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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.

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$_2$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.

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.

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)

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

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.

$\text{Mn}_{2}\text{Ru}_{\mathrm{x}}\text{Ga}$ (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

With the continuous shrinkage of the footprint of inductors and transformers in modern power supplies, higher flux, while still low-loss metallic replacements of traditional ferrite materials are becoming an intriguing alternative. One candidate replacement strategy is based on amorphous CoFeBSi soft-magnetic alloys, in their metallic glass form. Here the structural and magnetic properties of two different families of CoFeBSi-based soft magnetic alloys, prepared by arc-melting and subsequent melt spinning (rapid quenching) are presented, targeting potential applications at effective frequencies of 100 kHz and beyond. The nominal alloy compositions are Co67Fe4B11Si16Mo2 representing commercial Vitrovac and Co72-xFexB28-y (where B includes non-magnetic elements such as Boron, Silicon etc. x varies between 4 and 5 % and y is varied from 0 to 2 %) denoted Alloy #1 and prepared as a possible higher performance alternative, i.e. lower power loss and lower coercivity, to commercial Vitrovac. Room temperature magnetization measurements of the arc-melted alloys reveal that compared to Vitrovac, Alloy #1 already presents a ten-fold decrease in coercivity, with H-c similar to 1.4 Am-1 and highest figure of merit of (M-s/H-c > 96). Upon melt-spinning the alloys into thin (< 30 mu m) ribbons, the alloys are essentially amorphous when analyzed by XRD. Magnetization measurements of the melt-spun ribbons demonstrate that Alloy #1 possesses a coercivity of just 2 Am-1, which represents a significant improvement compared to melt-spun ribbons of Vitrovac (17 Am-1). A set of prototype transformers of approximately 10 turns of Alloy #1 ribbon exhibits systematically H-c < 10 Am-1 at 100 kHz, without a noticeable decrease in coupled flux and saturation. (C) 2018 Author(s).

Ionic liquid gating is a versatile method for inducing a metal-insulator transition in field-effect transistor device structures. The mechanism of carrier doping in metal oxide films is under debate. Ionic liquid gating of a WO3 film-based field effect transistor is discussed in this report. Flat and relatively smooth WO3 films were deposited on SrTiO3 substrates by pulsed laser deposition. Swept and constant gate voltage characteristics are measured in both argon and oxygen atmospheres. The results show a clear dependence on the oxygen pressure of the experimental chamber. Metallic behavior in the films is attributed to oxygen vacancy formation in the WO3 layer induced by the high electric field at the oxide-ionic liquid interface. The density of states of a monoclinic supercell of oxygen deficient WO3 was studied by density functional theory (DFT). Calculated W and O partial densities of states verify metallic behavior even at dilute oxygen vacancy concentrations and show the role of W and O orbitals in the conductivity.

Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption spectroscopy, X-ray magnetic circular dichroism and Mossbauer spectroscopy with the aim of determining the structure and site-specific magnetism of this tetragonal, D0$_{22}$-structure Heusler compound. High-quality epitaxial films with low RMS surface roughness ($\sim 0.6$ nm) are grown by magnetron co-sputtering. The tetragonal distortion induces strong perpendicular magnetic anisotropy along the $c$-axis with a typical coercive field $\mu_0 H\sim 0.8$ T and an anisotropy field ranging from $6$ to $8$ T. Upon increasing the Fe content $x$, substantial uniaxial anisotropy, $K_\mathrm{u} \geq 1.0$ MJ/m$^3$ can be maintained over the full $x$ range, while the magnetisation of the compound is reduced from $400$ to $280$ kA/m. The total magnetisation is almost entirely given by the sum of the spin moments originating from the ferrimagnetic Mn and Fe sublattices, with the latter being coupled ferromagnetically to one of the former. The orbital magnetic moments are practically quenched, and have negligible contributions to the magnetisation. The films with $x=0.73$ exhibit a high anomalous Hall angle of $2.5$ % and a high Fermi-level spin polarisation, above $51$ %, as measured by point contact Andreev reflection. The Fe-substituted Mn$_2$Ga films are highly tunable with a unique combination of high anisotropy, low magnetisation, appreciable spin polarisation and low surface roughness, making them very strong candidates for thermally-stable spin-transfer-torque switching nanomagnets with lateral dimensions down to $10$ nm.

Deterministic switching of magnetization via spin-orbit torque, without an external magnetic field, is an attractive approach for nonvolatile memory and logic devices. This can be accomplished using in-plane exchange bias instead of an applied field. The authors study the mechanism of this switching, and expose the importance of Joule heating: Field-free current-driven switching is achieved in experiments, but care must be taken so that heating does not decrease exchange bias and spoil the switching.

