Magnetic Properties Of Films Research Articles

Investigation of magnetic and structural properties of Au capped Fe thin films

In order to understand the effect of microstructure on the magnetic properties of thin films, we are reporting Fe thin film of two different thicknesses prepared via electron beam deposition on Si (100) substrate whose structural and magnetic properties have been studied using different characterization techniques. The structural measurements carried out using XRD and XRR techniques show variation in structural properties with change in film thickness. The magnetization measurements show increase in coercivity and change in loop shape when the film thickness was changed from 5 nm to 40 nm. The overall results are correlated in terms of thickness induced changes in structural properties which in turn influence the magnetic properties of the film.

Perforated alumina templates as a tool for engineering of CoPd film magnetic properties

Abstract The patterning of the CoPd films was performed by the deposition of the Co/Pd multilayers on the nanoperforated templates of anodic aluminum oxide (AAO). We observed that the morphology of aluminum oxide is represented by the hexagonal packed hemispherical wells with a pore in the middle. The morphology of the patterned films follows the features of the initial templates; the magnetic material is deposited mainly in the regions between the pores and on their perimeter. The Co atoms diffuse into the Pd layer already during the film deposition, and discontinuous interfaces of Co and Pd are formed leading to the creation of the CoPd solid solution. The out-of-plane hysteresis loops of the nanoporous films exhibited high values of the coercive field (HC = 2.0–3.6 kOe) and squareness ratio (Mr/MS = 0.7–0.8). This indicates that the nanoporous films retain the perpendicular magnetic anisotropy observed for continuous film. Deteriorated values of effective anisotropy constant Keff for the porous films with respect to the continuous film are explained by the complex morphology of the nanoporous films, which leads to partial deviation of magnetic moments from the direction normal to the sample plane. On the other hand the increase of the values of the coercive field HC of the nanoporous films in comparison to the continuous films is related to the pinning of the magnetic moments on the nanopores. We observed the transition of the magnetization reversal mechanism from the domain wall motion observed for the continuous film, to coherent rotation mode for the nanoporous films. We show that this approach allows us to tune the coercive field HC and the effective magnetic anisotropy constant Keff of the CoPd film by engineering the pore size of the templates.

Epitaxial Growth and Magnetic Properties of NiMnAs Films on GaAs Substrates**Supported by the National Key Research and Development Program of China under Grant No 2017YFB0405701, the National Natural Science Foundation of China under Grant Nos U1632264 and 11706374, and the Key Research Project of Frontier Science of Chinese Academy of Science under Grant No QYZDY-SSW-JSC015.

Single-phase Ni0.92Mn1.08As films with strained C1b symmetry are grown on GaAs (001) substrates. In addition, a preferred epitaxial configuration of (110)-orientated Ni0.92Mn1.08As on (001)-orientated GaAs is revealed by synchrotron radiation measurement. The magnetic properties of the films are found to be significantly influenced by the growth temperature and the optimized growth temperature is determined to be ∼370°C. According to the results of x-ray absorption spectroscopy, these phenomena can be attributed to the variation of the local electronic structure of the Mn atoms. Our work provides useful information for the further investigations of NiMnAs, which is a theoretically predicted half-metal.

Магнитострикционный эффект в ферромагнитных пленках с анизотропией типа "легкая ось" и "легкая плоскость"

AbstractMagnetostriction 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.

Модифицирование магнитных свойств сплава CoPt путем ионного облучения

The effect of ion irradiation on the magnetic properties of films of the ferromagnetic CoPt alloy made by the method of electron beam evaporation is investigated. It has been established that with an increase in the He+ ion fluence from 1×1013 to 1×1016 cm-2, a decrease in the coercive field and an increase in the planar component of the axis of easy magnetization are observed. Using magnetic force microscopy and Mandel'shtam-Brillouin spectroscopy, it was shown that with certain ion fluence (3 × 1014 cm-2), the formation of isolated round domains representing magnetic skyrmions is observed in the CoPt layer.

