Applied Field Parallel Research Articles

Anisotropic properties of a noncentrosymmetric NbReSi superconducting single crystal

A single crystal of NbReSi which crystallizes in the hexagonal structure with the noncentrosymmetric space group $P\overline{6}2m$ (No. 189) has been grown by the Czochralski method using a tetra-arc furnace. The anisotropic physical properties have been studied by measuring the magnetic susceptibility and electrical transport. The superconducting transition temperature $({T}_{\mathrm{c}})$ is around 6.1 K, and the measured upper critical field $({H}_{\mathrm{c}2})$ values are 8.39 T and 11.65 T for applied field parallel to [0001] and $[11\overline{2}0]$, respectively. The anisotropy ratio $\mathrm{\ensuremath{\Gamma}}={H}_{\mathrm{c}2}^{a}/{H}_{\mathrm{c}2}^{c}$ is close to 1.38. The GL parameters ${\ensuremath{\kappa}}_{c}$ and ${\ensuremath{\kappa}}_{a}$ are much larger than $1/\sqrt{2}$, indicating that NbReSi is a strong type-II superconductor. The lower critical field $({H}_{\mathrm{c}1})$ values are very small (1.65 mT for $H\phantom{\rule{0.16em}{0ex}}||\phantom{\rule{0.16em}{0ex}}[0001]$ and 1.22 mT for $H\phantom{\rule{0.16em}{0ex}}||\phantom{\rule{0.16em}{0ex}}[11\overline{2}0]$) compared to ${H}_{\mathrm{c}2}$. From the magnetization hysteresis loops, calculated critical current at low field is of the order ${10}^{4}$ $\mathrm{A}/{\mathrm{cm}}^{2}$ which indicates the presence of strong pinning in the sample.

Microscopic parameters of the van der Waals CrSBr antiferromagnet from microwave absorption experiments

Microwave absorption experiments employing a phase-sensitive external resistive detection are performed for a topical van der Waals antiferromagnet CrSBr. The field dependence of two resonance modes is measured in an applied field parallel to the three principal crystallographic directions, revealing anisotropies and magnetic transitions in this material. To account for the observed results, we formulate a microscopic spin model with a bi-axial single-ion anisotropy and inter-plane exchange. Theoretical calculations give an excellent description of full magnon spectra enabling us to precisely determine microscopic interaction parameters for CrSBr.

The process of magnetic flux penetration into superconductors

Abstract In the present paper the magnetic flux penetration dynamics of type-II superconductors in the flux creep regime is studied by analytically solving the nonlinear diffusion equation for the magnetic flux induction, assuming that an applied field parallel to the surface of the sample and using a power-law dependence of the differential resistivity on the magnetic field induction. An exact solution of nonlinear diffusion equation for the magnetic induction B(r, t) is obtained by using a well-known self-similar technique. We study the problem in the framework of a macroscopic approach, in which all length scales are larger than the flux-line spacing; thus, the superconductor is considered as a uniform medium.

Kerr microscopy real-time imaging of the magnetization reversal process in kagome artificial spin ice

The magnetization reversal process in an interconnected kagome artificial spin ice has been investigated using high-resolution Kerr microscopy. The magnetization switching with two-dimensional system-size avalanches has been directly imaged for the applied field parallel to one of the sublattice branches, suggesting very low disorder in our sample. The discrete one-dimensional Dirac-string-like magnetization reversal is found for the field with a certain angle. The real-time imaging under the field suggests that the reversal of the third bars next to the reversed Dirac string can mediate the reversal of the neighboring Dirac string. The observed reversal behaviors can be understood by the ice rule, consistent with the micromagnetic simulation results. Our studies demonstrate that Kerr microscopy can be applied to study the magnetization reversal process in artificial spin ice structures in real space and real time under an external magnetic field.

Comparison Study of the Flux Pinning Enhancement of YBa2Cu3O7−δ Thin Films With BaHfO3 + Y2O3 Single- and Mixed-Phase Additions

Incorporating nano-scale insulating phases to YBa2Cu3O7−δ (YBCO) superconductor thin films enhances flux pinning by combining different pinning mechanisms, which in turn increases the current density. This research explores the effects of addition of the non-reactive phases of barium hafnate (BHO) and yttrium oxide Y2O3. Pulsed laser deposition (PLD) produces thin films on SrTiO3 (STO) substrates at various deposition temperatures ranging from 790 °C to 840 °C. PLD target compositions vary the volume percent of BHO from 2 to 6 vol% while maintaining 3 vol% Y2O3 and the remaining vol% YBCO. Examining the microstructure through SEM, TEM, and XRD analyses provides insight into the impact of the additions of BHO and Y2O3 on the YBCO thin films’ magnetic and transport current densities measured with an applied field parallel to the c and ab directions, and on the films’ critical temperature measurements. The Y2O3 additions decrease the variability in the current density between the c and ab directions, which is an important aspect to consider in applications, such as for HTS wires for motors.

