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We report the complex implications of inter-diffusion between polycrystalline FePt/FeCo layers as an impact of the FeCo underlayer on the structural and magnetic properties of the system. The crystalline growth of FePt strongly reduces in an entirely diffused system compared to the one with lesser diffusion, while the crystalline structure of FeCo is apparently less affected. Charge redistribution occurs between Fe, Co and Pt ensuring increased Co-Pt and Fe-Pt interactions with higher diffusion. Thereafter, we combine hysteresis and magnetic force microscopy measurements to show that the interfacial deformations result in the distinct out-plane magnetic behaviour of the system. FeCo@FePt nano-composite like structure, originating due to interfacial diffusion, shows interactions between two magnetic phases with in-plane low anisotropy exhibiting wasp-shaped out-plane hysteresis loop. Whereas the layered structure of FePt/FeCo films shows random anisotropy with a significant out-plane contribution even in the polycrystalline films. Micromagnetic modelling demonstrates coercivity deterioration and reduction of switching field due to the formation of a slightly diffused interface. Contrarily, the experimental observations for complete diffusion between the two layers are explained by simulating the inhomogeneous distribution of anisotropies along the film plane. These studies provide deep perceptions of the magnetic properties of FePt/FeCo system governed by diffusion kinetics which are valuable to achieve desired magnetic characteristics using this system.

We report on observation of the exchange bias effect in AuFe co-sputtered alloy films in the as-deposited state and following swift heavy ion irradiation. The Mössbauer spectrum for the as-deposited film shows a broad paramagnetic doublet together with a small contribution from hyperfine magnetic sextets. The magnetization behavior exhibits a spontaneous exchange bias effect at room temperature without application of an external triggering field. The magnitude of exchange bias in the as-deposited sample increases with decreasing temperature, at first gradually down to about 50 K and then more rapidly down to 5 K. Irradiation of AuFe film with 100 MeV Au9+ ions transforms the Mössbauer spectrum into a broad magnetic sextet, with asymmetric broadening characteristic of the formation of α-Fe magnetic nanoclusters surrounded by shells of reduced Fe concentration. At room temperature the exchange bias field is in the same sense as that for the as-deposited sample, but decreases with temperature until it reverse its sign at below about 50 K. In both the as-deposited and irradiated samples a well-defined uniaxial magnetic anisotropy, consequent on a stress induced texturing of the Fe precipitate distribution, is observed.

Enhanced magnetic moment and coercivity in SrRuO3 thin films are significant issues for advanced technological usages and hence are researched extensively in recent times. Most of the previous reports on thin films with enhanced magnetic moment attributed the high spin state for the enhancement. Our magnetization results show high magnetic moment of 3.3 Bohr-magnetron/Ru ion in the epitaxial thin films grown on LSAT substrate against 1.2 Bohr-magnetron/Ru ion observed in bulk compound. Contrary to the expectation the Ru ions are found to be in low spin state and the orbital moment is shown to be contributing significantly in the enhancement of magnetic moment. We employed x-ray absorption spectroscopy and resonant valance band spectroscopy to probe the spin state and orbital contributions in these films. The existence of strong spin-orbit coupling responsible for the de-quenching of the 4d orbitals is confirmed by the observation of the non-statistical large branching ratio at the Ru M2,3 absorption edges. The relaxation of orbital quenching by strain engineering provides a new tool for enhancing magnetic moment. Strain disorder is shown to be an efficient mean to control the spin-orbit coupling., 10 pages, 6 figures

Nano-scale diffusion at the interfaces in organic spin valve thin films plays a vital role in controlling the performance of magneto-electronic devices. In the present work, it is shown that a thin layer of titanium dioxide at the interface of Co/Alq3 can act as a good diffusion barrier. The buried interfaces of Co/Alq3/Co organic spin valve thin film has been studied using x-ray standing waves technique. A planar waveguide is formed with Alq3 layer forming the cavity and Co layers as the walls of the waveguide. Precise information about diffusion of Co into Alq3 is obtained through excitation of the waveguide modes. It is found that the top Co layer diffuses deep into the Alq3 resulting in incorporation of 3.1% Co in the Alq3 layer. Insertion of a 1.7 nm thick barrier layer of TiO2 at Co/Alq3 interface results in a drastic reduction in the diffusion of Co into Alq3 to a value of only 0.4%. This suggests a better performance of organic spin valve with diffusion barrier of TiO2.

