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Pendant droplets of water and paramagnetic solutions are studied in the presence of uniform and nonuniform magnetic fields produced by small permanent magnet arrays, both in static conditions and during dynamic pinch-off. Static measurements of the droplet shape are analyzed in terms of an apparent surface tension γapp or an effective density ρeff. The change of surface tension of deionized water in a uniform field of 450 mT is insignificant, 0.19 ± 0.21 mNm−1. Measurements on droplets of compensated zero-susceptibility solutions of Cu2+, Mn2+, and Dy3+, where the shape is unaffected by any magnetic body force, show changes of surface tension of about −1% in 500 mT. Magnetic field gradients of up to 100 T2 m−1 deform the droplets and lead to changes of ρeff that are negative for diamagnetic solutions (buoyancy effect) and positive for paramagnetic solutions. The droplet profile of strongly paramagnetic 0.1 molar DyCl3 solution is analyzed, treating the nonuniform vertical field gradient as a spatial variation of gravity. The influence of Maxwell stress on the droplet shape is discussed. In dynamic measurements, the droplet shape at pinch-off is recorded by high-speed photography and analyzed in terms of a relative change of dynamic surface tension in the presence of a magnetic field. The surface-tension-dependent prefactor of the scaling law that governs the pinch-off dynamics shows no difference for pure water or 0.11 M DyCl3 solutions in the field. The nonuniform field has no influence in the pinch-off region because the filament diameter is much less than the capillary length.

We present the nanofabrication and transport properties of single silicon nanowires (NWs) having mean widths in the range from sub-30 to 500 nm. Hall effect measurements are undertaken in the magnetic fields of 14 T at 300 K. The NWs are defined by electron-beam lithography (EBL) using the negative tone resist hydrogen silsesquioxane (HSQ) as a mask for reactive ion etching (RIE). Silicon NWs are patterned on nonuniform highly doped n-type silicon-on-insulator (SOI) substrates. The doping profile has been observed to show a significant effect on the NW electrostatics, which in turn influences the contact and transport properties of the NWs. For the formation of Hall electrodes, we have employed an angled substrate evaporation technique, where the NW itself is used as a shadow mask and an intimate sidewall contact has been formed. The Hall electrodes are not opposite to each other in this case; therefore, the longitudinal resistance pickup had to be considered when extracting the Hall signal of the NW. The mobility of these NWs is discussed. For the narrowest 40-nm-wide silicon NW, the obtained value of mobility is 292 ± 6 cm2/Vs and, for the blanket, nonpatterned device layer, it is 100 ± 0.1 cm2/Vs. The effective mobility increases as the width of the NWs decreases. This is attributed to the reduced dimensionality of the electron transport in the NWs. Both the electrical and effective thicknesses of the NW change at small physical width, which results in enhanced electron transport within the channel and enhances the value of the measured Hall signal.

The ongoing miniaturization of devices and development of wireless and implantable technologies demand electromagnetic interference (EMI)-shielding materials with customizability. Additive manufacturing of conductive polymer hydrogels with favorable conductivity and biocompatibility can offer new opportunities for EMI-shielding applications. However, simultaneously achieving high conductivity, design freedom, and shape fidelity in 3D printing of conductive polymer hydrogels is still very challenging. Here, an aqueous Ti

Ultra-thin soft magnetic amorphous ribbons of Co-Fe-B-Si-Nb alloy were synthesised by a single step rapid-quenching approach to acquire advantage of improved material performance and lower costs over commercial amorphous alloys. The amorphous ribbons of approximately 5.5 µm thicknesses were quenched by a single roller melt spinner in a single-step production process and characterised for their structural and magnetic properties. The disordered atomic structure of amorphous ribbons was confirmed by the X-ray diffraction. A surface morphology study revealed the continuity of ultra-thin ribbons without pores over a large scale. The amorphous alloy showed the ultra-soft magnetic properties in the as-quenched state. The observed thickness dependency of the magnetic properties was attributed to the increased surface roughness and possibly due to a lack of densely packed atomic structure resulting from the extremely high cooling rates experienced by ultra-thin ribbons. We propose that in-situ thinning process of amorphous ribbons significantly reduces the basic material cost and eliminates the need for post-processing steps; hence it provides the opportunity for mass production of high-performance soft magnetic amorphous ribbons at relatively lower costs.

