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In this study, the electronic behavior and mechanical properties of the ferromagnetic chalcospinel manganese-based selenide (AgMn2Se4) which crystallized in face centered cubic structure with space group Fd3 ̅m and space number 227, were investigated. All ab initio calculations were carried out by Generalized Gradient Approximation (GGA) under spin polarization. For this composition, three different type magnetic orders were considered to detect the most stable magnetic character. For the given composition, the results of the computations indicate its ferromagnetic nature since this compound has a lower ground state energy in this magnetic order than in other magnetic phases. After determining the most energetically stable magnetic phase, the electronic behavior in this magnetic arrangement was examined. The observed electronic band structure under spin polarization of this compound shows that this selenide system is almost half-metallic material due to having small band gap (Eg = 0.09 eV) in the minority spin state. In addition, the mechanical stability was determined with the help of elastic constants which were also employed to determine the mechanical characteristics of this compound.

We report the superconducting properties of the Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$/Cu/Ni/Cu/Pb spin-valve structure which magnetic part comprises the Heusler alloy layer HA = Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ with a high degree of spin polarization (DSP) of the conduction band and the Ni layer of variable thickness. We obtained that the separation between the superconducting transition curves measured for the parallel ($\alpha = 0^\circ$) and perpendicular ($\alpha = 90^\circ$) orientation of the magnetizations of the HA and Ni layers reaches up to 0.5 K ($\alpha$ is an angle between the magnetization of two ferromagnetic layers). For all studied samples the dependence of the superconducting transition temperature $T_c$ on $\alpha$ demonstrates a deep minimum in the vicinity of the perpendicular configuration of magnetizations. This suggests that the observed minimum and the corresponding full switching effect of the spin valve is caused by the long-range triplet component of the superconducting condensate in the multilayer. Such a large effect can be attributed to a half-metallic nature of the HA layer which in the orthogonal configuration efficiently draws off the spin-polarized Cooper pairs from the space between the HA and Ni layers. Our results indicate a significant potential of the concept of the superconducting spin-valve multilayer comprising a half-metallic ferromagnet recently proposed by A. Singh et al., Phys. Rev. X 5, 021019 (2015) in achieving large values of the switching effect., Comment: 6 pages with 4 figures

We report on the optical properties from terahertz (THz) to Near-Infrared (NIR) of the layered magnetic compound CrI3 at various temperatures, both in the para- magnetic and ferromagnetic phase. In the NIR spectral range, we have observed an insulating electronic gap around 1.1 eV which strongly hardens with decreasing temperature. The blue shift observed represents a record in insulating materials and it is a fingerprint of a strong electron-phonon interaction. Moreover, a further gap hardening is observed below the Curie temperature, indicating the establishment of an effective interaction between electrons and magnetic degrees of freedom in the ferromagnetic phase. This interaction is confirmed by the disappearance of some phonon modes in the same phase as expected from a spin-lattice interaction theory. Therefore, the optical properties of CrI3 reveal a complex interaction among electronic, phononic and magnetic degrees of freedom, opening many possibilities for its use in 2-Dimensional heterostructures.

Publisher Copyright: © 2021 The Author(s). Published by IOP Publishing Ltd. Magnonics is a budding research field in nanomagnetism and nanoscience that addresses the use of spin waves (magnons) to transmit, store, and process information. The rapid advancements of this field during last one decade in terms of upsurge in research papers, review articles, citations, proposals of devices as well as introduction of new sub-topics prompted us to present the first roadmap on magnonics. This is a collection of 22 sections written by leading experts in this field who review and discuss the current status besides presenting their vision of future perspectives. Today, the principal challenges in applied magnonics are the excitation of sub-100 nm wavelength magnons, their manipulation on the nanoscale and the creation of sub-micrometre devices using low-Gilbert damping magnetic materials and its interconnections to standard electronics. To this end, magnonics offers lower energy consumption, easier integrability and compatibility with CMOS structure, reprogrammability, shorter wavelength, smaller device features, anisotropic properties, negative group velocity, non-reciprocity and efficient tunability by various external stimuli to name a few. Hence, despite being a young research field, magnonics has come a long way since its early inception. This roadmap asserts a milestone for future emerging research directions in magnonics, and hopefully, it will inspire a series of exciting new articles on the same topic in the coming years.

