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To identify the generation of various contributions in the electrical response of EuTiO3, a series of pure and doped, morphologically different and crystallographically oriented thin films prepared through RF magnetron sputtering and polycrystalline samples prepared through solid state reaction method have been investigated. Effect of stoichiometry, morphology and crystallographic orientation on the electrical response have been traced. Interestingly, in case of thin films, synthesis in more reducing atmosphere led to an in-plane crystallographic re-orientation from [110] to [100], accompanied by the observation of a prominent intrinsic antiferrodistortive phase transition. At temperatures above the antiferrodistorive phase transition, potential barriers to conduction at grain boundary are found to be directly proportional to the oxygen vacancy concentration, and inversely proportional to the average grain size. The relaxation times obtained from the frequency dependent dielectric response show an anomalous non-monotonic variation with temperature, which arises due to the variation of octahedral tilt angle.

We demonstrate direct probing of strong magnon–photon coupling using Brillouin light scattering (BLS) spectroscopy in a planar geometry. The magnonic hybrid system comprises a split-ring resonator loaded with epitaxial yttrium iron garnet thin films of 200 nm and 2.46 μm thickness. The BLS measurements are combined with microwave spectroscopy measurements where both biasing magnetic field and microwave excitation frequency are varied. The cooperativity for the 200 nm-thick YIG films is 1.1, and larger cooperativity of 29.1 is found for the 2.46 μm-thick YIG film. We show that BLS is advantageous for probing the magnonic character of magnon–photon polaritons, while microwave absorption is more sensitive to the photonic character of the hybrid excitation. A miniaturized, planar device design is imperative for the potential integration of magnonic hybrid systems in future coherent information technologies, and our results are a first stepping stone in this regard. Furthermore, successfully detecting the magnonic hybrid excitation by BLS is an essential step for the up-conversion of quantum signals from the microwave to the optical regime in hybrid quantum systems.

With the realization of stress-induced perpendicular magnetic anisotropy, efficient spin-orbit torque switching, and room temperature topological Hall effect, interest in rare earth iron garnets has been revived in recent years for their potential in spintronic applications. In this study, we investigate the magnetic properties of micrometer-thick Bi and Ga substituted thulium iron garnets (BiGa:TmIG) grown by the liquid-phase epitaxy method. Above the magnetization compensation (MC) temperature, anomalous triple hysteresis is observed in BiGa:TmIG/Pt heterostructures by anomalous Hall effect measurements. X-ray magnetic circular dichroism and energy dispersive spectroscopy measurements reveal its origin as an internal exchange bias (EB) effect arising from inhomogeneities localized at the surface of the film. Possibly depending on the difference in thickness and defect realization of the EB layer, two types of magnetization reversal mechanisms, namely, the Stoner-Wohlfarth type and the reversible domain-wall motion type, are observed. Our results show that rich meta-magnetic phases exist in garnets close to MC, which can be robustly tuned by chemical composition engineering and conveniently probed by electrical transport measurements.

Magnetic nanowire arrays grown in anodized alumina templates offer a fertile ground to investigate the interplay among the exchange interaction, dipolar interaction, and magnetocrystalline anisotropy. In this study, we have successfully fabricated Co nanowire arrays with gradient diameter while maintaining the nanowire separation. Consequently, we are able to obtain nanowire arrays with dominant exchange interaction at one end with small nanowire dimeter and dominant dipolar interaction at the other with large nanowire diameter. These samples show very different magnetic properties from those observed in magnetic nanowire arrays with uniformly diameter. The easy magnetization axis, coercivity, saturation field, and reversal processes are all controlled collectively by both ends of the nanowires, which cannot be viewed as the combination of magnetic nanowire arrays with thin and thick diameters.

We demonstrate simultaneous detection of current-driven dampinglike and fieldlike spin–orbit torques in heavy metal/ferromagnetic metal bilayers by measuring all three magnetization components $m_{x},m_{y}$ , and $m_{z} $ using a vector-resolved magnetooptic Kerr effect (MOKE) technique based on quadrant detection. We investigate the magnitude and direction of spin–orbit torques in a series of platinum/permalloy samples, finding good agreement with results obtained via polar and quadratic MOKE measurements without quadrant detection.

