared by changing the deposition conditions. A relatively small saturation magnetization is maintained after annealing up to 400 °C for the samples with bcc-W, bcc-Mo, and amorphous-like Mo buffers. A small variation in magnetic dead layer thickness with annealing is observed for the samples with bcc-crystalline buffer layers. The interfacial anisotropy is found to mainly depend on the element of the buffer layer used regardless of its crystalline structure, and is larger for the samples with W and Mo buffers than those with Ta buffer. The sample with bcc-Mo buffer shows the highest robustness against annealing among the studied systems. We give a systematic picture based on the thermochemistry that can reasonably explain the observed buffer layer dependence of the variations in magnetic properties with annealing.

Engineering the magnetic anisotropy of an ultrathin Co layer sandwiched between films of Mo or Au

Magnetic properties of an ultrathin Co layer deposited on the Mo(1 1 0) or Au(1 1 1) buffers crucially depend on magnetic layer thickness and a cap layer type (Au or Mo, studied in this work). Depending on the sandwich configuration, magnetization is oriented in a perpendicular direction to the plane in the range of smaller Co layer thickness (below 2 nm) or in the sample plane for a thicker layer (3 nm). Moreover, a well-developed two-fold in-plane magnetic anisotropy occurs in the Co layer deposited on the Mo buffer. These features are correlated with crystalline structure studied with the use of numerous complementary methods: reflection high-energy electron diffraction, x-ray diffraction, x-ray reflectivity, nuclear magnetic resonance, and element-sensitive synchrotron techniques, i.e. x-ray linear dichroism and x-ray absorption near edge spectroscopy. Magnetic behaviour, exhibiting volume and surface contributions, is thoroughly discussed in terms of the buffer and cap layer type, thickness-dependent crystalline structure of the Co layer, and the interface quality.

Magnetic behaviour of multisegmented FeCoCu/Cu electrodeposited nanowires

Understanding the magnetic behaviour of multisegmented nanowires (NWs) is a major key for the application of such structures in future devices. In this work, magnetic/non-magnetic arrays of FeCoCu/Cu multilayered NWs electrodeposited in nanoporous alumina templates are studied. Contrarily to most reports on multilayered NWs, the magnetic layer thickness was kept constant (30 nm) and only the non-magnetic layer thickness was changed (0 to 80 nm). This allowed us to tune the interwire and intrawire interactions between the magnetic layers in the NW array creating a three-dimensional (3D) magnetic system without the need to change the template characteristics. Magnetic hysteresis loops, measured with the applied field parallel and perpendicular to the NWs’ long axis, showed the effect of the non-magnetic Cu layer on the overall magnetic properties of the NW arrays. In particular, introducing Cu layers along the magnetic NW axis creates domain wall nucleation sites that facilitate the magnetization reversal of the wires, as seen by the decrease in the parallel coercivity and the reduction of the perpendicular saturation field. By further increasing the Cu layer thickness, the interactions between the magnetic segments, both along the NW axis and of neighbouring NWs, decrease, thus rising again the parallel coercivity and the perpendicular saturation field. This work shows how one can easily tune the parallel and perpendicular magnetic properties of a 3D magnetic layer system by adjusting the non-magnetic layer thickness.

Controlling the canted state in antiferromagnetically coupled magnetic bilayers close to the spin reorientation transition

Canted magnetization is obtained in ultrathin, antiferromagnetically coupled magnetic bilayers with thicknesses around the spin reorientation transition. The canting angle is controlled by both the magnetic layer thickness and interlayer coupling strength, which are tuned independently. Hysteresis loops are obtained, where magnetization components parallel and transverse to the applied field are measured, and analyzed by comparison to micromagnetic simulations. This enables the canting angle to be extracted and the behavior of the individual layers to be distinguished. Two types of canted systems are obtained with either single-layer reversal or complex, coupled two-layer reversal, under moderate external magnetic fields. Controlling the magnetization canting and reversal behavior of ultra-thin layers is relevant for the development of magnetoresistive random-access memory and spin-torque oscillator devices.

Perpendicular magnetic anisotropy of CoFeB\Ta bilayers on ALD HfO2

Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-κ dielectric (relative permittivity κ=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy Ki up to 0.49 mJ/m2 appears after annealing the stacks between 200°C and 350°C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350°C coincides with the onset of interdiffusion in the materials. High-κ dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-κ dielectrics.