Following its discovery in the aftermath of Nd2Fe14B, Sm2Fe17N3 seemed to offer intrinsic magnetic properties that were superior or comparable to those of its famous predecessor. But the promise of the new material to challenge Nd2Fe14B was not realized, mainly because the 2:17 nitride powder, prepared by a low-temperature gas-phase interstitial modification process, was unstable at the temperatures needed to process dense sintered magnets. Here we discuss the magnetic properties of Nitroquench, a melt-spun Sm-Fe-N material, which offers superior corrosion resistance and thermal stability compared to melt-spun Nd-Fe-B. The powder, with a crystallite size of approximately 30 nm is in the form of flakes 15–18 µm thick and about 100 µm in diameter. Room-temperature coercivity is 690 kAm−1 after saturation in 14 T, with a remanence of 92 Am2kg−1 and an extrapolated saturation magnetization of 160 Am2kg−1. The remanence enhancement is reflected in a preferred orientation seen in 57Fe Mossbauer spectra of magnetized isotropic powder, which exhibits different relative intensities of the ΔM = 0 absorption lines according to the direction of the field used to saturate the magnetization. When measured in zero internal field, the remanence ratio Mr/Ms is 64%. The remanence enhancement is attributed to a nanocrystallite size that is not very much greater than the exchange length. The maximum energy product for the powder, assuming full density, is 162 kJm−3. Nitroquench powder may be used to produce bonded magnets with an energy product >100 kJm−3.

All-optical re-switching has been investigated in the half-metallic Heusler ferrimagnet Mn2Ru0.9Ga, where Mn atoms occupy two inequivalent sites in the XA-type structure. The effect of a second 200 fs 800 nm pump pulse that follows a first pulse, when both are above the threshold for switching, is studied as a function of t12, the time between them. The aims are to identify the physical mechanisms involved and to determine the minimum time needed for re-switching. The time trajectory of the switching process on a plot of sublattice angular momentum, S4a vs S4c, is in three stages; When t < 0.1 ps, the sublattice moments are rapidly disordered, but not destroyed, while conserving net angular momentum via optical spin-wave excitations. This leads to transient parallel alignment of the residual Mn spins in the first quadrant. The net angular momentum associated with the majority sublattice then flips in about 2 ps, and a fully-reversed ferrimagnetic state is then established via the spin-lattice interaction, which allows re-switching provided t12 > 10 ps., 13 pages - 4 figures

We report on first-principles calculations of spin-transfer torque (STT) in epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal Mn$_3$Ga electrodes, both as analyzer in an Fe/MgO stack, and also in an analogous stack with a second Mn$_3$Ga electrode (instead of Fe) as polarizer. Solving the ballistic transport problem (NEGF + DFT) for the nonequilibrium spin density in a scattering region extended to over 7.6 nm into the Mn$_3$Ga electrode, we find long-range spatial oscillations of the STT decaying on a length scale of a few tens of angstroms, both in the linear response regime and for finite bias. The oscillatory behavior of the STT in Mn$_3$Ga is robust against variations in the stack geometry and the applied bias voltage, which may affect the phase and the amplitude of the spatial oscillation, but the wave number is only responsive to variations in the longitudinal lattice constant of Mn$_3$Ga (for fixed in-plane geometry) without being commensurate with the lattice. Our interpretation of the long-range STT oscillations is based on the bulk electronic structure of Mn$_3$Ga, taking also into account the spin-filtering properties of the MgO barrier. Comparison to a fully Mn$_3$Ga-based stack shows similar STT oscillations, but a significant enhancement of both the TMR effect at the Fermi level and the STT at the interface, due to resonant tunneling for the mirror-symmetric junction with thinner barrier (three monoatomic layers). From the calculated energy dependence of the spin-polarized transmissions at 0 V, we anticipate asymmetric or symmetric TMR as a function of the applied bias voltage for the Fe-based and the all-Mn$_3$Ga stacks, respectively, which also both exhibit a sign change below 1 V. In the latter (symmetric) case we expect a TMR peak at zero, which is larger for the thinner barriers because of a spin-polarized resonant tunneling contribution., 15 pages and 15 figures

We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn

We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pulses are studied to reveal the roles played by the spin and intersublattice exchange. We find a two-step demagnetization process, similar to the well-established case of Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization rates. The behaviour is analysed using a four-temperature model, assigning different temperatures to the two manganese spin baths. Even in this strongly exchange-coupled system, the two spin reservoirs have considerably different behaviour. The half-metallic nature and strong exchange coupling of Mn$_2$Ru$_x$Ga lead to spin angular momentum conservation at much shorter time scales than found for Gd(FeCo)$_3$ which suggests that low-power, sub-picosecond switching of the net moment of Mn$_2$Ru$_x$Ga is possible., 5 pages, 3 figures, J. Phys.: Condens. Matter (2021)