Both polycrystalline and single-crystal films of iron-substituted strontium titanate, Sr(Ti0.65Fe0.35)O3-delta, prepared by pulsed laser deposition, show room-temperature magnetism and Faraday rotation, with the polycrystalline films exhibiting higher saturation magnetization and Faraday rotation. The magnetic properties vary with the oxygen pressure at which the films are grown, showing a maximum at pressures of approximately 4 mu Torr at which the unit-cell volume is largest. The results are discussed in terms of the oxygen stoichiometry and corresponding Fe valence states, the structure and strain state, and the presence of small-volume fractions of metallic Fe in single-crystal films grown at the optimum deposition pressure. Integration of magneto-optical polycrystalline films on an optical-waveguide device demonstrates a nonreciprocal phase shift., JST PRESTO, JSPS Postdoctoral Fellowships for Research Abroad; NSF; FAME; DARPA; MARCO; Center for Development of Nanoscience and Nanotechnology, CEDENNA, Chile; Fondecyt; DGIIP USM, Chile; JSPS; Center for Materials Science and Engineering (CMSE)

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A3+/Fe3+ cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

Historically, ferromagnetic resonance has been dominated by inductive techniques, for the best part of the last 80 years. It has been only in the last 20 years that non-inductive techniques, such as Ferromagnetic Resonance Force Microscopy (FMRFM) and Magneto-optical Kerr Effect (MOKE), have been used to study, for example, the spatial distribution of resonance modes. Neither of these techniques is absolute - i.e. provides information on the amplitude of excitation as a function of absorbed microwave power. Here we extend on the recent demonstration of SQUID-detected FMR [J. M. O’Reilly and P. Stamenov, Rev. Sci. Instrum. 89, 044701 (2018)], of absolute scalar resonance measurements in single-crystalline and poly-crystalline YIG, at various fields and temperatures, by introducing a new set-up, where the microwave power, instead of being sunk in a matched load at the cryogenic end of the measurement probe is brought back to the ambient environment and is both metered and sunk in high dissipation power (>50 W @ 50 Ω) matching load. The here suggested methodology allows for the absolute excitation amplitude of modes excited during high-power operation of critical microwave devices, such as filters and Y-junction stripline circulators, to be predicted based on direct measurements of the same material in a known geometry.Historically, ferromagnetic resonance has been dominated by inductive techniques, for the best part of the last 80 years. It has been only in the last 20 years that non-inductive techniques, such as Ferromagnetic Resonance Force Microscopy (FMRFM) and Magneto-optical Kerr Effect (MOKE), have been used to study, for example, the spatial distribution of resonance modes. Neither of these techniques is absolute - i.e. provides information on the amplitude of excitation as a function of absorbed microwave power. Here we extend on the recent demonstration of SQUID-detected FMR [J. M. O’Reilly and P. Stamenov, Rev. Sci. Instrum. 89, 044701 (2018)], of absolute scalar resonance measurements in single-crystalline and poly-crystalline YIG, at various fields and temperatures, by introducing a new set-up, where the microwave power, instead of being sunk in a matched load at the cryogenic end of the measurement probe is brought back to the ambient environment and is both metered and sunk in high dissipation power (>50...

SrTiO3 plays a central role in oxide electronics. It is the substrate of choice for functional oxide heterostructures based on perovskite-structure thin-film stacks, and its surface or interface with a polar oxide such as LaAlO3 can become a two-dimensional conductor because of electronic reconstruction or the presence of oxygen defects. Inconsistent reports of magnetic order in SrTiO3 abound in the literature. Here we report a systematic experimental study aimed at establishing how and when SrTiO3 can develop a magnetic moment at room temperature. Polished 100, 110 or 111 crystal slices from four different suppliers are characterized before and after vacuum annealing at 750 {\deg}C, both in single-crystal and powdered form. Impurity content is analysed at the surface and in the bulk. Besides the underlying intrinsic diamagnetism of SrTiO3, magnetic signals are of three types-a Curie law susceptibility due to dilute magnetic impurities at the ppm level, a hysteretic, temperature-dependent ferromagnetic impurity contribution, and a practically-anhysteretic, defect-related temperature-independent component that saturates in about 200 mT. The latter component is intrinsic. It is often the largest, reaching 10 Bohr magnetons per nm2 of surface area or more and dominating the magnetic response in low fields at room temperature. It is associated with defects near the surface, and can be destroyed by treatment with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong complex with titanium at the surface. The origin of this unusual high-temperature ferromagnetic-like response is discussed.

