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We report the influence of magnetic NiFe artificial spin ice (ASI) on the transport properties of superconducting Nb thin film. Resistivity (ρ) as a function of temperature (T ~ 1.8 to 300 K) and magnetic field (B ~ 0 to 40 kOe in parallel and perpendicular orientations with respect to the film plane) has been examined for two samples, a plain Nb thin film and a hybrid thin film of NiFe-ASI and Nb (Nb-NiFe). The impact of the magnetic NiFe-ASI on superconducting Nb is clearly visible in the transport properties, where, in comparison with plain Nb, for the Nb-NiFe hybrid thin film: (1) the normal state resistivity increases by a factor ~ 1.5; (2) the superconducting transition temperature (Tc) at B = 0 reduces from 7.31 to 6.51 K; (3) the surface sheath superconductivity vanishes as reflected by the parallel upper critical field, Bc2(T); and (4) the perpendicular Bc2(T) is suppressed in the entire T range. Interestingly, with the applied field, $$ {T}_{\mathrm{c}}^{\mathrm{Nb}}-{T}_{\mathrm{c}}^{\mathrm{Nb}-\mathrm{NiFe}} $$ |B increases in perpendicular and decreases in parallel field orientation. The magnetoresistance measurements near Tc for our Nb-NiFe hybrid thin film show shallow minima revealing matching pinning effects with respect to the ASI square lattice. The results are understood in terms of the thin film nature of our samples, geometrically frustrated magnetism of ASI and the proximity between the magnetic NiFe-ASI and superconducting Nb at the interface.

A floating-catalyst spray pyrolysis method was used to synthesize carbon nanotube (CNT) thin films. With the use of ammonium chloride as a pore-former and epoxy resin (EP) as an adhesive, CNT/EP composite films with a porous structure were prepared through the post-heat treatment. These films have excellent thermal insulation (0.029–0.048 W·m−1·K−1) at the thickness direction as well as a good thermal conductivity (40–60 Wm−1·K−1) in the film plane. This study provides a new film material for thermal control systems that demand a good thermal conductivity in the plane but outstanding thermal insulation at the thickness direction.

The ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi2Te3 thermoelectric films are studied through transient differential transmission spectroscopy. An ultralow frequency coherent optical phonon at 0.16 THz emerges, especially in ultrathin films, and it is ascribed to interlayer breathing modes. It can divide the ultrathin films into two groups which have out-of-phase vibration along the normal of a film plane, causing a destructive interference between in-plane propagating thermal waves in the two groups of quintuple layers, and thus possibly reducing the thermal conductivity of the ultrathin films. The excitation power dependence of ultrafast dynamics reveals carrier-carrier scattering dominating thermalization, which provides a microscopic understanding of the reported high electrical conductivity and anomalously high power factor of ultrathin Bi2Te3 films at room temperature.

(Bi1−xLax)(Fe,Co)O3 multiferroic magnetic film were fabricated using pulsed DC (direct current) sputtering technique and demonstrated magnetization reversal by applied electric field. The fabricated (Bi0.41La0.59)(Fe0.75Co0.25)O3 films exhibited hysteresis curves of both ferromagnetic and ferroelectric behavior. The saturated magnetization (Ms) of the multiferroic film was about 70 emu/cm3. The squareness (S) (= remanent magnetization (Mr)/Ms) and coercivity (Hc) of perpendicular to film plane are 0.64 and 4.2 kOe which are larger compared with films in parallel to film plane of 0.5 and 2.5 kOe. The electric and magnetic domain structures of the (Bi0.41La0.59)(Fe0.75Co0.25)O3 film analyzed by electric force microscopy (EFM) and magnetic force microscopy (MFM) were clearly induced with submicron scale by applying a local electric field. This magnetization reversal indicates the future realization of high performance magnetic device with low power consumption.

Recent discoveries of topological superconductivity and Majorana bound states in Fe(Te,Se) bulk crystals have broadened the research topics in iron-based superconductors. Compared with the bulk samples, thin films possess the advantages in fabrication and manipulation. In the present work, we investigated Fe1.1Te0.7Se0.3 thin films grown by pulsed laser deposition (PLD), focusing on the transport properties, including electrical resistivity and magnetoresistivity in magnetic fields both perpendicular and parallel to the film plane. The activation behavior related to the vortex pinning and the upper critical field were analyzed as well.

In this work, we have investigated the microscopic magnetic properties of c-axis oriented hcp-CoIr soft magnetic thin films (SMTFs) by using Mossbauer spectroscopy. We have found that the deviation of magnetic moments from the film plane slowly increases with increasing film thickness due to perpendicular magnetic anisotropy coming from the film growth procedure. Our results also suggest that optimizing the growth conditions at the initial stage of the film growth should be very important to further reduce this deviation. These results will be beneficial for further improving the soft magnetic properties of these SMTFs for functional electronic devices.

