Amorphous Magnetic Films Research Articles

Actuation of microstructures with spin-current volume effect

Microactuators are essential for advances in micro-optics, ultrasonic transducers and microsensors, and there is a growing demand for miniaturization and improved power. Here we demonstrate the actuation of micromechanical structures based on spin-current volume effect using an amorphous magnetic film of TbFeCo with volume magnetostriction. A 2 mm-diameter circular polyimide diaphragm coated with thin TbFeCo/non-magnetic metal films is prepared as the micromechanical structure. When an alternating charge current flows through the TbFeCo/non-magnetic metal films on the diaphragm under an external magnetic field orthogonal to the charge current, an alternating spin-current flows in the non-magnetic metal film due to the spin-Hall effect. In the spin-current volume effect, the spin-current transports angular momentum from the non-magnetic metal to TbFeCo film, and the spin-transfer torque modulates the magnetization fluctuation of the TbFeCo film, causing the diaphragm to vibrate due to spin-lattice coupling. The power density of the TbFeCo/Pt films actuator is larger than 1.17 × 106 W m−3 at 20 mA charge current under 7.2 kOe magnetic field. This value is much higher than that of various existing film-type microactuators. This spin-current volume effect is effective as a new actuation mechanism for microactuators used in micro-optical systems, acoustic diagnostic equipment, and micro-fluidic systems etc.

Tuning in-plane magnetic anisotropy and temperature stability in amorphous trilayers

Better understanding of the nature of magnetic coupling in soft/hard nanocomposites paves the way for tailored exchange-spring magnets. We have investigated a series of amorphous magnetic thin films and trilayers of magnetically soft Co85(Al70Zr30)15 and magnetically hard Sm12Co81Ti7, produced with DC magnetron sputtering. The overall magnetic properties of the trilayers were investigated with focus on the effects of layer configuration and thicknesses on coercivity, originating from the Sm12Co81Ti7 phase, and uniaxial in-plane anisotropy induced from the Co85(Al70Zr30)15 phase. In addition, we found that the thermal stability of a 20 nm Sm12Co81Ti7 layer was significantly increased if surrounded by two 10 nm Co85(Al70Zr30)15 layers in a trilayer structure.

Anomalous hysteresis loops of ferrimagnetic Gd-Co films of different thickness near the magnetic compensation temperature

Triple hysteresis loops were observed for amorphous ferrimagnetic Gd-Co films near the magnetic compensation temperature, which can be a consequence of both the spin-flop transition and the chemical composition gradient. In the work, an assessment of the possible chemical inhomogeneity of the films based on magnetic measurements was carried out and its relationship with the thickness of the samples was observed. Keywords: amorphous magnetic films, perpendicular magnetic anisotropy, ferrimagnetism, magnetic domain structure, magnetic hysteresis.

Increased intrinsic anomalous Hall effect from rare earth content in amorphous SmxCo1−x films

The low temperature anomalous Hall effect in amorphous sputtered SmxCo1−x films is investigated. The microstructure and amorphous nature of the films were characterized by local area diffraction through transmission electron microscopy. The Sm/Co ratio was changed to elucidate the origin of the anomalous Hall effect, which is a proxy for spin polarized transport. The anomalous Hall effect obeys a scaling relation that points to an intrinsic Berry-curvature based mechanism, consistent with recent reports on other amorphous magnetic materials. The anomalous Hall angle increases with increasing Sm content and reaches large values of ∼1%. This observation is related to recent measurements of the local structure in amorphous Sm–Co alloys and suggests that rare earth elements can be utilized to improve electrical control over spin polarization in amorphous magnetic films.

