In-plane Angular Dependence Research Articles

Ferromagnetic Resonance Study of Magnetic Anisotropy in Epitaxial Fe<sub>3</sub>O<sub>4</sub> Thin Film

Ferromagnetic resonance (FMR) is used to investigate the magnetic anisotropy of a 25.5 nm thin Fe <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">4</sub> film above and below its Verwey transition temperature (TV). Epitaxial smooth film of Fe <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">4</sub> is deposited by oxygen-assisted molecular beam epitaxy. FMR spectra are recorded using a 9.49 GHz Brucker EMX system from 80 K to room temperature with a magnetic field applied along [100] direction. The resonance field (Hr) and linewidth (AH) are extracted by fitting the FMR line with a Lorentzian function. Temperature dependence of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and ΔH shows a transition at T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> . Furthermore, the data of in-plane angular dependence of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> at 300 and 83 K indicated a change in symmetry from fourfold to twofold below TV, consistent with a transformation of Fe <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">4</sub> from cubic (fourfold) to monoclinic (twofold) structure with its easy axis switching from [110] to [100]. Complex symmetry pattern is found in angular dependence of ΔH below TV, which is attributed to the in-plane twinning of Fe <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">4</sub> lattice.

In-plane angular-dependent exchange bias and blocking temperature of a Cr2O3 () film system prepared by post annealing

A ()-oriented Cr2O3 film was prepared, and the in-plane angular dependence of both its exchange bias (Hex) and blocking temperature (TB) were investigated. By changing the applied magnetic field direction, we modulated the relative angle between the magnetic anisotropy direction of Cr2O3 and the applied magnetic field direction. We found that TB ∼ Néel temperature (TN) for a sufficiently large relative angle, while TB is smaller than TN for a small relative angle, reflecting a change in the effective exchange coupling energy. By tuning the applied magnetic field direction, we demonstrated extrinsic control of Hex and TB.

Noncollinear ferromagnetic easy axes in Py/Ru/FeCo/IrMn spin valves induced by oblique deposition

We present an investigation on the magnetic properties of Py/Ru/FeCo/IrMn spin valves grown by dc magnetron sputtering. The sample fabrication setup has two important features, (i) the five magnetron sputtering sources are placed in a cluster flange 72° from each other, and (ii) each source is tilted with respect to the sample normal. In-plane angular dependence of the ferromagnetic resonance (FMR) was used to obtain the relevant magnetic anisotropies, such as uniaxial and exchange bias fields. The oblique deposition geometry employed has induced non-collinear easy axes of the two ferromagnetic (FM) layers, with high uniaxial field strengths. The symmetry shift of the angular dependence of the FMR resonances of the two FM layers gives us directly the angle between the easy axes of FM1 (Py) and FM2 (FeCo), which turned out to be the angle between two adjacent sputtering sources. The observations of the present study suggest that, by combining oblique deposition and appropriate angles of incidence of the deposition flux, the uniaxial (and unidirectional) axes of individual FM layers can be precisely engineered in spin valve fabrication.

Spin Reorientation Transition and Magnetization Reversal Mechanism of Gd Doped FeCo High-Frequency Soft Magnetic Thin Films

The magnetic FeCoGd thin films with various sputtering power from 10 to 30 W were fabricated on glass substrates by magnetron co-sputtering. The crystal structure of as-deposited FeCoGd thin films was investigated by X-ray diffraction. And an increasing trend of grain size with the increasing sputtering power was shown. When sputtering power is below 30 W, the films exhibited obviously in-plane uniaxial magnetic anisotropy, and the in-plane magnetic anisotropy field Hkdecreased with increasing deposition power. Moreover, good high frequency characteristics were obtained. The magnetization reversal mechanism has been investigated via the in-plane angular dependences of the magnetization and the coercivity. The experimental data points indicated that the magnetization reversal mechanism of FeCoGd film with in-plane uniaxial anisotropy is domain-wall depinning and coherent rotation when the applied field is close to the easy axis and hard axis, respectively. A spin reorientation transition phenomenon was observed when deposition power is larger than 30 W. A stripe domain structure for the sample with 30 W deposition power was developed due to a dominated perpendicular magnetic anisotropy.

