Direction Of Magnetic Easy Axis Research Articles

Effect of element doping on the structural stability, magnetic properties and electronic structure of SmCo5-based rare earth permanent magnets

Doping transition metals has been proven as an effective method to enhance the performance of Sm-Co based rare earth permanent magnets. However, due to the complex interactions involved, the specific effects on magnetic properties, atomic occupancy preferences and structural stability mechanisms are still to be further investigated. In this study, we systematically investigated the influence of various transition metal dopants on the structural stability, magnetic properties and electronic structure of SmCo5 rare earth permanent magnet using first-principles calculations. Our calculations show that Ti, V, Cr, Mn, Ni, Cu, Zn elements preferentially occupy the 3 g site, while Sc and Zr tend to occupy the 1a site, and Fe elements have a preference for the 2c site. Regarding structural stability, doping with Sc, Cr, Mn, Fe, Ni, Cu, Zn and Zr all contribute to enhancing structural stability, while Ti and V doping exhibit adverse effects. Magnetic calculations indicate that doping with Mn and Fe significantly increases the total magnetic moment of the SmCo5 system. Notably, at a high doping concentration of 60 at%, the Ni and Zn-doped systems exhibit an exceptionally large magnetocrystalline anisotropy energy Additionally, a change in the magnetic easy axis direction occurs when the doping concentrations of Cr, Fe, Cu and Zn reach 60 at%, 40 at%, 40 at% (and 60 at%), 40 at% (and 60 at%), respectively. Our work provides important theoretical guidance for further optimizing the performance of Sm-Co based rare earth permanent magnets.

Nickel nanobrush platform for a magnetic field-assisted electrochemical response enhancement

A single-step electrochemical procedure to synthesize a brush-like platform, which composed of a nickel nanowire array attached to a nickel continuous layer acting as a solid base, is described. Room temperature hysteresis properties of this brush-like architecture (nanobrush) and those of the individual components (nanowires and layer) are determined. It is shown that the direction of the nanobrush magnetic easy axis may be tailored, being also possible to control the magnetic system's coercivity and remanence. The electrochemical response and the catalytic activity of a Ni nanobrush towards the redox probes [Fe(CN) 6 ] 4-/3- and ethanol were evaluated in the presence and absence of an applied magnetic field. The external field strongly affects the system's behavior by enhancing the electrode charge-transfer response, even at fields as low as 6 mT. This improvement was further investigated by Electrochemical Impedance Spectroscopy and Electrochemical Capacitance Spectroscopy studies. It is concluded that the enhanced electrochemical charge-transfer process of the Ni nanobrush electrode, with a magnetic field applied along the Ni nanowires axis, arises from a larger electroactive area. • A Ni nanobrush electrode is obtained by a single step electrodeposition route. • Nanobrush architecture consists of Ni NWs perpendicularly attached to a Ni layer. • The whole platform easy axis orientation is controlled by the brush shape and crystalline texture. • Catalytic activity towards redox probes Fe(CN) 6 −4/−3 and ethanol are evaluated. • A small magnetic field drastically reduces the nanobrush impedance.

Magnetic Anisotropy of Individual Nanomagnets Embedded in Biological Systems Determined by Axi-asymmetric X-ray Transmission Microscopy.

Over the past few years, the use of nanomagnets in biomedical applications has increased. Among others, magnetic nanostructures can be used as diagnostic and therapeutic agents in cardiovascular diseases, to locally destroy cancer cells, to deliver drugs at specific positions, and to guide (and track) stem cells to damaged body locations in regenerative medicine and tissue engineering. All these applications rely on the magnetic properties of the nanomagnets which are mostly determined by their magnetic anisotropy. Despite its importance, the magnetic anisotropy of the individual magnetic nanostructures is unknown. Currently available magnetic sensitive microscopic methods are either limited in spatial resolution or in magnetic field strength or, more relevant, do not allow one to measure magnetic signals of nanomagnets embedded in biological systems. Hence, the use of nanomagnets in biomedical applications must rely on mean values obtained after averaging samples containing thousands of dissimilar entities. Here we present a hybrid experimental/theoretical method capable of working out the magnetic anisotropy constant and the magnetic easy axis of individual magnetic nanostructures embedded in biological systems. The method combines scanning transmission X-ray microscopy using an axi-asymmetric magnetic field with theoretical simulations based on the Stoner-Wohlfarth model. The validity of the method is demonstrated by determining the magnetic anisotropy constant and magnetic easy axis direction of 15 intracellular magnetite nanoparticles (50 nm in size) biosynthesized inside a magnetotactic bacterium.