High reflection loss, wide bandwidth and low density are desirable attributes of electromagnetic wave absorption materials. Here, an ultra-thin MnO2/Fe3O4/carbon nanotube film has been synthesized in two steps using solvothermal deposition and electrochemical deposition. The Fe3O4 nanoparticles and the MnO2 sheets form a nano-scale core-shell structure on the surface of the carbon nanotube film. A series of this hierarchical composite film with different shell structures and MnO2 weight ratios were successfully synthesized. Their unique micro-structure greatly enhances the electromagnetic wave absorption capability of the composites. Instrinsic ferromagnetism is confirmed by the magnetic hysteresis loops. The strong couplings among dielectric loss, hysteresis loss and multiple scattering resulted in the reflection loss up to −42.2 dB with the bandwidth of 7.1 GHz at 10% MnO2 weight ratio for a flexible composite film of 1 mm thick.

Advanced permanent magnets based on rare-earth-free MnBi intermetallic alloys are considered energy-critical materials due to their applications in high temperature power electronics and green energy-related generators and motors, owing to their positive temperature coefficient of magnetic anisotropy. However, a direct method to achieve high saturation magnetization, without the significant loss of coercivity, is critical for attaining high performance MnBi magnets. Here, we demonstrate the synthesis and processing of magnetic nanocomposites, consisting of metal-redox MnBi nanoparticles and electro-spun FeCo nanowires. The composition ratio, processing dependent magnetism, and increased coercivity with increasing temperature, were studied in MnBi-FeCo nanocomposites. The magnetic performance of nanocomposites was dictated by interfacial coupling between magnetically hard MnBi and semi-hard FeCo nanowires, as well as the composition ratio and processing conditions. Solution processed MnBi-FeCo nanocomposites allow the potential for the development of high temperature and high performance rare-earth-free permanent magnets.

A systematic study of the electrodynamic coupling between the ferromagnetic resonance (FMR) and the cavity mode of a microwave cavity is presented. The nature of the FMR and cavity modes, described by their resonance position and line width, is measured and compared with a classical model based on the Landau–Lifshitz–Gilbert equation and an RLC circuit, which explicitly implement Faraday’s and Ampere’s laws. The relationship between the coupling gap, which can be accessed experimentally, and the coupling strength, which is a fundamental property of the FMR/cavity system, is discussed on the basis of this model. A straightforward method is experimentally developed to control the coupling gap. The capability of using such a tunable cavity-FMR coupling in combination with spin pumping could provide us with new technologies that utilize the light-matter interaction to control spin current in cavity spintronics.

NiZn spinel ferrite nanofibers with diameters in 50-100 nm were fabricated by electrospinning followed by thermal treatment. Deploying a rotating collector, nanofibers can achieve certain degree of alignment. The morphology phase contents, static, and dynamic magnetic properties of ferrite fibers were experimentally studied. Measured magnetic hysteresis loops indicate that the NiZn ferrite nanofibers are anisotropic with easy magnetization axis along the fiber alignment direction. The relationship between ferromagnetic resonant frequencies of nanofibers and bias magnetic fields was determined and can be described using a modified Kittel's formula developed for polycrystalline ferrites.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) in ultrathin magnetic thin film heterostructures provides a new approach for controlling spin textures on mesoscopic length scales. Here we investigate the dependence of the interfacial DMI constant $D$ on a Pt wedge insertion layer in Ta/CoFeB/Pt(wedge)/MgO thin films by observing the asymmetric spin-wave dispersion using Brillouin light scattering. Continuous tuning of $D$ by more than a factor of 3 is realized by inserting less than one monolayer of Pt. The observations provide new insights for designing magnetic thin film heterostructures with tailored $D$ for controlling skyrmions and magnetic domain-wall chirality and dynamics.

The magnetoresistance (MR){=[R(H) - R(0)]/R(0)} properties in ferromagnetic shape memory alloy of NiMnFeGa ribbons and single crystals, and NiFeGa ribbons have been investigated. It is found that the NiMnFeGa melt-spun ribbon exhibited GMR effect, arising from the spin-dependent scattering from magnetic inhomogeneities consisting of antiferromagnetically coupled Mn atoms in B2 structure. In the absence of these magnetic inhomogeneities, Heusler alloys seem to show a common linear MR behavior at around 0.8T(C), regardless of sample structures. This may be explained by the s-d model. At low temperatures, conventional AMR behaviors due to the spin-orbital coupling are observed. This is most likely due to the diminished MR from s-d model because of much less spin fluctuation, and is not associated with martensite phase. MR anomaly at intermediate field (rho(perpendicular to) > rho(parallel to)) is also observed in single crystal samples, which may be related to unique features of Heusler alloys. (C) 2011 Elsevier B.V. All rights reserved.