Compensated ferrimagnets are promising materials for fast spintronic applications based on domain-wall motion as they combine the favorable properties of ferromagnets and antiferromagnets. They inherit from antiferromagnets immunity to external fields, fast spin dynamics, and rapid domain-wall motion. From ferromagnets they inherit straightforward ways to read out the magnetic state, especially in compensated half metals, where electrons flow in only one spin channel. Here, we investigate domain structure in compensated half-metallic ${\mathrm{Mn}}_{2}{\mathrm{Ru}}_{0.5}\mathrm{Ga}$ films and assess their potential in domain-wall motion-based spin-electronic devices. Our focus is on understanding and reducing domain-wall pinning in unpatterned epitaxial thin films. Two modes of magnetic reversal, driven by nucleation or domain-wall motion, are identified for different thin film deposition temperatures (${T}_{\mathrm{dep}}$). The magnetic aftereffect is analyzed to extract activation volumes (${V}^{*}$), activation energies (${E}_{\mathrm{A}}$), and their variation ($\mathrm{\ensuremath{\Delta}}{E}_{\mathrm{A}}$). The latter is decisive for the magnetic reversal regime, where domain-wall motion dominated reversal (weak pinning) is found for $\mathrm{\ensuremath{\Delta}}{E}_{\mathrm{A}}l0.2\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ and nucleation dominated reversal (strong pinning) for $\mathrm{\ensuremath{\Delta}}{E}_{\mathrm{A}}g0.5\phantom{\rule{4pt}{0ex}}\mathrm{eV}$. A minimum $\mathrm{\ensuremath{\Delta}}{E}_{\mathrm{A}}=28\phantom{\rule{4pt}{0ex}}\mathrm{meV}$ is found for ${T}_{\mathrm{dep}}=290{\phantom{\rule{4pt}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Prominent pinning sites are visualized by analyzing virgin domain patterns after thermal demagnetization. In the sample investigated they have spacings of order 300 nm, which gives an upper limit of the track width of spin-torque domain-wall motion-based devices.

Energy-efficient control of magnetization without the help of a magnetic field is a key goal of spintronics. Purely heat-induced single-pulse all-optical toggle switching has been demonstrated, but so far only in Gd-based amorphous ferrimagnet films. In this work, we demonstrate toggle switching in films of the half-metallic ferrimagnetic Heusler alloys Mn2RuxGa, which have two crystallographically-inequivalent Mn sublattices. Moreover, we observe the switching at room temperature in samples that are immune to external magnetic fields in excess of 1 T, provided they exhibit a compensation point above room temperature. Observation of the effect in compensated ferrimagnets without Gd challenges our understanding of all-optical switching. The dynamic behavior indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis for fast optical switching of magnetization and break new ground for engineered materials that can be used for nonvolatile ultrafast switches using ultrashort pulses of light., Femtosecond laser pulses allow for extremely fast switching of magnetization in ferromagnetic films, but all examples so far contained gadolinium. Here the authors demonstrate room temperature all-optical toggle switching in a ferrimagnetic manganese-based half-metal without gadolinium.

$\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ permanent magnets are of great technological interest due to their good magnetic performance and excellent thermal stability. The Fe content plays a key role for magnetic properties, determining the maximum energy product and the highest working temperature. Here we investigated the Fe site preferences in $\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ magnets with Fe content up to 26 wt. %, the solubility limit in sintered magnets by first-principles calculations. It is shown that Fe dissolves preferably in the rhombohedral $\mathrm{T}{\mathrm{h}}_{2}\mathrm{Z}{\mathrm{n}}_{17}$-type (2:17 $R$) phases, with a strong preference for the dumbbell ($6c$) sites. After $6c$ sites are fully occupied, Fe distributes in $18f$ sites as scattered as possible. The crystal structures of 2:17 $R$ type $\mathrm{S}{\mathrm{m}}_{2}{(\mathrm{Co},\phantom{\rule{0.16em}{0ex}}\mathrm{Fe})}_{17}$ lattice were presented with varying Fe content. The calculated structure and magnetic properties were analyzed comparing with experimental results of 2:17 $R$ phases in multicomponent alloys. Also, the gradually increased substitution energy with continuous doping explained the difficulty in preparation of $\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ magnets with much Fe.

Structural, magnetic and electromechanical changes resulting from spin crossover between the spin quintet and spin triplet forms of a mononuclear Mn

Phase transformation driven soft magnetic properties have been correlated through different stages of nano-crystallization of Co-based amorphous alloys, via transverse magnetic annealing, by combining structural, magnetothermal, domain imaging, and AC/DC magnetometry techniques. The nano-crystallization starts by nucleation and growth process of soft magnetic meta-stable, thermodynamically favored, Co23B6 phase with less nucleation activation energy compared to other stable phases. In the second crystallisation stage, Co2B and Co3B, as a semi-hard magnetic phase, are identified in the alloys, magnetically annealed at 525 and 550 °C, respectively. Field-induced anisotropy dominates over the residual contributions of magneto-crystalline anisotropy of the phases, precipitated after field annealing at 510, 515, and 525 °C. The anomalous loss is significantly reduced as by annealing in a transverse magnetic field due to the reorientation of the preferred magnetisation axis, and consequently, change in dominant magnetization reversal mechanism from domain wall motion to magnetization rotation. In addition, magnetic annealing causes a measurable decrease in the domain width, which, in turn, promotes pinning and inhibits domain wall motion, thus further favours coherent domain rotation as the primary mechanism of magnetization. The combined mechanism of nanocrystallisation and coherent magnetisation rotation accounts for a 70% decrement in the anomalous loss in the so-processed ribbons at 525 °C, which renders them attractive for applications in mid- and high-frequency power supplies and inverters.

