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We present a detailed investigation on the effects of C-implantation on low temperature magnetic behavior in Fe93Zr7 amorphous films using spin wave theory, law of approach to saturation, and Alben and Becker's theory. Significant increase in Curie temperature with a decrease in coercivity were observed upon C-implantation. Bloch's law was used to analyze the temperature dependence of magnetization, and several important param-eters were extracted such as the stiffness constant of the spin wave, and the exchange constant. The local random anisotropy constant decreases from 0.35 to 0.19 MJ/m(3) with increasing carbon concentration from 0 to 11%. The ferromagnetic correlation length for which the anisotropy directions are assumed to be arbitrarily oriented in-creases significantly with increasing carbon content. By the use of the theory of Alben and Becker, we also extracted the local anisotropy from coercivity, and reasonable agreement was found with random magnetic anisotropy approach.

The effects of hydrogen implantation on the magnetic properties in amorphous Fe88.4Zr11.6Hx films with different hydrogen contents (0≤ x≤16) were investigated. The Curie temperature increases with increasing hydrogen content while the coercivity presents an important decrease upon H implantation. Based on the analysis of the approach to saturation in magnetization, the local random anisotropy constant KL was extracted. The local random anisotropy constant decreases from 1.468 MJ/m3 to 0.667 MJ/m3 when the concentration of H increases from 0 to 16%. The ferromagnetic correlation length was found to significantly increase with increasing hydrogen content. The local anisotropy was also extracted from the coercivity based on the Alben and Becker theory, which fits reasonably with that obtained using random magnetic anisotropy approach., Title in Web of Science: Random magnetic anisotropy approach in amorphous Fe(88.4)Zr1(1.6) films: Effects of hydrogen implantation

We report on the effects of H-implantation on the magnetic and magnetocaloric properties of amorphous FeZr films. Arrott plots reveal a second order ferromagnetic to paramagnetic phase transition for the as-grown and H-implanted films, with an increase in T-C from 160 to 200 K upon implantation. The maximum change in magnetic entropy (-Delta S-M) increases from 0.66 to 0.77J/kgK for a field change mu 0 Delta H = 1.5T, as well as the relative cooling power (RCP) values were improved from 84.5 to 108.6J/kg. This improvement was attributed to the increase in magnetization and chemical inhomogeneity induced by the implantation process. The increase in the chemical inhomogeneity was supported by the determination of the local exponent n extracted from the slope of Ln(-Delta S-M) as a function of Ln(mu 0H), which is line with the simulated depth profile of hydrogen atoms through the FeZr film.

The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.

For a high magnetic refrigeration efficiency, a large change of magnetic entropy (-Delta S-M) associated with a high relative cooling power (RCP) are highly desirable. Here, the ion implantation is used to enhance both parameters in FeZr amorphous films. A considerable enhancement of both (-Delta S-M) and RCP, from 0.66 to 1.01 J/kg K and 84.5 to 155.5 J/kg respectively, for the as-grown sample compared to the C -implanted sample is obtained for a magnetic field change of mu(0)Delta H = 1.5 T. The increase of (-Delta S-M) and RCP values, are attributed to the increase of the magnetization and the chemical inhomogeneity, respectively upon C implantation.

The Curie temperature (T-c) of amorphous FeZr alloys can be greatly enhanced by doping with light elements. In this investigation, ion implantation is used to dope Fe93Zr7 thin films with H, He, B, C, and N. Extended X-ray absorption fine structure measurements confirm that the amorphous structure is preserved upon implantation for all samples, except for the N-implanted sample which is partially crystallized. The Curie temperature increases from 124 K for the pristine FeZr sample to about 400 K for the (FeZr)B-0.11 sample. The increase of T-c is proportional to the increase in the average Fe-Fe distance, which allows us to conclude that the dominant cause of the T-c enhancement of amorphous Fe93Zr7 upon doping is a volume effect.

We investigate the magnetic anisotropy and domain structure of amorphous Tb (x) Co(1-x) films grown in external in-plane magnetic field by high-frequency ion sputtering. Films with different thicknesses 100 and 500 nm and rare-earth element concentrations x = 12 % and x = 34 % present strong imprinted in-plane uniaxial anisotropy. Measurements of magnetic properties and domain structure imaging were performed by means of longitudinal and polar magneto-optical Kerr effect (MOKE). The coercivity fields increase by an order of magnitude for the higher Tb concentration and increase with film thickness (H (c) along the hard axis are 495, and 580 Oe, for 100 and 500 nm, with x = 34 % and 65, and 95 Oe for 100 and 500 nm with x = 12 %, respectively). Polar MOKE measurements revealed the existence of an out-of-plane magnetization component for the films with a Tb concentration of 34 % in lower fields. Large-scale domain structure of TbCo films with imprinted anisotropy was also studied as a function of applied field. Kerr imaging shows a zigzag domain structure of Tb12Co88 films, while no domains were found in Tb34Co66 samples. We also demonstrate that the zigzag angle depends on the film thickness. We suggest that domain structure in these films is determined by the interplay of imprinted and local magnetic anisotropies as well as exchange interaction.

We report on the changes in magnetic properties of SmCo/BaTiO3 multiferroic heterostructures as the BaTiO3 substrate undergoes its structural phase transitions. The observations show that the macroscopic magnetization of the SmCo film is affected by the structural phase transitions of the BaTiO3 substrate. Kerr microscopy images show that the magnetic domains of SmCo films have a zigzag shape but their shape is not influenced by the strain transferred from the substrate during the structural phase transitions. Analysis of the magnetoelastic energy shows that the macroscopic change of the magnetization is accompanied by an enhancement of the magnetic anisotropy for the orthorhombic phase of the BaTiO3 substrate and not a change in symmetry of the anisotropy.