Series of iron thin films have been deposited under vacuum, by thermal evaporation, onto monocrystalline Si(100) and Si(111) substrates. The thickness ranges from 13 to 69 nm. The structural properties have been studied by X-ray diffraction technique, working in the θ–2θ mode and with the Kα Cu radiation (λ = 1.54056 A). The films morphologies have been scanned using atomic force microscopy. Most of the films present a flat surface. The static magnetic measurements were performed by means of a vibrating sample magnetometer, with the external magnetic field applied parallel and perpendicular to the surface of the films. All the films are polycrystalline and present well defined Bragg peaks. Most of the films are under stress. The easy magnetization axis lies in the film plane for all the samples. Values of squareness up to 1 have been measured in the longitudinal configuration. In Fe/Si (100), coercivity seems to depend closely on crystallite size. All these results will be presented and discussed.

A series of MoS2 films were prepared by the chemical bath deposition method at different temperatures (60–80 °C). The film thicknesses range from 0.988 up to 10.25 µm. The films are polycrystalline. Vibrating sample magnetometer (VSM) was used to study the magnetic properties of these MoS2 films. The experiments were done at room temperature with the magnetic field applied in the film plane. The magnetization curves indicate the coexistence of ferromagnetism and diamagnetism. The saturation and remnant magnetizations, the coercive and saturation fields as well as the diamagnetic susceptibility have been measured and are discussed as a function of the film thickness and the synthesis temperature. A change in the magnetic anisotropy is observed, and the magnetization easy axis direction switches from in-plane to out-of-plane as the thickness increases. The magnetic properties are correlated with the structural ones.

TEMPO-oxidized cellulose nanofiber (TOCN) has been drawing much attention as a useful material for preparation of transparent and stiff films or substrates. In this work, reducing ability of TOCN was investigated in both photochemical and chemical synthesis of gold nanoparticles (AuNPs) from chloroauric acid (HAuCl4). Based on the results, AuNPs-TOCN composite films were prepared by heat drying the solutions containing only HAuCl4 and TOCN. Blue and yellow films were obtained depending on different contents of HAuCl4 and the yellow film showed high light reflection which was similar to gold film. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that gold plates were generated in the TOCN film, and their flat (1 1 1) crystal plane were oriented parallel to the film plane.

Structure of amorphous nangranular composite (Co86Nb12Ta2) x (SiO2)1−x films was studied by means of grazing-incidence small-angle X-ray scattering as a function of atomic concentration x of the metal fraction in vicinity of the percolation threshold. It has been established that the average size of magnetic nanoparticles increases with x and this increment exhibit the anisotropic character. It was found that in a whole concentration range the particles are elongated along the growth direction perpendicular to the film plane. For the lowest concentration x = 0.193, clusters with isotropic shape and average radius of 1 nm were observed, while for higher concentrations up to x = 0.665, the average cluster length along the film normal is 1.5–7 nm and the cross-section is 1–2 nm.

In this study, we demonstrate the effect of localized surface plasmon resonance (LSPR) on magneto-optical (MO) activity of Co thin films incorporating Ag nanoparticles (NPs) so that the Ag NPs were surrounded by TiO2 (Ag [TiO2]). The deposition of Co on glass substrates was performed using an oblique deposition technique, thereby obtaining a variable film thickness. Three samples of glass/Co, glass/Co/Ag NPs, and glass/Co/Ag [TiO2] were compared with each other in terms of Kerr signal intensity. Our results show that while all samples have an easy axis in the film plane, the corresponding Kerr signal is amplified in the glass/Co/Ag [TiO2] structure. A combination of SPR and light localization is the reasoning behind the amplification. These studies may open a new route in the research area of LSPR-based MO Kerr effect since the improved LSPR enhances MO properties.

Development of ultra-sensitive mechanical pressure sensors is required for various technological fields such as medical diagnosis and gas leakage. Aluminum nitride (AlN) thin films deposited by rf reactive sputtering on flexible aluminum substrates show a piezoelectric response to an ultra-small mechanical pressure in the scale of few Pa. This result is achieved only in the case where the residual average stress in the AlN film is close to zero. The deposition temperature determines the crystallographic orientation of the grains relative to the AlN film plane and consequently the type and magnitude of the residual stress in the film. Various sources of mechanical pressures were applied on the AlN films including a stream of air from a narrow diameter nozzle, sound waves in air and a piezoelectric actuator. In addition, a thermally induced pressure was tested. The scale of the applied mechanical pressures was calibrated and found to be in the range of few Pascals. The piezoelectric response of the AlN film is correlated with the mismatch of atomic arrangement at the AlN film/Al substrate interface.

Magnetic properties and high frequency characteristics of (Fe70.6Co29.4)100−xZrx (x = 4.0 − 18.2 at.%) thin films have been investigated. The saturation magnetization 4πM s decreases continuously from 21.7 kGs for x = 4.0 at.% to 12.2 kGs for x = 18.2 at.% and it is consistent with the decreasing of Fe-Co composition. It is found that the films show nearly isotropic magnetic behavior in the film plane for the Zr content ranging from 7.2 to 18.2 at.%. These films exhibit a weak perpendicular magnetic anisotropy with coercivity values of 24–67 Oe. Meanwhile, the in-plane isotropic FeCoZr films show a good high frequency response of permeability. In particular, the film with x = 7.2 at.% shows a resonance frequency of 2.8 GHz along the direction perpendicular to the stripe domain axis. The permeability spectra of the thin films with higher Zr content display multiple resonance peaks, which may be due to the perpendicular magnetic anisotropy induced by the stress.