We have studied superconducting properties of spin-valve thin-layer heterostructures CoOx/F1/Cu/F2/Cu/Pb in which the ferromagnetic F1 layer was made of Permalloy while for the F2 layer we have taken a specially prepared film of the Heusler alloy Co2Cr1−xFexAl with a small degree of spin polarization of the conduction band. The heterostructures demonstrate a significant superconducting spin-valve effect, i.e., a complete switching on and off of the superconducting current flowing through the system by manipulating the mutual orientations of the magnetization of the F1 and F2 layers. The magnitude of the effect is doubled in comparison with the previously studied analogous multilayers with the F2 layer made of the strong ferromagnet Fe. Theoretical analysis shows that a drastic enhancement of the switching effect is due to a smaller exchange field in the heterostructure coming from the Heusler film as compared to Fe. This enables to approach an almost ideal theoretical magnitude of the switching in the Heusler-based multilayer with a F2 layer thickness of ca. 1 nm.

Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D2d symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole–dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction. Antiskyrmions are topological spin textures with negative vorticity. Like skyrmions, they have considerable technological promise, but have only been stabilised in Heusler compounds. Here, Heigl et al. succeed in stabilising first and second order antiskyrmions in a new class of materials.

In this article, we review the magnetostriction and magneto-volume effects of Ni2MnGa-type ferromagnetic Heusler alloys at the martensitic, premartensitic, and austenitic phases. The correlations of forced magnetostriction (ΔV/V) and magnetization (M), using the self-consistent renormalization (SCR) spin fluctuation theory of an itinerant electron ferromagnet proposed by Takahashi, are evaluated for the ferromagnetic Heusler alloys. The magneto-volume effect occurs due to the interaction between the magnetism and volume change of the magnetic crystals. The magnetic field-induced strain (referred to as forced magnetostriction) and the magnetization are measured, and the correlation of magnetostriction and magnetization is evaluated. The forced volume magnetostriction ΔV/V at the Curie temperature, TC is proportional to M4, and the plots cross the origin point; that is, (M4, ΔV/V) = (0, 0). This consequence is in good agreement with the spin fluctuation theory of Takahashi. An experimental study is carried out and the results of the measurement agree with the theory. The value of forced magnetostriction is proportional to the valence electron concentration per atom (e/a). Therefore, the forced magnetostriction reflects the electronic states of the ferromagnetic alloys. The magnetostriction near the premartensitic transition temperature (TP) induces lattice softening; however, lattice softening is negligible at TC. The forced magnetostriction at TC occurs due to spin fluctuations of the itinerant electrons. In the martensitic and premartensitic phases, softening of the lattice occurs due to the shallow hollow (potential barrier) of the total energy difference between the L21 cubic and modulated 10M or 14M structures. As a result, magnetostriction is increased by the magnetic field.

Several realistic spin-orbital models for transition metal oxides go beyond the classical expectations and could be understood only by employing the quantum entanglement. Experiments on these materials confirm that spin-orbital entanglement has measurable consequences. Here, we capture the essential features of spin-orbital entanglement in complex quantum matter utilizing 1D spin-orbital model which accommodates SU(2)xSU(2) symmetric Kugel-Khomskii superexchange as well as the Ising on-site spin-orbit coupling. Building on the results obtained for full and effective models in the regime of strong spin-orbit coupling, we address the question whether the entanglement found on superexchange bonds always increases when the Ising spin-orbit coupling is added. We show that (i) quantum entanglement is amplified by strong spin-orbit coupling and, surprisingly, (ii) almost classical disentangled states are possible. We complete the latter case by analyzing how the entanglement existing for intermediate values of spin-orbit coupling can disappear for higher values of this coupling., Proceedings paper [Quantum Complex Matter Conference, June 2020, Frascati] reporting on the research first presented in Physical Review Research 2, 013353 (2020) [arXiv:1911.12180]

