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We achieved nearly ideal spin tunneling efficiency \ensuremath{\eta} by lowering the interface trap density ${D}_{\mathrm{it}}$ with a $\mathrm{Si}{\mathrm{O}}_{x}$ insertion layer in Fe/Mg/amorphous-MgO(1.0--1.5 nm)/plasma-oxidized $\mathrm{Si}{\mathrm{O}}_{x}(\ensuremath{\sim}0.2\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{n}^{+}\text{\ensuremath{-}}\mathrm{Si}(001)$ junctions. The spin polarization ${P}_{\mathrm{S}}$ of tunneling electrons was estimated from three-terminal Hanle signals at 4 K. At the optimum MgO thickness and oxidation time, we obtained ${P}_{\mathrm{S}}$ which is nearly equal to the spin polarization ${P}_{\mathrm{FM}}$ of Fe at the Fermi level, that is, $\ensuremath{\eta}={P}_{\mathrm{S}}/{P}_{\mathrm{FM}}=0.93$. By quantitatively estimating ${D}_{\mathrm{it}}$ and ${P}_{\mathrm{S}}$ of various junctions, we show that lowering ${D}_{\mathrm{it}}$ is crucial to obtain \ensuremath{\eta} \ensuremath{\cong} 1.

We theoretically investigate the effective exchange interaction, $J_\mathrm{eff}$, mediated by conductive electrons within a nonmagnetic metal spacer, in the presence of a bias voltage, sandwiched by two ferromagnetic insulators. On the basis of the tight-binding model, we show the voltage and spacer thickness dependences of $J_\mathrm{eff}$, and its contorollability is demonstrated. We also propose a new magnonic device with the functions of both field effect transistor and non-volatile memory.

The anomalous low-temperature behaviour of the spontaneous magnetization of ordered arrays of quantum dots is discussed. It is shown that the experimental results can be well understood, within a mean field approximation, assuming collective response through rather strong spin tunneling processes between neighbouring dots.

In this study the role of the antiferromagnetic interactions in recently synthesized dinuclear Cr(III) complex has been investigated. Since there was not enough structural information for the characterization of the synthesis, we claim that there should be antiferromagnetic interactions between the dinuclear Fe(III) ions, if the proposed structure is the real structure. A new experiment is proposed to test the predictions of this theoretical investigation.

A series of Co, Ni and Co–Ni granular thin films with variable nitrogen content in the range 0–16 at.% N were prepared by electrodeposition onto aluminum substrate. The nitrogen content was varied in order to analyze its influence on the magnetoresistance. The morphology, structure and magnetic properties of electrodeposited Co, Ni and Co–Ni granular thin films were also studied as a function of the nitrogen content. The magnetoresistance (MR) ratio of Co–Ni–N granular films initially increased and then decreased when increasing the nitrogen content. The films exhibit a granular morphology, with rich in nitrogen frontiers between grains and some un-deposited sites on the aluminum substrate, which easily oxidize even during the process of preparation, favoring the spin tunneling transport. We obtained tunneling magnetoresistance (TMR) effect in the Co–Ni–N granular thin films in the range 3–159%; this large effect obtained in Co–Ni–N granular thin films makes them suitable for applications in electronics.

We theoretically investigate the spin--wave spin current induced by the spin Seebeck effect in magnonic spin tunneling junctions (MSTJs) for arbitrary magnetization directions. We show that the MSTJ functions as a \textit{tunable} spin Seebeck diode in which the tunneling spin current can be turned on and off with high efficiency by controlling the magnetization direction., 3 pages, 1 figure

arXiv:1509.07291v1, We report characterization and magnetic studies of mixtures of micrometer-size ribbons of Mn12 acetate and micrometer-size particles of YBaCuO superconductor. Extremely narrow zero-field spin-tunneling resonance has been observed in the mixtures, pointing to the absence of the inhomogeneous dipolar broadening. It is attributed to the screening of the internal magnetic fields in the magnetic particles by Meissner currents flowing between superconducting grains surrounding the particles., The work at the University of Barcelona has been supported by the Spanish Government Project No. MAT2011-23698. A.G.-S. acknowledges support from Universitat de Barcelona. I.I. and J.E. thank the MINECO for the Ramon y Cajal contract and the FPI fellowship, respectively. The work of EMC at CUNY Lehman College has been supported by the Office of Science of the U.S. Department of Energy through grant No. DE-FG02-93ER45487.

