Amorphous Magnetic Thin Films Research Articles

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.

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.

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.

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.

Centimeter-order view for magnetic domain imaging with local magnetization direction by longitudinal Kerr effect

An observation system of centimeter-order of view of magnetic domain with local magnetization direction was developed by designing a telecentric optical system of finite design through the extension of microscope technology. The field of view realized in the developed system was 1.40 × 1.05 cm as suppressing defocus and distortion. Detection of the local magnetization direction has become possible by longitudinal Kerr observation from the orthogonal two directions. This system can be applied to the domain observation of rough surface samples and time resolved analysis for soft magnetic materials such as amorphous foil strips and soft magnetic thin films.

Effects of Ar pressure on magnetic and magnetocaloric properties of sputtered Er–Co thin films

The magnetic and magnetocaloric properties of Er–Co thin films fabricated by sputtering under an Ar pressure (PAr) varying from 2 to 10mTorr in steps of 2mTorr are investigated. The content of Co in the sputtered thin films decreases slightly as the PAr increases from 2 to 10mTorr, resulting in a film composition varying from ErCo1.07 to ErCo0.93. Extensive changes in the magnetic and magnetocaloric properties are observed. As the PAr increases, the compensation temperature increases substantially from 83 to 141K, as well as the temperature at which the maximum change in the magnetic entropy occurs, particularly in the low PAr range. Considering the small change observed in the composition of the thin films as a function of PAr, the changes in the magnetic and magnetocaloric properties are extensive, indicating that the PAr plays an important role in affecting the aforementioned properties in amorphous magnetic thin films.

Sputtering preparation and magneto-optical properties of GdTbFeCo thin films

Amorphous GdTbFeCo magnetic thin films were successfully prepared on glass substrates by RF magnetron sputtering system from a mosaic target. The influences of sputtering parameters on the magnetooptical properties GdTbFeCo thin film were investigated by the variable control method. And the influence mechanism was analyzed in detail. After the sputtering parameters were optimized, it was found that when the distance between target and substrate was 72 mm, the thin film thickness was 120 nm, and the sputtering power, sputtering pressure and sputtering time was 75 W, 0.5 Pa and 613 s, respectively, the coercivity with perpendicular anisotropy could be as high as 6735 Oe, and the squareness ratio of the hysteresis loop was almost equal to 1.

Structural Study of Amorphous CoFeB Magnetic Thin Films by Electron Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Metglas thin film based magnetostrictive transducers for use in long period fibre grating sensors

Metallic glass alloy Metglas 2826 MB based amorphous magnetic thin films were fabricated by the thermal evaporation technique. Transmission electron micrographs and electron diffraction pattern showed the amorphous nature of the films. Composition of the films was analyzed employing X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy techniques. The film was integrated to a long period fibre grating. It was observed that the resonance wavelength of the fibre grating decreased with an increase in the magnetic field. Change in the resonance wavelength was minimal at higher magnetic fields. Field dependent magnetostriction values revealed the potential application of these films in magnetostrictive sensor devices.

Study of dynamic process of domain change in the stepped giant magnetoimpedance element

A giant magnetoimpedance (GMI) element with stepped impedance property was reported for rectangular amorphous soft magnetic thin film with an in-plane uniaxial easy axis in a controlled direction. This stepped change of impedance occurs simultaneously with a change in a magnetic domain, and its physical basis was explained as the intersection of the level of magnetic energy in each case of these domain structures. In this paper, an induced pulse-voltage caused by a non-linear leap of magnetization in the domain change is studied, for the purpose of making dynamics of the domain change clear. We report the results of detecting a pulse signal by using a planar coil fabricated with the stepped GMI element. Some fundamental properties of the pulse signal are also reported, such as its form, and variations in its height as a function of the frequency of the external magnetic field. As a result we found that the domain change in the stepped GMI element is a kind of Barkhausen jump.

Existence of Three Stable States of Magnetic Domain for the Stepped Giant Magnetoimpedance Element and Proposal for Sensor With Memory Function

In this paper, a giant magnetoimpedance (GMI) element with stepped impedance property was reported for rectangular amorphous soft magnetic thin film with an in-plane uniaxial easy axis in a controlled direction. This stepped change of impedance occurs simultaneously with a change in a magnetic domain, and its physical basis was explained as the intersection of the level of magnetic energy in each case of these domain structures. The variation of stepped impedance as a function of external magnetic field typically has a hysteretic property. The hysteretic property is explained based on an existence of threshold energy barrier which is needed overcoming to change the magnetic domain. In this paper, we will show experimentally both an existence of three stable magnetic domains around zero external magnetic field by using the stepped GMI element, and a possibility to detect these states by impedance measurement. We also propose an application of this phenomenon for a magnetic sensor which has a memory function.