Point contact Andreev reflection spectroscopy is employed to extract the effective Fermi-level spin polarization of three distinct compositions from the (${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$)${}_{2}{\mathrm{Te}}_{3}$ topological insulator family. The end members, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$, exhibit high polarization of 70(4)% and 57(3)%, respectively. High-field $({\ensuremath{\mu}}_{0}H=14\phantom{\rule{0.16em}{0ex}}\mathrm{T})$ point contact spectroscopy shows carrier depletion close to the Fermi level for these two compositions with small activation gaps of 0.40(4) and 0.28(2) meV, respectively. The almost fully suppressed bulk conductivity in the (${\mathrm{Bi}}_{0.18}{\mathrm{Sb}}_{0.82}$)${}_{2}{\mathrm{Te}}_{3}$ results in an even higher spin polarization of 83(9)%. Further, it is demonstrated that magnetic doping with Cr and V tends to reduce the spin-polarization values with respect to the ones of the pure compositions. ${\mathrm{Bi}}_{1.97}{\mathrm{Cr}}_{0.03}{\mathrm{Te}}_{3}, {\mathrm{Sb}}_{1.975}{\mathrm{Cr}}_{0.025}{\mathrm{Te}}_{3}, {\mathrm{Bi}}_{1.975}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}_{0.025}{\mathrm{Te}}_{3}$, and ${\mathrm{Sb}}_{1.97}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}_{0.03}{\mathrm{Te}}_{3}$ exhibit spin polarization of 52%, 52%, 58%, and 50%, respectively. In view of the rather high effective polarization, nonmagnetic topological insulators close to (${\mathrm{Bi}}_{0.18}{\mathrm{Sb}}_{0.82}$)${}_{2}{\mathrm{Te}}_{3}$ may provide a path towards the characterization of pair-breaking mechanisms in spin-triplet superconductors.

An innovative passive near-field 13.56 MHz RFID system for financial payment and national identity smartcard applications is presented. The system utilizes reactive coupling using a slit of defined width in a metal (copper) foil layer to concentrate surface eddy current density in the vicinity of a transponder having a laser-etched antenna structure.

The site-specific magnetic properties of thin films of the Heusler compound ${\text{Mn}}_{2}{\text{Ru}}_{x}\text{Ga}$, $0.6lxl1.0$, are studied using x-ray absorption and dichroism spectroscopy. There is evidence of half metallicity up to $x=0.7$, and compensation of the Mn $4a$ and $4c$ moments in this range, leading to a zero-moment half metal. We also also discuss the effect of substrate-induced strain on the magnetic properties. By tuning the biaxial strain, simultaneous perfect magnetic compensation and half-metallic character is achievable at, below, or above room temperature.

Tunnel magnetoresistance ratios of up to 40% are measured between 10 K and 300 K when the highly spin-polarized compensated ferrimagnet, Mn2RuxGa, is integrated into MgO-based perpendicular magnetic tunnel junctions. Temperature and bias dependences of the tunnel magnetoresistance effect, with a sign change near −0.2 V, reflect the structure of the Mn2RuxGa interface density of states. Despite magnetic moment vanishing at a compensation temperature of 200 K for x≈0.8, the tunnel magnetoresistance ratio remains non-zero throughout the compensation region, demonstrating that the spin-transport is governed by one of the Mn sub-lattices only. Broad temperature range magnetic field immunity of at least 0.5 T is demonstrated in the same sample. The high spin polarization and perpendicular magnetic anisotropy make Mn2RuxGa suitable for applications in both non-volatile magnetic random access memory cells and terahertz spin-transfer oscillators.

The Heusler compound Mn2RuxGa (MRG) may well be the first compensated half metal. Here, the structural, magnetic and transport properties of thin films of MRG are discussed. There is evidence of half-metallicity up to x = 0.7, and compensation of the two Mn sublattice moments is observed at specific compositions and temperatures, leading to a zero-moment half metal. There are potential benefits for using such films with perpendicular anisotropy for spin-torque magnetic tunnel junctions and oscillators, such as low critical current, high tunnel magnetoresistance ratio, insensitivity to external fields and resonance frequency in the THz range.

Spin-dependent transport properties of Mn2RuxGa thin-films are studied as function of the Ru concentration and the substrate-induced strain. The large spontaneous Hall angle of 7.7% twenty times bigger than in other 3d metals is a signature of its half-metallicity. The compensation temperature where the magnetization of the two inequivalent antiferromagnetically coupled Mn sublattices cancel can be tuned by varying x or the biaxial strain. This zero-moment half metal is free from demagnetizing forces and creates no stray field, effectively removing two obstacles to integrating magnetic elements in densely packed, nanometer-scale memory elements, and millimeter-wave generators.

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 favourable 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 Ti3 C2 MXene-functionalized PEDOT:PSS ink is developed for extrusion printing to create 3D objects with arbitrary geometries, and a freeze-thawing protocol is proposed to transform the printed objects directly into highly conductive and robust hydrogels with high shape fidelity in both macro and micro scales. The as-obtained hydrogel exhibits a high conductivity of 1525.8 S m-1 at water content up to 96.6 wt% and also satisfactory mechanical properties with flexibility, stretchability, and fatigue resistance. Furthermore, we demonstrate the use of the printed hydrogel for customizable EMI shielding applications. The proposed easy-to-manufacture approach, along with the highlighted superior properties, expands the potential of conductive polymer hydrogels in future customizable applications and represents a real breakthrough from the current state-of-the-art. This article is protected by copyright. All rights reserved.