Repeated uniform switching of the magnetization of thin films of ferrimagnetic amorphous Gdx(FeCo)1−x in response to single fast laser pulses is well established. Here, we report unusual toggle switching in thin films of sperimagnetic amorphous DyxCo1−x and TbxCo1−x with x ≈ 0.25 irradiated with single 200 fs pulses of 800 nm laser light. The samples have strong local random anisotropy due to the non-S state rare earth. The compensation temperature of the films is ≤180 K, and their Curie temperature is ≈500 K. They are largely switched by the first pulse, and subsequent pulses lead to partial re-switching of a decreasing amount of the irradiated area, with a granular structure of submicrometer regions of switched and unswitched material. Individual switched regions about 700 nm in size are observed around the edge of the irradiated spots where the fluence is at the threshold for switching. Results are discussed in terms of a random anisotropy model where the ratio of local anisotropy to exchange is temperature dependent.

Although printed networks of semiconducting nanosheets have found success in a range of applications, conductive nanosheet networks are limited by low conductivities (10

Three natural specimens of hematite are characterized using X-ray diffraction, magnetometry, IR/Raman and Mossbauer spectroscopy, with focus on the Morin transition. All are exfoliated by grinding and prolonged sonication in dimethylformamide, followed by centrifuging to extract exfoliated debris from the supernatant. This material is characterized by electron microscopy and atomic force microscopy. There are three main Fe2O3 constituents: lamellae that are hundreds of nanometers in diameter and typically 1–10 nm thick, nanoparticles that are about 100 nm in size and ultra-fine nanoparticles smaller than 10 nm. Estimated yield of the lamellae is 10−3−10−4 by volume. All the iron in the debris is antiferromagnetically ordered at room temperature, including 30% that is superparamagnetic and contributes to a quadrupole doublet in the Mossbauer spectrum, but the characteristic weak net moment due to spin canting is absent. Unlike the normal hematite nanoparticles, there is no Morin transition and no net moment in the range of 100 to 300 K. The absence of a net moment is understandable because the lamellae cleave in planes that make small angles with the c-axis.

A thermodynamics-based approach, Calculation of Phase Diagram (CALPHAD), combined with topological instability parameters are proposed and experimentally evaluated, in order to optimise in-situ nanocrystallisation of rapidly quenched CoFeB alloys and exploit their remarkable Bs = 1.57 T. The high Ms of the alloy is attributed to the precipitation of the metastable Co7Fe3 nanocrystalline phase dispersed heterogeneously in the amorphous matrix. High Ms of Co7Fe3 phase can also be inferred from the high hyperfine magnetic field of the Fe nuclei deduced from Mossbauer spectra. It is worth noting that the in-situ nanocrystallisation is a volume phenomenon, instead of surface crystallisation at the air-side of ribbons owning to lower cooling rates. We judge, based on nucleation theory, that the formation of the metastable phase is kinetically favoured, when compared to the equilibrium phases, hence promoting the high Ms, when compared with conventional Co-rich amorphous alloys. The local atomic order of nanocrystallised phase was confirmed by X-ray and electron diffraction techniques. Using Mossbauer spectroscopy and the extracted distribution of the hyperfine magnetic field, it is asserted that cobalt atoms form clusters, as they attract each other to form ordered structures, and boron atoms undergo only short-range ordering, likely due to covalent bond formation, governed by the size and electronegativity differences with the atoms in the amorphous matrix. We suggest the proposed CALPHAD-assisted design of nanostructured alloys, along with an in-situ nanocrystallisation, provides a practical scheme to develop novel functional alloys with the best possible balance of coercivity and saturation, exclusively aimed for a high-tech application.

An increase in microwave permeability is a prerequisite for reducing the thickness of radar absorber coatings. The aim of this paper is to increase the magnetic loss of commercial carbonyl iron particles for fabricating wideband microwave absorbers with a multilayer structure. For this purpose, carbonyl iron particles were milled and their static and dynamic magnetic properties were studied before and after milling. A distinct morphological change from spherical to flake-like particles is measured with increased milling time, whereas no distinct changes in magnetic properties are measured with increased milling time. The imaginary part of the permeability (µ״) of the milled carbonyl iron particles increased from 1.23 to 1.88 and showed a very broad peak over the entire frequency range 1–18 GHz. The experimental results were modeled using the Rousselle effective medium theory (EMT) in the Neo formulation. The theoretical predictions showed good agreement with the experimental results. Two layer absorbers were designed according to the measured microwave parameters and the multilayer design. The results revealed that a thin multilayer with a thickness of 1.75 mm can effectively absorb microwaves in both the entire X and Ku frequency bands. The results suggest that microwave absorbers with excellent absorption properties could be mass-produced, using commercial carbonyl iron particles.

The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin‐film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m-3 is combined with a saturation magnetization of μ0>7sub>Ms = 0.52 T at 2 K (2.2 MJ m-3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare‐earth‐free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m-1 K-1, make Rh2CoSb a candidate for the development of heat‐assisted writing with a recording density in excess of 10 Tb in.-2.

The authors experimentally resolve the pulse- and temperature-dependent limits of single-shot alloptical magnetic switching in the compensated three dimensional ferrimagnet, revealing that the process is driven by exchange relaxation.