Local setting of magnetic anisotropy in amorphous films by Co ion implantation

The local setting of magnetic anisotropy by low fluence Co ion implantation in amorphous magnetic thin films is demonstrated. For a wide range of ion fluences no structural changes occur and the adjustment of anisotropy is reversible. A quantitative relationship between the anisotropy change and the atomic displacements is found. Magnetic domain investigations of the purely magnetically patterned stripes reveal an effective quasi-cubic anisotropy below a critical width for orthogonal magnetic anisotropy alignment. The method of ion-annealing allows for a local setting of anisotropy without irreversible structural and magnetic alterations.

Study of Large Barkhauzen Sensor with Application of Step-like Giant Magnetoimpedance Element

A giant magneto-impedance element with step-like impedance properties was obtained for rectangular amorphous Co85Nb12Zr3 soft magnetic thin film with an in-plane uniaxial easy axis at approximately 60 degrees relative to the width of the element. This step-like impedance phenomenon occurred simultaneously with a change in the magnetic domain. We found through experiments that the magnetic field with changes in step-like impedance occurs had an almost constant value, with a standard deviation in the micro-tesla (μT) range, when an alternating magnetic field was applied. There is a possibility of applying this phenomenon to a large Barkhausen sensor with a constant magnetic field where a pulse signal appears. This paper reports a first trial where a step-like GMI element was applied to a large Barkhausen sensor. We present the results of measuring the MH loop for the step-like GMI element with resulting properties of a non-linear leap in magnetization, and also present the results of detecting a pulse signal by using a planar coil fabricated with the step-like GMI element. Some fundamental properties of the pulse signal are also reported, such as its form, variations in its height as a function of the frequency of the externa magnetic field, and variations in the pulse interval as a function of the frequency of the external magnetic field. We found that the domain change in the step-like GMI element is a kind of Barkhausen leap, and can be applied to a large Barkhausen sensor.

Magnetic behaviors of amorphous Fe78Si9B13 thin films prepared by pulsed laser deposition

Amorphous magnetic thin films have been deposited onto BK-7 substrates using the pulsed laser deposition technique. The source material irradiated by the laser was a pack of amorphous ribbons of composition Fe78Si9B13. The structural properties of thin films were investigated and a large number of droplets were observed in the magnetic layers. Electric current passing through the films causes significant deformation of droplets and consequently changes the magnetic thin films characteristics. Magnetic properties evolution after electrical processing was investigated using magneto-optical Kerr effect.

Study of hysteresis for steplike giant magnetoimpedance sensor based on magnetic energy

A giant magnetoimpedance sensor with a steplike impedance property was reported in the case of amorphous soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a controlled direction. The steplike change of impedance happens simultaneously with a change of magnetic domain, and its physical basis was declared as the intersection of the level of magnetic energy in each case of these domain structures. An actual variation of steplike impedance as a function of external magnetic field typically has a hysteretic property. In this study, an explanation of the hysteretic property is discussed based on an introduction of asymmetrical threshold energy, and then an experimental confirmation is carried out for the proposed analytical model.

不連続的ＧＭＩ素子におけるインピーダンス不連続点の外部磁界変動に対する安定性

A giant magnetoimpedance element with a step-like impedance property was obtained in the case of amorphous Co85Nb12Zr3 soft magnetic thin film in a rectangular shape with an in-plane uniaxial easy axis at an angle of approximately 60 degrees relative to the width direction of the element. It was shown experimentally that the magnetic field in which the step-like impedance change occurs has an almost constant value, with a standard deviation in the micro tesla (μT) range, when an alternating magnetic field of constant amplitude is applied. There is a possibility of applying this phenomenon to a magnetic switch. This application requires a constant impedance step-point uninfluenced by the route or amplitude of the external magnetic field. In this paper, a variation of the magnetic field in which the impedance step occurs as a function of the range of the alternating magnetic field is studied. As a result, a stability of less than 20 mOe (1.6 A/m) at about 1200 mOe (96 A/m) is obtained for the impedance step-point, with consideration given to every experimental condition of the range of applying magnetic field. This result means that it is possible to make a magnetic switch with a switching field accuracy of less than 2%.