Scandium substituted barium hexaferrite (BaFe12−xScxO19, BaM) were grown on platinum-coated Si substrates using sol–gel method. It is found that scandium pay an important role in the structure, magnetic and millimeter wave properties of BaM system. The number of hexagonal grains decreased with increasing the substituted contents x of Sc. XRD results confirmed that BaM films have crystal texture of c-axis grains perpendicular to film plane, and the degree of texture for all the films are as high as 92%. The anisotropy field decreased from 16.2 kOe (x = 0) to 2.5 kOe (x = 2), meanwhile, the saturated magnetization decreased from 4.1 to 1.8 kG. The millimeter wave loss was studied by ferromagnetic resonance (FMR) system from 35 to 60 GHz, it is found that it has lowest FMR linewith of 129 Oe at 45 GHz for x = 0 sample, and the FMR field shift to higher for substituted thin films, together with the FMR linewith became broader. These results mean that the anisotropy field and FMR of BaM thin films were tunable and these thin films can be used in millimeter wave devices.

Understanding film initiation and growth mechanisms at the atomic level is crucial to obtain high-quality nonpolar ZnO films. Using the advanced reactive force field-based molecular dynamics method, we theoretically studied the effect of substrate temperature (350–950 K) on the quality, layer develop mechanism and defect formation of ZnO films. Investigation of the energy, radial distribution function, layer coverage, sputtering and injecting phenomena indicated that the present films grown at 500–600 K possessed the optimal quality. Further investigation of the growth condition, instant film profiles, interfacial microstructure evolutions and layered snapshots revealed that, addition of atoms on newly formed localized films can induce some partially bonded or extruded atoms out of the film plane. Further adherence of depositing atoms to these unstable or extruded atoms induces the initiation and growth of a new layer.

Two series of Fe thin films have been electrodeposited onto polycrystalline porous Al substrates using two baths: iron chloride (FeCl2) and iron sulfate (FeSO4). The texture, strain, and grain size values have been derived from X-ray diffraction experiments. Scanning electron microscopy has been employed for surface morphology. The magnetic properties were inferred from hysteresis curves that were obtained from a vibrating sample magnetometer; the external magnetic field was applied in different directions of the film plane and also perpendicular to the film. Hysteresis curves have been obtained at low temperatures (120 K (−153 °C) to room temperature). We investigate the effects of Al porosity, bath type, and deposition rate on physical properties of these Fe films. A correlation between the structural and magnetic properties is made. Different mechanisms responsible for the coercive field (H C) behavior have also been investigated.

We present a study of precessional magnetization switching in orthogonal spin-torque spin-valve devices at low temperatures. The samples consist of a spin-polarizing layer that is magnetized out-of-the film plane and an in-plane magnetized free and reference magnetic layer separated by non-magnetic metallic layers. We find coherent oscillations in the switching probability, characterized by high speed switching (~200 ps), error rates as low as 10−5 and decoherence effects at longer timescales (~1 ns). Our study, which is conducted over a wide range of parameter space (pulse amplitude and duration) with deep statistics, demonstrates that the switching dynamics are likely dominated by the action of the out-of-plane spin polarization, in contrast to in-plane spin-torque from the reference layer, as has been the case in most previous studies. Our results demonstrate that precessional spin-torque devices are well suited to a cryogenic environment, while at room temperature they have so far not exhibited coherent or reliable switching.

The anisotropic effect of a giant magnetoresistance (GMR) in the three-layer FexNi1−x/Cu/FexNi1−x/Sub (x ≈ 0.5, Sub is the substrate) magnetically ordered film is analyzed experimentally and theoretically using the phenomenological approach. It is shown that in the case when the direction of the current density vector j coincides with the direction of the local magnetization vector M (j∥M) in magnetic layers, the consideration of the resistance anisotropy results in a decrease in the magnitude of the GMR effect; and while the vectors are mutually perpendicular in the film plane (j⊥M), the GMR value increases. The analysis of the size dependence (dependence of the top magnetic layer on the thickness dm2) of the magnetoresistance ratio (MR ratio) shows that, in the case of the isotropic GMR effect, when inequalities dm2 > dm1) (dm1 is the thickness of the bottom magnetic layer) hold, the indicated effect is negligible due to shunting of the top layer resistance by the base layer resistance (shunting of the base layer resistance by the top-layer resistance). In the case when the magnetic layer thicknesses are comparable in size (dm1 ~ dm2), the magnitude of the anisotropic giant magnetoresistance (AGMR) acquires its maximum (amplitude) value because of the absence of the shunting effect. The method for calculating the asymmetry parameter αlj=l0j+∕l0j– (l0js is the spin-dependent free path of charge carriers in the s = ±th spin channel of the jth magnetic layer), which characterizes the difference in the free paths of electrons in the spin conduction channels, is proposed for the first time.