We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor—YBa2Cu3O7−δ with Ba2Y(Nb/Ta)O6 nano-precipitates—by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin1,2. Triplet supercurrents were discovered in Josephson junctions with metallic ferromagnet spacers, where spin transport can occur only within the ferromagnet and in conjunction with a charge current. Ferromagnetic resonance injects a pure spin current from a precessing ferromagnet into adjacent non-magnetic materials3,4. For spin-singlet pairing, the ferromagnetic resonance spin pumping efficiency decreases below the critical temperature (Tc) of a coupled superconductor5,6. Here we present ferromagnetic resonance experiments in which spin sink layers with strong spin-orbit coupling are added to the superconductor. Our results show that the induced spin currents, rather than being suppressed, are substantially larger in the superconducting state compared with the normal state; although further work is required to establish the details of the spin transport process, we show that this cannot be mediated by quasiparticles and is most likely a triplet pure spin supercurrent.

NiCrO3 has been proposed as a likely candidate for antiferromagnetic half metallic behaviour. A sample prepared at high pressure adopts the corundum structure with Ni/Cr cation disorder, and is found to have off-stoichiometric composition Ni0.80Cr1.20O3. This material shows complex local magnetic ordering phenomena at temperatures below 120 K but without any long range spin order observed by neutron diffraction. The transition to local ferrimagnetism occurs at 50-100 K, with two distinct regimes at T-C1 = 95 and T-C2 = 53 K evidencing electronic phase separation driven by variations in local composition. At low temperature the system undergoes a further transition at T-C3 = 22 K, assigned to potential freezing of a cluster glass-like state, that results in a substantial increase in magnetic anisotropy. Ni0.80Cr1.20O3 is a bistable relaxor ferrimagnet where magnetic properties are linked to the lattice strain manifold that is determined by the peculiarities in the local chemical composition. (C) 2017 Elsevier B.V. All rights reserved.

We have tried to make the superconductor/half metal/superconductor (SC/HF/SC) Josephson junction to make clear a long range proximity effect. The structure was consisted of high- T c superconductor YBa 2 Cu 3 O 7-x and half metallic ferromagnet La 0.7 Sr 0.3 MnO 3 thin films deposited by pulse laser deposition on SrTiO 3 (100) single crystal substrates. The SC/HF/SC lateral structure was made by scratching with the atomic force microscope (AFM) probe. We could cut the ditch which has 30 nm width and 50 nm depth. We have investigated the I-V and R-T measurements of the structure. The structure after the fabrication did not show the superconducting state and we could not find the Josephson current.

We study the subgap charge and spin transport in normal-metal/ferromagnet/spin-triplet superconductor (N/F/TS) tunneling junctions induced by bias voltage. Charge and spin conductance are calculated following the extended Blonder–Tinkham–Klapwijk (BTK) theory. We show that the Andreev reflection, which governs the low-energy transport, may be influenced substantially by the exchange field in the ferromagnet giving rise to controllable giant charge and spin tunneling magnetoresistance (TMR) effect. We calculate also the quantum interference effects which lead to oscillatory behavior of charge and spin conductance.

Since the discovery of the giant magnetoresistance (GMR) effect the use of the intrinsic angular momentum of the electrons has opened up new spin based device concepts. The two channel model of spin-up and spin-down electrons with spin-dependent conductivities very well describes spin and charge transport in such devices. In studies of the interaction between heat and spin transport, or spin caloritronics, until recently it was assumed that both spin species are always at the same temperature. Here we report the observation of different temperatures for the spin up (T_\uparrow) and spin down (T_\downarrow) electrons in a nanopillar spin valve subject to a heat current. The weak relaxation, especially at room temperature, of the spin heat accumulation (T_s = T_\uparrow-T_\downarrow) is essential for its detection in our devices. Using 3D finite element modeling spin heat accumulation (SHA) values of 120 mK and 350 mK are extracted at room temperature and 77 K, respectively, which is of the order of 10% of the total temperature bias over the pillar. This technique uniquely allows the study of inelastic spin scattering at low energies and elevated temperatures, which is not possible by spectroscopic methods., Comment: 27 pages, 8 figures and 1 table (including supplementary information)

