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In this paper, we report a systematic study on effect of film thickness and substrate temperature on structural and magnetic behaviour of Fe-Ga films with Cu buffer layer, deposited on Si and Si/SiO2 substrates at room and high substrate temperatures. Grazing incidence X-ray diffraction studies reveal that all the films are crystalline with disordered alpha-Fe phase, which is BCC A2 phase. At 300 °C of substrate temperature, films deposited on Si/SiO2 substrate found to nucleate L12 phase from matrix of A2 phase, which is not seen in Si based films. Irrespective of substrate material, Fe-Ga films found to exist in dual phases at 500 °C substrate temperature. Lattice strains of the films were calculated from X-ray diffraction patterns, using Williamson-Hall method. From X- ray reflectivity analysis of all the films, film density, thickness and roughness of Fe-Ga layer and buffer layer were obtained after fitting the reflectivity data. Presence of an oxide layer is also evident from reflectivity fitting analysis. From magnetization studies it is clear that, all the films exhibited strong in-plane anisotropy. Saturation magnetization of films was found to vary with change in film density and oxide layer thickness of films. Saturation magnetization of films deposited on Si substrates found to decrease with decrease in film density. Coercivity of films found to vary with change in crystallite size, interface roughness and lattice strain of films. Films deposited on Si substrates are sensitive to strain with change in film thickness and films deposited on Si/SiO2 substrates are sensitive to strain with change in deposition temperature. Coercivity in films found to decrease with decrease in film roughness, increase in crystallite size and lowering the tensile lattice strain. [ABSTRACT FROM AUTHOR]

This paper portrays the effect of growth rate on the structural, magnetic, and electrical properties of sputtered Ni thin films. Seventy-five nanometer thick Ni films were grown on Si <100> substrates at room temperature by high power impulse magnetron sputtering with varying growth rates such as 0.27, 0.57, 1.01, 2.18, and 2.65 Å/s. All the films crystallized in a single FCC type structure devoid of any impurity phase. With an increase in the growth rate, the density of the Ni films was found to increase. The surface roughness and the stresses developed in Ni films were found to decrease with an increase in the growth rate. Microstructural investigations indicated an island of surface morphology for all the films. An increase in growth rate was also found to affect the magnetic properties of Ni thin films considerably. Saturation magnetization increased with an increase in growth rate both along the in-plane and out-of-direction owing to the increase in the density of the film and reduction in stresses and surface roughness. Further, the in-plane magnetization studies also showed an increase in in-plane magnetic anisotropy in Ni films with an increase in growth rate. Evidences for improvement in the in-plane magnetic anisotropy were derived from the increase in the in-plane coercivity and remanence. Temperature variation of electrical resistivity in Ni films indicated a metallic behavior. Films grown at higher growth rates exhibited high-temperature co-efficient of resistance suitable for resistance temperature detector applications. [ABSTRACT FROM AUTHOR]

We have looked at a very interesting class of Heusler alloy that has received a lot of theoretical research but a very little experimental attention. Mn2TiSi Heusler alloy was synthesized by a conventional vacuum arc remelting process. The formation of Heusler phase along with the secondary phases was observed after annealing it at 773 K for 120 h. The X-ray diffraction pattern illustrates the presence of cubic B2 disordered phase along with a secondary phase with a lattice parameter of 5.82 Å. The microstructure and compositional analysis of Mn2TiSi alloy shows the presence of distribution of Mn, Ti, and Si elements according to their stoichiometric ratio. The magnetic measurements show a ferromagnetic nature with Curie temperature (TC) around 203 K. With low magnetic moment and coercivity, Mn2TiSi can be used for switching applications because of its fast magnetization reversal. So, Mn2TiSi becomes the greatest choice for use in spintronics due to its low magnetic moment and low coercivity. [ABSTRACT FROM AUTHOR]