Electrical and magnetic properties of (Al, Co) co-doped ZnO films deposited by RF magnetron sputtering

In this work, (Al, Co)-ZnO films were co-sputtered on glass substrate through radio frequency sputtering at 100 °C. The film's structure, electrical and magnetic properties as a function of Al doping content is investigated. The results indicate that (Al, Co)-ZnO films crystallinity can be suppressed by Co doping or (Co, Al) co-doping. With the substitution of Zn2+ by Al3+, the film's conductivity improves. All the films present ferromagnetic behavior at room temperature. Upon increasing the Al doping amount, the film's saturation magnetization expresses a carrier-concentration dependent behavior. Three different regions can be defined, where BMP model and carrier-mediated exchange mechanisms play a role in the various regions.

Physical properties and structure of vapor-quenched immiscible alloys

The method of modernized ion-plasma sputtering produced metastable states, including nanocrystalline and amorphous phases in films of Fe-Ag, Fe-Bi, Fe-Ag-Bi, Fe-Co-Ag and Ni-Ag alloys whose components do not mixed in the liquid state. The periods of the crystal lattices and the dimensions of the crystallites of the nonequilibrium phases in the fresh-sputtered state and after the heating are determined. The temperatures of the beginning and the end of the decomposition of metastable phases are established when heated at a constant rate. The electric and hysteretic magnetic properties of films in freshly dusted and thermally processed states are measured. The compositions and conditions for obtaining films with low values of the temperature coefficient of electrical resistivity (~ 10-5 K-1) and high coercive force (HC ~ 150 kA/m) are established. Such films can be promising for use as thin-film precision resistors and magnetic information carriers with an increased recording density.

Effect of annealing on magnetic properties in ferrimagnetic GdCo alloy films with bulk perpendicular magnetic anisotropy

Magnetic properties in ferrimagnetic GdCo alloy films with bulk perpendicular magnetic anisotropy (PMA) are investigated as a function of annealing temperature (Tanneal) and annealing time for several capping layers. Magnetic properties in films capped by TaOx vary markedly with Tanneal; the saturation magnetization and coercivity vary progressively with increasing Tanneal up to 300°C, and above that temperature, PMA is lost abruptly. By comparing the annealing temperature dependence for Co-dominated and Gd-dominated compositions close to the magnetization compensation point, the data are readily explained by preferential oxidation of Gd during annealing. When films are capped by a Ta/Pt bilayer, the film properties are stable up Tanneal = 300 °C, indicating that oxidation at high temperatures is effectively blocked, but the abrupt loss of PMA for Tanneal > 300 °C is still observed. X-ray diffraction measurement reveals that the amorphous structure of the films remains the same after high-temperature annealing that is sufficient to remove PMA, indicating that crystallization from the amorphous phase is not responsible for the lack of PMA. Instead, our results suggest that high annealing temperatures may cause segregation of Co and Gd atoms in the films, which reduces anisotropic pair-pair correlations responsible for the observed bulk PMA in the as-grown state.

Structural, magnetic, and transport properties of Fe1−xRhx/MgO(001) films grown by molecular-beam epitaxy

Fe1−xRhx layers are grown with varying rhodium fraction x on (001)-oriented MgO substrates by molecular-beam epitaxy. Film structural, morphological, magnetic, and transport properties are investigated. At room temperature, layers are ferromagnetic (FM) for x < 0.48 and antiferromagnetic (AF) for x > 0.48. Separating the two magnetically ordered phases at x = 0.48 is an abrupt change in the Fe1−xRhx lattice parameter of Δa = 0.0028 nm (Δa/a = −0.9%). For AF layers, the FM state is recovered by heating across a first-order phase transition. The transition leads to a large resistivity modulation, Δρ/ρ = 80%, over a narrow temperature range, ΔT = 3 K, in stoichiometric Fe0.50Rh0.50/MgO(001). For samples with compositions deviating from x = 0.50, fluctuations broaden ΔT and defect scattering reduces Δρ/ρ.