In-plane polarization dependence of (Bi,Pb)2Sr2CaCu2O8+δ single crystals studied by X-ray absorption spectroscopy

The effects of in-plane polarization change on the determination of the hole density of weakly under-doped (Bi, Pb)-2212 single crystals has been studied by x-ray absorption spectroscopy (XAS). The XAS signal at the CuL3 edge (925–940eV) and O K edge (525eV to 539eV) were recorded under continuous rotation of the CuO2 plane from 0° to 180° with a minimum increment of 1.8°, yielding experimentally an in-plane polarization dependence for the absorption signals at the respective threshold. From that the in-plane angular dependence of the hole density (nH(φ)) could be determined. Fermi׳s golden rule was then used for the evaluation of the in-plane polarization dependence showing the expected polarization independence in disaccord to the experimental observations. Possible scenarios to solve this issue are discussed. Our results propose that polarization dependence could be due to inhomogeneous distribution of holes in the CuO2 planes which is also supported by models. Second, the role of out of plane orbitals has to be taken into account for interpretation.

In-Plane Anisotropy of Flux-Flow Resistivity in Layered Organic Superconductor λ-(BETS)2GaCl4

We recently observed in-plane fourfold-symmetric anisotropy in the flux-flow resistivity (FFR) of d-wave organic superconductor κ-(ET)2Cu(NCS)2. Origin of the fourfold-symmetric anisotropy was discussed in terms of the interplay between the Josephson-vortex dynamics and the superconducting gap structure. Here, we report the in-plane anisotropy of the FFR of layered organic superconductor λ-(BETS)2GaCl4. The in-plane angular dependence is mainly described by twofold symmetry. The dip structure appears when the magnetic field is applied parallel to the c-axis. These results are different from the case of κ-(ET)2Cu(NCS)2, even though the Fermi-surface topology of λ-(BETS)2GaCl4 is much similar to that of κ-(ET)2Cu(NCS)2. The different anisotropic behavior is discussed in terms of interlayer coupling strength.

Tunable in-plane uniaxial anisotropy and the magnetization reversal mechanism of patterned high-frequency soft magnetic FeTa strips

FeTa films with thickness of 110 nm are fabricated on glass substrates by magnetron sputtering, and then a series of strips is designed on the FeTa films by conventional optical lithography and the ion beam etching method. Patterned FeTa strips show a tunable in-plane uniaxial magnetic anisotropy property in contrast with the magnetic isotropic property of as-deposited FeTa thin films. The magnetization reversal mechanism of the patterned FeTa strips is investigated via the in-plane angular dependences of magnetization and coercivity. The angular dependence of coercivity (ADC) is explained well in terms of the two-phase model, giving good quantitative agreement with the experimentally measured M-shaped ADC curve. The domain structure and spatial resolution magneto-optical Kerr effect measurement indicate that the smaller the strip width, the stronger will be the anisotropy field. Regarding the dynamic magnetic properties, a transformation from Debye dispersion spectrum for strips with weak anisotropy to natural resonance spectrum for strips with strong anisotropy is finally obtained. The tunable in-plane anisotropy fields of the FeTa strips result in tunable high-frequency soft magnetic properties by altering the strip width, indicating that patterned FeTa strips have great potential in high-frequency soft magnetic application fields.