A simple theoretical analysis indicates that high permeability is possible in nanowire arrays with the magnetocrystalline anisotropy comparable to the demagnetization energy and its easy axis perpendicular to the nanowire. Both conditions can be satisfied in Co nanowire arrays. With proper fabrication conditions, we have fabricated Co nanowire arrays with crystalline easy axis perpendicular to the nanowire. For Co nanowire arrays with diameters of 50 nm and inter-pore distances of 90 nm, the real part of the permeability is about 3.5 and the loss tangent is about 0.045 below 4.5 GHz. We have also shown that by magnetizing the sample to different remanent states, its ferromagnetic resonance frequency can be tuned between 4.5 and 6.5 GHz.

Raman spectra of wurtzite CoxZn1−xS nanocrystals were investigated. Two main broad Raman peaks centered at 259 and 331 cm−1 were observed for low doping concentration, which are assigned to A1(TO) and E1(LO) phonon modes and had large redshift compared with that for bulk counterpart. It is suggested that such phenomena be attributed to phonon confinement effects, relaxation of the wave-vector selection rule due to doping effects. Besides two broad peaks, Raman spectra of high doping concentration exhibit five additional peaks at 229, 308, 340, 348, and 362 cm−1, whose relative intensities are enhanced while frequencies keep constant with increasing Co concentration due to the small reduced mass difference.

Carbon doped TiO2 nanocrystal powder samples with various C contents were synthesized by a low-temperature sol-gel method, and a large lattice C contents of 12.7% was obtained. We demonstrated that the C ions were homogenously doped into the TiO2 matrix at the form of substitutional C (Cs-o) and interstitial C (CI), without precipitation of TiC and other impurity phase. Our results show that C-doped TiO2 is ferromagnetic with the Curie temperature well above room temperature. The magnetization is mainly related to the content of Cs-o, suggesting that the intrinsic ferromagnetism originates from the Ti-C system in the TiO2 environment.

The pure single phase of Zn0.95Co0.050 bulks is successfully prepared by solid-state reaction method. The effects of annealing atmosphere on room-temperature ferromagnetic behaviour for the Zn0.95Co0.05O bulks are investigated. The results show that the air-annealed samples has similar weak ferromagnetic behaviour with the as-sintered samples, but the obvious ferromagnetic behaviour is observed for the samples annealed in vacuum or Ar/H2 gas, indicating that the strong ferromagnetism is associated with high oxygen vacancies density. High saturation magnetization Ms = 0.73 ?B/Co and coercivity Hc = 233.8 Oe are obtained for the Ar/H2 annealed samples with pure single phase structure. The enhanced room-temperature ferromagnetic behaviour is also found in the samples with high carrier concentration controlled by doping interstitials Zn (Zni).

Using Co2O3 as the Co source, doped cerium oxide thin films with the composition of Ce0.97Co0.03O2−δ (CCO) are deposited on Si(111) and glass substrates by pulse laser deposition technique. X-ray diffraction reveals that CCO films with (111) preferential orientation are grown on Si, while the film on glass is polycrystalline with nanocrystal. X-ray photoelectron spectroscopy shows that the Co displaces the Ce atom and exists in high spin state rather than low spin state, which contributes to the room-temperature ferromagnetism confirmed by vibration sample magnetometer. Films on Si and glass are different in ferromagnetism, which is believed to be induced by different film microstructures. Based on these results, the possible ferromagnetism in this insulating film is discussed. Anyway, successful fabrication of CCO films with room-temperature ferromagnetism on Si substrates is of great importance in both technological and theoretical aspects.

The authors’ theoretical investigation on the high-frequency response of magnetized metallic magnetic films showed that magnetic films may become left-handed materials (LHMs) near the ferromagnetic resonance frequency of incident waves with right-handed circular polarization (RCP) and linear polarization (LP). The frequency range where LHM exists depends on the waves polarization, the magnetic damping coefficient, and the ferromagnetic characteristic frequency ωm of the film. There also exists a critical damping coefficient αc, above which the left-handed properties disappear completely.

We have developed an experimental technique to electrically characterize ferromagnetic resonance (FMR) with a large precession cone angle by using magnetic tunnel junctions on a coplanar waveguide. We observed FMR of a Ni80Fe20 layer as the tunneling resistance change capturing the angle between the Ni80Fe20 precession magnetization and a fixed magnetization in a reference electrode. The resonant frequency shifts with increasing microwave power as a result of the large precession cone angle that reduces the effective anisotropy field. We confirmed the validity of our results by the numerical simulations based on the Landau- Lifshitz-Gilbert equation.

