Magnetic Properties Of Films Research Articles

Critical Role of Capping Layer in Determining Co−Fe−B/MgO Interfacial Magnetism Revealed by X-Ray Magnetic Circular Dichroism

Interfacial magnetism emerging from orbital hybridization is the key facilitator for practical nanoscale spintronic devices. Most devices require a capping layer, and it is widely assumed that capping-layer variations do not change the fundamental properties of magnetic films underneath. In a model $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}/\mathrm{Mg}\mathrm{O}$ system, interfacial investigations, so far, have been focused on the hybridization of $\mathrm{Fe}$ d and $\mathrm{O}$ p orbitals. However, the role of the capping layer has largely been ignored by adopting a reductionist scenario of just oxidation or charge modification. Here, we report strong modifications of interfacial magnetism in $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}/\mathrm{Mg}\mathrm{O}$ by systematically changing the $\mathrm{Ru}$ capping thickness using element-specific x-ray magnetic circular dichroism and x-ray absorption spectroscopy at $\mathrm{Fe}$ ${L}_{2,3}$, $\mathrm{Co}$ ${L}_{2,3}$, and $\mathrm{O}$ K edges, along with corresponding spin and orbital magnetic moment calculations and magnetometry measurements. We observe unusual spin-flip-like transitions due to capping layers and find direct evidence for systematic spin and orbital modifications, beyond just charge transformation, strikingly captured by oxygen x-ray absorption and dichroism spectra. Our result shows the importance of the capping layer and provides a complete picture of rich interfacial magnetism in the $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}/\mathrm{Mg}\mathrm{O}$ system.

Role of substrate on film thickness, structural, compositional and magnetic properties of CoNi alloy thin films by low temperature electrodeposition technique

Impressment of Cobalt and Nickel based alloys in industries for the last few years attracted many researchers due to its significant features of physical, chemical and magnetic properties. The present work focused the structural, compositional, morphological and magnetic properties of Cobalt Nickel alloy thin film growth by one of the chemical methods. Thin films of Cobalt Nickel have been deposited on various substrates by means of low cost galvanostatic electrodeposition technique. Structural investigation showed that the deposited films have face centred cubic structure with orientation of crystallites along (111) plane. The structural parameters such as crystallite size, rms microstrain, dislocation density and stacking fault probability are estimated for the deposited films. Morphological features along with film composition showed that the deposited films have smooth surface with stoichiometry. Magnetic properties such as coercivity, remanence, retentivity was estimated and the results are reported.

Magnetic coupling modulation of flexible Fe3O4/CoFe2O4 heterojunction grown on mica

Recently, flexible wearable devices have attracted enough attention due to their outstanding potential in practical applications. As two classic ferrite materials, Fe3O4 and CoFe2O4 (CFO) have been introduced in many applications such as catalyst, magnetic information and communication technologies. In this paper, a layer of CFO is epitaxially grown on a mica substrate deposited by pulsed laser deposition (PLD), and then a Fe3O4 films is further deposited, using sintered CFO and Fe3O4 poly crystalline targets. The as-deposited film material and surface roughness were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). By measuring the hysteresis loop of Fe3O4/CFO film, the magnetic properties of films with different curvatures were studied. The relationship between the thickness ratio of the CFO layer to the Fe3O4 layer and the magnetic properties of the thin film crystals was studied, and the tunability of the function was proved.

Thermally-induced phase transitions in Pt/Tb/Fe trilayers

Structural phase formation induced by thermally-activated diffusion processes and intermixing of layered structures is a promising reaction pathway for the synthesis of unexpected (metastable) thin film materials. Furthermore, the sequence of structural phase transitions during annealing can substantially differ from those predicted by corresponding bulk phase diagrams due to the underlying grain boundary diffusion mechanisms as well as surface and interface effects. In this study, phase transitions in Pt/Tb/Fe trilayers occurring during post-annealing up to 620°C were investigated by various techniques including x-ray diffraction, transmission electron microscopy, secondary neutral mass spectrometry, Auger electron spectroscopy depth profiling, and magnetic properties measurements. At an annealing temperature of 215°C pronounced Pt and Tb diffusion intermixing is observed leading to the formation of the binary Pt2Tb phase. Further annealing up to 280 °C is accompanied by the appearance of the chemically disordered A1-FePt phase and significant Tb segregation to the outer surface forming an oxide layer. The chemically ordered L10-FePt phase starts to form in parallel to the disappearance of the Pt2Tb phase at 450°C. The final phase product at 620°C is characterized by the coexistence of two remaining phases, L10-FePt and TbO2. Structural phase transitions have a significant impact on the films magnetic properties – heat treatment leads to an enhancement of the coercive field. This fact is associated with the formation of the hard magnetic L10-FePt phase, which might be accompanied by grain isolation induced by partially Tb/Tb-O grain boundary filling.