We image the remnant magnetization configurations of CoFeB and permalloy nanotubes (NTs) using x-ray magnetic circular dichroism photo-emission electron microscopy. The images provide direct evidence for flux-closure configurations, including a global vortex state, in which magnetization points circumferentially around the NT axis. Furthermore, micromagnetic simulations predict and measurements confirm that vortex states can be programmed as the equilibrium remnant magnetization configurations by reducing the NT aspect ratio., Comment: 14 pages, 4 figures, link to supplementary information

We have studied transport property of superconductor-ferromagnet hybridized structure in nanometer-scale processed by a focused ion beam technique. The structure was consisted of high- T c superconductor YBa2Cu3O 7-x and half metallic ferromagnet La0.7Sr0.3MnO3 thin films deposited by pulse laser deposition on SrTiO3 (100) single crystal substrates. We have measured the I-V characteristics of the sample with 400 nm ferromagnetic layer, but we could not observe the proximity effect.

© 2016 American Chemical Society. The combination of photonics and spintronics opens new ways to transfer and process information. It is shown here that in systems in which organic molecules and semiconductor nanoparticles are combined, matching these technologies results in interesting new phenomena. We report on light induced and spin-dependent charge transfer process through helical oligopeptide-CdSe nanoparticles' (NPs) architectures deposited on ferromagnetic substrates with small coercive force (∼100-200 Oe). The spin control is achieved by the application of the chirality-induced spin-dependent electron transfer effect and is probed by two different methods: spin-controlled electrochemichemistry and photoluminescence (PL) at room temperature. The injected spin could be controlled by excitation of the nanoparticles. By switching the direction of the magnetic field of the substrate, the PL intensity could be alternated.

This is a brief overview of the state of the art of spin caloritronics, the science and technology of controlling heat currents by the electron spin degree of freedom (and vice versa)., Comment: To be published in "Spin Current", edited by S. Maekawa, E. Saitoh, S. Valenzuela and Y. Kimura, Oxford University Press

The abilities to inject and detect spin carriers are fundamental for research on transport and manipulation of spin information(1,2). Pure electronic spin currents have been recently studied in nanoscale electronic devices using a non-local lateral geometry, both in metallic systems(3) and in semiconductors(4). To unlock the full potential of spintronics we must understand the interactions of spin with other degrees of freedom. Such interactions have been explored recently, for example, by using spin Hall(5-7) or spin thermoelectric effects(6,8,9). Here we present the detection of non-local spin signals using non-magnetic detectors, through an as-yet-unexplored nonlinear interaction between spin and charge. In analogy to the Seebeck effect(10), where a heat current generates a charge potential, we demonstrate that a spin current in a paramagnet leads to a charge potential, if the conductivity is energy dependent. We use graphene(11) as a model system to study this effect, as recently proposed(12). The physical concept demonstrated here is generally valid, opening new possibilities for spintronics.

The superconducting phase transition in Nb/Cu0.41Ni0.59/Nb trilayers, with superconducting (S) Nb and ferromagnetic (F) Cu0.41Ni0.59, has been experimentally studied as a function of the F-layer thickness by measuring the temperature dependence of the electrical resistance R (T). It is shown that the shape and the width of the R (T) curves depends on the Cu0.41Ni0.59 thickness, in particular in the regime where pi is the coupling between the S layers, which can be expected. To explain the data, we developed a qualitative model which makes the interconnection between the superconducting phase transition and the 0 to pi transition in SFS structures are more evident.

We develop a theoretical model to describe the transport properties of normal-metal/thin-ferromagnet/superconductor device. We perform experimental test of the model using a gold tip on PdNi/Nb bilayer. The resonant proximity effect causes conductance features very sensitive to the local ferromagnetic properties, enabling accurate measurement of polarization and thickness of the ferromagnet by point contact spectroscopy.