We report on the correlation between unidirectional and uniaxial anisotropy in exchange-biased ferromagnetic Permalloy layers. The dependence of exchange bias and coercivity on temperature and the antiferromagnetic and ferromagnetic layer thickness was studied and compared with the predictions of different theoretical models. A thorough explanation of the experimental data is provided by theoretical extension of Malozemoff's model.

New features in superconductor/ferromagnet multilayers have been observed. A nonmonotonic dependence of the superconducting Tc on the ferromagnetic layer thickness, due to the coupling across a thin magnetic layer, has been observed in both Nb/Gd multilayers and trilayers. The results are consistent with those of the predicted π-phase coupling. Effects on superconductivity due to insulating ferromagnetic layers have been observed in NbN/GdN multilayers, where the main pair-breaking effect is that of the ferromagnetic walls. The insulating ferromagnetic layers also give rise to very large superconducting critical fields.

The magnetic and electrical properties of crystalline Mn0.05Si0.95 films prepared by post-thermal treatment of the as-deposited amorphous Si-Mn (95at.%−5at.%) have been investigated. Both the temperature dependence and field dependence of magnetization were measured using superconducting quantum interference devices, and it has been indicated that the film materials are ferromagnetic with Curie temperature over 400K. X-ray diffraction analysis revealed full crystallization of the films and the incorporation of Mn into the host crystalline Si lattice. Behavior of thermally activated conduction processes of the films has been evinced by electrical property measurement for the films.

The spin-orbital interaction in heavy nonmagnetic metal/ferromagnetic metal bilayer systems has attracted great attention and exhibited promising potentials in magnetic logic devices, where the magnetization direction is controlled by passing an electric current. It is found that the spin-orbital interaction induces both an effective field and torque on the magnetization, which have been attributed to two different origins: the Rashba effect and the spin Hall effect. It requires quantitative analysis to distinguish the two mechanisms. Here we show sensitive spin-orbital effective field measurements up to 10 nm thick ferromagnetic layer and find the effective field rapidly diminishes with the increase of the ferromagnetic layer thickness. We further show that this effective field persists even with the insertion of a copper spacer. The nonlocal measurement suggests that the spin-orbital effective field does not rely on the heavy normal metal/ferromagnetic metal interface.

By incorporating magnetic particles into elevated temperature-curing adhesives, or hot-meltable thermoplastics, induction fields can be used to heat bondlines and join composite adherends. In this article we investigate the fundamental heating behaviors of such magnetic particles in order to aid in the design and selection of improved magnetic materials. Magnetic inductive heating tests were performed on two types of magnetic materials: Co2Ba2Fe12O22 semihard ferrites and NiFe2O4 soft ferrites. The Curie temperatures of these ferrites were also varied through Zn substitution. All of the samples clearly demonstrated Curie temperature-controlled final heating behavior. The magnitude of heat generation has been related to dc magnetic hysteresis measurements, with reasonable agreement. Deviations are theorized to be due to domain wall resonance effects.

A simple and effective method has been developed to coat soft ferromagnetic particles (e.g., FeCo alloy) with a thin (1–3 nm) CoFe2O4 or NiFe2O4 layer. A general tendency of coercivity enhancement after the ferrites coating has been observed, which we ascribe to the exchange coupling between the ferromagnetic core and the ferrimagnetic coating shell. Using explosion compaction technique, the ferrite-coated particles were compacted into fully dense bulk material with density very close to the ideal value. The impedance of the compacted sample was measured in the frequency range of 1 kHz–100 MHz. The real part of measured impedance for our compacted sample is very high and decreases with increasing frequency much slower than a standard ferrite sample in the range of 35 kHz–4.2 MHz. While the hysteresis loops at 5 K for free-standing ferrite-coated particles cooled under 5 T field show a few tens Oe shift in the negative field direction indicating a typical antiferromagnetic-like exchange coupling behavior, the compacted bulk materials give symmetrical hysteresis loops in both field or zero-field cooling. This may be understood in the context of exchange coupling in random anisotropic systems. Our results are promising for high frequency magnetic devices applications.A simple and effective method has been developed to coat soft ferromagnetic particles (e.g., FeCo alloy) with a thin (1–3 nm) CoFe2O4 or NiFe2O4 layer. A general tendency of coercivity enhancement after the ferrites coating has been observed, which we ascribe to the exchange coupling between the ferromagnetic core and the ferrimagnetic coating shell. Using explosion compaction technique, the ferrite-coated particles were compacted into fully dense bulk material with density very close to the ideal value. The impedance of the compacted sample was measured in the frequency range of 1 kHz–100 MHz. The real part of measured impedance for our compacted sample is very high and decreases with increasing frequency much slower than a standard ferrite sample in the range of 35 kHz–4.2 MHz. While the hysteresis loops at 5 K for free-standing ferrite-coated particles cooled under 5 T field show a few tens Oe shift in the negative field direction indicating a typical antiferromagnetic-like exchange coupling behavior, ...