Effect of the Interfacial Disorder on the Magnetotransport Properties in Ni81Fe19/Ti10 W 90 Multilayers

This work is a study of the interface structure effect on the magnetotransport properties in Ni81Fe19/Ti10 W 90 magnetic multilayer. The overall weakness showed by experimental magnetoresistance rate $\text {MR}_{\exp }$ is probably due to a degradation of the interface quality caused by the apparition of a disordered phase NiFeW at the interface. Thus, we propose in this paper an extension to the Johnson-Camley semi classical model that takes in consideration the evolution of the interface structure, which makes it possible to reproduce quite faithfully the experimental results $\text {MR}_{\exp } (t_{\text {NiFe}})$ for all ranges of magnetic layer thicknesses, confirming the important role of the interface structure on the electronic transport properties.

Tailoring the soft magnetic properties of sputtered multilayers by microstructure engineering for high frequency applications

Soft magnetic Ni78.5Fe21.5, Co91.5Ta4.5Zr4 and Fe52Co28B20 thin films laminated with SiO2, Al2O3, AlN, and Ta2O5 dielectric interlayers were deposited on 8” Si wafers using DC, pulsed DC and RF cathodes in the industrial, high-throughput Evatec LLS-EVO-II magnetron sputtering system. A typical multilayer consists of a bilayer stack up to 50 periods, with alternating (50-100) nm thick magnetic layers and (2-20) nm thick dielectric interlayers. We introduced the in-plane magnetic anisotropy in these films during sputtering by a combination of a linear magnetic field, seed layer texturing by means of linear collimators, and the oblique incidence inherent to the geometry of the sputter system. Depending on the magnetic material, the anisotropy field for these films was tuned in the range of ∼(7-120) Oe by choosing the appropriate interlayer thickness, the aspect ratios of the linear collimators in front of the targets, and the sputter process parameters (e.g. pressure, power, DC pulse frequency), while the coercivity was kept low, ∼(0.05-0.9) Oe. The alignment of the easy axis (EA) on the 8” wafers was typically between ±1.5° and ±4°. We discuss the interdependence of structure and magnetic properties in these films, as revealed by atomic force microscopy (AFM), X-ray reflectivity (XRR) with reciprocal space mapping (RSM) and magneto-optical Kerr effect (MOKE) measurements.

Magnetic anisotropy in multilayer nanogranular films (Co40Fe40B20)50(SiO2)50/α-Si:H

Macroscopic and local magnetic anisotropy of [CoFeB-SiO2/α-Si:H]60 multilayer films was studied in comparison with that for the thick CoFeB-SiO2 granular films. The volume fraction of magnetic component Co40Fe40B20 is ranged from 0.34 to 0.70. In the multilayer films the magnetic layer and silicon spacer thicknesses are 2.5÷4.5nm and 3.5nm correspondingly. The magnetization curves and ferromagnetic resonance measurements were used to determining magnetic anisotropy energy constants. The main contribution to the local magnetic anisotropy energy constant is found to be from surface magnetic anisotropy of magnetic granules. It is found that the magnetic percolation point of multilayer films (XC~40) is shifted in comparison with that in granular films (XC~30). Surface magnetic anisotropy energy constants of multilayer films with different X evaluated from the surface modes of spin-wave resonance are in the range 0.5<Ks <0.9erg/cm2.

Influence of the magnetic dead layer thickness of Mg-Zn ferrites nanoparticle on their magnetic properties

Nanoparticle ferrite with chemical formula Mg(1−x)ZnxFe2O4 (where x=0.0, 0.2, 0.4, 0.6, 0.8 and 1) were prepared by sol-gel technique. Single phase structure of these ferrites was confirmed using X-ray diffraction (XRD). Transmission Electron Microscope (TEM) showed that the particle size of the samples in the range of (5.7–10.6nm). The hysteresis studies showed superparamagnetic behaviour at room temperature. The magnetization behaviour with Zn-content is expressed in the light of Yafet-Kittel angles. The dead layer thickness (t) was calculated and its effect on the magnetization and magnetic losses was debated. The Specific Absorption Rate (SAR) in an alternating magnetic field with frequency 198kHz for these ferrites has been studied. It is found that, the thickness of magnetic dead layer of the surface of the materials has greatly affected the SAR value of the samples.