Temperature-dependent out-of-plane anisotropy in compressively strained La0.67Sr0.33MnO3 thin films

We studied the temperature and strain dependence of the perpendicular magnetic anisotropy in La0.67Sr0.33MnO3 thin films by performing temperature- and angle-dependent magnetotransport measurements. Three films of similar thickness (14 u.c., 14 u.c. and 15 u.c.) but with different out-of-plane crystallographic strain (1.9%, 0.9% and -0.7%) are studied. The films are grown on LaAlO3 and SrTiO3 substrates by pulsed laser deposition. We observe a clear increase in the out-of-plane magnetic anisotropy with increasing out-of-plane strain in the angle-dependent magnetotransport measurements which is present up to 80 K for the highest (1.9%) strained sample. The deformation of the unit cell, as discussed in earlier reports, point to the magnetocrystalline anisotropy as the main driver altering the magnetic easy axis direction. Our results highlight the utility of the effective magnetocrystalline anisotropy as a tool to control the desired anisotropy in crystalline thin films of La0.67Sr0.33MnO3.

Tunable electronic structure and magnetic anisotropy in bilayer ferromagnetic semiconductor Cr2Ge2Te6

The emergence of ferromagnetism in two-dimensional van der Waals materials has aroused broad interest. However, the ferromagnetic instability has been a problem remained. In this work, by using the first-principles calculations, we identified the critical ranges of strain and doping for the bilayer Cr2Ge2Te6 within which the ferromagnetic stability can be enhanced. Beyond the critical range, the tensile strain can induce the phase transition from the ferromagnetic to the antiferromagnetic, and the direction of magnetic easy axis can be converted from out-of-plane to in-plane due to the increase of compressive strain, or electrostatic doping. We also predicted an electron doping range, within which the ferromagnetism can be enhanced, while the ferromagnetic stability was maintained. Moreover, we found that the compressive strain can reverse the spin polarization of electrons at the conduction band minimum, so that two categories of half-metal can be induced by controlling electrostatic doping in the bilayer Cr2Ge2Te6. These results should shed a light on achieving ferromagnetic stability for low-dimensional materials.

Oxygen Reduction Reaction Activity for Surface-Magnetic-Anisotropy-Controlled Pt-Co/Pt(111) Bimetallic Surface