The strength of the exchange bias field is found to influence the low-frequency magnetoresistive noise associated with the magnetic reference layer in sputtered-deposited and electron-beam-evaporated CoFeB/MgO/CoFeB tunnel junctions. The noise is due to magnetic losses arising in the reference layer. The losses are parameterized by a phase lag e which exhibits a nontrivial dependence on the externally applied field. The general trend found among all devices is that the losses are largest in the antiparallel state. The effect of exchange bias on the reference layer’s noise is investigated at a field corresponding to maximum resistance susceptibility, Href. Higher values for the phase lag at Href, eref, are found in devices having a large exchange bias field. We also observed that Href and eref are larger in devices having thicker seed layers. This characteristic is also evident in double-barrier magnetic tunnel junctions. Prolonged thermal annealing is found to decrease eref, reduce Href, and alter the field profile of the resistance susceptibility of the reference layer to resemble that of a more magnetically soft behavior. In addition to its impact on the magnetoresistive noise, the incorporation of exchange bias layers into the materials stack also affects the tunneling magnetoresistance ratio with higher values found at smaller exchange bias fields. We attribute the magnitude of the magnetic losses, and hence the magnetoresistive noise, from the reference layer to disorder in its magnetic microstructure. Our results indicate that the nature and degree of disorder are correlated to the strength of the exchange bias coupling. The origin of this correlation may be due to a competition between different microstructures among various layers, one that leads to coherent tunneling (large tunneling magnetoresistance) in MgO-based tunneling devices and the other which promotes strong exchange bias coupling. A decrease in the exchange bias either through degradation from thermal treatments or by varying the thickness of the underlying seed layer will lead to less magnetic disorder in the system. We show that the magnetoresistive noise can be used to probe magnetic disorder in exchange-biased devices through the determination of the magnetic losses.

Platinum (Pt) metal, being nonmagnetic and with a strong spin-orbit coupling interaction, has been central in detecting the pure spin current and establishing most of the recent spin-based phenomena. Magnetotransport measurements, both electrical and thermal, conclusively show strong ferromagnetic characteristics in thin Pt films on the ferromagnetic insulator due to the magnetic proximity effects. The pure spin current phenomena measured by Pt, including the inverse spin Hall and the spin Seebeck effects, are thus contaminated and not exclusively established.

We propose a model for giant magnetoresistance (GMR) in granular magnetic solids where the moments within a grain form a single ferromagnetic domain. The electrical transport properties of such solids due to (1) the scattering from grains that act as centers for the potential barrier and (2) the magnetic scattering due to the dipole-dipole interaction between a ferromagnetic domain and spin of a conduction electron are calculated. The magneto-conductance computed as a function of the grain size and the global magnetization shows that GMR in magnetically inhomogeneous media may arise from the interplay between the potential-barrier and the magnetic scatterings.

Room temperature ferromagnetism in polycrystalline Co(x)Ce(1-x)O(2-δ) (0.001≤x≤0.10) bulk samples has been investigated. Annealing in the forming gas transformed the as-prepared paramagnetic into a ferromagnetic insulating material with over two orders of magnitude enhancement (from 3.7 × 10(-2) to 1.24 μ(B)/Co) in the magnetization. Structural characterization of both the as-prepared and H(2)-treated samples showed a single phase material. The incorporation of Co with the formation of oxygen vacancies in the oxide lattice was revealed by x-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies is indicated by the existence of mixed valence states of cerium (Ce(4+) and Ce(3+)) in the high resolution XPS 3d spectrum. The role of the donor defects (oxygen vacancies) has been verified through the removal of oxygen vacancies. The ferromagnetic insulating ground state has been explained in terms of the interaction of the F(+) center and 3d magnetic cations. The connection between magnetic properties, electronic structure of the magnetic impurity and donor defect has been established. First principle calculations have been performed using the full potential linearized augmented plane wave method within the density functional theory (DFT) framework; these support our experimental findings. Both the experiment and calculations reinforced the crucial role of oxygen vacancies.