Transport measurements are presented on thin-film superconducting spin-valve systems, where the controlled non-collinear arrangement of two ferromagnetic Co layers can be used to influence the superconducting state of Nb. We observe a very clear oscillation of the superconducting transition temperature with the relative orientation of the two ferromagnetic layers. Our measurements allow us to distinguish between the competing influences of domain averaging, stray dipolar fields and the formation of superconducting spin triplets. Domain averaging is shown to lead to a weak enhancement of transition temperature for the anti-parallel configuration of exchange fields, while much larger changes are observed for other configurations, which can be attributed to drainage currents due to spin triplet formation., 5 pages, 4 figures

The dependence of the critical Josephson current (I-C) and magnetoresistance (MR) on the relative orientation of the ferromagnetic layers is investigated in current perpendicular to plane (CPP) measurements of superconductor/ferromagnetic (S/F) multilayers. Two different CuxNi1-x alloys were chosen so that alternate F-layers reversed at different applied magnetic fields and that the ferromagnetic coherence length was of the order of several nanometres. These structures show a significant CPP high-bias MR, which enables the magnetic state of the devices to be determined directly. We found that I-C is substantially larger when the adjacent F-layers are aligned antiparallel compared to the case of parallel orientation. Since in a pseudo-spin-valve structure the relative F-layer orientation is approximately parallel for zero applied magnetic field, I-C can experience an enhancement when a magnetic field is applied in the plane of the junction. The maximum change of I-C corresponds to the maximum change of MR.

Spin-resolved photoemission and absorption studies of Fe 3 O 4 and CrO 2 epitaxial thin films have been reviewed to address the relationship between the electron correlation effects and the half-metallic properties of these two materials. Spin-resolved photoemission results suggest that Fe 3 O 4 should be considered as a strongly correlated system, and that Fe 3 O 4 is not a half-metal. Spin-resolved O 1s X-ray absorption measurements on ferromagnetic CrO 2 reveal that the spin polarization of the unoccupied states closest to the Fermi level approaches 100%, confirming the half-metallic ferromagnetic nature of the material. The spin polarization of the main line of the unoccupied states, on the other hand, is found to be only 50%, indicating a very atomic-like behavior of the Cr 3d2 ions.

The authors acknowledge the financial support of the EPSRC (Grant No. EP/J01060X). Muon-spin rotation has been used to observe directly the spatial variation of the magnetic flux density near the ferromagnetic-superconducting interface in a permalloy-niobium trilayer. Above the superconducting transition temperature Tc the profile of the induced magnetic flux density within the niobium layer has been determined. Below Tc there is a significant reduction of the induced flux density, predominantly near the ferromagnetic-superconducting interfaces. We are uniquely able to determine the magnitude and spatial variation of this reduction in induced magnetization due to the presence of the Cooper pairs, yielding the magnitude and length scale associated with this phenomenon. Both are inconsistent with a simple Meissner screening and indicate the existence of another mechanism, the influence of which is localized within the vicinity of the ferromagnetic interface. Publisher PDF

Exchange bias coupling at the multiferroic- ferromagnetic interface in BiFeO₃ /La₀.₇ Sr₀.₃ MnO₃ heterostructures exhibits a critical thickness for ultrathin BiFeO₃ layers of 5 unit cells (2 nm). Linear dichroism measurements demonstrate the dependence on the BiFeO₃ layer thickness with a strong reduction for ultrathin layers, indicating diminished antiferromagnetic ordering that prevents interfacial exchange bias coupling.

The behavior of a three-dimensional isotropic Heisenberg ferromagnet in the presence of a magnetic field H is investigated in the random phase approximation (RPA) near the Curie temperature Tc. It is shown that the magnetization M at the Curie temperature Tc is described by the law M ( T = T c ) ∼ H 1 / 5 and the initial magnetic susceptibility χ 0 at temperatures T ≥ T c is given by χ 0 ( T ≥ T c ) ∼ ( T − T c ) − 2 . It means that in the RPA the critical exponents for a three-dimensional Heisenberg ferromagnet coincide with the critical exponents for the Berlin-Kac spherical model of a ferromagnet rather than with the critical exponents of the mean field approximation (MFA). Hence it follows as well that, when a magnetic field H is risen from H=0 to H = H a , the magnetic entropy SM will be decreased as Δ S M ( T = T c ) ∼ − H a 4 / 5 at the Curie temperature Tc and as Δ S M ( T > T c ) ∼ − ( T − T c ) − 3 H a 2 at temperatures T > T c .