Four different types of stress relaxation responses have been observed in terms of local microstructural changes along grain boundaries (GBs) in large-grained high-Sn (Sn-3.0Ag-0.5Cu) solder films after thermal cycling. The grain boundaries were characterized using scanning electron microscopy, electron back scattered diffraction, and focused-ion beam (FIB) cross-section imaging. While the anisotropic coefficient of thermal expansion of Sn plays an important role in determining which boundaries have high local stresses relative to the film plane and trace of the grain boundary plane during thermal cycling, the four different relaxation behaviors of specific boundaries (no observable changes, surface defect/whisker formation, GB sliding, or a combination of GB sliding and whisker/defect formation) were determined by a combination of Sn anisotropy, the GB geometry, and crystallographic orientation relative to the film plane. The ability to separate GB sliding from surface defect formation provides insights into how long, straight whiskers form in polycrystalline thin films, particularly with respect to grain rotation at the early stages of their growth.

A series of iron thin films have been deposited under vacuum, by thermal evaporation, onto polycrystalline Cu substrates. The film thickness ranges from 13 to 69 nm. An X-ray diffraction (XRD) technique, working in the 𝜃–2𝜃 mode with the K α Cu radiation (λ = 1.54056 A), has been used to perform the structural properties. The static magnetic measurements were carried out using a vibrating sample magnetometer (VSM), with the external magnetic field applied parallel and normal to the surface of the films. All the films are polycrystalline and present well-defined Bragg peaks. The easy magnetization axis lies in the film plane for all the samples, and no in-plane magnetic anisotropy has been detected for all films. High values of squareness have been measured in the longitudinal configuration. All the findings will be presented and discussed.

The spin torque nano-oscillator (STNO) with out of film plane fixed layer magnetization, namely the tilted-polarizer spin torque nano-oscillator (TP-STNO), has the advantage of microwave generation without the help of a magnetic field, which makes it promising to be integrated into a chip. In this paper, we present a thermal stability study of TP-STNO by macrospin modeling, in which the thermal noise is induced into the H eff of the Landau-Liftshitz-Gilbert-Slonczewski equation in the form of a stochastic magnetic field. The TP-STNO with different tilted angles is studied by numerical simulations based on the macrospin model and nonlinear system theory. Depending on the analysis of Lyapunov exponents as a function of drive current density in the room temperature range, we obtain the drive current density ranges in which TP-STNO can oscillate stably in the presence of thermal noise. These quantified results are essential during the practical usage of TP-STNO.

Series of Fe films have been prepared by electrodeposition in a solution of iron chloride onto Al substrate. Different deposition times were used in the elaboration process. The texture, the strain, and the grain size values were derived from X-ray diffraction experiments. Scanning electron microscopy (SEM) has been used to get the surface and the cross section images. Vibrating Sample magnetometer has been used to obtain the hysteresis curves; the external magnetic field was applied in different directions in the film plane, and also perpendicular to the film. Hysteresis curves have been obtained at low temperatures [120 K (−153 °C) to room temperature]. The 〈100〉 texture, small strain, and grain size ranging from 58 to 113 nm are found for these Fe/Al films. All samples show an in-plane magnetic anisotropy, with no preferred orientation within the film plane. Depending on the film thickness range, different mechanisms have been found to be responsible for the coercive field H C behavior. These magnetic properties are correlated with the structural ones and with the SEM observations.

Oriented thin films of P3HT were obtained by a friction-transfer technique. The morphology and structure of the film were studied by means of optical microscopy, atomic force microscopy and transmission electron microscopy. Optical microscopy observation indicates that large size well-ordered P3HT thin films can be produced by a friction-transfer technique. Highly ordered lamellae were observed in P3HT friction-transferred films by electron microscopy. Electron diffraction results confirm the existence of high orientation with the a- and c-axes of P3HT crystals aligned in the film plane while the c-axis parallel to the friction-transfer direction. The atomic force microscopy observation of the as-prepared P3HT thin film shows, however, a featureless top surface morphology, indicating the structure inhomogeneity of the obtained film. To get highly oriented P3HT thin films with homogenous structure, high temperature annealing, solvent vapor annealing and self-seeding recrystallization of the friction-transferred film were performed. It is confirmed that solvent vapor annealing and self-seeding recrystallization methods are efficient in improving the surface morphology and structure of the frictiontransferred P3HT thin film. Highly oriented P3HT films with unique structure can be obtained through friction-transfer with subsequent solvent vapor annealing and self-seeding recrystallization.

This project is aimed to the fabrication of thin films of chromium-substituted cobalt ferrites (CoCr0.5Fe1.5O4) by electron beam deposition technique. After deposition, the thin films are post annealed at 200, 300, 400, and 500 ℃ for 1 h. The structural properties of thin films are investigated by X-ray diffraction (XRD) and Raman spectroscopy which confirm the inverse cubic spinel structure. It is revealed that the films become more crystalline as annealing temperature is increased. The films showed smooth surface morphology with RMS roughness of

Pseudo spin valves (SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm) and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively. The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity (H C) of both layers. The perpendicular giant magnetoresistance (GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.