The competition between the interface crystallization and diffusion processes, their influence on the onset of symmetry-filtering coherent tunneling of ${\ensuremath{\Delta}}_{1}$ band electrons in the MgO-based magnetic tunnel junctions is investigated. Systematic study of the transport and magnetoresistance during thermal annealing of these junctions shows a unique behavior of the tunneling conductance in the parallel state. The optimal annealing time for achieving giant tunneling magnetoresistance at different temperatures is determined. The evolution of magnetoresistance consists of three distinct regions, responsible by different contributions from CoFeB electrodes and the MgO barrier. The whole phenomenon can be understood through an empirical model based on the Landauer tunneling picture.

The TbCo/Si multilayers prepared by the rf magnetron sputtering system with various Si thickness have been investigated. X-ray diffraction, magnetic measurement and Kerr rotation have been performed. No antiferromagnetic coupling was found for the system. With the thickness of Si layer tSi increasing, the perpendicular anisotropy constant Ku, and the saturation magnetization Ms decreased rapidly. It was assumed that Co2Si and Tb had been formed in the interfacial zone between TbCo and Si layers due to the interlayer diffusion. The decreasing of Ms is attributed to the decreasing of the effective thickness of magnetic layer.

The mechanical properties of Ag‐Al2O3 and Ni‐Al2O3 granular metal films, as well as the magnetic behavior of the nickel‐based films, is presented. Enhancements in the mechanical properties of these materials, as measured by low load indentation techniques, were observed for a metal volume fraction p of about 0.55. This volume fraction corresponded to the percolation threshold pc as determined from the magnetic measurements. A peak in the compliance as a function of p was observed, similar to elastic anomalies reported for small bilayer period superlattices. A discontinuity in the rate of change of hardness as a function of p was also observed, and believed to result from a change in deformation mechanism at pc.

Chromium doped zinc telluride thin films with various doping concentrations are fabricated by magnetron sputtering. These films are ferromagnetic and the Curie temperature increases with Cr concentration. X-ray diffraction, transmission electron microscopy, and magnetic circular dichroism characterizations show that the films are free of Cr1-xTex impurities and the ferromagnetism is intrinsic. The transport study shows that the resistivity and magnetoresistance are governed by variable range hopping at low temperatures. A negative magnetoresistance as large as -57% is observed at 5 K. The magnetoresistance and its temperature dependence can be well explained by a model involving an increase in the localization length of carriers with a magnetic field in the hopping region. An anomalous Hall effect is also observed and a possible origin of the sign difference between the anomalous Hall resistance and ordinary Hall resistance is discussed.

We have conducted a systematic study on the effect of Cu-site doping in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ system. The relations between ${\mathit{T}}_{\mathit{c}}$ and doping level as well as the critical doping levels ${\mathit{x}}_{\mathit{c}}$ have been determined accurately for the Fe-, Co-, Ni-, Zn-, Ga-, and Al-doped systems. Every dopant either carries an intrinsic magnetic moment or induces a net moment on the Cu-${\mathrm{O}}_{2}$ plane. The size of the moment is correlated with the suppression of superconductivity, consistent with the magnetic-pair-breaking effect. The ground states of the dopants have also been determined.

We report the electrical detection of magnetization dynamics in an $\mathrm{Al}/{\mathrm{AlO}}_{x}/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Cu}$ tunnel junction, where a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ ferromagnetic layer is brought into precession under ferromagnetic resonance conditions. The dc voltage generated across the junction by the precessing ferromagnet is enhanced about an order of magnitude compared to the voltage signal observed when the contacts in this type of multilayered structure are Ohmic. We discuss the relation of this phenomenon to magnetic spin pumping and speculate on other possible underlying mechanisms responsible for the enhanced electrical signal.

Off-axis electron holography was used to investigate the barrier profile of the Py/AlOx/ZrOy/Py magnetic tunnel junctions with different ZrOy thicknesses. The tunneling magnetoresistance (TMR) has a strong dependence on bias voltage and the bias voltage for maximum TMR is shifted from zero. This shift increases with ZrOy barrier thickness due to the increasing barrier asymmetry in the junctions. The evolution of barrier asymmetry was directly observed by the phase change of the off-axis electron holography, which unambiguously shows the barrier profile changes from triangular to trapezoidal shape as increasing of ZrOy thickness.