Introduction Developments in effective oxygen reduction reaction (ORR) catalysts for the cathode of Polymer Electrolyte Fuel Cell is important to achieve “hydrogen society”. Because oxygen molecules (O2), the reactant of ORR, is paramagnetic having a triplet spin state, ORR that proceeds on the cathode catalyst surfaces might modify by magnetism of the catalyst materials. Indeed, ORR activity was improved by the influence of an external magnetic field applied to the catalyst [1]. The alloys of 3d transition magnetic elements M (M=Co, Fe, Ni) are known to exhibit ferromagnetism. Etz et al. reported that the direction of magnetization easy axis of the epitaxial Co/Pt(111) surface depends on the Co deposition thickness [2]. However, to our best knowledge, relation between the magnetic anisotropy of the cathode electrode surface and ORR activity is yet to be clarified. Therefore, to investigate influence of spontaneous magnetization of the material’s surface on the ORR should cast some light on the ORR activity enhancement mechanisms for such the Pt-M alloy surfaces with the magnetic. In this study, we fabricate Pt-Co/Pt(111) ferromagnetic bimetallic surfaces under ultra-high vacuum (UHV) through 1 monolayer(ML)-thick epitaxial growth of Co on the clean Pt(111) substrate at various temperatures and discuss the influence of magnetic anisotropy of the Pt-Co/Pt(111) bimetallic surface on corresponding ORR activity. Experimental The sample fabrication process of Pt-Co/Pt(111) bimetallic surface is as follows. After surface cleaning of the Pt(111) single crystal substrate through Ar+ sputtering and annealing at 1173 K in ultra-high vacuum (UHV: 10-8 Pa), 1ML-thick-Co was deposited on the clean Pt(111) by the molecular-beam epitaxy (MBE) method at elevated substrate temperature (723 K to 973 K) to generate the Pt(111)-skin through the surface segregation of substrate Pt atoms [3]. The Pt-Co/Pt(111) bimetallic surfaces are described hereafter by the Co deposition temperatures, for example Pt-Co773K/Pt(111), etc. The resulting surface structures were verified by the scanning tunneling microscopy (STM) and low-energy ion scattering spectroscopy (LE-ISS) in UHV. Then, polar magneto optical Kerr effect (polar MOKE), and in-plane XRD measurements are conducted in air to evaluate the surface magnetic anisotropies and compressive strains of the generated Pt(111)-skin surfaces. The MBE-prepared samples were transferred to electrochemical evaluation systems set in a N2–purged glove box without being exposed to air. Then, cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements were conducted in N2–purged and O2–saturated 0.1 M HClO4, respectively, in the glove box. ORR activities of the samples were evaluated based on j k values at 0.9 V vs. RHE by using Koutecky–Levich equation. Results and Discussion An LE-ISS spectrum of the Pt-Co773K/Pt(111) is shown in Fig. 1(a). Only the signal due to of the Pt atoms at the topmost surface is appeared on the spectrum, indicating that the Pt(111)-skin is generated for the Pt-Co773K/Pt(111) surface and the deposited Co should be located below the second atomic layer of the Pt-Co773K/Pt(111) as a result of surface segregation of the substrate Pt atoms at deposition temperature (of 773 K). Fig. 1(b) shows an STM image of the corresponding Pt-Co773K/Pt(111) surface. As shown in Fig. 1(b), the sample surface is atomically flat. One might notice that Moiré-pattern-like surface corrugations on the image (highlighted by white line), probably stemming from the lattice mismatch between Pt(111)-skin and underlying Co (Pt-Co alloy) [4]. The result also supports the Pt(111)-skin. Fig. 1(c) shows the polar MOKE curves of the Pt-Co773K/Pt(111) (red) and Pt-Co823K/Pt(111) (blue). Both the samples show the hysteresis loops of Kerr rotation angle vs. magnetic field H, indicating that perpendicular magnetic anisotropy (PMA) of the sample surfaces. Relation between the ORR activities and in-plane-XRD-estimated compressive strains of the Pt-Co773K/Pt(111) (red) and Pt-Co873K/Pt(111) (blue) surfaces are shown in Fig. 1(d). For comparison, the DFT-calculated ORR activities of the strained Pt(111) surfaces (green) are plotted in the figure [5]. The estimated ORR activities for both the Pt-Co773K/Pt(111) and Pt-Co873K/Pt(111) are 20 to 30 % higher than the DFT-calculated ones. The results suggest that PMA might affect ORR activity enhancements for the prepared PMA surfaces of the Pt-Co/Pt(111). At the meeting, effects of magnetic anisotropies (perpendicular and in-plane) are discussed more in detail.