NiFe 박막의 두께에 따른 강자성 공명 특성 분석

본 연구에서는 NiFe 박막 시편을 마그네트론 스퍼터링 방법으로 제조하여 박막면 기준으로 수직면(out-of-plane) 자기장 방향과 수평면(in-plane) 자기장 방향에 따른 강자성 공명 자기장을 측정하였다. 수직면 자기장 방향에 따른 강자성 공명 자기장으로부터 유효자화량(<TEX>$M_{eff}$</TEX>)을 도출하였으며, NiFe 두께에 따른 <TEX>$M_{eff}$</TEX>의 감소는 <TEX>$K_s=-0.23\;erg/cm^2$</TEX>의 값을 갖는 표면 이방성 상수에 기인하였다. 또한 수평면 자기장 방향에 따른 강자성 공명 자기장으로부터 수평면에서의 일축 이방성 자기장을 도출하였다. 한편, 일축 이방성 에너지의 자화 용이축이 두께가 감소함에 따라 시편 제조 시 인가한 자기장의 반대 방향으로 회전하고 있었으며, 이러한 현상은 시편 표면에 형성된 NiFeO의 반강자성 특성에 의한 현상으로 설명하였다. The out-of-plane and in-plane angular dependence of ferromagnetic resonance field was measured in NiFe thin films fabricated by magnetron sputtering. The effective magnetization was obtained from the out-of-plane angular dependence of ferromagnetic resonance field, which was well agreed with calculated one. The decrease of effective magnetization with NiFe thickness was due to the surface anisotropy constant of <TEX>$K_s=-0.23\;erg/cm^2$</TEX>. The in-plane uniaxial anisotropy fields were obtained from the in-plane angular dependence of ferromagnetic resonance field. The easy axis of in-plane uniaxial anisotropy field was rotated to the reverse direction of applied magnetic field during sample fabrication, which was explained by the antiferromagnetic NiFeO layer at sample surface.

NiFe/CoFe/Cu/CoFe/MnIr spin valves studied by ferromagnetic resonance

Ion-beam deposited (Glass/Ta/NiFe/CoFe/Cu/CoFe/MnIr/Ta) spin valves (SVs) with a Cu-spacer thickness (tCu) varying from 14 to 28 Å have been studied by ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements. With respect to the interlayer coupling strength between the free and fixed ferromagnetic layers, the samples have been divided in those with a weak coupling (for tCu &amp;gt; 16 Å) and a strong coupling regimes (for tCu ≤ 16 Å). The FMR behavior in these two regimes is quite different. For the weakly coupled series, there are two well-defined FMR peaks stemming from the free and fixed layers. Their in-plane angular dependences exhibit 180° and 360° symmetries, respectively. For the strongly coupled SVs, the resonance modes are hybridized and possess features of both layers simultaneously. The main coupling mechanism between the two layers, as concluded from the FMR and MR measurements, is the Néel “orange-peel” magnetostatic interaction, accompanied by a direct exchange due to pinholes in the Cu spacer for tCu &amp;lt; 17 Å.

The Fulde–Ferrell–Larkin–Ovchinnikov state in layered d-wave superconductors: in-plane anisotropy and resonance effects in the angular dependence of the upper critical field

We study the anisotropy of the in-plane upper critical magnetic field coupled to the orbital motion and the spins of electrons in a layered dx2−y2 organic superconductor in the spatially modulated Fulde–Ferrell–Larkin–Ovchinnikov phase. We show that the interplay between the nodal structure of the order parameter and its spatial modulation results in the very peculiar angular dependence of the onset of superconductivity in the high-field regime. The principal axis of the field-direction dependence of the onset of superconductivity is tilted by π/4 in the temperature range 0.056 ≲ T < 0.56. In some cases the resonance between the modulation wavevector and the vector potential of a parallel magnetic field may lead to anomalous cusps in the temperature and in-plane angular dependences of the onset of superconductivity. The obtained results support the interpretation of the recent experiments as evidence of the FFLO state.

Interface magnetism of iron grown on sulfur and hydrogen passivated GaAs(001)

Sulfur (S) and hydrogen (H) atom passivated GaAs(001) templates were used for deposition of ultrathin crystalline Fe films using molecular beam epitaxy, where the Fe thickness ranged from 10 to 45 atomic layers. Reflection high-energy electron diffraction patterns showed that the S- and H-passivated surfaces had no and very weak (1 × 2) superlattice reconstructions, respectively. This indicates that these GaAs(001) templates have a square-like symmetry. Magnetic anisotropies were investigated using the in-plane angular dependence of ferromagnetic resonance at 36 GHz. The in-plane cubic and uniaxial anisotropies and perpendicular uniaxial field were described by bulk and interface contributions, indicating that the Fe films have a high lattice coherence. The magnetic properties of the Fe films were compared to those grown on more commonly used GaAs(001) templates having a (4 × 6) reconstruction with an As-rich in-plane uniaxial symmetry. The Fe films grown on S-passivated templates exhibited unique magnetic properties caused by a decreased lattice spacing compared to the bulk Fe.