We have carefully designed an experiment to elucidate the interface and bulk contributions to spin-polarized transport in CoFe-based magnetic tunnel junctions (MTJ's). We demonstrated that the bulklike contribution to tunneling magnetoresistance (TMR) exists in the magnetic tunneling process, which is determined by the tunneling characteristic length of the ferromagnetic electrodes. This characteristic length in MTJ's is different from the spin diffusion length in metallic based spin valves or magnetic multilayers due to the fundamental different transport behaviors in two structures. The experiment designed with a wedge-shaped CoFe layer inserted at the interface between the insulating barrier and reference electrode offers a unique and simple way to determine this characteristic length, which is about 0.8 nm for the CoFe electrode. For interfacial contributions to dominate TMR, the magnetic electrodes should have a very short tunneling characteristic length of atomic scale.

In this Letter, we investigated the influence of the fast thermal treatment on the spin pumping in ferromagnetic insulator yttrium iron garnet (YIG)/normal metal Au bilayer system. The YIG/Au bilayer thin films were treated by fast annealing process with different temperatures from 0 to 800 °C. The spin pumping was studied using ferromagnetic resonance. The surface evolution was investigated using a high resolution scanning microscopy and an atomic force microscopy. A strong thermal related spin pumping in YIG/Au bilayer system has been revealed. It was found that the spin pumping process can be enhanced by using fast thermal treatment due to the thermal modifications of the Au surface. The effective spin-mixing conductance of the fast thermal treated YIG/Au bilayer has been obtained.

We report the first results of magnetic properties and giant magnetoresistance of granular permalloy in a metallic matrix. These new materials have resistivities comparable to those of the ferromagnetic alloys currently used in magnetoresistive devices, but yield significantly larger magnetoresistance effects that are nearly isotropic.

Granular Co-Ag materials with low Co contents exhibit giant magnetoresistance and single domain magnetic properties. In this paper, we discuss unusual hysteresis behavior that we have observed in Co rich samples, where the magnetization is approximately linear with the applied field up to saturation, and the coercivity and remnant magnetization are both nearly zero. We attribute this unusual behavior to a perpendicular anisotropy that depends on the nanostructure in the phase-segregated materials. These results are corroborated by magnetic domain imaging using scanning electron microscopy with polarization analysis (SEMPA).

Superconductor/insulating-ferromagnet NbN/GdN multilayers reveal that the superconducting properties of the NbN layers are dominated by the insulating nature of the GdN layers, which curtail the pair-breaking effect despite the strong ferromagnetism. The effects of ferromagnetic walls on superconducting slabs have been captured. Very large parallel critical fields have also been observed.

Ultrafast demagnetization processes in ferromagnetic films have been shown to produce terahertz (THz) emission. We present an experimental demonstration that, following ultrafast optical excitation, the magnitude of terahertz electromagnetic pulses emitted from a ferromagnetic film is proportional to the Gilbert damping constant, which is conventionally used to describe the damping of magnetization precession. The damping of a ferromagnetic thin film is tuned by using an adjacent nonmagnetic layer, which does not change the magnetization and anisotropy of the ferromagnetic film, allowing an unambiguous determination of the relationship between the THz emission and the damping constant.

The contrasting effects of ion implantation and thermal annealing on structural and magnetic properties of Co/Pd multilayers have been studied. Ion implantation causes local damage to the multilayers, resulting in enhanced magnetization due to the polarization of the neighboring Pd. Thermal annealing generates massive interdiffusion across the interfaces into the formation of Co-Pd alloys with a lower magnetization. Effects on coercivity and remanence have also been studied.

A quantitative method to detect ferromagnetic resonance using magnetic tunnel junction structure has been developed. Experimental results reveal three distinct regions for single elliptical permalloy film of micrometer lateral size. Above the spin wave instability threshold, the experimental results show a linear response of the longitudinal magnetization component to the microwave field amplitude over a large range rather than a lock-up phenomenon appeared in macroscopic permalloy films and then a phase limiting behavior. The linear behavior can be described by the theoretical model describing subsidiary resonance.