The applied magnetic field (H APP) dependence of the exchange bias (EB) is studied in an exchange-coupled thin-film bilayer composed of a hard ferromagnetic FePt layer in the proximity of a soft ferromagnetic FeCo layer. FePt/FeCo structure is deposited in an ultra-high vacuum chamber, where the FePt layer was first annealed at 823 K for 30 min and subsequently cooled to room temperature in the presence of an in-plane magnetic field, H MAX ~ 1.5 kOe to promote L10-ordered hard magnetic phase with magnetic moments aligned in one of the in-plane directions in the FePt layer. In-situ magneto-optical Kerr effect measurements during different stages of bilayer growth and detailed ex-situ superconducting quantum interference device-vibrating sample magnetometer measurements jointly revealed that due to the interplay between exchange coupling at the interface and dipolar energies of the saturated hard FePt layer, a hysteresis loop of FeCo layer shifts along the magnetic field axis. A clear dependence of EB field (H EB) on increasing maximum value of the H APP during the hysteresis loop measurement is understood in terms of the magnetic state of soft and hard magnetic layers, where EB increases with increasing H APP until the hard layer moment remains undisturbed in its remanence state. As soon as the field was sufficient to rotate the spins of the FePt layer, the loop became symmetric with respect to the field axis.

Co0.8Fe2.2O4 nano ferrite has been synthesized by sol gel auto-combustion method. X-ray diffraction (XRD) and Mossbauer spectroscopy were used to characterize the synthesized as burnt and thermally annealed (600 oC for 3 hours) samples. Both XRD and Mossbauer measurements confirm the formation of spinel phase with Scherrer's grain diameter (D s) ≈ 37 nm. Presence of α-Fe and, Fe2O3 was also observed. Thermal annealing induced decrease of ρ xrd (from 5267.9 to 5262.7 Kg/m3) for the annealed samples is ascribable to the fact that, increase of unit cell volume overtakes the increase in mass of the unit cell. Comparison of dry gel and thermally annealed sample shows that in dry gel, B site is more populated with Fe ions, whereas thermal annealing leads to migration of Co from A to B site with simultaneous migration of Fe from B to A site, thus dropping the Neel magnetic moment. Bond angle values clearly reveal that thermal annealing leads to strengthening of B-O-B interaction with simultaneous wreaking of A-O-B, and, A-O-A interaction.

The structure and magnetic properties of ion beam sputtered transition metal–metalloid FeCoNbB/Si(100) alloy thin film have been studied as a function of film thickness using complementary techniques of x-ray reflectivity (XRR), grazing incidence x-ray diffraction, and magneto optical Kerr effect. Thicknesses of the films range from ~200 to 1500 A. The coercivity of all the films ranges between 4 and 14 Oe, which suggests soft magnetic nature of FeCoNbB/Si thin films. Films with thickness up to 800 A are amorphous in nature and are found to possess uniaxial magnetic anisotropy in the film plane, although no magnetic field was applied during deposition. The presence of the two fold symmetry in such amorphous thin films may be attributed to quenched-in stresses developed during deposition. Upon increasing the film thickness to ~1200 A and above, the structure of FeCoNbB films transforms from amorphous to partially nanocrystalline structure and has bcc-FeCo nanocrystalline phase dispersed in remaining amorphous matrix. The crystalline volume fraction (cvf) of the films is found to be proportional to the film thickness. Azimuthal angle dependence of remanence confirms the presence of in-plane four-fold anisotropy (FFA) in the crystalline film with cvf ~75%. Synchrotron x-ray diffraction measurement using area detector suggests random orientation of crystallites and thus clearly establishes that FFA is not related to texture/cubic symmetry in such polycrystalline thin films. As supported by asymmetric Bragg diffraction measurements, the origin of FFA in such partially crystalline thin film is ascribed to the additional compressive stresses developed in the film upon crystallization. Results indicate that promising soft magnetic properties in such films can be optimized by controlling the film thickness. The revelation of controllable and tunable anisotropy suggests that FeCoNbB thin films can have potential application in electromagnetic applications.

This paper reports the synthesis and characterization of nanoparticles of Zn Fe2O4 by spray pyrolysis method. XRD studies indicates that the particle formed are ultra fine (20 nm) associated with strain. The particle size is confirmed by TEM analysis. The room temperature Mossbauer spectrum shows only a doublet which could be indicative of either paramaganetic or superparamagnetic phase. The value of isomer shift is in the range 0.34±0.01 mm/s while quadruple splitting is in the range 0.48±0.01 mm/s. A series of low temperature studies has been performed and the spectra obtained at 20 K and 5K show the presence of two well resolved sextets, which are attributed to the Fe3+ ion in the tetrahedral and octahedral sites of the spinel structure. The application of external magnetic field yields a better fitting resolution of the sub spectra between A and B sites. The temperature dependant and in-field measurements yielded valuable insights about magnetic phase (superparamagnetic), local cation distribution among A sites and B sites, inversion parameter (δ =0.74), canted spin alignment (ψA = 29.58, ψB= 48.46) and the blocking temperature (TB= 50 K).