A strong narrow peak in the field dependence of the radio-frequency absorption (the magnetic pseudoresonance) has been found and investigated in epitaxial thin films of La2/3Sr1/3MnO3 possessing uniaxial magnetic anisotropy in the film plane. The peak is observed when the in-plane external magnetic field H is directed perpendicular to the easy axis and equals to the anisotropy field H u. The frequency dependence of the peak magnitude measured in the frequency range of 10–300 MHz approximately follows the Debye law behavior with the characteristic relaxation time of about 2.2 ns. The physical model of the phenomenon is suggested, based on the giant increase in static transversal susceptibility due to a sharp reorientation of the equilibrium magnetization when approaching the pseudoresonance conditions.

A sputter-deposited strontium ferrite film with perpendicular anisotropy has been developed. The film, composed of La0.33Sr0.67Co0.25Fe11.75O19, has been fabricated directly on quartz glass substrates by radio frequency magnetron sputtering with various heat treatments. The structural and magnetic property dependence of those films on heat treatments has also been studied. The optimized condition is the heat treatment of in situ heating at 400°C and post-annealing at 850°C–900°C. When post-annealing temperature exceeds 900°C, parasitic phases of γ-Fe2O3 and LaFeO3 appear and gradually increase; meanwhile, the magneto plumbite phase gradually decreases. High c-axis perpendicularly oriented films with the coercivity (4148 Oe), remanence squareness ratio (0.89) and perpendicular magnetic anisotropy energy density (1.65 × 106 erg/cm3) are achieved, which is attributed to the single magneto plumbite phase with compact platelet grains and almost complete (0 0 l) texture of the c-axis normal to the film plane.

A strategy for identifying the preferred sites and overall propensity of a Sn film to form whiskers has been developed based on film textures, local grain orientations, and elastic strain energy densities (ESEDs), with preferred sites predicted to be grains with local high ESEDs. Using β-Sn films with various textures, ESED distributions were simulated for elastic and thermoelastic stresses depending on isothermal aging or thermal cycling conditions. Local high ESEDs are preferentially induced in (110) or (100) oriented grains with c-axes nearly parallel to the film plane; films with overall low ESEDs have strong (100) textures for elastic stresses and strong (001) textures for thermoelastic stresses, suggesting low propensities to form whiskers. This work establishes a model for understanding the effect of the β-Sn anisotropy on whisker formation and provides guidelines for testing whether engineering specific film textures will reduce a film’s propensity to form whiskers.

Ternary CoFeCu films, relating their magnetic and magnetoresistance properties with film composition, surface morphology and the corresponding crystal structure, were investigated in terms of different deposition potentials in electrodeposition. The films were grown on polycrystalline titanium substrates. The potentials were obtained from cyclic voltammetry and the current-time transients were also recorded to control the growth of proper films. From the structural analysis by X-ray diffraction, all films had a face-centred cubic structure and the calculated grain size increased with increasing deposition potential. The film compositions by energy dispersive X-ray spectroscopy revealed that the Co, Fe and Cu contents varied and the scanning electron microscope images disclosed that the film morphologies changed as the deposition potential changed. The saturation magnetization was high and coercivity was low at high deposition potential. The easy axis of magnetization was parallel to the film plane for all films. All films showed anisotropic magnetic resistance and their magnitudes were between 3.2 and 3.8 %. The variations in magnetic and magnetoresistive properties related to the microstructure were attributed to the variation of the film contents caused by deposition potential. Balıkesir Üniversitesi (BAP 2008/05) - (BAP 2001/0 2) - (BAP 2005/18) Türkiye Cumhuriyeti Kalkınma Bakanlığı (2005K120170)

Magnetic tunnel junctions (MTJs), as the seminal spintronic devices, are expected for applications in magnetoresistive sensors due to their large magnetoresistance (MR) and high field sensitivity. Two hybrid Co/insulator/ZnO:Co junctions were fabricated with two different barriers to investigate the magneto-transport properties. Experimental results indicate that, both Co/MgO/ZnO:Co and Co/ZnO/ZnO:Co junctions show the positive and nearly linear MR, and their tunnel magnetoresistances (TMR) are 21.8% and 13.6%, respectively, when the current is applied perpendicular to the film plane under the magnetic field of 2 T at 4 K. The nonlinearity of MR is less than 1% within the magnetic field (H) of 1 kOe < H < 12 kOe at low temperature, making them attractive as magnetoresistive sensors. The higher MR of Co/MgO/ZnO:Co junctions is due to the superior spin filtering effect and larger effective barrier height of the MgO barrier. This linear MR characteristic of Co/insulator/ZnO:Co structures shows a promising future on the applications of diluted magnetic semiconductors in magnetoresistive sensors.