Effect of different post-annealing durations on electromagnetic properties of La0.67Ca0.33MnO3:Ag0.2 thin films prepared by pulsed laser deposition

La0.67Ca0.33MnO3:Ag0.2 thin films were obtained by pulsed laser deposition followed by post-annealing at 1200 °C for varied durations. Surface morphologies, structures, and electrical and magnetic properties of films prepared with different annealing durations were significantly different. X-ray diffraction results showed that annealed films exhibited stronger diffraction peaks and C-axis preferred growth. Regarding their electrical properties, metal-insulator transition temperature (TMI) and temperature coefficient of resistance (TCR) increased first and then decreased with the increase in annealing duration. In terms of their magnetic properties, thin films displayed ferromagnetic-paramagnetic transition. With the increase in annealing duration, Curie temperature increased first and then decreased. Specifically, the film annealed for 3 h showed excellent electromagnetic properties, with relatively high TCR of 20.3%·K-1 and near room temperature TMI of 285.7 °C. Owing to these excellent properties, as-prepared thin films have application potential in infrared detectors.

Enhanced band structure, optoelectronic and magnetic properties of spray pyrolysis Ni-doped SnO2 nanostructured films

Pure and Nickel-doped Tin Oxide at 0, 1, 2, 4, 5, 6, and 7 wt % of Ni nanocrystalline thin films were synthesized by home-made Spray Pyrolysis technique on glass substrate. The microstructural, morphological, optical and magnetic properties of the films have been investigated. The XRD patterns of the films exhibit a tetragonal type structure with no signature of extra phases. The solubility limit of the incorporation of Ni into the SnO2 semiconducting matrix has been observed at x > 0.05. The nanocrystalline feature of the films is confirmed from AFM and SEM investigations. It was found that the optical energy gap Eg diminishes with the increasing of Ni content up to x ≤ 0.05 and then increases due to the solubility limit of Ni, suggesting the enhancement in the band structure. The decrease of the optical band gap could be attributed to the sp-d exchange interaction while the increase of Eg is explained according to the Burstein–Moss effect. The dispersion and single oscillator parameters of the films were estimated by analyzing the dispersion data based on Wemple–DiDomenico single-effective-oscillator model. The room temperature ferromagnetic behaviour of the films has been observed and discussed according to the bound magnetic polarons model.

Nanocrystallization in FINEMET-Type Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 Thin Films.

A growing variety of microelectronic devices and magnetic field sensors as well as a trend of miniaturization demands the development of low-dimensional magnetic materials and nanostructures. Among them, soft magnetic thin films of Finemet alloys are appropriate materials for sensor and actuator devices. Therefore, one of the important directions of the research is the optimization of thin film magnetic properties. In this study, the structural transformations of the Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 films of 100, 150 and 200 nm thicknesses were comparatively analyzed together with their magnetic properties and magnetic anisotropy. The thin films were prepared using the ion-plasma sputtering technique. The crystallization process was studied by certified X-ray diffraction (XRD) methods. The kinetics of crystallization was observed due to the temperature X-ray diffraction (TDX) analysis. Magnetic properties of the films were studied by the magneto-optical Kerr microscopy. Based on the TDX data the delay of the onset crystallization of the films with its thickness decreasing was shown. Furthermore, the onset crystallization of the 150 and 200 nm films began at the temperature of about 400–420 °C showing rapid grain growth up to the size of 16–20 nm. The best magnetic properties of the films were formed after crystallization after the heat treatment at 350–400 °C when the stress relaxation took place.

Effect of annealing on the electrical and magnetic properties of electrodeposited Ni and permalloy nanowires