We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 10(9) A/m(2) can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque. Published by AIP Publishing.

The Peltier coefficient describes the amount of heat that is carried by an electrical current when it passes through a material(1). When two materials with different Peltier coefficients are placed in contact with one another, the Peltier effect causes a net flow of heat either towards or away from the interface between them. Spintronics(2) describes the transport of electric charge and spin angular momentum by separate spin-up and spin-down channels in a device. The observation that spin-up and spin-down charge transport channels are able to transport heat independently of each other(3) has raised the possibility that spin currents could be used to heat or cool the interface between materials with different spin-dependent Peltier coefficients. Here, we report the direct observation of the heating and cooling of such an interface by a spin current. We demonstrate this spin-dependent Peltier effect in a spin-valve pillar structure that consists of two ferromagnetic layers separated by a non-ferromagnetic metal. Using a three-dimensional finite-element model, we extract spin-dependent Peltier coefficients in the range -0.9 to -1.3 mV for permalloy. The magnetic control of heat flow could prove useful for the cooling of nanoscale electronic components or devices(4).

In the presence of a periodic scattering potential the spin relaxation in ultrathin ferromagnets is not a monotonous function of the frequency. The spin relaxation rate is found to substantially increase at characteristic frequencies related to the periodicity of the magnon scattering potential (see Fig. 1). This is experimentally confirmed in Ni80Fe20 thin films by artificially introducing different scattering periodicities [1]. The lateral struvturing of the thin film is achieved by Cr+ ion implantation with at an energy of 5 keV and a fluence of 5 × 10E15 ions/cm2 through a 100 nm thick polymethyl methacrylate (PMMA) resist covering the whole sample area. Electron beam lithography was used to fabricate 1 mm long-stripes of width s0 and spacing s1 (i.e., with periodicity l = s0 + s1) within the PMMA resist so that the surface becomes Cr-implanted in a stripewise manner. Frequency dependent Ferromagnetic resonance spectroscopy reveals that the magnetic damping may be increased at specific frequencies by a factor of up to 100%. This work is supported by the DFG, SFB 491, Grants No. FA 314/6-1 and No. FA 314/3-2. [1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)

uperconductor/normal metal/ferromagnetic structures have been prepared in order to study the proximity effect between the superconductor and the ferromagnet via the normal metal layer. In particular, [25 nm Nb/Pt/10 nm Fe(0 0 1)] trilayers have been grown by DC sputtering with Pt layer thicknesses in the 2–30 nm range. For the samples with the thinnest Pt layers, the superconducting transition temperature is reduced by more than 1 K, in comparison with a control series of [Nb/Pt] bilayers. As the Pt thickness is increased, the transition temperature also increases, until the effect of the Fe layer is completely screened for a 30 nm thick Pt layer. This sets a length scale for this phenomenon comparable to the normal metal coherence length in the Pt, ξN≈32 nm., Work supported by Spanish CICYT and Comunidad de Madrid under contracts MAT99-0724 and CAM-07N/0056/1999.

We address and resolve the fundamental contradiction that has existed from the earliest studies on magnetic phase transitions between theoretical models that ignore the role of thermal vibrations and represent the exchange interaction as a constant, Jij(0), and analysis of neutron diffraction data that always incorporates thermal vibrations even though it is also possible to analyze the same data by ignoring them. Of the two possibilities, ignoring thermal vibrations in both theoretical models and analysis of diffraction data leads to the latter giving different magnetic order parameters for different reciprocal lattice lines. This appears to be the first report of a unique consequence, viz. the assumption to neglect a physical phenomenon turns a single-valued experimental observable into a multiple-valued one where all values are equally valid. This assumption is clearly unacceptable and must be rejected. The second possibility of incorporating thermal vibrations in both leads to single-valued theoretical and experimental order parameters. Thus, analysis of neutron diffraction data constrain the exchange interaction in all theoretical models to be temperature dependent and represented as Jij(T). Additional experimental and theoretical evidences in support of this conclusion are presented., Submitted for publication