Magnetic Characteristics of Ni-Filled Luminescent Porous Silicon.

The aim of the presented work is to combine luminescent porous silicon (PSi) with a ferromagnetic metal (Ni) to modify on the one hand the photoluminescence by the presence of metal deposits and on the other hand to influence the optical properties by an external magnetic field. The optical properties are investigated especially with respect to the wavelength-shift of the photoluminescence due to the metal filling. With increasing metal deposits within PSi the photoluminescence peak is blue-shifted and furthermore an increase of the intensity is observed. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm for a deposition time of 15 min. Field dependent magnetic measurements performed with an applied field parallel and perpendicular to the surface, respectively, show a magnetic anisotropy which is in agreement with a thin film. This film-like behavior is caused by the interconnected Ni structures due to the branched porous silicon morphology. The coercivity increases with increasing metal deposition from about 150 Oe to about 450 Oe and also the magnetic anisotropy is enhanced with the growth of metal deposits. Within this work the influence of the magnetic metal filling on the optical properties and the magnetic characterization of the nanocomposites are discussed. The presented systems give not only rise to optoelectronics applications but also to magneto optical integrated devices.

NMR studies on antiferromagnetic fluctuation in [formula omitted

We have carried out 195Pt-NMR measurements on a heavy Fermion superconductor UPt3 at H∼1.5−2.0T to investigate the in-plane anisotropy in the normal state. For an applied field parallel to [112¯0] direction, split 195NMR line are observed, which has not been reported previously. Such a line splitting is explained by anisotropic Knight shift tensors associated with the local symmetry of Pt-site in UPt3.

Optical Properties of Nanoporous Silicon in the Presence of Magnetic Nanostructures

This work aims to combine luminescent microporous silicon with a ferromagnetic metal to create a nanocomposite system with modifiable photoluminescence due to the presence of metal deposits as well as to influence the optical properties by an external magnetic field. Due to the metal filling of the porous silicon (PSi) the peak of the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties is discussed and the magnetic characterization of the samples is presented. The microporous silicon is fabricated by anodization of a moderately doped p-silicon wafer. The electrolyte consists of HF, distilled water and ethanol in the ratio 1:1:2. The deposition of the magnetic metal has been performed by pulsed electrodeposition in using in the case of Ni the so called Watts electrolyte (NiCl2 and NiSO4). First the optical properties of the luminescent PSi are investigated, second the magnetic metal is electrochemically deposited within the porous silicon and subsequently the nanocomposite specimens are characterized optically and magnetically. The samples are structurally characterized by SEM, EDX and TEM. The optical properties are investigated with respect to the shift of the photoluminescence peak due to the metal filling. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm depending on the metal deposition time and furthermore the luminescence intensity is increased. The deposition of the metal is crucial since the metal has to be incorporated within the nanopores but has to be avoided on the sample surface to still enable the luminescence. Furthermore the oxide layer between PSi and metal is essential to guarantee a photoluminescence of the specimens. Concerning the magnetic properties of the nanocomposites the embedded Ni structures offer the same branched morphology as the porous silicon template and thus these interconnected Ni-structures do not offer a superparamagnetic behavior which is confirmed by temperature dependent magnetization measurements. Generally superparamagnetic behavior is possible due to the pore diameters in the nanometer range. Field dependent magnetization measurements have been performed with a magnetic field applied perpendicular and parallel to the sample surface showing a high magnetic anisotropy. Due to the interconnected Ni-structures the samples offer a film-like behavior with the easy axis parallel to the surface. Figure 1 shows the film-like behavior of a Ni-filled sample. In the frame of this work the optical characterization of luminescent PSi with respect to the peak position of the photoluminescence compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites. Furthermore the influence of an external magnetic field on the optical properties is elucidated. The presented systems give not only rise to optoelectronic applications but also to magneto optical integrated devices. Figure 1: Field dependent magnetization measurements performed in two directions, showing a high magnetic anisotropy with the easy axis for an applied field parallel to the surface. Figure 1