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Here we study both static and time-resolved dynamic magnetic properties of the compensated ferrimagnet from room temperature down to 10K, thus crossing the magnetic compensation temperature $T_{M}$. The behaviour is analysed with a model of a simple collinear ferrimagnet with uniaxial anisotropy and site-specific gyromagnetic ratios. We find a maximum zero-applied-field resonance frequency of $\sim$160GHz and a low intrinsic Gilbert damping $\alpha$$\sim$0.02, making it a very attractive candidate for various spintronic applications., Comment: 6 pages, 6 figures, accepted paper in PRB (https://journals.aps.org/prb/accepted/df07aOb2T7f1e845c21429304f825e825c3a5f190)

Over the past decade intensive research has focused on the use of plasmonic structures and metamaterials for the control of electromagnetic radiation. Response of such structures is highly dependent on factors set during fabrication, such as the combination of materials used and as well as their structural dimensions. Despite having many promising optoelectronic applications, the inability to tune the optical response of such structures post fabrication presents serious limitations. To overcome this, we present tunable plasmonic elements formed of plasmonic nanostructures on a thin film of vanadium dioxide (VO 2 ), a phase change material. VO 2 is an attractive option as a phase change material due to its large, reversible transition from a semiconducting to a metallic phase at a critical temperature of 68°C, close to room temperature. While much research on VO 2 is centred on the large changes in the optical properties occurring in the NIR spectral range (above 1 μώ) upon the phase transition, in this work we focus on the changes in the dielectric function of VO 2 in the visible spectral range. In particular, we experimentally and numerically investigate the possibility to use the phase change of VO2 to dynamically tune the plasmonic properties of noble metal nanostructures as well as to manipulate the emission properties of quantum emitters near plasmonic nanostructures. We observe a drastic change in the plasmonic properties of gold nanorods arrays fabricated on a thin layer of VO 2 as the phase transition from the semiconducting to metallic phase of VO 2 is thermally triggered. Upon phase transition, a >50% decrease in scattering in the red spectral region, especially around 650 nm, was detected in dark field scattering experiments (Figure 1a). Moreover, our spectrally and time resolved measurements reveal that the emission properties of quantum dots (CdSeS/ZnS) in the vicinity of the gold nanorod arrays can be modified through the thermal phase change of the underlying thin layer of VO 2 (Figure 1b). When VO 2 is in its semiconducting phase the photoluminescence (PL) of QDs on the nanorods array is quenched compared to the PL of QDs on the same VO 2 thin film but off the array. In contrast, we observe an enhanced light emission of QDs on the array when the VO 2 layer is in its thermally actuated metallic phase. Additionally, the main PL emission peaks of QDs on the nanorod arrays as well as off the arrays red shift by 15 nm, as an effect of heating. The experimental results are accompanied by supporting FDTD simulations.

Soft magnetic amorphous materials with ultra-low power loss are highly desirable for high-frequency drive applications. The present work demonstrates the high-frequency power loss performance and underlying loss mechanisms in ultra-thin amorphous alloys. This is achieved by rapid-quenching amorphous alloys of Co-, CoFe- and Fe-rich systems, investigating their amorphous atomic structure, quantifying the saturation magnetostriction constants (λs), imaging magnetic domains at remanent magnetization, analyzing magnetization reversal from various magnetization levels, and finally, investigating the material loss performance over a broad frequency range (f = 50 kHz–2 MHz) at various excitation levels (Bm = 25–100 mT). The ultra-high performance of ultra-thin Co-rich amorphous ribbons, as compared to CoFe- and Fe-rich alloys, was attributed to the significantly low eddy current loss, due to the reduced thickness, and a minimal amount of excess loss, owning to minimal magnetoelastic contributions and magnetization reversal by rotation. The underlying loss mechanisms were analyzed by decomposing material loss into primary components and identifying the magnetization reversal mechanisms using minor hysteresis loops. In the Co-rich amorphous alloys, we suggest that magnetization reversal by rotation dominates, at least at low excitations, while in CoFe- and Fe-rich alloys domain wall displacement prevails and contributes significantly to the excess loss up to the MHz frequency range. Magnetization reversal by rotation in Co-rich alloys could be attributed to the zero/near-zero λs, and eventually low residual stress, leading to a homogeneous magnetic domain structure, as compared to the inhomogeneous “fingerprint-like” complex domains in highly magnetostrictive CoFe-rich alloys.

A new approach to magnetic switching by spin–orbit torque uses interlayer exchange coupling to overcome the need for an external magnetic field. Manipulation of the magnetization of a perpendicular ferromagnetic free layer by spin–orbit torque (SOT)1,2,3,4 is an attractive alternative to spin-transfer torque (STT) in oscillators and switches such as magnetic random-access memory (MRAM) where a high current is passed across an ultrathin tunnel barrier5. A small symmetry-breaking bias field is usually needed for deterministic SOT switching but it is impractical to generate the field externally for spintronic applications. Here, we demonstrate robust zero-field SOT switching of a perpendicular CoFe free layer where the symmetry is broken by magnetic coupling to a second in-plane exchange-biased CoFe layer via a nonmagnetic Ru or Pt spacer6. The preferred magnetic state of the free layer is determined by the current polarity and the sign of the interlayer exchange coupling (IEC). Our strategy offers a potentially scalable solution to realize bias-field-free switching that can lead to a generation of SOT devices, combining a high storage density and endurance with a low power consumption.