Magnetic properties of a mixed spin- 1 2 and spin- 3 2 Ising model on honeycomb lattice are investigated within the framework of an exact star-triangle mapping transformation. The particular attention is focused on the effect of uniaxial and biaxial crystal-field potentials that basically influence a magnetic behavior of the spin- 3 2 atoms. Our results for basic thermodynamic quantities as well as dynamical time-dependent autocorrelation function indicate a spin tunneling between | ± 3 2 〉 and | ∓ 1 2 〉 states in two different magnetically ordered phases OP1 and OP2, respectively.

We have applied Buttiker's gauge invariant, charge conserving dc transport theory to investigate the spin-polarized tunneling in ferromagnet–insulator–ferromagnet junctions at finite temperatures. It is observed that the spin polarization direction and temperature have remarkable effects on the differential conductance as well as the derivative of the conductance. At low temperatures the quantum resonant tunneling is dominant, while the thermal activated process plays a great role at high temperatures. A so-called spin-valve phenomenon is clearly seen at low temperatures. The results for asymmetric and symmetric junctions differ. The quantum electrochemical capacitance for such a junction is also calculated. Our findings are expected to be confirmed experimentally.

Magnetic sensors based on spin-dependent tunneling (SDT) have been theoretically simulated, fabricated, and experimentally tested. In particular, SDT sensors that possess even and odd input–output characteristics have been introduced, designed, and studied. In-depth theoretical analysis of their static and dynamic response characteristics has been carried out. It showed good performance of the even-and the odd-type sensors up to 1 GHz and above 1 GHz, respectively. This holds much promise for ultra-fast magnetic reading. A novel type of a SDT sandwich has been developed, which simplifies the microfabrication procedure. A variety of such SDT structures of different compositions was produced and found to reveal effective coupling interaction. A magnetoresistive effect up to 28% under magnetic field perpendicular to the easy magnetization axis has been recorded.

The magnetoresistance across interfaces in the itinerant ferromagnetic oxide ${\mathrm{SrRuO}}_{3}$ have been studied. To define appropriately the interfaces, epitaxial thin films have been grown on bicrystalline and laser-patterned ${\mathrm{SrTiO}}_{3}$ substrates. Comparison is made with results obtained on similar experiments using the double-exchange ferromagnetic oxide ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}.$ It is found that in ${\mathrm{SrRuO}}_{3},$ interfaces induce a substantial negative magnetoresistance, although no traces of the low-field spin tunneling magnetoresistance are found. We discuss these results on the basis of the distinct degree of spin polarization in ruthenates and manganites and the different nature of the surface magnetic layer formed at interfaces.

A criterion is derived for the determination of parameter domains of first-order phase transitions in quantum-mechanical tunneling models. The criterion is tested by application to various models, in particular to some that have been used recently to explore spin tunneling in macroscopic particles. In each case agreement is found with previously heuristically determined domains.

We prove that the spin-boson system is ergodic, for arbitrary strengths of the coupling between the spin and the boson bath, provided the spin tunneling matrix element is small enough.