Tuning the magnetic properties of V2O3/CoFeB heterostructures across the V2O3 structural transition

In this work, we investigate the effects of the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural phase transition on the magnetic properties of an amorphous magnetic thin film of CoFeB in contact with it. ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ thin films are deposited epitaxially on sapphire substrates, reaching bulklike properties after few nm of growth. By means of temperature dependent Kerr effect characterizations, we prove that crossing the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural phase transition induces reproducible and reversible changes to CoFeB magnetic properties, especially to its coercive field. By decreasing the oxide layer thickness, its effects on the magnetic layer decreases, while reducing the magnetic layer thickness maximizes it, with a maximum of 330% coercive field variation found between the two ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural phases. By simply tuning the temperature, this systematic study shows that the engineering of ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural transition induces large interfacial strain and thus strong magnetic property variations to an amorphous thin film, opening wide possibilities in implementing strain-driven control of the magnetic behavior without strict requirements on epitaxial coherence at the interface.

Quantification of residual stress governing the spin-reorientation transition (SRT) in amorphous magnetic thin films

Soft magnetic thin films with in-plane uniaxial magnetic anisotropy are of significant importance for a broad range of technological applications, including high-frequency power conversion. In-plane uniaxial anisotropy in amorphous films is of particular interest for ultra-low materials loss and MHz frequency operations. The present work is focused on one of the fundamental mechanisms, i.e., residual stress, that can negate the uniaxial anisotropy in amorphous films by engendering perpendicular magnetisation and hence, undermining the soft magnetic performance. It is quantified how the nature of residual stress, compressive or tensile, transforms the magnetisation from an in-plane to an out-of-plane configuration, also well-known as spin-reorientation transition (SRT). A correlation between engineered residual stress in multilayer stacks, induced by the uneven expansion of metallic/dielectric layers following a thermal-shock scheme, and SRT mechanism demonstrates tensile stress inside the films undermines the soft magnetic performance. We suggest the magnetic softness can be retained by eluding sources of tensile stress during fabrication or post-processing of the amorphous films.

Multilevel nonvolatile regulation of magnetism by electric field in amorphous hard magnetic SmCo/PMN-PT(011) heterostructure

Multilevel nonvolatile regulation (MNR) is demonstrated in a heterostructure composed of an amorphous hard magnetic SmCo thin film and a (011)-oriented ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrate. Two alternative ways of obtaining MNR are employed: the quasi-unipolar method and the quasi-minor-loop method, both of which utilize the transition from the rhombohedral (R) to monoclinic (MB) and then to orthorhombic (O) phase in a PMN-PT substrate. The mechanism is distinct from the conventional unipolar method inducing MNR, which mainly makes use of switching the ferroelectric domain in the R phase. The introduction of these two methods provides different ideas for achieving MNR in ferromagnetic/PMN-PT heterostructures. The observed MNR in an amorphous SmCo/(011) PMN-PT heterostructure demonstrates the potential applicability of hard magnetic materials for multifunctional information storage and spintronic devices.

Tailoring the magnetic properties of sputtered amorphous CoZrTa/metal-oxide (MO) by interfacial oxygen migration

Modulating the soft magnetic properties of amorphous magnetic thin films is important for constructing energy-efficient and high performance thin film inductors. Here, a metal (Pt) and an oxide (Al2O3) are selected as the covering layer to investigate the effect of the interfacial microstructure on the magnetic properties of CoZrTa thin films. The results show that the magnetic dead layer thickness (tDL) and coercivity (Hc) decrease and saturation magnetization (Ms) increases with the annealing temperature for the CoZrTa/Al2O3 sample. However, tDL, Hc, and Ms of the CoZrTa/Pt sample show an opposite variation tendency with the annealing temperature. Interfacial structural results indicate that different magnetisms can be ascribed to different interfacial oxygen migration and interfacial diffusion processes. The effective interfacial oxygen migration in CoZrTa/Al2O3 reconstructs oxygen atom distribution at the interface and provides an effective way to enhance the magnetic properties of CoZrTa, whereas the intensified interfacial diffusion between CoZrTa and Pt after annealing in the CoZrTa/Pt sample caused the deterioration of the magnetism. This study will be helpful in advancing the development of magnetic thin film inductor devices.