Structural, magnetic and electromechanical changes resulting from spin crossover between the spin quintet and spin triplet forms of a mononuclear Mn3+ complex embedded in six lattices with different charge balancing counterions are reported. Isostructural ClO4- and BF4- salts (1) and (2) each have two unique Mn3+ sites which follow different thermal evolution pathways resulting in a crossover from the spin quintet form at room temperature to a 1:1 spin triplet:quintet ratio below 150 K. The PF6- (3) and NO3- (4) salts which each have one unique Mn3+ site show a complete conversion from spin quintet to spin triplet over the same temperature range. A complete two step spin crossover is observed in the CF3SO3- lattice (5) with a 1:1 ratio of spin quintet and spin triplet forms at intermediate temperature, while the BPh4- lattice (6) stabilizes the spin triplet form over most of the temperature range with gradual and incomplete spin state switching above 250 K. An electromechanical piezoresponse was detected in NO3- complex 4 despite crystallization in a centrosymmetric space group. The role of defomations associated with strain-induced spin triplet-spin quintet switching in breaking the local symmetry are discussed and computational analysis is used to estimate the energy gap between the two spin states.

The mechanisms that limit the power loss performance in melt-spun amorphous ribbons have been investigated through DC and AC magnetic characterization methods. The measured total power loss is resolved into hysteresis, eddy current, and anomalous losses. The anomalous loss is found to account for more than 90% of the total loss, which significantly reduced by annealing in a transverse magnetic field. This is attributed to the reorientation of preferred magnetisation axis perpendicular to the length of ribbons. Transverse magnetic annealing promotes the relative contribution of domain rotation over domain wall motion during magnetisation reversal process. Magnetic annealing also causes a measurable decrease in the domain width, which promotes pinning and inhibits domain wall motion, thus further favoring coherent domain rotation as the primary mechanism of magnetization. This combination accounts for a 75% decrease in the total power loss in the so-processed ribbons and renders them attractive for applications in mid-and high-frequency power supplies and inverters.

As-cast ingots of Mn100−xZx with Z = Al, Ge, Mn, Fe and Co all have the A13 βMn structure up to some maximum value of x. The magnetic susceptibility of pure βMn is ≈ 9 × 10−4 from 4 to 400 K, but the field-cooled and zero-field-cooled susceptibilities of all doped samples increase at low temperature and they bifurcate at a spin-freezing temperature Tf that increases with x, linearly at first. Point contact Andreev reflection shows evidence of a net spin polarization in a spin glass sample but not in the pure βMn spin liquid. Fixed-moment density functional calculations indicate a very shallow energy minimum (

We show how a charge current through a single antiferromagnetic layer can excite and control self-oscillations. Sustained oscillations with tunable amplitudes and frequencies are possible in a variety of geometries using certain classes of non-centrosymmetric materials that exhibit finite dissipative spin-orbit torque. We compute the steady-state phase diagram as a function of the current and spin-orbit torque magnitude. The anisotropic magnetoresistance causes the conversion of the resulting AF oscillations to a terahertz AC output voltage. These findings provide an attractive and novel route to design terahertz antiferromagnetic spin-orbit torque oscillators in simple single-layer structures., 5 pages, 3 figures and a supplemental material

An experimental time-domain, room-temperature study of magnetization precession in ultra-thin Mn3-xGa films excited by femtosecond laser pulses is presented. The thickness dependence of the parameters of THz waves emitted from coherently driven magnetic resonances is investigated.

A flux source with four rotatable permanent magnet rods having access from two perpendicular directions through gaps exceeding the rod diameter can produce a continuously-variable flux density of up to ±300 mT at the centre when high-grade Nd-Fe-B magnets are used. The trade-off between field, access and torque in this mangle design is discussed. The maximum field, achievable when the magnets touch, is equal to the remanence of the Nd-Fe-B. The torque needed to rotate the rods scales as the square of the remanence, and it increases faster than the inverse square of the separation when the separation is comparable to the rod diameter. End effects reduce the torque significantly, but appropriate gearing is needed to ensure smooth operation. Modifications of the basic design can reduce or compensate the torque by using special end pieces, and improve access to fields > 1000 mT at small rod separation.

Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn2RuxGa in pulsed magnetic fields of up to 58T. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature (155K), where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673Ω−1 m−1 and the coercivity exceeds 9T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216kJm−3 and predict the magnetic resonances frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems.