Effect of Cu intermediate layer thickness on microstructure and magnetic properties of fcc-FePt/L10-FePt exchange-coupled composite films

The fcc-FePt/Cu/L10-FePt exchange-coupled composite films with different Cu intermediate layer thicknesses were prepared on (100)-oriented single-crystal MgO substrates using DC magnetron sputtering, and the effect of Cu intermediate layer thickness on microstructure and magnetic properties of films were investigated. High (001) orientation and low coercivity field were obtained in the fcc-FePt/Cu/L10-FePt composite films. With increasing Cu intermediate layer thickness, the chemical order parameter and coercivity of the fcc-FePt/Cu/L10-FePt film decrease gradually. For the film with 4 nm Cu intermediate layer, annealing at an appropriate temperature could promote the interdiffusion between Cu intermediate and bottom/top FePt layers and strengthen the exchange-coupled interaction of the composite films.

Nanoscale magnetic localization in exchange strength modulated ferromagnets

Although ferromagnetism is in general a long-range collective phenomenon, it is possible to induce local spatial variations of magnetic properties in ferromagnetic materials. For example, systematic variation of the exchange coupling strength can be used to create systems that behave as if they are comprised of virtually independent segments that exhibit "local" Curie temperatures. Such localization of thermodynamic behavior leads to boundaries between strongly and weakly magnetized regions that can be controllably moved within the material with temperature. The utility of this interesting functionality is largely dependent on the inherent spatial resolution of magnetic properties - specifically the distance over which the exchange strength and corresponding properties behave locally. To test the degree to which this type of localization can be realized in materials, we have fabricated epitaxial films of Co[1-x]Ru[x] alloy featuring a nanometer scale triangular wave-like concentration depth profile. Continuous nanoscale modulation of the local Curie temperature was observed using polarized neutron reflectometry. These results are consistent with mean-field simulations of spin systems that encompass the possibility of delocalized exchange coupling, and show that composition grading can be used to localize magnetic properties in films down to the nanometer level. Since this is demonstrated here for an itinerant metal, we assert that for virtually any modulated magnetic material system, collective effects can be suppressed to length scales smaller than about 3 nm, so that magnetic behavior overall can be well described in terms of local material properties.

Anion Doping of Ferromagnetic Thin Films of La0.74Sr0.26MnO3−δ via Topochemical Fluorination

Chemical doping via insertion of ions into the lattice of a host material is a key strategy to flexibly manipulate functionalities of materials. In this work, we present a novel case study on the topotactic insertion of fluoride ions into oxygen-deficient ferromagnetic thin films of La0.74Sr0.26MnO3−δ (LSMO) epitaxially grown onto single-crystal SrTiO3 (STO) substrates. The effect of fluorination on the film structure, composition, and magnetic properties is compared with the case of oxygen-deficient and fully-oxidized LSMO films. Although incorporation of F− anions does not significantly alter the volume of the LSMO unit cell, a strong impact on the magnetic characteristics, including a remarkable suppression of Curie temperature and saturation magnetization accompanied by an increase in magnetic coercivity, was found. The change in magnetic properties can be ascribed to the disruption of the ferromagnetic exchange interactions along Mn-anion-Mn chains driven by F− doping into the LSMO lattice. Our results indicate that F− doping is a powerful means to effectively modify the magnetic functional properties of perovskite manganites.

Tens of micron-thick, crack-free yttrium iron garnet films on a Gd3Ga5O12 substrate based on the layer by layer growth method

In this paper, the maximum thickness of crack-free yttrium-iron-garnet ferrite film was increased from 7 to 13 µm by layer by layer growth method. Also, the effect of a layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ–2θ revealed the orientation of crystal structure could be increased by the layer-by-layer growth method. Scanning electron microscopy and stylus profiler measurement showed the roughness and morphology of film surface were improved efficiently after using the layer-by-layer growth method. Magnetic hysteresis loops and FMR spectrum representing this layer-by-layer growth method could efficiently increase film magnetism and decrease FMR linewidth. Consequently, this innovative method of layer-by-layer growth efficiently provides a pathway to prepare excellent properties, tens of micron-thick, crack-free yttrium iron garnet films and creates unique significance in the electronics industry.