Magnetic oscillation at remanence is a key technological route for the realization of bias-field-free passive microwave devices and magnonic waveguides that support magnon transport. Here, exchange biased NiFe/FeMn bilayers have been shown to offer excellent opportunities for a new class of bias-field-free magnonic/microwave medium. Magnetic hysteresis measurements reveal a dependence on the exchange bias effect as a function of FeMn layer thickness. Ferromagnetic resonance measurements reveal magnetic oscillations at remanence for various thicknesses of FeMn, which also determines the frequency of the mode oscillations. Angular field dependent results indicate uniaxial anisotropy present in the bilayers. The in-plane magnetic anisotropy field is found to be decreased with an increase in the FeMn thickness. Further investigation on the invariance of resonance field and linear increase of linewidth with frequency shows the negligible extrinsic contribution to the overall effective damping. Relatively large effective Gilbert damping values are obtained for the higher FeMn thickness and can be attributed to the exchange bias anisotropy. Observation of low inhomogeneous linewidth broadening indicates a good quality of magnetic layer and the interfaces in our systems. Our results offer a novel route for the bias-field-free magnetic medium that supports high-frequency oscillations along with its suitability for on-chip device integration. [ABSTRACT FROM AUTHOR]

We report on the zero-field-cooled exchange bias (EB) and domain wall dynamics in IrMn (111)/Fe2CoSi bilayers. Essentially, a room temperature exchange bias without field cooling in the bilayers is evidenced and the same is attributed to (111) crystal plane orientation of IrMn layer. The crystal plane orientation of IrMn is confirmed with GI–XRD and selected area electron diffraction (SAED) pattern using transmission electron microscope (TEM). Evolution of exchange bias is evidenced with the thicknesses of Fe2CoSi layer. Indeed, there is perfect correlation between the bulk magnetization measurements and microscopic data obtained from longitudinal magneto-optical Kerr effect (L-MOKE). L-MOKE measurements infer the single-layer Fe2CoSi films are isotropic in nature; however, bilayers of IrMn/Fe2CoSi are anisotropic and unidirectional in nature. Our micro-magnetic simulations infer pinning of the spins at the interface and support aforementioned results and lead to new idea about the exchange mechanism. Present results would indeed be helpful for future spintronic device applications. [ABSTRACT FROM AUTHOR]

Fe2CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L21 crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe2CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (Ms = 948 emu/cc) and low coercivity (Hc = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe2CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin -based device applications. [ABSTRACT FROM AUTHOR]

In this study, we report our approach to manipulate the strength of perpendicular magnetic anisotropy (PMA) at oxide/ferromagnetic metal of Heusler alloy (HA) interface by tuning the parameter of annealing temperature. Robust PMA energy density (Keff) of ∼ 0.43 × 106 erg/cm3 and small saturation magnetization (Ms) as low as ∼ 248 emu/cm3 have been achieved for MgO/Co2FeAl (CFA)/Mo stacks at 400 ∘ C. We identify that PMA energy is thermally stable up to the maximum temperature of 400 ∘ C. Effect of annealing temperature on surface morphology, grain distribution, and surface roughness of the stacks are investigated by atomic force microscopy (AFM). Further, X-ray photoelectron spectroscopy (XPS) study demonstrates that the interfacial oxidation decides the strong PMA property at MgO/Co2FeAl interface during the annealing process. This MgO/CFA/Mo trilayer system can be a suitable candidate for the development of low-power consumption, huge-density data storage, high-thermal stability against the annealing temperature, and nonvolatile magnetic memories. [ABSTRACT FROM AUTHOR]

Structural, magnetic and magnetocaloric properties of Gd5Si2Ge2B0.05 alloy, ball milled for different time intervals in the range of 2–50 h were studied. The x-ray powder diffraction analysis of the alloy prior to milling revealed the presence of mixed orthorhombic and monoclinic phases at room temperature. For a milling duration up to 15 h, the alloy powder displayed crystalline nature. Upon further milling, the alloy powder started to lose the crystallinity and after 50 h of milling, the alloy powder displayed amorphous nature. The average particle size of milled samples was found to decrease with increase in milling time. The saturation magnetization value of the bulk alloy 80 emu/g was found to decrease with increase in milling time due to structural disorder. The transition temperature of the milled alloy powder was found to be around 295 K and the transition was found to become broader with increase in milling time. A maximum isothermal entropy change (ΔSmax) of ∼12 J/kg K was obtained in bulk alloy. For a milling duration of 2 h, a marginal decrease of ΔSmax (∼11 J/kg K) was obtained. Whereas, for higher milling durations, (≥ 15 h) a significant decrease in ΔSmax values were observed. However, the broad operating temperature range of the milled powders can be exploited for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