Multimodal behavior of the dynamic magnetic susceptibility spectrum in amorphous CoZrTaB magnetic thin films

The origins of sub-Ferromagnetic Resonance (FMR) multimodal behavior in the magnetic susceptibility spectrum of amorphous CoZrTaB magnetic thin films are investigated using Brown's diffusion model describing continuous diffusion of magnetic spins. Brown's diffusion model is regressed onto experimental data for the amorphous CoZrTaB magnetic thin films with thicknesses spanning 80–530 nm. The mathematical model presented successfully reproduces the thickness dependent dynamic magnetic susceptibility of the amorphous CoZrTaB magnetic thin films with strong statistical significance. The model proposes the formation of additional energy wells in the uniaxial anisotropy energy plane of the material after a critical film thickness. The sub-FMR resonance peaks arise when the frequency of the external excitation field approaches the natural frequency of the well. Furthermore, the additional energy wells in the anisotropy energy plane cause a breakdown in the axial symmetry of the anisotropy energy plane. This breakdown of axial symmetry results in dynamic coupling between the transverse (χ⊥) and longitudinal (χ∥) magnetic susceptibility. This dynamic coupling results in the initial low frequency step-down in the magnetic susceptibility observed in the thicker CoZrTaB magnetic thin films. It is found that the application of an external bias magnetic field along the easy axis of the amorphous CoZrTaB magnetic thin films suppresses the sub-FMR resonance peaks by restoring the axial symmetry of the anisotropy energy plane.

Study on magnetic and electrical properties of CoFeTaBO films with different oxygen content based on two-state model

Amorphous magnetic CoFeTaBO granular films with different oxygen contents are fabricated by using magnetron sputtering. The effect of oxygen contents on magnetic and electrical properties of the amorphous CoFeTaBO granular films are investigated, and a model for the coexistence of two states of oxygen-dependent metallic oxides in the CoFeTaBO film is proposed to explain magnetic and electrical characteristics in amorphous film system. It is expected that our proposed two-state model can provide a new perspective for understanding the physical properties of amorphous magnetic granular film materials.

Experiments and simulations on the magnetization of transparent Co-Fe-Ta-B-O heteroamorphous films

Inducing oxygen into Co-Fe-Ta-B amorphous alloy system makes the transparent amorphous magnetic thin film (Co20Fe47Ta20B13)1-xOx. Oxygen content plays a major role in the magnetization properties of the films. Samples with x=0.41 have a large coercivity ∼1000 Oe, which is 20 times larger than the low oxygen content samples. The forming of a set of single domain magnetic granules rather than continuous magnetic film makes the different magnetization mechanisms. The deviation from Bloch law of saturation magnetization with temperature indicates the Bose-Einstein condensation occurring in magnetic nanostructures. According to the superparamagnetic theory, magnetic phase diagram of the system has been obtained. Monte-Carlo method is used for the simulation of the magnetization of a single domain magnetic granular system at a finite temperature. The simulation results match the experiment to some extent in magnetization-filed curve and field-cooling and zero-field-cooling magnetization curve. This work provides a systematical study of transparent amorphous magnetic thin film system and helps us to know better of this material.

Review of Power Electronics Components at Cryogenic Temperatures.

In order to apply power electronics systems to applications such as superconducting systems under cryogenic temperatures, it is necessary to investigate the characteristics of different parts in the power electronics systems. This paper reviews the influence of cryogenic temperature on power semiconductor devices including Si and wide bandgap switches, integrated circuits, passive components, interconnection and dielectric materials, and some typical cryogenic converter systems. Also, the basic theories and principles are given to explain the trends for different aspects of cryogenically cooled converters. Based on the review, Si active power devices, bulk CMOS based integrated circuits, nanocrystalline and amorphous magnetic cores, NP0 ceramic and film capacitors, thin/metal film and wirewound resistors are the components suitable for cryogenic operation. Pb-rich PbSn solder or In solder, classic PCB material, most insulation papers and epoxy encapsulant are good interconnection and dielectric parts for cryogenic temperatures.