Temperature-dependent magnetic properties of YIG thin films with grain size less 12 nm prepared by a sol-gel method

We report on YIG film with small grain size (<12 nm) that has the potential to be used in microwave device application. The nanostructured film has been deposited on quartz substrate by a sol-gel spin coating technique, followed by annealing at temperatures in the range between 700 and 900 °C. The structural and magnetic properties of the film in the range 10–610 K were investigated. The X-ray diffraction results demonstrate that the films formed in a polycrystalline structure with lattice parameter in the range of 12.249–12.359 Å, lower than that of bulk materials. The saturation magnetization decreased not linearly with increasing the temperature from 10 to 300 K, differently from that reported for the bulk YIG. The coercivity value decreased with increasing temperatures (10–300 K), except for the film annealed at 800 °C. The Curie temperature of the film annealed at 700 °C was 554 K, however, other films showed higher Curie temperature values than that reported for bulk YIG. These properties are strongly influenced by the stress in the film’s structure due to the different thermal expansion coefficient of the YIG and the quartz substrate.

Temperature-and thickness -dependent dynamic magnetic properties of sputtered CoFeB/Ta bilayer films

A series of CoFeB/Ta bilayer nano-thin films was fabricated on Si substrate using magnetron sputtering at room temperature. The temperature-and thickness-dependent dynamic magnetic properties of these films were investigated in detail using commercialized coplanar waveguide ferromagnetic resonance technique. The results showed that the Gilbert damping constant of bilayer films was monotonically decreases with the increase of temperature and thickness within certain range. We considered that the reasons for enhanced damping for the thinner magnetic films were derived from spin-pumping effect, two-magnon scatter, and magnetic dead layer. From thickness-dependent data, the surface/interface anisotropy constant, bulk damping contribution, and surface/interface damping contribution were obtained. Our results indicated that the bilayer films had perpendicular anisotropy when the CoFeB thickness was less than 1.38 nm. The results suggested that the influence of Ta on the dynamic properties of magnetic films cannot be ignored. The simplest stack structure of films was beneficial to understand the physical mechanism clearly.

Preparation and Characterization of Magnetic Force Microscopy Tips Coated with Nickel Films by e-Beam Evaporation

In this work, magnetic force microscopy (MFM) tips coated with a nickel thin-film were prepared and characterized for applications in the measurement of the magnetic write field. Nickel films with various thicknesses in a range of 20 – 80 nm were deposited on silicon substrates and silicon atomic force microscopy (AFM) tips by electron beam evaporation. Film surface morphologies and magnetic properties of the coated nickel films were investigated by using AFM and vibrating sample magnetometry (VSM). The rms roughness increased with the film thickness and was in a range between 0.1 and 0.3 nm. VSM results revealed that the mean coercive field of the nickel films was 20 Oe and there was an increase in the coercivity as the film thickness increased. In addition, the prepared MFM tips were evaluated for the tip response to the dc and ac magnetic field generated from perpendicular write heads. It was found that the MFM tip had the best response to the write field when coated with 60 nm thick nickel film. The coating thickness over 60 nm was inapplicable due to the cantilever bending caused by the film stress.

Effect of doping SiO2 and applying high magnetic field during the film growth on structure and magnetic properties of evaporated Fe films

Huge difference of surface energies between dielectric and metal provides an effective method to tune the structure and magnetic properties of films. Due to the difference of surface energies between SiO2 and Fe, dopant of SiO2 with 3.6% in atomic ratio in Fe film transforms the strip and column structure in the Fe films to equiaxed crystal formed by nanoparticles of the Fe-SiO2 films. Zeeman energy of applying high magnetic field (HMF) during film growth increases Fe atomic aggregation and atomic diffusion of SiO2 into the grain boundary. This leads to the improvement of the particle size with applying HMF during the film growth. These structural evolutions have a significant effect on the performance of the films. After the dopant of SiO2, the saturation magnetization Ms of the Fe-SiO2 film (324.6 kA/m) is 73.2% less than that of the Fe films. The coercivity Hc decreases 204.0% to 788.04 A/m. However, the Ms increases 44.3% and the Hc increases 27.4% for the Fe-SiO2 film with applying HMF during the film growth.