Orbital Magnetic Moments in Strained SrRuO3 Thin Films

We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and evaluated orbital magnetic moments in compressively strained tetragonal and tensilely strained monoclinic SrRuO3 epitaxial thin films whose magnetic easy axis directions and behavior of the transverse resistivity differ from each other. We found that regardless of the types of the strain, SrRuO3 films have negative orbital magnetic moments arranged antiparallel to the spin magnetic moments along the magnetic easy axis directions. The magnitudes of the orbital moments for both films are similar: ∼−0.17 μB/Ru at 20 K. These observations indicate that the films’ structures tie only to the direction of the orbital magnetic moments and consequently determine the magnetic easy axis direction in SrRuO3 through the strong magnetocrystalline effect. This highlights the significance of the orbital magnetic moment as a factor determining of the magnetic anisotropy of this oxide. Our results provide important physical insight into magnetic and magneto-transport properties of SrRuO3.

Tuning the exchange coupling in pulse laser deposited cobalt ferrite thin films by hydrogen reduction

Abstract Pulse laser deposited cobalt ferrite CoFe2O4 (CFO) thin films were transformed to CFO/Co-Fe solid solution hard/soft nanocomposite thin films by annealing the CFO films in hydrogen atmosphere. By controlling the annealing time, the level of transformation between the two phases was controlled thereby the exchange coupling and magnetic properties of the nanocomposite layer. X-ray diffraction patterns showed the formation of (0 0 l) orientation for the CFO hard phase and (0 l l) orientation for bcc Co-Fe solid solution soft phase in all samples. Atomic force microscopy images revealed that by increasing the annealing time, the surface roughness of the films increased. Magnetic measurements demonstrate that the more the annealing time, the higher the saturation magnetization and the lower their coercivity and magnetic anisotropy. Hysteresis loops of the films show that these samples behave like single-phase materials indicating the presence of exchange coupling between two different hard and soft phases. Using X-ray photoelectron spectroscopy (XPS), we determined the cations distribution variation in our samples thus a change in the spinel inversion parameter (y) from 0.70 for the as-deposited CFO to 0.49 for the films reduced in hydrogen for 60 min. The Raman spectroscopy confirms the XPS results in our samples. The present approach may help the development of methods for tuning the saturation magnetization, coercivity and magnetic easy axis direction in magnetic nanocomposite thin films and magnetic oxide-based spintronic devices.

Control of magnetic anisotropy by orbital hybridization with charge transfer in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice

The chemical asymmetry at the hetero-structure interface offers an effective opportunity to design desirable electronic structures by controlling charge transfer and orbital hybridization across the interface. However, controlling the hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells of La0.67Sr0.33MnO3 with a fixed thickness of ~120 unit cells. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87, where TS is the temperature at the onset of magnetization. Transmission electron microscopy reveals an enlarged tetragonal ratio >1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of {3d}_{3z^2-r^2} orbitals at the interface and induces a stronger electronic hopping integral and interfacial magnetic anisotropy along the out-of-plane direction, which contributes to the rotation towards the out-of-plane direction of an effective magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization with charge transfer in the superlattice of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications.

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

Two-dimensional (2D) structures that exhibit intriguing magnetic phenomena such as perpendicular magnetic anisotropy and its switchable feature are of great interests in spintronics research. Herein, the density functional theory studies reveal the critical impacts of strain and external gating on vacancy-induced magnetism and its spin direction in a graphene-like single layer of zinc oxide (ZnO). In contrast to the pristine and defective ZnO with an O-vacancy, the presence of a Zn-vacancy induces significant magnetic moments to its first neighboring O and Zn atoms due to the charge deficit. We further predict that the direction of magnetization easy axis reverses from an in-plane to perpendicular orientation under a practically achievable biaxial compressive strain of only ~1–2% or applying an electric field by means of the charge density modulation. This magnetization reversal is mainly driven by the strain- and electric-field-induced changes in the spin–orbit coupled d states of the first-neighbor Zn atom to a Zn-vacancy. These findings open interesting prospects for exploiting strain and electric field engineering to manipulate magnetism and magnetization orientation of 2D materials.