The tunneling magnetoresistance and perpendicular magnetic anisotropy in CoFeB(1.1-1.2 nm)/MgO/CoFeB(1.2-1.7 nm) junctions were found to be very sensitively dependent on annealing time. During annealing at a given temperature, decay of magnetoresistance occurs much earlier compared to junctions with in-plane magnetic anisotropy. Through a rapid thermal annealing study, the decrease of magnetoresistance is found to be associated with the degradation of perpendicular anisotropy, instead of impurity diffusion as observed in common in-plane junctions. The origin of the evolution of perpendicular anisotropy as well as possible means to further enhance tunneling magnetoresistance is discussed.

This letter reports a demonstration of microwave assisted magnetization reversal (MAMR) in a CoFeB film and the damping dependence in MAMR through the measurement of ferromagnetic resonance (FMR). Spin-pumping in non-ferromagnetic/ferromagnetic films provides a large range variation of Gilbert damping constants in magnetic samples when changing the thickness of non-ferromagnetic layers without changing the ferromagnetic film. An evident dependence of switching fields on the damping constant is observed in the presence of microwaves. The trend of the experimental data is well reproduced by a numerical simulation based on the Landau–Lifshitz–Gilbert equation. The result indicates that the large damping decreases the efficiency of microwaves in reducing the magnetization switching field.

We studied the real-time evolution of magnetic dynamic and static properties of 20 nm CoFeB thin film during annealing at 380 °C. The ferromagnetic resonance linewidth quickly reduces by 30% within 300 s annealing, and monotonically increases upon longer annealing. The magnetic static coercivity shows similar trend. The underlying physical relation between linewidth and anisotropy can be connected by the two-magnon scattering theory. By doping of Nb into CoFeB films, the damping was maintained at a low value within 2000 s annealing. This method to tailor the dynamic properties of CoFeB may benefit the development of magnetics and spintronics based microwave devices.

Since the discovery of giant magnetoresistance (GMR) in Fe/Cr multilayers1, the magneto-transport properties of magnetic multilayers have received considerable attention over the past few years2–12. The GMR effect is of fundamental importance in that it reveals the interplay between electron transport and magnetism. It has been associated with the existence of antiferromagnetic exchange coupling between the ferromagnetic layers across the non-magnetic layers2, 3. Furthermore, the electrical resistivity of some of these multilayers can be reduced by as much as a factor of two upon the application of an external magnetic field1; the sheer size of this effect makes these materials potential candidates for magneto-resistive applications. A number of other magnetic multilayer systems, such as Co/Ag4and (Ni81Fe19)/Cu5, have also been found to exhibit the GMR effect as the result of extensive research efforts.

We report on the evolution of equilibrium magnetoresistive (MR) 1/f noise due to the exchange-biased magnetic layer in MgO-based magnetic tunnel junctions as a function of annealing time at 380 and 430 °C. The resistance susceptibility and MR noise are observed to increase rapidly with annealing time at a fixed temperature. The magnetic losses responsible for MR noise are not significantly affected by the structural crystallization at the CoFeB/MgO interface during short annealing times. After prolonged annealing, the decrease in magnetic losses is attributed to reduced disorder in the magnetic layers that result in thermally driven fluctuations in local micromagnetic structure.

We have investigated the evolution of the magnetic transport properties as a function of short annealing time in CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJs) with a free layer of 2 nm. It is found that the hysteresis behaviors in magnetoresistance (MR) loops disappear in samples annealed for 17 min. The linear region between MR and the applied field gradually increases. The MR loops without hysteresis can be well fitted by using the superparamagnetism theory, suggesting the formation of superparamagnetic particles in the free layer during the high temperature annealing. The control of MTJ properties with annealing time is desirable in magnetic field sensor productions.

The low-frequency resistance noise in sputtered-deposited magnetic tunnel junctions with MgO barriers has been measured as a function of annealing time at different annealing temperatures. The noise has a 1/f spectrum and it is quantified by a Hooge-like parameter α given in units of μm2. Unannealed devices have the highest noise levels and their α parameters exhibit a pronounced dependence on the voltage bias across the junction. A significant increase in tunneling magnetoresistance (TMR) is observed for short annealing times (on the order of minutes) at high temperatures and it is correlated with a large reduction in noise and in its bias dependence. The maximum TMR and minimum noise levels are reached at a later time that depends on temperature, being shorter at higher annealing temperatures. Devices annealed at 380 and at 430 °C exhibit the same minimum noise levels, α≈2×10−10 μm2. The origin of the resistance noise, its annealing time evolution, and its bias dependence are discussed and they are attr...