Effect of film thickness and strain state on the structure, magnetic and transport properties of La0.9Sr0.1CoO3 films

In this paper, we investigate the effects of film thickness and strain state on the structure, magnetism and electrical transport properties of La0.9Sr0.1CoO3 (LSCO) thin films. The x-ray diffraction analysis shows that the out-of-plane lattice parameters of LSCO films grown on different substrates gradually approach those of the bulk LSCO with increasing film thickness, indicating that the strain induced by the substrates is partially relaxed in thick films, i.e. 100 nm. The film magnetism is gradually enhanced with increasing film thickness. For the 20-nm-thick film, it is almost non-magnetic. However, the film becomes ferromagnetic when its thickness increases up to 100 nm. The magnetism is stronger for the film under compressive strain than that under tensile strain. The change in the magnetic properties of films is attributed to the lattice strain, which can affect the spin state of Co ions. Regarding the conductivity, all the samples show a semiconducting-like behavior, and the resistivity is inversely proportional to the film thickness. The electrical transport mechanism of the films with different thickness transforms from a three-dimensional variable range hopping (VRH) to a small-polaron hopping conduction (SPC) with increasing temperature. Fascinatingly, the temperature for transport mechanism transformation decreases gradually with increasing film thickness. This work could shed light on the electrical transport mechanism of LSCO films with different thickness.

Oriented of micron-thick Y3Fe5O12 film on Gd3Ga5O12 substrate based on layer by layer growth method

In this paper, oriented of micron-thick yttrium-iron-garnet ferrite films were deposited on Gd3Ga5O12 substrate by magnetron sputtering based on layer-by-layer growth method. The effect of layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ-2θ reveals the maximum thickness of oriented film was increased by layer-by-layer growth method. In addition, scanning electron microscopy displays excellent morphology with uniform size of grain for the film prepared under 2.4 μm@800 nm condition. Magnetic hysteresis loops and FMR spectrum represent this layer-by-layer growth method can effective increase film saturation magnetization and decrease FMR linewidth. Specifically, oriented micron-thick (2.4 μm) YIG film with only 12 Oe of FMR linewidth has been obtained by this layer-by-layer growth method.

Manipulation of film quality and magnetic properties of CrO2 (100) films on TiO2 substrates with carrier gas and growth temperature.

High-quality CrO2 films were synthesized on TiO2 (100) substrates at different temperatures using the chemical vapor deposition method in argon or nitrogen atmosphere. It was found that the lower limit for the growth temperature of CrO2 films can be reduced to 310 or 300 °C when using Ar or N2 as the carrier gas, respectively. The quality of CrO2 film on TiO2 substrate can thus be improved by optimizing growth temperature in a much larger range (310–400 °C in Ar and 300–430 °C in N2, in contrast with 390–410 °C in O2), which is significant for the practical application of CrO2 films. The best film quality was achieved at 320 °C in either Ar or N2 atmosphere, at which CrO2 film has its narrowest orientation distribution and lowest roughness. Compared to films grown in O2, films grown in Ar were found to have larger saturation magnetizations (Ms) and magnetic anisotropies, possibly due to numerous O vacancies. Films grown in N2 are actually N-doped films, and have lower Ms than those grown in O2. The Curie temperature (Tc) was also tuned by the carrier gas and growth temperature. Films grown in Ar or N2 generally have a higher Tc value than those grown in O2. Furthermore, the thermal stability of the films was found to be remarkably improved when using N2 as the carrier gas.