We report on magnetoresistance measurements in SmCo5 amorphous films with a giant imprinted magnetic anisotropy. At low applied field parallel to the easy axis, the magnetoresistance exhibits a hysteretic, square, and antisymmetric shape. The antisymmetry in the magnetoresistance is a result of the non-uniform distribution of the magnetization direction over the sample in conjunction with the extraordinary Hall effect. Moreover, the combination of anisotropic magnetoresistance measurements and magnetic domain imaging demonstrates that the symmetry depends on the magnetization orientation with respect to the applied field.

We report on the origin of the anomalous temperature dependence of coercivity observed in some soft ferromagnets by studying the magnetic and electronic properties of FeZr films doped using ion implantation by H, He, B, C, and N. The anomalous increase of the coercivity with temperature was observed only in the C- and B-doped samples. Using x-ray photoelectron spectroscopy, we show that the anomalous behavior of the coercivity coincides with the occurrence of an electron charge transfer for those implanted samples. The origin of the anomaly is discussed in terms of (i) magnetic softness, (ii) nature of the Fe-C and -B covalent bonds, and (iii) large charge transfer. (C) 2014 AIP Publishing LLC.

The potential for tuning of magnetic properties and the exceptional uniformity are among the features that make amorphous magnetic materials attractive for technology. Here it is shown that the magnetization reversal in amorphous SmCo thin films takes place through the formation of giant magnetic domains, over a centimeter across. The domain structure is found to be dictated by the direction of the imprinted in-plane easy axis and the film boundaries. This is a consequence of the size of the anisotropy and the structural uniformity of the films, which also allows the movement of millimeter-long domain walls over distances of several millimeters. The results demonstrate the possibility of tailoring the magnetic domain structure in amorphous magnets over a wide range of length scales, up to centimeters. Moreover, they highlight an important consequence of the structural perfection of amorphous films.

We examine the magnetostriction in amorphous SmCo thin films with a composition in the range 4-27 at.% Sm. The magnetostriction increases significantly with increasing Sm content but is small compared to terbium-based ferromagnetic compounds, despite the large imprinted anisotropy. The magnetostriction and anisotropy both increase approximately linearly as the temperature is reduced. The magnetoelastic energy is found to be far smaller than the anisotropy energy so the magnetoelastic atomic displacements during growth cannot be the origin of the imprinted anisotropy. The anisotropy is only slightly altered by the application of large tensile stresses, indicating that the local strain fields involved in magnetostriction are not equivalent to the global strain produced by mechanical bending.

SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2-35 at.% Sm. Films with 5 at.% or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11-22 at.% Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.

A clear change in the magnetic anisotropy in a layer of amorphous Co95Zr5 is obtained at the orthorhombic phase transition of the BaTiO3 substrate. The use of an amorphous buffer layer between the ferroelectric substrate and amorphous magnetic film shows that bulk strain governs the change in themagnetic anisotropy of our ferromagnetic-ferroelectric heterostructure. Moreover, we show that the thermal magnetization curves exhibit anisotropic behavior.

The thickness dependence of magnetic properties has been studied in SmCo5 amorphous films with imprinted in-plane anisotropy for thicknesses ranging down to the nanometer scale (2.5-100 nm). The field induced in-plane magnetic anisotropy decreases considerably when the film thickness is below 20 nm. Analysis of the magnetic anisotropy energy shows that the decrease of the induced in-plane anisotropy is accompanied by the development of an out-of-plane interface anisotropy. Two different regimes for the coercivity (H-c) change are found: below 3.75 nm, the H-c decreases continuously with decrease of the film thickness, whereas at above 3.75 nm, the H-c decreases with increase of the film thickness. This change in Hc can be understood by considering the decrease of the short range chemical order for the thinnest films (<3.75 nm) and the relative decrease of the interface contribution with increasing film thickness. The changes in anisotropy have a profound influence on the domain structure, in which the angle of the zigzag domain boundaries decreases with the inverse thickness of the layers.

We report on the effect of carbon implantation on the structural, electronic, and magnetic properties of Fe93Zr7 (FeZr) amorphous films. Extended X-ray absorption fine structure measurements on (FeZr)(100-x)C-x (x = 0, 5.5, and 11) indicate the incorporation of carbon in the FeZr matrix, with an increase of the Fe-Fe distance by implanting carbon. X-ray photoelectron spectroscopy measurements reveal the creation of Fe-C bonds after implantation. A significant enhancement of the Curie temperature and decrease of the coercivity are observed in the carbon-implanted films. Moreover, the non collinear ferromagnetism of the as-grown FeZr film diminishes upon carbon implantation., QC 20130627

We show that Sm10Co90 amorphous films exhibit anisotropic magnetostriction effects when a magnetic field is applied perpendicular to the imprinted easy axis of magnetization. At low applied fields (0-100 mT), we observe strong anisotropy in the field response. Parallel to the applied field, the strain scales linearly with the applied field while the strain perpendicular to the field direction ( easy axis) is close to the detection limit. This behavior is accompanied by zigzag domain wall motion with the corners pointing along the easy axis. The origin of the anisotropic magnetostriction is discussed.

The application of solution-processable graphene oxide (GO) as a hole injection layer in organic light-emitting diodes (OLEDs) is demonstrated. High luminance of over 53 000 cd m(-2) is obtained at only 10 V. The results will unlock a route to apply GO in flexible OLEDs and other electrode applications.