The influence of annealing on the microstructure and the electrical and magnetic properties of cylindrical nickel-based nanowires has been investigated. Nanowires of nickel of ~275 nm diameter and of permalloy (Py) of ~70 nm diameter were fabricated by electrochemical deposition into nanoporous templates of polycarbonate and anodic alumina, respectively. Characterization was carried out on as-grown and up to 650 °C heat-treated nanowires. Transmission electron microscopy imaging and diffraction of the nanowires showed a temperature-correlated grain growth of an initially nanocrystalline structure (untreated) with <8 nm (Ni) and <20 nm (Py) grains towards coarser poly-crystallinity after heat treatment with grains up to ~160 nm (Ni) and ~70 nm (Py), the latter being limited by the nanowire width. The electrical conductivity of individual as-grown and 650 °C annealed Ni nanowires was measured in-situ by scanning electron microscopy. At low current densities, the conductivity of annealed nanowires was estimated to have doubled over as-grown nanowires. We attribute this increase to the observed grain growth. The annealed nanowire was subsequently subjected to increasing current densities. Above 120 kA.mm−2 the nanowire resistance started to rise. At 450 kA.mm−2, the nanowire melted and current flow ceased. Magnetometry of as-grown and annealed nanowire arrays showed them to display quasi-thin film magnetic properties. Coercivity and saturation field were inversely correlated in annealed wires and a 25% tunability in these properties was achieved at just 200 °C.

Influence of Ga evaporation rate on the magnetic properties of Amorphous FeGaSiB thin films

In this study, amorphous FeGaSiB thin films have been fabricated on silicon (1 0 0) substrates using a co-sputtering-evaporation deposition system. By fixing the sputtering parameters (chamber pressure and power of the FeSiB target), and only varying the Ga evaporation rate, how the morphology, magnetic properties, and magnetostriction constants changed with the addition of Ga were investigated. This was to increase the Ga concentration, while maintaining the optimized fabrication parameters established in previous work. It was determined that the percentage of Ga increased linearly as the Ga evaporation rate was increased. The x-ray diffraction (XRD) results indicated that all the films were amorphous and the only detected peaks were for the Si substrate. The results showed that varying Ga evaporation rate, thus Ga content, affected the magnetic properties of the films by reducing the saturation induction along with increasing the uniaxial anisotropy within the films. The magnetostriction constants measured were in the range of 10.2–17.2 ppm.

Magnetostriction Effect in Ferromagnetic Films with Easy-Axis and Easy-Plane Anisotropies

Magnetostriction properties of Ni and FeGa films with easy-plane anisotropy and Co/Pt multilayer structures with perpendicular anisotropy have been experimentally investigated. The magnetic properties of films have been studied by magneto-optical methods. Magneto-optical measurements have been performed with controlled bending of the substrate on which the magnetic film is deposited. It is shown that substrate bending induces rotation of the anisotropy axis of the Ni and FeGa films by 90° relative to its initial direction in an unstrained film. The value of perpendicular anisotropy in the Co/Pt multilayer films is shown to change at substrate bending. The layer parameters, at which the magnetostriction effect can be observed in films with perpendicular anisotropy, are established.

Structure, electrical and magnetic properties of Co0.8Zn0.2Fe2O4/(K0.47Na0.47Li0.6) NbO3 bilayered thin films grown by pulsed laser deposition

Structural, ferroelectric, and magnetic properties of lead-free bilayer composite films with composition (K, Na, Li) NbO3-CoZnFe2O4 (P-S) and CoZnFe2O4-(K, Na, Li) NbO3 (S-P) layers deposited on Pt/Si substrates by a pulsed laser deposition technique have been studied. Structural analysis carried out by X-ray diffraction and Raman scattering confirmed the formation of individual phases of perovskite and spinel without any intermediate/secondary phase. To probe the stoichiometric elemental composition and cationic distribution at the interstitial sites, X-ray photoelectron spectroscopy measurement was carried out, which confirmed the mixed state of Fe-ions valence, while the Zn2+ state was retained. Ferroelectric and ferromagnetic behavior of the bilayered films was observed concurrently depending upon the growth sequence adopted. Magnetic properties of the film with spinel on the top layer exhibited higher saturation magnetization. Dielectric permittivity follows the Maxwell–Wagner polarization caused by thermally agitated carriers. Appreciable ferroelectric properties were achieved in S-P films while the P-S film exhibited a lossy ferroelectric hysteresis loop, which is attributed to a high leakage current value.

Influence of temperature on the texture and magnetic properties of IrMn-based spin-valve multilayers

Top-pinning, spin-valve multilayer films with the structure Ta (5 nm)/Co75Fe25 (5 nm)/Cu (2.5 nm)/Co75Fe25 (5 nm)/Ir20Mn80 (12 nm)/Ta (8 nm) were prepared by high-vacuum DC magnetron sputtering. The effects of temperature on the film microstructure and magnetic properties were investigated by X-ray diffraction, atomic force microscopy, transmission electron microscopy, and vibrating sample magnetometry. The effects of temperature on the thermomagnetic stability of the spin-valve multilayers were studied based on the residence time of the sample in a reverse saturation field. The following effects were observed with increasing temperature: the IrMn(111) texture weakened; surface/interface roughness increased; interfacial diffusion was enhanced; the coercivities of the exchange bias field and pinned layer decreased; the coercivity of the free layer increased; relaxation became more obvious; and thermomagnetic stability decreased.