Insight in the interplay between work function and stability is important for many areas of physics. In this paper, we calculate the anisotropy in the work function and the surface stability of $\mathrm{Cr}{\mathrm{O}}_{2}$, a prototype half-metal, and find an anisotropy of $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. An earlier model for the relation between work function and surface stability is generalized to include the transition-metal oxides. We find that the lowest work function is obtained for surfaces with the most electropositive element, whereas the stable surfaces are those containing the element with the lowest valency. Most $\mathrm{Cr}{\mathrm{O}}_{2}$ surfaces considered remain half-metallic, thus the anisotropy in the work function can be used to realize low resistance, half-metallic interfaces.

Spin-polarized transport is investigated in normal metal--superconductor (NS) junctions as a function of interface transmissivity as well as temperature when the density of states of a superconductor is Zeeman-split in response to an exchange field $({h}_{\text{exc}})$. Similarly to the ``absolute spin-valve effect'' predicted by Huertas-Hernando et al. [Phys. Rev. Lett. 88, 047003 (2002)] in superconducting proximity structures, we show that NS junctions can be used to generate highly spin-polarized currents, in alternative to half-metallic ferromagnets. In particular, the spin-polarized current obtained is largely tunable in magnitude and sign by acting on bias voltage and ${h}_{\text{exc}}$. While for tunnel contacts the current polarization can be as high as 100%, for transparent junctions it is dominated by the minority spin species. The effect can be enhanced by electron ``cooling'' provided by the superconducting gap.

In this paper, we report on field-effect experiments in ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_{3}$ side-gate channels patterned on ultrathin epitaxial films having thickness ranging from 12 to 4 unit cells. Transport mechanisms and competition between phases, under the effect of electric and magnetic fields, as well as of other perturbations such as disorder and proximity to the interface with substrate are explored. We observe, in a 7 unit cells thick sample, a shift of the metal-insulator transition temperature as high as 43 K and a resistivity modulation up to 250% at low temperatures. In striking contrast, the 6--4 unit cells thick samples result to be insulating and almost insensitive to field-effect modulation. Such a finding indicates that for films thinner than 7 unit cells, a strong localization mechanism develops, which cannot be healed by band refilling. On the other hand, our results are compatible with a Mn ${e}_{g}$ orbital rearrangement driven by the broken translational symmetry at the surface and/or interface, which suppresses the double-exchange mechanism and localizes the carriers.

Superconductors separated by a thin tunneling barrier exhibit the Josephson effect that allows charge transport at zero voltage, typically with no phase shift between the superconductors in the lowest energy state. Recently, Josephson junctions with ground state phase shifts of pi proposed by theory three decades ago have been demonstrated. In superconducting loops, pi-junctions cause spontaneous circulation of persistent currents in zero magnetic field, analogous to spin-1/2 systems. Here we image the spontaneous zero-field currents in superconducting networks of temperature-controlled pi-junctions with weakly ferromagnetic barriers using a scanning SQUID microscope. We find an onset of spontaneous supercurrents at the 0-pi transition temperature of the junctions Tpi = 3 K. We image the currents in non-uniformly frustrated arrays consisting of cells with even and odd numbers of pi-junctions. Such arrays are attractive model systems for studying the exotic phases of the 2D XY-model and achieving scalable adiabatic quantum computers., Comment: Pre-referee version. Accepted to Nature Physics

Proximity effect in $\mathrm{Nb}∕{\mathrm{Pd}}_{0.86}{\mathrm{Ni}}_{0.14}$, $\mathrm{Nb}∕{\mathrm{Cu}}_{0.46}{\mathrm{Ni}}_{0.54}$, and $\mathrm{Nb}∕{\mathrm{Cu}}_{0.42}{\mathrm{Ni}}_{0.58}$ bilayers has been studied in the presence of an external magnetic field. Upper critical field measurements, performed in parallel configuration, reveal a shift of the two-dimensional--three-dimensional crossover temperature, which we relate to the different interface transparencies of the three analyzed systems.