AC heat capacities of κ-(BEDT-TTF)2Cu2(CN)3 measured by microchip calorimeter

Thermodynamic measurements of an organic spin liquid compound of κ-(BEDT-TTF)2Cu2(CN)3 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene were performed by the ac calorimetry technique using a microchip device of TCG3880. This technique is effective to measure relative temperature and magnetic-field dependences of heat capacity for tiny single crystal samples less than 1μg. Broad hump structures in Cp vs T which are known as so-called 6 K anomaly were observed in κ-(BEDT-TTF)2Cu2(CN)3 and its deuterated compound. The hump temperatures are evaluated as 5.7 K in both compounds. This result demonstrates that the TCG3880 is useful for performing thermodynamic investigations of such kind of organic charge transfer complexes with much reduced sample quantity than the conventional techniques and that the existence of hump structure is intrinsic for κ-(BEDT-TTF)2Cu2(CN)3. The in-plane angular dependence of the magnetic field of 7 T applied parallel to the two dimensional layer is also studied and absence of in-plane anisotropy of the hump structure is discussed in both pristine and deuterated compounds.

Magnetic Properties of Single Crystalline Co2MnAl Heusler Alloy Thin Films

Ferromagnetic resonance measurements were carried out for single crystalline Co2MnAl thin films as a function of the angle between applied external magnetic field and normal of the film surface. In- and out-of-plane angular dependence of the resonance field and only out-of-plane angular dependence of the linewidth of FMR spectra were analyzed using the Landau–Lifshitz–Gilbert equation. The easy and hard axes were determined by analyzing the in-plane angular dependence of resonant field. The films annealed at various temperatures showed four-fold magnetic anisotropy symmetry and the damping factor was estimated from the analysis of the angular dependency of FMR spectra.

Analysis of the weak coupling of the IrMn/Co/Ru/NiFe structures by ferromagnetic resonance

The Ir20Mn80/Co/Ru/Ni81Fe19 spin valve structures have been produced by sputtering deposition and analyzed by ferromagnetic resonance. Two well resolved modes are identified in the FMR spectra as the resonance of the Co and NiFe layers. The in-plane angular dependence of the resonance peaks for the NiFe layer present a small asymmetry, which is attributed to the interlayer exchange interaction between ferromagnetic layers across the nonmagnetic spacer. The data were analyzed considering the exchange bias at the IrMn/Co interface and the indirect coupling between Co and NiFe. The in-plane angular dependence of the resonance fields of both Co and NiFe layers present an upward (downward) shift for antiferromagnetic (ferromagnetic) coupling with respect to a system with no interlayer coupling.

Spin dynamics and magnetic anisotropies at the Fe/GaAs(001) interface

20Au/(d)Fe/GaAs(001) structures were deposited using molecular beam epitaxy, where Fe thickness d = (5...90) atomic layers. Interface anisotropies were investigated using the in-plane angular dependence of ferromagnetic resonance (FMR). Intrinsic and extrinsic contributions to magnetic damping were investigated using FMR linewidth (ΔH) measurements at 9, 24, 36, and 72 GHz (in-plane configuration) and 9, 24, and 36 GHz (perpendicular configuration). The in-plane cubic and uniaxial perpendicular anisotropies were well described by the bulk and interface contributions indicating that the Fe films have a high lattice coherence and high critical Curie temperature Tc. The in-plane uniaxial anisotropy is more complex and will be discussed in detail. The frequency dependence of ΔH(f) was analyzed using the Gilbert damping, two magnon scattering, and long range magnetic inhomogeneity contributions. The thickness dependence of the Gilbert damping parameter α was found to be well described by the bulk and interface terms.

Low-temperature onset of the spin glass correlations in the ensemble of oriented Stoner–Wohlfarth nanoparticles

We reveal the low-temperature anomaly in the temperature and angular dependencies of the coercivity in granular (CoFeB)x–(SiO2)1−x films with oriented in-plane anisotropy. Namely, at T&amp;lt;100 K the in-plane angular dependence of coercive field acquires two maxima corresponding to easy and hard (in a film plane) directions. This signifies the emergence of coercivity for hard direction in a film plane. The experimental results are explained in terms of a random field model, which describes the onset of spin glass-like correlations in the ensemble of oriented weakly interacting Stoner–Wohlfarth particles.