Nanocrystalline ε-FeN and γ′-NiFeN (0.2 ≤ x ≤ 0.8) nitride materials are synthesized in pure phase via sol-gel-mediated oxide precursors. The materials are characterized using XRD, SEM (EDX), and magnetic measurements. ε-FeN and γ′-NiFeN (0.2 ≤ x ≤ 0.8) materials crystallize in hexagonal and cubic structures, respectively. The lattice parameters are estimated to be a = 4.7812(36) Å and c = 4.4232(31) Å for ε-FeN and in the range of 3.7922(10)-3.7957(3) Å for various γ′-NiFeN (0.2 ≤ x ≤ 0.8) materials. The values of the lattice parameters show increasing trend up to x = 0.6, showing a peak, and thereafter decreases with the increase in Ni weight percent in γ′-NiFeN (0.2 ≤ x ≤ 0.8) materials. The average crystallite sizes are in the range of 31-54 nm and confirm the nanocrystalline nature of the materials. The SEM particle sizes are in the range of 153(7)-250(14) nm. For pure ε-FeN, the values of saturation magnetization ( M) and coercivity ( H) are 12 emu/g and 225 Oe, respectively. With the progressive substitution of Ni atoms, hexagonal ( ε-phase) changes to cubic ( γ′-phase) at the same reaction temperature, which is evident from the increase in M and H values, i.e., in the range of 144-181 emu/g and 76-109 Oe, respectively, for γ′-NiFeN (0.2 ≤ x ≤ 0.8) compounds. The values of the saturation magnetization for γ′-NiFeN (0.2 ≤ x ≤ 0.8) are found to increase with the increase in Ni content in the materials up to the value of x = 0.6 and decrease thereafter. These results have been interpreted in terms of size and shape effects in nanomaterials including lattice strain and surface effects. [ABSTRACT FROM AUTHOR]

Magnetostrictive bimorphs consisting of positive and negative magnetostrictive materials such as FeGa and Ni respectively were made in the form of (a) multilayers containing Si/Ni/FeGa and (b) stacking consisting of Ni/Si/FeGa by sputtering technique on Si substrates. While the thickness of the FeGa film was maintained at 200 nm for all the films, Ni films were grown with two different thicknesses, viz., 100 and 200 nm. Magnetostrictive response of these bimorphs was compared with FeGa unimorph deposited on Si. Structural studies indicated FCC and BCC structure for Ni and FeGa films respectively. Magnetization studies showed a decrease in saturation magnetization with increase in Ni content owing to the lower magnetization of Ni when compared to FeGa. Considerable enhancement in tip deflection has been observed in the bimorph structure when compared with pure FeGa film. [ABSTRACT FROM AUTHOR]

Compared to single-phase multiferroic materials, multiferroic (MF)-magnetoelectric (ME) composites, which combine magnetic and ferroelectric materials, show improved (many orders of magnitude) ME coupling and a higher operating temperature (beyond room temperature). In the present study, lead-free multiferroic Ni0.5Co0.5Fe2O4/BaTiO3 (NCFO/BTO) composites with different weight percentages were prepared through the solid-state reaction approach. The phase purity and structural confirmation were carried out using X-ray diffractograms. The XRD peak shifting in the composites has been observed, and it is attributed to the formation of residual stresses/strains during the sample’s grinding, heating, and freezing processes. Fourier-transformative infrared spectroscopy confirmed the presence of metal-oxygen bonds in spinel NCFO and Ti-O and Ba-O bonds in perovskite BaTiO3. UV-vis spectra disclose the energy gap values of the magnetoelectric composites. It has been found that the energy gap values for pure ferrite are 1.53 eV, the pure ferroelectric phase is 2.99 eV, and the composites possess the Eg values of 1.78 eV, 2.33 eV, 2.77 eV with decreasing ferrite concentration. The M-H hysteresis loops reveal the ferromagnetic nature of pure ferrite as well as the presence of ferromagnetism in composites. The magnetic moment of the NCFO has been found as 2.26 µB and it further decreased to 0.59 µB for the 0.25NCFO-0.75BTO compound. The magneto crystalline anisotropy has been calculated using the law of approach (LA) method and the details are discussed in the paper. [ABSTRACT FROM AUTHOR]