Electric-field-induced modulation of the anomalous Hall effect in a heterostructured itinerant ferromagnet SrRuO3

We fabricated electric-field-effect transistor structures with a channel layer of an itinerant ferromagnet ${\mathrm{SrRuO}}_{3}$ (SRO) heterostructured with a cap layer of ${\mathrm{BaTiO}}_{3}$ and investigated the electric field effects on the anomalous Hall effect (AHE) in SRO. We show that by applying positive and negative gate voltages (${V}_{\mathrm{G}}$), the anomalous Hall conductivity in the heterostructured SRO increases and decreases, respectively, regardless of its sign, while no change in the magnetic easy axis direction is observed. The results indicate that the observed ${V}_{\mathrm{G}}$-induced modulations of the AHE do not simply originate from changes in the magnetization and magnetic anisotropy and indicate that ${V}_{\mathrm{G}}$-induced changes in an integral of the Berry curvature over the filled electronic states play a key role in the observed electric field effects on the AHE in SRO. We also found that ${V}_{\mathrm{G}}$-induced modulations on the AHE are negligibly small for transistor structures with a SRO channel having no BTO cap layer. This implies that the cap-layer-induced modifications in the Ru-O-Ru bond angles in the channel affect the Berry phase, enhancing the electric field effects on the AHE in SRO.

Electric field modulation of reversible and non-volatile magnetic anisotropy transition in (0 1 1) 0.7[Pb(Mg1/3Nb2/3)O3]–0.3[PbTi0.3O3]/FeSi heterostructures

Electric-field-modulated magnetic properties are investigated on FeSi films with a (0 1 1) preferred orientation on (0 1 1) 0.7[Pb(Mg1/3Nb2/3)O3]–0.3[PbTi0.3O3] (PMN–0.3PT) single crystal substrates. When saturated and reversed coercive electric fields are alternately applied to the Pt/PMN–0.3PT/FeSi/Ta heterostructures, a reversible and non-volatile magnetic transition between four-fold and two-fold anisotropy is demonstrated by means of the angular dependence of remanent magnetization measurements. Based on the electric field control of the 90° magnetic easy axis direction transition of the FeSi film, we also achieve electric-field-mediated giant 180° magnetization switching with the assistance of the magnetic field pulse.

Orbital magnetic moments in SrRuO3 epitaxial thin films with interfacially controlled magnetic anisotropy

Using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy, we evaluated the orbital magnetic moments of itinerant ferromagnet $\mathrm{SrRu}{\mathrm{O}}_{3}$ (SRO) epitaxial thin films with interfacially controlled magnetic anisotropy. We found that the orbital moment is closely correlated with the SRO's magnetic anisotropy, which can be controlled by interfacially engineering the $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedral rotations. For the monoclinic film with magnetization along the direction 45\ifmmode^\circ\else\textdegree\fi{} from the out-of-plane direction, the orbital moment is $\ensuremath{\approx}\ensuremath{-}0.1\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Ru}$ along the magnetic easy axis direction and is aligned antiparallel to the direction of the spin magnetic moments. For the tetragonal film with in-plane magnetization, on the other hand, the out-of-plane component of the orbital moment is as small as $\ensuremath{\approx}\ensuremath{-}0.04\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Ru}$, accounting for the film's in-plane magnetic anisotropy. Our results highlight that the magnetic anisotropy of SRO can be controlled by engineering the orbital magnetic moment through the octahedral distortions.

Magnetic properties of <italic>L</italic>1<sub>0</sub>-FePt(001)/<italic>A</italic>1-FePt bilayer exchange springs