We present a theory whose goal is to account for the recent exciting hysteresis experiments on the spin cluster crystal Mn12-acetate that indicate the occurrence of spin tunneling. We have found the tunneling probability P for the tunneling of spin from one spin state into another at a spin level crossing in response to a swept applied magnetic field H. It is shown that P is a function of only one parameter, the dimensionless sweep rate ρ given by ρ ≡ 2/Δ20, where 2 is the rate at which the two energy levels approach each other as the field is swept (being proportional to the sweep rate dH/dt). Δ0 is the minimum energy gap at the anti-crossing, Δ0/ being the tunneling rate thereat. Numerical integration leads to P(ρ) = 1 − exp [ − [(π)/(2ρ)]]. We find that, contrary to widespread belief, the experiments cannot be understood in terms of tunneling of individual spin clusters in the presence of a static applied transverse field. Rather, the required transverse field must have dynamic nuclear spins and other dynamic spin clusters as its source.

The laser-induced ultrafast demagnetization of CoFeB/MgO/CoFeB magnetic tunneling junction is exploited by time-resolved magneto-optical Kerr effect (TRMOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electrons tunneling current. It opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions.

In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of silicon spintronics, namely the creation, detection and manipulation of spin polarization in silicon. Ferromagnetic tunnel contacts are the key elements and provide a robust and viable approach to induce and probe spins in silicon, at room temperature. We describe the basic physics of spin tunneling into silicon, the spin-transport devices, the materials aspects and engineering of the magnetic tunnel contacts, and discuss important quantities such as the magnitude of the spin accumulation and the spin lifetime in the silicon. We highlight key experimental achievements and recent progress in the development of a spin-based information technology.

Spin tunneling in molecular magnets controlled by dipole-dipole interactions (DDI) in the disordered state has been considered numerically on the basis of the microscopic model using the quantum mean-field approximation. In the actual case of a strong DDI spin coherence is completely lost and there is a slow relaxation of magnetization, described by t^{3/4} at short times. Fast precessing nuclear spins, included in the model microscopically, only moderately speed up the relaxation., Comment: 10 pages, 9 figures, to be published in EPJB

Combination of the thermal effet in magnetic deflagration with resonance spin tunneling controlled by the dipole-dipole interaction in molecular magnets leads to the increase of the deflagration speed in the dipolar window near tunneling resonances., 4 pages, 4 figures

Results of an experiment on a Fe8 powder done in the solid state physics laboratory in Orsay have been presented in the literature. In the present contribution, a more simple interpretation of these results is given. Moreover, the Fe8 powder is studied with a SQUID magnetometer and is shown to be non-oriented.

We report here on anisotropy of spin polarization obtained in lateral all-semiconductor all-electrical spin injection devices, employing $p^{+}-$(Ga,Mn)As/$n^{+}-$GaAs Esaki diode structures as spin aligning contacts, resulting from the dependence of the efficiency of spin tunneling on the orientation of spins with respect to different crystallographic directions. We observed an in-plane anisotropy of $~8%$ in case of spins oriented either along $[1\bar{1}0]$ or $[110]$ directions and $~25%$ anisotropy between in-plane and perpendicular-to-plane orientation of spins., 9 pages, 3 figures

We study the quantum dynamics of a system consisting of a magnetic molecule placed on a microcantilever. The amplitude and frequencies of the coupled magneto-mechanical oscillations are computed. Parameter-free theory shows that the existing experimental techniques permit observation of the driven coupled oscillations of the spin and the cantilever, as well as of the splitting of the mechanical modes of the cantilever caused by spin tunneling., 4 pages, 3 figures

We study spin-rotation effects in a magnetic molecule bridged between two conducting leads. Dynamics of the total angular momentum couples spin tunneling to the mechanical rotations. Landau-Zener spin transition produced by the time-dependent magnetic field generates a unique pattern of mechanical oscillations that can be detected by measuring the electronic tunneling current through the molecule., Comment: 5 pages, 2 figures

We study low temperature resonant spin tunneling in molecular magnets induced by a field sweep with account of dipole-dipole interactions. Numerical simulations uncovered formation of self-organized patterns of the magnetization and of the ensuing dipolar field that provide resonant condition inside a finite volume of the crystal. This effect is robust with respect to disorder and should be relevant to the dynamics of the magnetization steps observed in molecular magnets., 4 Phys. Rev. pages, 5 figures