Magnetic field annealing effect and superparamagnetic contributions in one-dimensional CoPt nanostructures

A low cost versatile electrochemical method has been employed to synthesize highly ordered CoPt nanowires (NWs) in anodic aluminum oxide (AAO) templates with average pore diameter of about 100 nm. The structural properties of as deposited NWs have been studied through XRD analysis showing face centered cubic (fcc) as the dominant phase of CoPt NWs. Magnetic properties at room temperature and lower temperature has been investigated with applied field parallel and perpendicular to NWs axis. The easy magnetization axis is aligned perpendicular to NWs owing to the strong magnetostatic interactions among the NWs due to smaller interwire distance (∼15 nm). Furthermore, the as deposited arrays of NWs have been annealed for 2 h at 300 °C in the presence of 1 T magnetic field applied in the direction perpendicular to NWs axis. Magnetic field annealing gives improved structural and magnetic behavior of these one-dimensional (1D) nanostructures resulting improved crystallinity and increased values of coercivity (Hc) and remnant squareness (SQ). Superparamagnetic contributions at lower temperature due to presence of fine nanoparticles in blocking state play important role and leads to enhanced magnetic behavior of CoPt NWs.

Simplified Calculation of the Maximum Energy Product for the Hard/Soft/Hard Trilayers

Energy products of the hard/soft/hard trilayer system with the directions of easy axes and applied field parallel to the plane have been calculated by a simplified method. The simplified calculation of the maximum energy product (BH) $_{\max }$ has been concluded, which indicates that (BH) $_{\max }$ for a given trilayer system can be calculated though solving the maximum value of energy product in the domain of the applied field. Energy products of systems with the infinite hard and the finite hard phases calculated by the simplified method have been compared with those calculated by the traditional method, which shows that the simplified method is applicable. The maximum energy product of trilayer system as a function of L h has been calculated systematically by the simplified method. The result shows that the energy product first increases then declines as the hard phase thickness increases, and an optimal hard thickness for a fixed soft thickness can be found. Consequently, the optimal proportion of composite phase can be obtained, which is significant to the experiment.

Magnetic behaviour of multisegmented FeCoCu/Cu electrodeposited nanowires

Understanding the magnetic behaviour of multisegmented nanowires (NWs) is a major key for the application of such structures in future devices. In this work, magnetic/non-magnetic arrays of FeCoCu/Cu multilayered NWs electrodeposited in nanoporous alumina templates are studied. Contrarily to most reports on multilayered NWs, the magnetic layer thickness was kept constant (30 nm) and only the non-magnetic layer thickness was changed (0 to 80 nm). This allowed us to tune the interwire and intrawire interactions between the magnetic layers in the NW array creating a three-dimensional (3D) magnetic system without the need to change the template characteristics. Magnetic hysteresis loops, measured with the applied field parallel and perpendicular to the NWs’ long axis, showed the effect of the non-magnetic Cu layer on the overall magnetic properties of the NW arrays. In particular, introducing Cu layers along the magnetic NW axis creates domain wall nucleation sites that facilitate the magnetization reversal of the wires, as seen by the decrease in the parallel coercivity and the reduction of the perpendicular saturation field. By further increasing the Cu layer thickness, the interactions between the magnetic segments, both along the NW axis and of neighbouring NWs, decrease, thus rising again the parallel coercivity and the perpendicular saturation field. This work shows how one can easily tune the parallel and perpendicular magnetic properties of a 3D magnetic layer system by adjusting the non-magnetic layer thickness.