Ternary NiCoFe films were potentiostatically electrodeposited from the electrolytes with low (3.0) and high (3.6) pH levels, and differences in their compositional, structural, magnetic and magnetoresistance properties were studied. The compositional analysis demonstrated that the Ni content in the films decreased, and Co and Fe content increased while electrolyte pH was changed from low to high level. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD data revealed that the films have a strong (111) texture of the face-centred cubic (fcc) structure at low pH, while for the films at high pH a mixture of dominantly fcc and hexagonal closed packed structure was observed. The SEM studies showed that films grown at low pH level had comparatively larger grains than those at high pH. The magnetic characteristics studied by a vibrating sample magnetometer and magnetotransport properties were seen to be changed by the electrolyte pH. However, all films have in-plane magnetic anisotropy. The differences observed in the magnetic and magnetotransport properties were attributed to the microstructural changes caused by the electrolyte pH. Turkiye Cumhuriyeti Kalkınma Bakanlığı (2005K120170) Balıkesir Üniversitesi BAP (2001/02)

SrFe12O19 hexaferrite thick films were prepared by tape casting method followed by a two-step sintering process. X-Ray diffractometer, field emission scanning electron microscope and vibrating sample magnetometer were used to investigate the microstructure and magnetic properties of samples. Results show that high density films with nanocrystalline grains, high crystallographic c-axis orientation of crystals perpendicular to the film plane with high squareness (M r/M s = 0.93) and moderate coercivity (H c = 3,750 Oe) can be obtained with two-step sintering. Grains growth is controllable by this sintering method. The average grain size of the films strongly depends on final stage of sintering and quality of starting powders and ranging between 0.5 and 10 μm. The thick films with starting powders from coprecipitation method are denser with smaller grain size rather than those with starting powders from solid state reactions. This work reveals the feasibility of fabrication of thick hexaferrite films with a simple and effective method for next generation of self-biased planar microwave devices.

Exchange bias is one of the most extensively studied phenomena in magnetism, since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled to an antiferromagnet (AFM) and the control of the exchange bias is therefore very important for technological applications, such as magnetic random access memory and giant magnetoresistance sensors. In this letter, we report the crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3 films. By epitaxially growing twined (10-10) oriented Cr2O3 thin films, of which the c axis and spins of the Cr atoms lie in the film plane, we demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy layer is tuned to in-plane from out-of-plane that has been observed in (0001) oriented Cr2O3 films. This is owing to the collinear exchange coupling between the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic exchange bias phenomenon is not possible in polycrystalline films., To be published in Scientific Reports, 12 pages, 6 figures

Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

M-type barium ferrite thin films with hexagonal platelets on sapphire were fabricated by spin-coating of precursors. Fourier-transform infrared spectra indicated that bonds between the metal and oxygen were formed at about 500°C. X-ray diffraction showed that the films had preferred c-axis orientation. Surface morphology of the film was investigated by scanning electron microscopy. Textures of the films were influenced by the amount of ethylenediamine tetraacetic acid (EDTA). The film with the least pores and the most c-axis-textured platelet hexagonal grains was obtained when the ratio of EDTA to metal ions was 1.0. At the same time, the magnetic hysteresis loops in directions parallel and perpendicular to the film plane demonstrated that the films were almost isotropic. The maximum coercive forces of 43.23 kA/m in plane and 54.70 kA/m out of plane were achieved when the ratio of the amount of EDTA to metal ions was 0.5. The highest in-plane remanence ratio was 0.32 when the ratio of EDTA to metal ions was 1.5, while the highest out-of-plane value was 0.28 in the other two cases.

Specific effects observed in small metal particles due to their distinction from bulk material as well as phenomena inherent to an ensemble of these particles coupled by electron tunneling have attracted considerable attention to nanosized systems. Electron and photon emission was revealed as a power was fed into the metal nanoparticle films deposited on insulating substrates either by passage of an electrical current in the film plane or by laser irradiation in the infrared and visible range. The electrical conductivity of metal nanoparticle films close to the percolation threshold is sensitive to temperature, substrate bending and adsorption of various gases. Besides, the current–voltage characteristics of the conduction current of a system consisting of a metal nanoparticle film and an adsorbate exhibit a voltage-controlled negative resistance region. These peculiar properties enable nanosized particle systems to be used for various applications. The present review deals with a variety of sensors for physical properties and microelectronics elements based on nanoparticle films. The mechanisms underlying the special properties are discussed. Some technological methods ensuring better parameter definition and long-term stability of sensors are also described.

We report on the structural and magnetic properties of exchange-biased Fe/CoO bilayers grown on MgO (001) substrates by using rf-sputtering. For varying Fe thicknesses (4 nm, 10 nm, and 20 nm) the ferromagnetic resonance (FMR) spectra of bilayers have been studied as a function of temperature at X-band frequency. The resonance lines of FMR spectra have a relatively small linewidth indicating a high crystallinity of the Fe films. The room-temperature FMR data also show that the easy axis of Fe is in the film plane and parallel to the [110] crystallographic direction of MgO substrate. In addition, M versus H loops were recorded at selected temperatures by using VSM magnetometry. The VSM measurements indicate that the Fe thickness and temperature dependence of exchange-bias properties are in good agreement with the previous results on similar systems. However, the blocking temperature of the exchange-biased system is strongly reduced compared to the bulk values. This reduction in the blocking temperature is explained by both the thickness and superstoichiometric structure of antiferromagnetic CoO layer.