Alternating Magnetic Force Microscopy: Effect of Si doping on the temporal performance degradation of amorphous FeCoB magnetic tips

In order to increase the resolution of traditional MFM and extend its applications in the past, we created an Alternating Magnetic Force Microscopy (A-MFM) with a magnetic force modulation by applying an off-resonance AC magnetic field. A new magnetic tip has been developed for A-MFM in this work. Perpendicular magnetic recording medium with 500 kfci recording density is successfully imaged and analyzed by using the new tips coated by 6–15 nm amorphous FeCoSiB-based soft magnetic film. The effect of Si doping to the magnetic film on the A-MFM imaging was studied. It was found that Si additive had no effect on the imaging properties, such as signal-to-noise ratio and spatial resolution (kept at ∼5 nm level). But on other side, Si additive significantly degraded the chemical stability of FeCoSiB film due to oxidation in ambient atmosphere. Surface passivation by metal and boron oxides is considered to have a main effect on improvement of chemical stability of Si-free magnetic coating. The results have shown that Si-free FeCoB-based magnetic tips are appropriate candidates for A-MFM imaging in ambient conditions.

PCB Embedded Bondwire Inductors With Discrete Thin-Film Magnetic Core for Power Supply in Package

This paper details the design, assembly, and detailed characterization of printed circuit board (PCB) embedded thin magnetic film inductors for Power Supply in Package applications. Solenoidal inductors were assembled on copper tracks printed on PCB with wire bonds to complete the copper loop. Furthermore, the solenoid inductors have laminated amorphous soft magnetic thin films embedded between the two conductor layers. The devices have chemically thinned Vitrovac films laminated as core material. Three different designs of solenoid inductors with different numbers of turns are assembled and characterized. The assembled PCB inductor measured a highest quality factor of 8.5 for a three-turn device at 10 MHz.

The sign of the interfacial Dzyaloshinskii–Moriya interaction in ultrathin amorphous and polycrystalline magnetic films

We investigate the sign of the interfacial Dzyaloshinskii–Moriya interaction (iDMI) energy density in system with inversion symmetry breaking for amorphous and polycrystalline ferromagnetic layers (CoFeB, Co) sandwiched by two different or the same heavy metals (Pt, Ta). By employing Brillouin light scattering, we observe non-reciprocal spin-wave dispersions which is a fingerprint of iDMI in SiO2/(Pt,Ta)/(CoFeB, Co)/(Pt,Ta) systems. We carefully confirm that the signs of DMI of structurally inverted systems are changed accordingly. Negative iDMI for SiO2/Pt/(CoFeB, Co)/Ta and positive iDMI for SiO2/Ta/(CoFeB, Co)/Pt are observed, and iDMI of the symmetric structures (Pt/CoFeB/Pt and Ta/CoFeB/Ta) are not measureable with our Brillouin light scattering setup due to a negligible iDMI. For amorphous CoFeB, the magnitudes of iDMI are the same within the experimental error regardless the stacking order. For the textured Co, however, the magnitude of iDMI for Pt/Co/Ta is about 30 % larger than Ta/Co/Pt structure.

Enhanced stress-invariance of magnetization direction in magnetic thin films

Spin valve devices, consisting of a free magnetic layer, a spacer layer, and a pinned magnetic layer, are widely used in magnetic sensors and nonvolatile magnetic memories. However, even a slight bending deformation can affect the magnetization direction of the free magnetic layer, which will change the magnetoresistance signal of the devices. Therefore, it is a challenge to develop a flexible spin valve device with controllable performance. Here, an enhanced stress-invariance of the magnetization direction in amorphous CoFeB magnetic films on flexible polyimide substrates is achieved. The uniaxial anisotropy is induced by growing on the bent substrate under a magnetic field, which aligns more magnetic domains with easy axes along the direction perpendicular to the subsequently applied stress. Theoretical calculations indicate that pre-induced anisotropy with an easy axis perpendicular to the applied stress effectively resists the change in the magnetization direction during bending. These results are of importance for realizing better performance of flexible spin valve devices and the development of flexible spintronics.