The transport properties of superconductor/weak ferromagnet Nb/Pd86Ni14 sputtered bilayers have been studied. The critical thickness needed for superconductivity to develop is determined from the dependence of the transition temperature T-c on d(Nb). (c) 2005 Elsevier Ltd. All rights reserved.

We discuss the particularities of the proximity effect in superconductor–ferromagnet systems: the damped oscillatory behavior of the Cooper pair wave function, the oscillations of the critical temperature in S/F bilayers and multilayers and the conditions for the π -Josephson junctions formation. Also we outline the possibility of the formation of the novel type of the Josephson junction, intermediate between the 0 and π junctions. To cite this article: A.I. Buzdin, V.V. Ryazanov, C. R. Physique 7 (2006).

We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co L-2,L-3 edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may, therefore, open new opportunities for applications in the field of exchange bias in multilayered magnetic films.

The new hydrides CeNiSnH 1.0(2) and CeNiSnH 1.8(2) have been investigated by X-ray powder diffraction, magnetization, electrical resistivity and specific heat measurements. The hydrogen insertion into CeNiSn reveals an interesting magnetic transition: Kondo insulator (CeNiSn)→antiferromagnet (CeNiSnH 1.0(2) )→ferromagnet (CeNiSnH 1.8(2) ). The physical properties of these compounds are influenced by the Kondo effect.

Ferromagnetic particles used for the catalytic growth of single-walled carbon nanotubes (SWNTs), which are embedded in a graphitic shell, represent a major obstacle in studying the bulk material. We have explored a purification method that is based on a mixing of the SWNT suspension with inorganic nanoparticles in an ultrasonic bath, which causes ferromagnetic particles to be mechanically removed from their graphitic shells. By trapping these magnetic particles with permanent magnetic poles and with a subsequent chemical treatment, a high purity SWNT material was obtained.

Current–voltage characteristics for junctions involving normal and superconducting charge-density-wave metals in the magnetic field were calculated. Spin splitting was found both for symmetrical and non-symmetrical junctions.

International audience; The reversible stress-induced magnetization (inverse magnetostriction or Villari effect) has been measured in a polycrystalline Ni-Fe-Ga-Co ferromagnetic martensite. The samples were mechanically excited using longitudinal resonant oscillations at frequencies close to 100 kHz, and experiments were performed over the temperature range 170 - 350 K under variable polarizing fields. It has been found that the reversible inverse magnetostriction changes its sign under low polarizing fields over a certain temperature range with its upper limit close to the Curie temperature. We argue that the variations of sign of the reversible inverse magnetostriction effect are related in the present experiments with the change of the sign of magnetostriction, as has additionally been verified in test measurements performed for pure Ni and Fe. The observed peculiarity of magnetoelastic coupling is also reflected in the temperature dependence of electrical resistance and even produces a minor effect in calorimetry scans. Possible origins of these features of magnetoelastic coupling are discussed.

In this letter, the effect of reversed magnetic domains of BaFe12O19 on superconductivity is investigated in Pb/BaFe12O19 hybrids. The critical field of the Pb film is increased by about 5 kOe due to the compensation of the applied field by the stray field above the reversed domains. Being related to smaller critical fields of Pb, at,fields near the saturation field of BaFe12O19, the superconductivity can only exist above the reversed domains even at low temperatures. As a consequence of the pure reversed domain superconductivity, magnetic-field-induced superconductivity is observed in a broad temperature range. (c) 2006 American Institute. of Physics. ispartof: Applied Physics Letters vol:88 issue:23 status: published

The techniques of microwave quantum optics are applied to collective spin excitations in a macroscopic sphere of a ferromagnetic insulator. We demonstrate, in the single-magnon limit, strong coupling between a magnetostatic mode in the sphere and a microwave cavity mode. Moreover, we introduce a superconducting qubit in the cavity and couple the qubit with the magnon excitation via the virtual photon excitation. We observe the magnon–vacuum-induced Rabi splitting. The hybrid quantum system enables generation and characterization of non-classical quantum states of magnons.