Soft A 1-FePt (30 nm) films were magnetron-sputtered on MgO(001) single-crystal substrates at an elevated temperature of 400°C, and subsequently annealed at diffrent temperatures in range of T a=[400°C, 700°C] for 6 h in order to turn them into hard magnets with different degrees of A 1→ L 10 transformation. Then second layers of A 1-FePt with different thicknesses were covered at 100°C to obtain L 10-FePt/ A 1-FePt bilayer magnetic exchange springs with (001) textures. At T a≤600°C, the coverage of hard layer was ~100%, though the grain size increased with T a. The surface roughness reduced from 2.45 to 1.02 nm if the film was annealed at T a=500°C. The surface of hard layer flattened by annealing should benefit to improve the strength of interlayer exchange interaction. At T a=500°C and 600°C, A 1-FePt and L 10-FePt coexisted in the hard layer with an ordering degree of 0.61 and 0.84, respectively. The direction of magnetic easy axis began to switch from in plane to out of plane at T a=500°C, indicating a vertical magnetocrystalline anisotropy was generated. The out-of-plane magnetization curves showed rectangle-like shapes at 500°C≤ T a≤600°C, in spite of the soft phase left in hard layer, and a moderate coercive force of ~5 kOe was obtained at T a=500°C. This indicates the exchange interaction between coexistent two phases in hard layer was strong enough to pin the soft magnetic moments with the hard ones. At T a=700°C, the coercive force exceeded 20 kOe, which is too huge to be affected by exchange springs. By using the film of T a=500°C as hard layer, L 10/ A 1-FePt bilayer film with 20 nm thick soft layer kept rigid behaviors with almost the same coercive force of single hard layer, and respective reversal steps for soft layer and hard layer appeared in the magnetization curve if the thickness of soft layer was 30 nm, with a reduced coercive force of ~4 kOe. As double shoulders should appear in the hysteresis loop if the thickness of soft layer exceeds twice of domain wall thickness of hard layer, i.e., the so-called interlayer exchange length, this indicates that the hard/soft interlayer exchange length was in the range of 20 nm l ex L 10/ A 1-FePt exchange spring. The reason is due to that the coexistence of A 1-FePt and L 10-FePt in hard layers lowered the efficient uniaxial magnetocrystalline anisotropy. This lengthened distance of interlayer exchange could be maintained at T a=600°C. This is benefit to design the properties of magnetic springs for different applications.

TAILORING OF MAGNETIC EASY AXIS OF NICKEL NANOWIRES BY VARYING DIAMETER

Anodized aluminum oxide (AAO) templates with an average diameter of [Formula: see text][Formula: see text]nm and [Formula: see text][Formula: see text]nm are synthesized by two-step anodization. Nickel nanowires are fabricated by AC electro deposition with less microstructure defects at low voltage in AAO templates. Magnetic properties of compact nickel (Ni) nanowires show that easy axis is parallel to nanowire axis for diameter [Formula: see text][Formula: see text]nm while by varying diameter from [Formula: see text][Formula: see text]nm to [Formula: see text][Formula: see text]nm, easy axis shifts to perpendicular direction of nanowire axis. This shifting of magnetic easy axis from parallel to perpendicular direction is mainly due to shape anisotropy and interactive fields between the wires. The competition between shape anisotropy (due to individual wire) and interactive fields by varying diameter of nanowires could result in tailoring of the direction of magnetic easy axis of nanowires.

Thickness dependence of voltage-driven magnetization switching in FeCo/PI/piezoelectric actuator heterostructures

Strain mediated magnetization switching of ferromagnetic/substrate/piezoelectric actuator heterostructures has become a hot issue due to the advantage of low-power consumption. In this work, Fe65Co35 thin films were deposited on a flexible polyamides (PI) substrate, which has quite low Young’s module (~4 GPa for PI as compared to ~180 GPa for Si) and benefits from complete transfer of the strain from the piezoelectric actuator to magnetic thin films. A complete 90° transition of the magnetic easy axis was realized in 50 nm thick FeCo films under the voltage of 70 V, while a less than 90° rotation angle of the magnetic easy axis direction was observed in other samples, which was ascribed to the distribution of the anisotropy field and/or the orthogonal misalignment between stress induced anisotropy and original uniaxial anisotropy. A model considering two uniaxial anisotropies with orthogonal arrangement was used to quantitatively understand the observed results and the linear-like voltage dependent anisotropy field, especially for 10 nm FeCo films, in which the switching mechanism along the easy axis direction can be explained by the domain wall depinning model. It indicates that the magnetic domain-wall movement velocity may be controlled by strain through tuning the energy barrier of the pinning in heterostructures. Moreover, voltage-driven 90° magnetization switching with low-power consumption was achieved in this work.