The characterisation of BaTiO 3 thin films by direct piezoelectric effect microscopy (DPFM) is presented. The technique allows for both the mapping of the polarisation of the surface, by imaging lines of constant electrostatic force over a polarised region, but also for the characterisation of the direct piezo coefficient, via the acoustically excited, lock-in demodulated, induced piezo-voltage response of the same region. The ability to objectively discriminate between piezo-effect and surface polarisation is crucial for the characterisation of artificial multiferroic stacks, where the polarisation response of buried layers can be masked by conductive caps, but the piezo response persists.

$\text{Mn}_{2}\text{Ru}_{\mathrm{x}}\text{Ga}$ (MRG) is a fully compensated half-metallic ferrimagnet [1]. We aim to engineer the position of the Fermi level in MRG thin films to modify the spin polarisation. Previous investigations of magnetoresistance of MRG indicate that the Fermi level is positioned below the middle of the gap [1]. DFT calculations show that $\text{Mn}^{4a}-\text{Ga}^{4b}$ antisites provide $\sim 1$ electron/antisite thereby increasing the electronic pressure in $\text{Mn}_{2}\text{Ru}_{\mathrm{x}}\text{Ga}$ thin films and raising the Fermi level [2]. To investigate this effect, Mn-deficient and Mn-rich MRG films with varying Ru content, were prepared by magnetron sputtering. The structural properties of the films were investigated using X-ray diffraction spectroscopy and X-ray reflectometry. The electronic and magnetic properties were investigated using the Anomalous Hall effect and the Van der Pauw method. Our results show that the $\text{Mn}^{4c}$ occupancy can be controlled. Films with low Ru content show an increase in Hall angle up to 2% in Mn-rich films. These films can be expected to have high spin polarization which can be verified using point contact Andreev reflection (PCAR) measurements.

This work reports the successful fabrication of an all-oxide heteroepitaxial structure with a bilayer tunnel junction consisting of ferroelectric and ferrimagnetic layers. Each layer of the structure exhibits high crystallinity and well-defined interfaces. The transport properties of the junction are found to be well described by the characteristics of an asymmetric ferroelectric tunnel junction.

Here two new techniques for the detection of broadband (100 MHz–20 GHz) ferromagnetic resonance (FMR)/ferrimagnetic resonance in single and poly-crystalline materials, which rely on SQUID-based gradiometry detection of small changes in the magnetisation, are developed. In the first method, small changes in the along-the-applied-field projection of the coupled magnetic moment (Δmz) are detected as the material is driven into resonance. Absolute measurement of the longitudinal component of the magnetisation and the resonance induced lowering of this moment makes estimation of the precession cone angle accessible, which is typically difficult to extract using conventional cavity or stripline based detection methods. The second method invokes the change in Δmz with the resonance-induced thermal heating dmzdT. Magnetisation dynamics in bulk Y3Fe5O12 are observed over a broad range of experimental temperatures (4 K–400 K) and fields (10–500 mT). The inhomogeneous microwave excitation allows for the observation ...

Advances in power conversion technologies have highlighted the need for development of new class of magnetic components (inductors, transformers etc) with lower footprint and higher efficiency. Presently, the sizes of these magnetic components have been limited due to the use of low flux density ferrite as a core material. In this paper, the assembly and working of an amorphous ribbon transformer with low loss performance as a replacement for ferrite based ones were studied. The minimum amount of power loss of the material was measured as

The discovery of the interstitial rare earth nitride Sm 2 Fe 17 N 3 came about seven years after the discovery of the rare earth iron boride Nd 2 Fe [1],[2], and the nitride initially seemed to offer intrinsic magnetic properties that were superior (Curie temperature $T_{C}$, magnetocrystalline anisotropy $K_{1})$ or comparable (spontaneous magnetization $M_{s})$ to those of its illustrious predecessor. However, the promise of the new material to seriously chal- lenge Nd 2 Fe 14 B was not realized. The 2:17 nitride powder, prepared by a low-temperature gas-phase interstitial modification process proved difficult to orient and worse still, it lost its nitrogen at the temperatures needed to process dense sintered magnets [3]. Attempts at explosive compaction [4] or spark sintering [5] failed to yield material with good enough coercivity. Nevertheless, work continued in Japan and China to develop a coercive powder that could be used for bonded magnets. An early realization was zinc-bonded Sm 2 Fe 17 N 3 [6] with an energy product of 84 kJm 3 but a rather low coercivity of 480 kAm $^{-1}$, less than 5 % of the anisotropy field $( H_{a} \quad = 2 K_{1}/ M_{s} \approx 11$ MAm $^{-1})$. The anisotropy field of Nd 2 Fe 14 B is significantly less (6 MAm $^{-1})$ yet several decades of intensive development have led to higher values and continuous improvements of the coercivity, even in unsubstituted material. Historical experience with permanent magnets shows that a long period of materials development is needed to arrive at the best composi- tion and processing conditions tfor a microstructure that allows the hard magnetism to be optimized. Coercivities of about 25% of the anisotropy field are utimately achieved. Here we compare the magnetic properties of melt-spun material. Our Nitroquench powder, produced by Daido Steel, was in the form of flakes $10 \mu \mathrm {m}$ thick and up to $100 \mu \mathrm {m}$ in diameter. A crystal- lite size of approximately 15 nm deduced from Scherrer broadening of the X-ray reflections. Composition was checked by EDX microprobe analysis. Hysteresis loops have been measured in applied fields of up to 14 T, at room temperature and at 4 K.The material exhibits a room-temperature coercivity of 690 kAm $^{-1}$ after saturation in 14 T, with a remanence of 700 kAm $^{-1}$ in zero applied field and an extrapolated saturation magnetization of 1230 kAm $^{-1}$. The remanence ratio $M_{r}/ M_{s}$ of 63% when the remanence is corrected to zero internal field, is reflected in a preferred orientation seen in the X-ray powder diffraction patterns and in 57 Fe Mossbauer spectra of magnetized powder. Spectra obtained after saturation of an immobilized powder absorber either in-plane or perpendicular to the sample plane exhibit distinctly different relative intensities of the $\otimes \mathrm {M}=0$ absorption lines. The maximum energy product for the powder, assuming full density, is 162 kJm $^{-3}$. The remanence enhancement is attributed to fact that the nanocrystallite size is not much greater than the exchange length. Melt-spun Sm-Fe-N powder has superior corrosion resistance and thermal stability compared to melt-spun Nd-Fe-B. The Nitroquench powder may be used to produce polymer-bonded magnets with an energy product in excess of 100 kJm $^{-3}$.