Spin resonance and spin fluctuations in a quantum wire

This is a review of theoretical works on spin resonance in a quantum wire associated with the spin-orbit interaction. We demonstrate that the spin-orbit induced internal “magnetic field” leads to a narrow spin-flip resonance at low temperatures in the absence of an applied magnetic field. An applied dc magnetic field perpendicular to and small compared with the spin-orbit field enhances the resonance absorption by several orders of magnitude. The component of applied field parallel to the spin-orbit field separates the resonance frequencies of right and left movers and enables a linearly polarized ac electric field to produce a dynamic magnetization as well as electric and spin currents. We start with a simple model of noninteracting electrons and then consider the interaction that is not weak in 1d electron system. We show that electron spin resonance in the spin-orbit field persists in the Luttinger liquid. The interaction produces an additional singularity (cusp) in the spin-flip channel associated with the plasma oscillation. As it was shown earlier by Starykh and his coworkers, the interacting 1d electron system in the external field with sufficiently large parallel component becomes unstable with respect to the appearance of a spin-density wave. This instability suppresses the spin resonance. The observation of the electron spin resonance in a thin wires requires low temperature and high intensity of electromagnetic field in the terahertz diapason. The experiment satisfying these two requirements is possible but rather difficult. An alternative approach that does not require strong ac field is to study two-time correlations of the total spin of the wire with an optical method developed by Crooker and coworkers. We developed theory of such correlations. We prove that the correlation of the total spin component parallel to the internal magnetic field is dominant in systems with the developed spin-density waves but it vanishes in Luttinger liquid. Thus, the measurement of spin correlations is a diagnostic tool to distinguish between the two states of electronic liquid in the quantum wire.

Positive magnetoresistance of single-crystal bilayer manganites (La1−zNdz)1.4Sr1.6Mn2O7 (z = 0, 0.1)

We investigate magnetoresistance, ρc, of single-crystal bilayer lanthanum manganites (La1−zNdz)1.4Sr1.6Mn2O7 (z = 0 and 0.1) at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La1.4Sr1.6Mn2O7 manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab sample plane at the temperatures T < 60 K, along with the negative magnetoresistance typical of all the substituted lanthanum manganites. In the (La0.9Nd0.1)1.4Sr1.6Mn2O7 sample, the positive magnetoresistance effect is observed at temperatures of 60–80 K in an applied field parallel to the c axis. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic...

Resonant spin-wave modes in trilayered magnetic nanowires studied in the parallel and antiparallel ground state

Brillouin light scattering has been utilized to study the field dependence of resonant spin-wave modes in layered NiFe(30nm)/Cu(10nm)/NiFe(15nm)/Cu(10nm)/NiFe(30nm) nanowires of rectangular cross section, 150nm wide and formed in arrays that are spaced laterally by 400nm. The major and minor longitudinal hysteresis curves have been measured by the magneto-optical Kerr effect technique, with applied field parallel to the length of the nanowires. The light-scattering spectra were recorded as a function of the magnetic field strength, encompassing both the parallel and antiparallel alignments of the middle stripe with respect to the magnetization direction of the outermost ones. The field ranges for the antiparallel state are different from those for the parallel case, while the mode frequencies change abruptly at the parallel-to-antiparallel transition field (and vice versa). The modes detected in the antiparallel state are found to have only a weak dependence on the applied magnetic field, whether along the major or minor hysteresis curves, while in the parallel state the mode frequencies monotonically increase with the applied magnetic field. The experimental results have been successfully interpreted, across the whole range of the magnetic fields investigated, in terms of the mode localizations across the width and in the layered structure. This was accomplished by means of a microscopic (Hamiltonian-based) theory, which has been extended here to the case of non-parallel magnetic ground states.

Optimization of the &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\hbox{BaSnO}_{3}$&lt;/tex&gt;&lt;/formula&gt; Doping Content in &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\hbox{GdBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-\delta}$&lt;/tex&gt; &lt;/formula&gt; Coated Conductors by Pulsed Laser Deposition

We tried to optimize the BaSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BSO) doping content in GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (GdBCO) coated conductors (CCs) on CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -buffered ion-beam assisted deposition (IBAD)-MgO templates. The BSO-doped GdBCO CCs with various x vol% ( x=0, 2, 3, 4, 5, and 6) relative to GdBCO were prepared at 800°C with the oxygen pressure of 300 mtorr by pulsed laser deposition (PLD), and their pinning properties were characterized by measuring magnetic hysteresis curves for the applied field parallel to the c-axis of GdBCO (B//c) up to 5 T and field-orientation dependence of transport critical currents for 1, 3, and 5 T at 65 and 77 K, respectively. Among all samples, a 5 vol% BSO-doped GdBCO CC exhibited the highest maximum pinning force density (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p,max</sub> ) values of 32.5 GN/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> near 4 T at 65 K and 6.5 GN/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> near 3.2 T at 77 K, for B//c (θ = 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> ), and also the highest minimum transport critical current density (Jc,min) of 0.39 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K in 1 T and 0.68 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 65 K in 3 T, for θ = 120 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , evidencing that 5 vol% is the optimum BSO content. Observation of BSO-doped GdBCO CCs by transmission electron microscopy revealed that the effective flux pinning of BSO-doped GdBCO CC was attributed to the BSO nanorods of ~ 10-nm diameters roughly aligned along the c-axis of the GdBCO matrix.