The effects of the ferromagnetic (FM) Co layer thickness on magnetic anisotropies and exchange bias (EB) properties of Co/CoO bilayers have been investigated by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The temperature and thickness dependence of EB were studied in temperature range of 4–320 K. FMR and VSM measurements show that Co/CoO bilayers exhibit negative exchange bias just below the blocking temperature (T B). Room-temperature in-plane FMR measurements reveal that the Co layer was epitaxially grown on MgO substrate with four-fold magneto-crystalline symmetry. The data also show that the easy axis of magnetization is in the film plane and parallel to the 〈110〉 crystallographic directions of MgO substrate in all samples.

Bi2Sr2Ca2Cu3O10+δ HTSC epitaxial thin films with thickness in the order of 6.0 nm were prepared onto (100) aligned SrTiO3 single-crystal substrates by DC sputtering from stoichiometric targets. As-grown samples were characterized by X-ray diffraction, AC-susceptibility and scanning electron microscopy. X-ray diffraction patterns show that all obtained superconducting thin films were c-axis oriented with a Bi-2223 phase. All reflections (except the substrate ones) can be assigned to the (00l) reflections of the film material (h=k=0, l≠0), indicating that the films were grown preferentially with the c-axis normal to the film plane. In order to investigate the crystal quality of these Bi-2223 films, the rocking curves of the (0012) peaks were explored by ω-scans. The rocking curve of the (0012) reflection had a full width at half maximum (FWHM) of 0.30°. This demonstrates that our prepared Bi-2223 thin films have good crystalline quality and high degree of c-axis orientation. The grain size has well known important effects in the magnetic, optical, and electrical properties of metals and alloys. High temperature superconducting thin films, obtained in this work, have nanometer grain size. The mean size of the grains of the samples were determined by X-ray diffraction (XRD) and found to be in the order of 34.8 nm. The superconducting transitions temperature of several Bi-2223 samples is about 103 K. Surface morphology of the films and chemical composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX).

We report the characteristics of epitaxial growth and properties of vanadium oxide (VO2) thin films on sapphire (0001) substrates. Pulsed laser deposition was used to grow (002) oriented VO2 films on sapphire (0001). Transmission electron microscopy studies showed that the orientation relationship between the substrate and the thin film is: (002)f2∥(0006)sub3 and [010]f2 ∥sub. It was also established that VO2 has three different orientations in the film plane which are rotated by 60° from each other. The epitaxial growth of vanadium oxide on sapphire (0001) has been explained in the framework of domain matching epitaxy (DME). Electrical resistivity measurements as a function of temperature showed a sharp transition with a hysteresis width ˜5 °C, and large resistance change (˜1.5 × 104) from the semiconductor phase to the metal phase. It is interesting to note that in spite of large angle twin boundaries in these VO2 films, the SMT characteristics are better than those observed for polycrystalline films. The higher width of thermal hysteresis for the VO2 film on c-sapphire compared to a bulk single VO2 crystal and a single-crystal VO2 film on r-sapphire can be attributed to the existence of these large-angle twin grain boundaries. These findings can provide insight into the phase transformation characteristics of VO2, which has important applications in switching and memory devices.

The thermal stability and magnetic anisotropies of nickel nanoplates with {111} planes as the exposure plane are studied. The melting point of Ni nanoplates drastically drops as compared to that of the bulk one due to the significant increase in the surface free energy. For the large aspect ratio, these nanoplates tend to lie flat on silicon wafer and form a thin Ni {111} plane film. Both the coercivity and the remnant magnetization of the Ni film deeply depend on the applied field direction. As the angle between the film plane and the applied field direction varies from zero to 45° and to 90°, the coercivity measured at 5 K increases from 335 Oe to 373 and to 410 Oe. Correspondingly, the remnant magnetization decreases from 18.1 to 15.8 to be 10.4 emu/g.

Thin bi-layers constituted by a hard L10-FePt layer and a soft Fe layer were obtained using respectively an rf sputtering device and an UHV e-beam evaporation technique. Magneto-Optical Kerr Effect magnetometry, Atomic/Magnetic Force Microscopy and Conversion Electron Mossbauer Spectroscopy were used in order to correlate the magnetic properties of the bi-layers with the effects of the interdiffusion at the interfaces. It has been found that the evaporated Fe can easily diffuse into the hard film, giving raise to the formation of a region containing small particles of both Fe and Fe-rich FePt which show a superparamagnetic behaviour. The ferromagnetic Fe film can grow only on this region. The system shows (i) a preferred orientation of the easy magnetization axis along the direction normal to the film plane, and (ii) a single-phase magnetic behaviour due to the strong exchange coupling which established between the constituent phases.

[Tb/Fe/Dy] n nano-multilayer films, with precise composition of Tb0.27Dy0.73Fe2, were prepared by the multi-targets magnetron sputtering technique at room temperature (sample A) and 300°C substrate temperature (sample B). Both of the nano-multilayer films show columnar structures perpendicular to the film plane according to the scanning electron microscopy results. The magnetic hysteresis loops and the giant magnetostriction (GMS) property of the two samples indicate the perpendicular anisotropy in them. In spite of the perpendicular anisotropy, both of the samples present GMS effect. In a very low applied field of 0.18 T, the GMS value in sample B is 89.3 ppm, which is about four times of that in sample A, 23.5 ppm. The good low-field GMS effect in sample B might attribute to the Laves phase of R-Fe2 segregated from the amorphous matrix under the thermal annealing of the substrate. The relation between the magnetization process and GMS property of the perpendicular anisotropy nano-multilayer films is further investigated.