Fe-Ga alloys (Galfenol) are known to exhibit an unusually large magneto- striction, of order 320 ppm, which is attributed to the presence of nanoscale tetragonal Ga-rich $\mathrm {L}6 _{0}$ inclusions embedded in the bcc A2 Fe-rich matrix solid solution. The tetragonal axis in a particular nanoinclusion is determined by the orientation of nearest-neighbour Ga-Ga pairs. The distribution of these axes parallel to the three {100}directions means that the maximum magnetostriction can be achieved in a single crystal when the magnetic field is applied parallel to any cube edge. More recently it has been shown that traces of rare-earth atoms, $\approx 0.1$ at. %, which can be incorporated into these alloys when they are rapidly cooled, can greatly increase the magnetostric- tion by a factor of 2 – 3 [1]–[3]. The mode of action of the trace dopants has yet to be determined. Here we employ Mossbauer spectroscopy in an attempt to gain some insight into the location and mode of action of the trace rare earth dopants. The samples were produced by melt spinning. Precursor ingots of Fe 83 Ga 17 M x , with $\mathrm {M}=$ La, Nd, Sm, Tb and Tm and $x =0$, 0.05 or 0.25 were first prepared from 4N pure Fe and Ga by arc melting under argon four times and annealed at $1000 ^{o}\mathrm {C}$ in Ar to ensure homogeneity. The ingots were then melt spun on a copper wheel with a surface velocity of 20 ms $^{-1}$, to obtain ribbons about $50 \mu \mathrm {m}$ thick, and 5 mm wide. Transverse magnetostriction was measured by the strain gauge method in the direction of the ribbon length, with the field applied perpendicular to the plane of the ribbon. A field of up to 2 T was used to saturate the magnetization. Mossbauer spectra were obtained at room temperature in a conventional constant acceleration spec- trometer with a source of 57 Co in Rh. The spectrum of undoped Fe 83 Ga 17 is shown in Figure 1, together with associated fit to six hyperfine components [3]. It is composed of two main broad overlapping components with hyper- fine fields of 31.2 and 26.9 T, associated with iron in the A2 phase with 0 or 1 Ga neighbours [3]–[5]. They constitute 87 % of the total spectral area, and their ratio is 66:34, compared to a ratio 37:63 expected for a purely random distribution of Ga in the bcc phase. The Ga concentration in A2 on this basis should be 4.8 %, and the remainder is therefore Ga-rich. We identify two minor components with the tetragonal nanoinclusions, which make up 4.8 % of the total volume. One typical example of a doped sample, with 0.5 % La is shown in Figure 2. The sum of the spectra of iron with 0 and I Ga neighbours again represents 87 % of the total area, but the ratio to rises to 68:32, and the amount of iron in the tetragonal nanoinclusions rises to 5.6 % of the total. These are small changes, but they are observed systematically in spectra with five different rare earth dopants. We can therefore conclude that the rare earths serve to increase the volume of nanoinclusions in the sample, and they increase the amount of Ga present in the nanoinclusions. A second conclu- sion from the data is that there is no significant difference between the 0.05 % and 0.25 % doping, when they are measured for the same dopant. This shows that the solubility limit for the rare earth in these melt-spun ribbons is below 0.05 %. The conclusions are consistent with electron microscopy observations. We consider that the rare-earth dopant is probably initially incorporated into the nanoinclusions and it enhances their tetragonality up to the metastable solubility limit, which is less than 0.05 %. Beyond that, there is no further effect and the rare earth probably precipitates out in a 2:17 or 1:2 phase. In this way we can understand the strong influence of very small amounts of rare earth doping on the magnetostriction of Fe 83 Ga 17 .