We have shown that the size of the magnetization step due to resonant spin tunneling in a molecular magnet can be strongly affected by sound. The transverse acoustic wave can also generate macroscopic quantum beats of the magnetization during the field sweep., Comment: 4 pages, 6 figures

Spin tunneling in the particular case of the magnetic molecular cluster octanuclear iron(III), Fe8, is treated by an effective Hamiltonian that allows for an angle-based description of the process. The presence of an external magnetic field along the easy axis is also taken into account in this description. Analytic expressions for the energy levels and barriers are obtained from a harmonic approximation of the potential function which give results in good agreement with the experimental results. The energy splittings due to spin tunneling is treated in an adapted WKB approach and it is shown that the present description can give results to a reliable degree of accuracy., Comment: 17 pages, 2 figures, preprint submitted to Physica A

A storage mechanism in ferromagnetic-insulator-ferromagnetic spin-polarized tunneling junctions has been found by us. Based on this mechanism, we designed and fabricated a 2/spl times/2 bit Spin Tunneling Random Access Memory (STram). These junctions provide an excellent means of storing a binary data in the hard components, and sensing its remanent state by switching the soft component in such a way that the magnetic state of the hard component remains unaltered.

Magnetic properties of a mixed spin-$\frac{1}{2}$ and spin-1 Ising model on honeycomb lattice are exactly investigated within the framework of generalized star-triangle mapping transformation. The particular attention is focused on the effect of uniaxial and biaxial crystal-field anisotropies that basically influence the magnetic behavior of the spin-1 atoms. Our results for the basic thermodynamic quantities, as well as the dynamical time-dependent autocorrelation function indicate the spin tunneling between the $\ensuremath{\mid}+1⟩$ and $\ensuremath{\mid}\ensuremath{-}1⟩$ states in the magnetically ordered phase.

Oxidation states of AlOx in Co/AlOx/Co spin tunneling junctions were studied using X-ray photoelectron spectroscopy. Co(10nm)/AlOx/Co(50nm) spin tunneling junctions were fabricated on glass substrates by ion-beam mask sputtering. The Al layers were deposited in various thicknesses and were oxidized in pure O2 gas for 24-48 hours at room temperature. Co/AlOx bilayers simultaneously fabricated were analyzed by XPS. The thicker the Al layer is deposited, the more the unoxidized Al remains. MR ratio of the junctions increasedas the unoxidized Al decreased, and this result is qualitatively in agreement with the LMTO calculation result. The O/Al ratio of AlOx layer is about 1.9-2.0, which means existence of the higher order oxides than Al2O3. XPS depth profiles showed that the unoxidized Al remains not only near the interface with Co but also near the surface when the deposited Al layer thickness isthick.

One of the most famous single molecule magnets is Mn12(-acetate), in which the Mn cations are coupled into the magnetic unit of spin 10. Besides the high magnetic anisotropy, the crystal composed of these non-interacting uniformly oriented magnetic molecules showed the hysteresis loop with steps. These steps were explained by the thermally assisted/activated quantum tunneling of spin. At certain magnetic fields the relaxation becomes much faster, showing the resonant character of tunneling. The relaxation curve measured if quantum tunneling is present seems different from thermal exponential relaxation. Besides classical decreasing of blocking temperature in applied magnetic field, also the local minima at the resonant field appear. After zero-field cooling the dependences of magnetic moment on temperature measured in the resonant fields are different than out of the resonance. All these differences become more pronounced if the transversal magnetic field is applied. Still mysterious question is about the origin of the tunneling. Among many different explanations of the provided inner transversal field are those with hiperfine fields and dislocations in the crystal. This poster will give an overwiev of these facts originating from the combination of the classical and quantum magnetic relaxation of Mn12 toward the equilibrium.