We have investigated the influence of drawing on orientation, crystallinity, and structural properties of polyamide 6 films using X-ray diffraction. The samples were uniaxially and biaxially stretched resulting in the formation of monoclinic crystallites (α-form) in the size range of 8–10 nm. Depending on the drawing ratio, a degree of crystallinity of up to 60% is obtained. The average orientation of the crystallite axes was evaluated using the pole figure technique. The b*-axis, which corresponds to the chain direction of the polyamide molecules, lies in the film plane and shows a preferred orientation upon drawing. For uniaxial drawing, b* aligns with the drawing direction. For biaxially drawn films, which were prepared using the sequential stretching method, the second drawing determines the orientation of b*, at least at the center of the films. At the sides, b* is located between the two drawing directions reflecting the inhomogeneous distribution of mechanical stress during stretching.

Patterns separated by approximately 55-nm-wide lines on Co/Pt multilayers have been fabricated using a focused ion beam with a 30-keV Ga + ion source. The ion irradiation allows the magnetic moment in the irradiated lines to rotate 45 deg to 90 deg toward the film plane. The in-plane magnetization component of the irradiated lines increases as the ion dose increases. The balance of incoming and outgoing flux at intersections is maintained in orthogonal patterns, while exceptions have been observed in hexagonal and triangular patterns. In all patterns, irradiated lines and adjacent unirradiated elements have no magnetic interaction.

Room temperature CEMS spectra and field-cooled and zero field-cooled hysteresis loops have been measured on oxidized iron films of 100 nm thickness. The iron films were sputtered on a Si substrate, while the substrate temperature, T s, was kept at 200 K and 300 K, and subsequently oxidized. The magnetization of the T s = 200 K sample decreases ca. 40% with respect to the T s = 300 K one, and a small exchange bias appears. The CEMS spectra show a preferential orientation of the magnetization of the films, which is more tilted toward a direction parallel to the film plane as T s is decreased, which is attributed to a competition between shape anisotropies.

Mono- and multilayer HfO2 sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO2 grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO2 layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.

A series of TbDyFe films were prepared by DC magnetron sputtering. The effects of substrate temperature and annealing temperature on the phase structure and the magnetic properties of the sample films were investigated. The annealing treatment has a significant influence on the microstructure and the magnetic properties of the sample. The results obtained by XRD indicate that the films deposited at a temperature lower than 525°C are amorphous and have an easy magnetization direction perpendicular to the film plane. An RFe 2 phase is formed in the sample annealed at 550°C and the residual phases observed are Fe and rare earth oxide. The magnetic properties H c and M l / M S of the film annealed at 550°C obtain the maximum values, for which the formation of the RFe 2 phase is mainly responsible. An annealing treatment leads to a rotation of the sample's easy axis from being parallel to the film surface to becoming vertical.

The highly oriented perovskite-phase PT/PZT/PT ferroelectric thin film was prepared by sol-gel method. The domain structures and polarization retention properties were investigated by scanning force microscopy. The amplitude and phase images of piezoresponse show complex various contrasts of dark, bright and gray. The complex variation of contrast in piezoresponse images results from the perplexing orientation of grains and arrangement of domains in the ferroelectric films. The bright and dark areas in phase images correspond to top-to-bottom and bottom-to-top polarization oriented c-domain, respectively. The gray areas are c-domains with the polarization vector deviating from the direction normal to the film plane. The surface potential images of EFM are bright contrast, which is due to positive charges trapped on the film surface after being polarized by positive voltage. And the brighter contrast is obtained from the higher electric field. The time-dependent surface potential images and line potential profiles show that the potential decays with time. And the decay in the region polarized by higher electric field is faster, especially at 15 min. This indicates that the polarization retention is related to the polarized electric field. Better retention properties may be obtained from a proper polarized electric field.

Strain engineering is an effective way to modify functional properties of thin films. Recently, the importance of octahedral rotations in pervoskite films has been recognized in discovering and designing new functional phases. Octahedral behavior of SrRuO3 film as a popular electrode in heterostructured devices is of particular interest for its probable interfacial coupling of octahedra with the functional overlayers. Here we report the strain engineering of octahedral rotations and physical properties that has been achieved in SrRuO3 films in response to the substrate-induced misfit strains of almost the same amplitude but of opposite signs. It shows that the compressively strained film on NdGaO3 substrate displays a rotation pattern of a tetragonal phase whilst the tensilely strained film on KTaO3 substrate has the rotation pattern of the bulk orthorhombic SrRuO3 phase. In addition, the compressively strained film displays a perpendicular magnetic anisotropy while the tensilely strained film has the magnetic easy axis lying in the film plane. The results show the prospect of strain engineered octahedral architecture in producing desired property and novel functionality in the class of perovskite material.