Dual band microwave ferromagnetic resonance absorption in annealed cobalt nanowire arrays

In this letter, we present a dual band microwave absorption phenomenon in 60 nm diameter Co ferromagnetic nanowire arrays annealed at 500 °C in nitrogen atmosphere. The frequency dependent microwave response of the wires is obtained for applied field parallel to the nanowire axis, below 4 kOe and above saturation magnetization up to 8 kOe, in steps of 1 kOe. For applied magnetic fields above saturation magnetization, two sets of absorption peaks are observed, while below saturation, only one single peak is obtained. Combining structural characterization and ferromagnetic resonance measurements, it is proven that the two ferromagnetic resonance peaks are associated with a coexistence of two kinds of nanopillars with different crystal structure in annealed nanowires, one for nanopillars with hexagonal close packed structure at higher ferromagnetic resonance frequency, and the other with face center cubic structure.

Submicrometric 2D ratchet effect in magnetic domain wall motion

Strips containing arrays of submicrometric triangular antidots with a 2D square periodicity have been fabricated by electron beam lithography. A clear ratchet effect of 180° domain wall motion under a varying applied field parallel to the walls has been observed. The direction is determined by the direction of the triangle vertices. In contrast, no ratchet effect is observed when the antidot array is constituted by symmetric rhomb-shaped antidots.

Epitaxial Co metal thin film grown by pulsed laser deposition using oxide target

We report here the growth of epitaxial Co-metal thin film on c-plane sapphire by pulsed laser deposition (PLD) using Co:ZnO target utilizing the composition inhomogeneity of the corresponding plasma. Two distinct plasma composition regions have been observed using heavily alloyed Co0.6Zn0.4O target. The central and intense region of the plasma grows Co:ZnO film; the extreme tail grows only Co metal with no trace of either ZnO or Co-oxide. In between the two extremes, mixed phases (Co+Co-oxides+Co:ZnO) were observed. The Co metal thin film grown in this way shows room temperature ferromagnetism with large in-plane magnetization ~1288emucm−3 and a coercivity of ~230Oe with applied field parallel to the film–substrate interface. Carrier density of the film is ~1022 cm−3. The film is epitaxial single phase Co metal which is confirmed by both X-ray diffraction and transmission electron microscopy characterizations. Planar Hall Effect (PHE) and Magneto Optic Kerr Effect (MOKE) measurements confirm that the film possesses similar attributes of Co metal. The result shows that the epitaxial Co metal thin film can be grown from its oxides in the PLD.

Antisymmetric magnetoresistance in SmCo5 amorphous films with imprinted in-plane magnetic 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.

Electrodeposition of Fe–Ga thin films from eutectic-based ionic liquid

Abstract In the present work, a novel process for Fe–Ga thin films electrodeposition is addressed and the magnetic properties of the films are studied. The electrodeposition was carried out under ambient conditions using an ionic liquid electrolyte consisting of a mixture of choline chloride and ethylene glycol in the molar ratio 1:2, containing 0.3 M FeCl2 and 0.1 M GaCl3, either in the absence or in the presence of oxalic acid at 4 or 17 mM concentration. The effect of oxalic acid on the discharge reaction of the single ionic species Fe2+ and Ga3+ and on their codeposition was investigated by linear sweep voltammetry, suggesting a specific action of oxalic acid on the cathodic reduction of Ga3+ ionic species. Depending on deposition potential and oxalic acid concentration, alloy films with Ga content variable in the range up to about 20 at.% could be obtained. The Fe–Ga thin films showed a disordered body-cantered cubic phase (A2) with (1 1 0) preferred orientation and columnar microstructure, with a drastic change from pyramidal to granular surface morphology revealed raising the deposition potential. No superlattice reflections, indicating the formation of the D03 structure, were observed. A vibrating sample magnetometer was employed to measure hysteresis loops by applying longitudinal and transversal magnetic field on the Fe–Ga film plane. The saturation magnetization of as-deposited film reached 1.75 T for Fe83Ga17 thin films, confirming that good quality films were obtained. For the same alloy composition, the coercivity values were 67 Oe and 200 Oe, with applied field parallel and perpendicular to the film plane, respectively.