Diffraction and interference pattern by 4f imaging system to determine the thin film magnetic properties

Determine the magnetic properties of thin film material using X-ray has been attracting enormous attention in recent years. In this work, we propose a simple method to determine base on 4F imaging system. The narrow slit is applied to produce diffraction pattern in the X-ray scale. The slit width variation is applied to numerically obeserve the Fraunhofer diffraction pattern sequential changes. To demonstrate the sensitivity of the method, the power distribution of the temporal observed patterns was also measured. The selection of the object shape also discussed for comprehensive discussion.

Stoichiometry, phase, and texture evolution in PLD-Grown hexagonal barium ferrite films as a function of laser process parameters

Barium hexaferrite (BaFe12O19 or BaM) films were grown on c-plane sapphire (0001) substrates by pulsed laser deposition (PLD) to evaluate the effects of laser fluence on their composition, structure, and magnetic properties. A Continuum Surelite pulsed 266 nm Nd:YAG laser was employed, and the laser fluence was varied systemically between 1 and 5.7 [J/cm2]. As the laser fluence changed the stoichiometric transfer between the BaM targets and deposited thin films were affected. The Fe to Ba ratio in the films increased with laser fluence. The films deposited at laser fluences below 4 J/cm2 showed undesirable 3-dimensional island growth. Moreover, an insufficient laser energy resulted in deposition of secondary phases corresponding to Barium monoferrite (BaFe2O4) and Magnetite (Fe3O4). Alternatively, laser fluences above 5 J/cm2 promoted resputtering of the growing film at the substrate and degraded film quality, structure, and magnetic properties. BaM films deposited at 4.8 J/cm2 - the optimal laser fluence - showed excellent c-axis orientation perpendicular to the film plane with an anisotropy field of 16 kOe and saturation magnetization of 4.39 kG. These results clearly demonstrate a strong influence of laser parameters on PLD-grown hexaferrite films and provide a path for high-yield production using pulsed laser depositions systems.

Enhancement of magnetic properties by adjusted structure in Fe nanocrystalline films via annealing and applying high magnetic field at different film-formation stages

To improve the magnetic properties of films applied in spintronic devices, this article explored the microstructure and magnetic properties of Fe nanocrystalline films via annealing and applying high magnetic field (HMF) during different film-formation stages. The results indicate that both annealing and HMF inhibited the sloping and overlapping of the columnar grains in the as-deposited film. Annealing promoted the formation of nanoparticles, while annealing with HMF arrayed the columnar grains along the direction of HMF. A chain arrangement with mixture columnar grains and nanoparticles was observed by combined film-growth HMF and annealing. Different-stage HMFs and annealing improved the particle size but suppressed the stain and surface roughness of the Fe films. The film-growth HMF and annealing both enhanced the saturation magnetization (Ms) of the Fe films. Especially, combined film-growth HMF and annealing obtained 10% larger Ms than Fe bulk. The low disordered structure, average grain size and grain shape anisotropy under film-growth HMF and annealing remarkably decreased the coercivity (by 91%) but increased the remanence ratio (by 67%) of films. However, annealing with HMF did not obviously improve the magnetic properties of Fe films. These indicated that film-growth HMF and annealing provide useful ways to adjust structure and enhance properties.

Modification of Magnetic Properties of a CoPt Alloy by Ion Irradiation

The effect of ion irradiation on magnetic properties of films of the ferromagnetic CoPt alloy fabricated by electron-beam evaporation has been studied. It is found that the coercive force decreases and the lateral component of the easy-magnetization axis increases as the He+ ion fluence increases from 1 × 1013 to 1 × 1016 cm–2. It is shown by magnetic-force microscopy and the Mandelstam–Brillouin spectroscopy that the formation of isolated circle domains which are magnetic skirmions in the CoPt layer is activated at certain ion-irradiation fluence (3 × 1014 cm–2).