The use of a non-destructive nuclear-physical method, namely 57Fe Mossbauer spectroscopy, is discussed for the investigation of magnetic and structural arrangement of Fe-based nano-crystalline nickel-zinc-indium ferrites (NZIFO). Nano NZIFO particles (Ni0.58Zn0.42InxFe2−xO4) with varied quantities of indium (x = 0, 0.1, 0.2) have been chemically synthesized through a reverse micelle reaction and investigated by X-ray diffraction, transmission electron microscopy and by magnetic and Mossbauer spectral studies. Here a comparison between low-temperature and room temperature Mossbauer spectra is presented. Well defined sextets at 5 K provide information about the structure and magnetic states of atoms located in different structural positions. The dependence of Mossbauer parameters, viz, isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on In3+ concentration have been discussed. Detailed Mossbauer results, as well as the interest of these materials both for applied science perspectives are presented. Mossbauer results are also supported by magnetization data. With these interesting ferromagnetic properties Indium substituted nano nickel-zinc ferrites have potential applications in magnetic storage data.

Zinc ferrite nanoparticles of different size were irradiated in vacuum with 100 Mev O7+ ion beam at a fluence of 5×1013 ions/cm2. Presence of ZnO phase was observed after the irradiation in the samples. 57Fe Mossbauer spectroscopy shows the presence of well defined doublets in case of pristine and irradiated samples which are the attributes of superparamagnetism in the specimen. The variation of Mossbauer hyperfine parameters is discussed.

Using a combination of x-ray diffraction, transmission electron microscopy, room temperature (RT) and in-field M?ssbauer studies and dc magnetization, the structural and magnetic properties of nano-sized Cu0.25Co0.25Zn0.5Fe2O4, prepared by the chemical co-precipitation method, have been studied. Although the crystallite sizes are only of about 40?nm, these samples show a very large magnetic moment at RT. The moment of 81?A?m2?kg?1 obtained in one of the samples is comparable to one of the largest reported values in spinel ferrites as that found in bulk CoFe2O4. This can be explained in terms of the enhancement in the B?B interaction because of the distortion in the octahedral B site due to the presence of the Jahn?Teller cation Cu at this site. The dependence of magnetic properties on the ?-Fe2O3 content has also been investigated.

We present here the structural, electronic structure, magnetic and Mössbauer studies of NdFe(1-x)Ni(x)O(3) (0≤x≤0.3) samples. All the samples exhibit a single-phase orthorhombic structure with space group Pbnm. The near-edge x-ray absorption fine structure (NEXAFS) studies reveal that, with the Ni substitution at Fe sites, a new spectral feature about 1.5 eV lower than the pre-edge structure of NdFeO(3) in the O K edge is observed due to the 3d contraction effect and is growing monotonically with the increase of Ni concentration. The Fe L(3,2), Ni L(3,2) and Nd M(5,4) edges confirm the trivalent state of Fe, Ni and Nd ions. The Mössbauer spectra fitted with two Zeeman sextets confirm the different surroundings of Ni around Fe ions. With the increase in Ni concentration, the sextets are broadened. The increase of quadrupole splitting and the decrease of the hyperfine field suggest the change in the ordered regime of the system. The magnetic behaviour at low temperatures is explained in the context of competition among moments of rare earth (Nd) and transition metal ions (Fe/Ni). The strong paramagnetic contribution of the Nd magnetic sublattice and spin flip phenomenon is observed from the temperature dependence of zero-field-cooled and field-cooled magnetization where spin crossover is observed. The isothermal hysteresis loops show a decrease of magnetization and increase of coercivity with the increase in temperature and complements magnetization versus temperature. The results are explained on the basis of the spin reorientation phenomenon.

An UHV chamber is designed and developed for preparing thin films and multilayers of various elements, alloys and compounds using electron beam evaporation (EB) and ion beam sputtering (IBS) techniques. The developed chamber is equipped with magneto- optic Kerr effect (MOKE) and resistivity techniques in order to perform in-situ magnetic and transport properties measurements of ultra thin films. The calibration and performance of the developed chamber with deposition techniques is evaluated by depositing films of Fe and Si on float glass substrates. Systematic illustration of the versality of the UHV system has been done by performing in-situ MOKE and resistivity measurements simultaneously during the growth of Co film (from a fraction of a nm to 17 nm) on float glass (surface roughness 0.5 nm) and sheet glass (surface roughness 1.6 nm) substrate using electron beam evaporation. It is found that the substrate with higher roughness display maximum coercive field at Co thickness of 3.0 nm, while in case of smoother substrate the maximum coercive field is observed at 1.3 nm thick film.

Swift heavy ion irradiation induced intermixing in Si/Ti thin films has been studied using x-ray waveguide structures. The tri-layer Si/Ti/Si embedded in a planar waveguide provides detailed information about the depth distribution of Ti layer through x-ray fluorescence measurement. Raman spectroscopy shows that the Si layers are amorphous in nature. Quantitative information about the amount of mixed Si as a function of irradiation fluence is obtained from the intensity of the Raman peaks. It is found that the Ti layer gets significantly mixed with Si and at the same time the position of the Ti layer exhibits a small shift towards the surface. Comparison with the results in other metal/silicon systems suggests that the shift of the position of the marker layer is correlated with the sensitivity of the metal layer to electronic energy loss, as envisaged in the thermal spike model. An asymmetric mixing at the two interfaces may be a possible cause of this observed shift.