Monte Carlo simulation of magnetic properties of mixed spin (3/2, 1) ferromagnetic and ferrimagnetic disordered binary alloys with amorphous structure

Monte Carlo simulation is used to study the magnetic properties of mixed spin (3/2, 1) disordered binary alloys on simple cubic, hexagonal and amorphous magnetic ultra-thin films with 18×18×2 atoms. To this end, at the first approximation, the exchange coupling interaction between the spins is considered as a constant value and at the second one, the Ruderman–Kittel–Kasuya–Yosida (RKKY) model is used. Effects of concentration, structure, exchange interaction, single ion-anisotropy and the film size on the magnetic properties of disordered ferromagnetic and ferrimagnetic binary alloys are investigated. Our results indicate that the spontaneous magnetization and critical temperatures of rare earth-3d transition binary alloys are affected by these parameters. It is also found that in the ferrimagnetic state, the compensation temperature (Tcom) and the magnetic rearrangement temperature (TR) appear for some concentrations.

Electrochemical synthesis of Fe-W and Fe-W-P magnetic amorphous films and Fe-W nanowires

Binary and ternary Fe-W and Fe-W-P films have been obtained electrochemically by using an alkaline stable bath of Fe(III) with a new complexing agent (nitrilotriacetic acid trisodium salt monohydrate-NTA), adequate to avoid carbon incorporation in the deposits and assure the bath durability. The different stages to obtain the alloy deposits through induced co-deposition have been proposed. Significant tungsten percentages in the deposits have been obtained, resulting stable amorphous films with soft-magnetic properties. However, it has been necessary to simplify the deposition process to obtain Fe-W alloy nanowires by means of induced co-deposition in the interior of polycarbonate membranes. For first time, Fe-W magnetic nanowires have been synthesised by templated induced co-deposition.

Interface Magnetic and Electrical Properties of CoFeB /InAs Heterostructures

Amorphous magnetic CoFeB ultrathin films have been synthesized on the narrow band gap semiconductor InAs(100) surface, and the nature of the interface magnetic anisotropy and electrical contact has been studied. Angle-dependent hysteresis loops reveal that the films have an in-plane uniaxial magnetic anisotropy (UMA) with the easy axis along the InAs [0-11] crystal direction. The UMA was found to be dependent on the annealing temperatures of the substrates, which indicates the significant role of the Fe, Co-As bonding at the interface related to the surface condition of the InAs(100). $I$ – $V$ measurements show an ohmic contact interface between the CoFeB films and the InAs substrates, which is not affected by the surface condition of the InAs (100).

Partial crystallization in amorphous magnetic film induced by Ru layer interface

Partial crystallization in amorphous magnetic film is observed in this study. The film of Co46Fe46Zr5B3/Ru/Co46Fe46Zr5B3 (CFZB/Ru/CFZB) was prepared on glass substrate by DC magnetron sputtering. The CFZB underlayer (CFZB‐UL) and the CFZB overlayer (CFZB‐OL) were deposited under nominally same sputtering conditions, i.e. target, working gas, working pressure, input power, and deposition duration. The transmission electron microscopy (TEM) images with fast Fourier transform (FFT) patterns revealed that the CFZB‐UL was amorphous while the CFZB‐OL became unexpectedly partially crystallized. The result of X‐ray diffraction (XRD) spectra verified the TEM observation. The cause of the partial crystallization is attributed to the lower concentration of glass formers and the lattice matching between the overlayer and the Ru layer below.