Deposition rate effect on microstructure and perpendicular magnetic anisotropy of iron films prepared by ion-beam-assisted deposition

Thin films of iron with different thickness (⁓40–300 nm) were deposited on quartz and silicon substrates by using ion beam assisted deposition (IBAD) technique. The influence of film thickness and deposition rate on microstructure, magnetic phase composition and perpendicular magnetic anisotropy (PMA) of iron films were studied by electron microscopy, X-ray diffraction, Mössbauer spectroscopy, vibrating-sample magnetometry and differential thermomagnetic analysis. Shown, that phase composition and magnetic properties of films depend substantially on the deposition rate, and, in fact, don't depend on both film thickness and the type of substrate. The strong PMA is observed in iron films formed at low (~3 nm/min) and medium (~10 nm/min) deposition rates only. The microstructure is characterized by the presence of nanocrystalline grains of α-Fe phase, as well as a significant fraction of disordered iron phase and nonmagnetic oxide phase of FeO (up to 20%). The FeO phase occurs due to the reaction of iron atoms with the residual atmosphere of the vacuum chamber. Moreover, significant positive deformation (about 3%) of crystal lattice of α-Fe grains was observed. The effect of deposition rate on the crystallinity, phase composition and PMA in thin iron films we associate with the features of the IBAD process.

Relevance of the Preparation of the Target for PLD on the Magnetic Properties of Films of Iron-Doped Indium Oxide

This paper concerns the importance of the preparation of the targets that may be used for pulsed laser deposition of iron-doped indium oxide films. Targets with a fixed concentration of iron are fabricated from indium oxide and iron metal or one of the oxides of iron, FeO, Fe3O4 and Fe2O3. Films from each target were ablated onto sapphire substrates at the same temperature under different oxygen pressures such that the thickness of the films was kept approximately constant. The films were studied using X-ray diffraction, X-ray absorption (both XANES and EXAFS), optical absorption and magnetic circular dichroism. The magnetic properties were measured with a SQUID magnetometer. At the lowest oxygen pressure, there was evidence that some of the iron ions in the films were in the state Fe2+, rather than Fe3+, and there was also a little metallic iron; these properties were accompanied by a substantial magnetisation. As the amount of the oxygen was increased, the number of defect phases and the saturation magnetisation was reduced and the band gap increased. In each case, we found that the amount of the oxygen that had been included in the target from the precursor added to the effect of adding oxygen in the deposition chamber. It was concluded that the amount of oxygen in the target due to the precursor was an important consideration but not a defining factor in the quality of the films.

Structural and magnetic properties of MnCoGe ferromagnetic thin films produced by reactive diffusion

The structure, the chemistry, and the magnetic properties of MnCoGe thin films elaborated by reactive diffusion were investigated. In situ X-ray diffraction (XRD) was used to study phase formation during thin film reaction. MnCo, MnGe, and CoGe binary systems were studied before investigating phase formation during Mn-Ge-Co ternary system reaction. Three pure layers of Mn, Ge, and Co were successively deposited by magnetron sputtering on SiO2 to form a 200 nm-thick Co/Ge/Mn stack, and annealed. Six phases were observed during reaction, first following the sequential phase formation observed for the binary systems at the two Mn/Ge and Ge/Co interfaces, and ending with the formation of a single ternary compound MnCoGe at 673 K. The structure and the composition of the MnCoGe films were characterized using XRD, atomic force microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The magnetic properties of the films were studied using superconducting quantum interference device (SQUID) and ferromagnetic resonance (FMR) measurements. The obtained MnCoGe thin films are polycrystalline with the stoichiometric composition Mn:Co:Ge(1/3:1/3:1/3), and show high porosity. They are made of grains exhibiting both the Ni2In-type hexagonal structure and the TiNiSi-type orthorhombic structure.

Ion-Implantation-Induced Disorder in FePt-C Thin Films

The effects of ion implantation through a mask on the structural and magnetic properties of FePt-C films were investigated. The mask pattern was fabricated using self-assembly of di-block copolymers. For implantation, high- (40 keV for 14N+ and 100 keV for 40Ar+) and low- (7.5 keV for 14N+ and 4.5 keV for 40Ar+) energy 14N+ and 40Ar+ ions were used to modify the structural and magnetic properties of these films. The X-ray diffraction and transport of ions in matter simulations were performed for understanding the structural changes due to the ion implantations. These results revealed the conversion of face-centered tetragonal phase to face-centered cubic (FCC) phase for 40Ar+ ion implantations and increase in inter-planar spacing of FCC FePt (111) planes for 14N+ ion implantations. Magnetic properties were then probed by using a vibrating sample magnetometer (VSM), torque magnetometer, and magnetic force microscopy (MFM). The results from VSM and torque magnetometer showed a change in anisotropy from out-of-plane to in-plane directions for all the implantation cases except for low-energy 40Ar+ ion implantations. The MFM images also showed an absence of stripe domains confirming the above-mentioned effects.