Antiferromagnetic layer thickness dependence of noncollinear uniaxial and unidirectional anisotropies in NiFe/FeMn/CoFe trilayers

We have investigated the dependence of magnetic anisotropies of the exchange-biased NiFe/FeMn/CoFe trilayers on the antiferromagnetic (AF) layer thickness $({t}_{\text{AF}})$ by measuring in-plane angular-dependent ferromagnetic resonance fields. The resonance fields of NiFe and CoFe sublayers are shifted to lower and higher values compared to those of single unbiased ferromagnetic (F) layers, respectively, due to the interfacial exchange coupling when ${t}_{\text{AF}}\ensuremath{\ge}2\text{ }\text{nm}$. In-plane angular dependence of resonance field reveals that uniaxial and unidirectional anisotropies coexist in the film plane, however, they are not collinear with each other. It is found that these peculiar noncollinear anisotropies significantly depend on ${t}_{\text{AF}}$. The angle of misalignment displays a maximum around ${t}_{\text{AF}}=5\text{ }\text{nm}$ and converges to zero when ${t}_{\text{AF}}$ is thicker than 10 nm. Contributions from thickness-dependent AF anisotropy and spin frustrations at both F/AF interfaces due to the structural imperfections should be accounted in order to understand the AF-layer thickness dependence of noncollinear magnetic anisotropies.

Anisotropic Josephson-vortex dynamics in layered organic superconductors

To study the anisotropic Josephson-vortex dynamics in the d-wave superconductors, the interplane resistance has been measured on layered organic superconductors κ ‐ ( ET ) 2 Cu ( NCS ) 2 and β ‐ ( BDA ‐ TTP ) 2 SbF 6 under magnetic fields precisely parallel to the conducting planes. For κ ‐ ( ET ) 2 Cu ( NCS ) 2 , in-plane angular dependence of the Josephson-vortex flow resistance is mainly described by the fourfold symmetry and dip structures appear when the magnetic field is applied parallel to the b- and c-axes. The obtained results have a relation to the d-wave superconducting gap symmetry. However, the absence of in-plane fourfold anisotropy was found for β ‐ ( BDA ‐ TTP ) 2 SbF 6 . The different anisotropic behavior is discussed in terms of the interlayer coupling strength.

Properties of inductance and magnetic penetration depth in (103)-orientedYBa2Cu3O7−δthin films

We present a study of the anisotropy of the inductance in (103) ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) films. YBCO superconducting quantum interference devices (SQUIDs) were fabricated by the biepitaxial technique. SQUIDs with (001)- and (103)-oriented YBCO electrodes characterized by different grain-boundary angles were realized on the same chip. Two extrainjection lines were attached to the (103) YBCO electrode. These devices, when operated in current injection mode, allow us to measure the inductance of the (103) YBCO electrode. We have found that the inductance $L$ of the (103) YBCO can differ by a factor of 20 in the two extreme cases: $L$ determined by current transport parallel to the $ab$ planes and $L$ dominated by the transport in the $c$-axis direction. The full in-plane angular dependence of the inductance has been obtained by considering geometrically identical SQUIDs oriented with different angles with respect to the [100] direction of the (103) film. From these measurements, we have determined the London penetration depths in the $ab$ direction ${\ensuremath{\lambda}}_{ab}$ and the $c$ direction ${\ensuremath{\lambda}}_{c}$ and their temperature dependence.

Ferromagnetic Resonance Study of Annealed NiFe/FeMn/CoFe Trilayers

The effect of a thermal treatment on the exchange field in 19-nm NiFe(bottom)/15-nm FeMn/19-nm CoFe(top) trilayers has been investigated by employing a vibrating sample magnetometer (VSM) and a ferromagnetic resonance (FMR) spectrometer. FMR spectra as a function of applied dc field reveal that there are two distinct resonance peaks corresponding to each ferromagnetic layer. It is found that exchange fields determined from the in-plane angular dependence of the resonance field are in accord with that determined through the magnetic hysteresis loops for the NiFe/FeMn interface rather than the CoFe/FeMn one. A FMR linewidth broadening as a function of the annealing temperatures is attributed to the interdiffusion between the two magnetic interfaces across a FeMn layer.