Toward uniform electrodeposition of magnetic Co-W mesowires arrays: direct versus pulse current deposition

Template-assisted electrodeposition of Co-rich Co-W alloys into mesoporous anodized aluminum oxide from ammonia-free solutions is investigated. The optimum deposition conditions rendering uniform filling of the pores, either by direct current (DC) or pulse current (PC) methods, are established. Contrary to the DC deposition on flat surfaces (which is kinetically controlled), the DC electrodeposition in the mesopores of the template is limited by mass transfer. Conversely, under PC mode, the Co-W electrodeposition process is controlled by kinetics at frequencies > 0.3Hz; and by diffusion at lower frequencies. The obtained mesowires are nanocrystalline and exhibit a hexagonal closed packed (hcp) structure. The magnetic properties of selected Co-W mesowires, with variable aspect ratio, are also studied. The arrays of mesowires exhibit a semi-hard ferromagnetic behavior with coercivity values that surpass those of Co mesowires with similar dimensions. The interplay between interwire dipolar interactions, magnetocrystalline anisotropy and shape anisotropy on the overall shape of the hysteresis loops (in particular, on the coercivity and squareness ratio values, as well as on the effective magnetic easy axis direction) is investigated in a semiquantitative manner.

Magnetic and optical properties of the nickel thin film deposited by GLAD technique

In this work, nickel thin film was deposited on glass sample using Glancing Angle Deposition (GLAD) technique, to a thickness of 1 μm. Glass sample was positioned 15 degrees with respect to the nickel vapor flux. The nickel thin film was characterized by Atomic Force Microscopy (AFM), Magneto- Optical Kerr effect Microscopy and Spectroscopic Ellipsometry. According to an AFM cross-section imaging, it was found that the nickel thin film has a columnar structure. The values of the coercively, obtained from the magnetic hysteresis loops, were analyzed as a function of the sample rotation in the magnetic field. It was found that the direction of magnetization easy axis lies toward the structure growth. Optical properties of the nickel thin film were studied at the wavelength of 455 nm. From the shape of the refractive index and the extinction coefficient diagrams could be concluded that the nickel thin film has an optical anisotropy.

Pressure and field tuning the magnetostructural phases of Mn3O4: Raman scattering and x-ray diffraction studies

We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of single crystal Mn3O4, combined with temperature- and field-dependent x-ray diffraction studies, revealing the novel magnetostructural phases in Mn3O4. Our temperature-dependent studies showed that the commensurate magnetic transition at T2=33K in the binary spinel Mn3O4 is associated with a structural transition from tetragonal to orthorhombic structures. Field-dependent studies showed that the onset and nature of this structural transition can be controlled with an applied magnetic field, and revealed evidence for a field-tuned quantum phase transition to a tetragonal spin-disordered phase for H||[1-10]. Pressure-dependent Raman measurements showed that the magnetic easy axis direction in Mn3O4 can be controlled---and the ferrimagnetic transition temperature increased---with applied pressure. Finally, combined pressure- and magnetic-field-tuned Raman measurements revealed a rich magnetostructural phase diagram---including a pressure- and field-induced magnetically frustrated tetragonal phase in the PH phase diagram---that can be generated in Mn3O4 with applied pressure and magnetic field.

Fast detection of the magnetic easy axis on steel sheet using the continuous rotational Barkhausen method

The magnetic behaviour of most commercial ferromagnetic steels is usually anisotropic presenting a magnetic easy axis. Changes in the direction of this axis can be related to mechanical changes and anomalies that occur in the fabrication process. The present work describes a method that uses a device with permanent magnets to create a precise rotational magnetic field. The device measures continuous Magnetic Barkhausen Noise signals related to the angle of magnetization, in order to determine the direction of the macroscopic magnetic easy axis. It also offers the possibility of obtaining real time parameters that quantify the magnetic anisotropy of the sample.