Flowing an electrical current that is both of high areal density and large spin polarization across a magnetic tunnel junction (MTJ) can, through spin-transfer torque (STT), alter the relative magnetic orientation of the MTJ’s ferromagnetic electrodes. This effect has enabled key next-generation MTJ applications and commercialized products, from memories to artificial synapses and energy harvesters. As MTJs are now downscaled to 2 nm, basic experimental data challenge the accepted understanding of their operation. From transport spectroscopy, ferromagnetic resonance experiments and ab-initio calculations it is revealed that the high conductivity of STT-ready MTJs, and the STT effect therein, is mediated by oxygen vacancy complexes within the MgO barrier. Our work positions the oxygen vacancy at the core of MgO spintronics. This should disrupt the status-quo on STT-MRAM R&D, by generating defect-specific research and new ideas to confer additional functionality to these next-generation electronic devices, as a nanoelectronics platform to industrialize quantum physics.

We report the dynamic characterization of the spin-torque-driven in-plane precession modes of a spin-torque nano-oscillator based on two different synthetic ferrimagnets: a pinned one characterized by a strong RKKY interaction which is exchange coupled to an antiferromagnetic layer; and a second one, non-pinned characterized by weak RKKY coupling. The microwave properties associated with the steady-state precession of both SyFs are characterized by high spectral purity and power spectral density. However, frequency dispersion diagrams of the damped and spin transfer torque modes reveal drastically different dynamical behavior and microwave emission properties in both SyFs. In particular, the weak coupling between the magnetic layers of the non-pinned SyF raises discontinuous dispersion diagrams suggesting a strong influence of mode crossing. An interpretation of the different dynamical features observed in the damped and spin torque modes of both SyF systems was obtained by solving simultaneously, in a macrospin approach, a linearized version of the Landau-Lifshitz-Gilbert equation including the spin transfer torque term.

Recent theory and experiments have showcased how to harness quantum mechanics to assemble heat/information engines with efficiencies that surpass the classical Carnot limit. So far, this has required atomic engines that are driven by cumbersome external electromagnetic sources. Here, using molecular spintronics, an implementation that is both electronic and autonomous is proposed. The spintronic quantum engine heuristically deploys several known quantum assets by having a chain of spin qubits formed by the paramagnetic Co center of phthalocyanine (Pc) molecules electronically interact with electron-spin-selecting Fe/C60 interfaces. Density functional calculations reveal that transport fluctuations across the interface can stabilize spin coherence on the Co paramagnetic centers, which host spin flip processes. Across vertical molecular nanodevices, enduring dc current generation, output power above room temperature, two quantum thermodynamical signatures of the engine's processes, and a record 89% spin polarization of current across the Fe/C60 interface are measured. It is crucially this electron spin selection that forces, through demonic feedback and control, charge current to flow against the built-in potential barrier. Further research into spintronic quantum engines, insight into the quantum information processes within spintronic technologies, and retooling the spintronic-based information technology chain, can help accelerate the transition to clean energy.

Abstract A recently discovered the rare-earth-rich site in Capacsaya, located at 123 km northwest of Cusco, at the south of Peru, contains significant quantities of light and heavy rare-earth elements such as neodymium, lanthanum, cerium, europium, and yttrium. This work reports the identification of rare-earth elements and their associated minerals using scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analyses. Five (5) samples extracted from different locations at the Capacsaya site were characterized and identified K-feldspar as the mineral associated with the rare-earth elements in a representative sample with a high concentration of lanthanum and cerium. The results showed rare-earth elements contained within the mineral phase monazite, being cerium the dominant element in the phase (La, Ce, Nd)PO $$_4$$ 4 . Finally, through the electrostatic separation process we demonstrate that it was possible to achieve an efficient separation of the K-feldspar phase in the particle size range 75–150 $$\upmu$$ μ m.

In this manuscript we propose a calculation method where the magneto-resistive elements are modelled as fluctuating resistances to correct the output voltage noise of magnetic tunnel junction (MTJ) from standard electronic circuits. This method is validated on single elements, partial and full Wheatstone bridge circuits, giving rise to a correction factor affecting the output voltage noise as well as sensitivity values. Combining the correction factor and a normalization by the number of MTJs pillars and the pillar surface, we show that the performances extracted by this method allow universal comparison between any results from literature.

In this letter, we present a study of optimized TMR magnetic field sensors as a function of voltage bias. The 1/f low-frequency noise is quantified by the Hooge-like parameter α which allows to compare the low-frequency behavior of various TMR sensors. The sensitivity as well as the detectivity of the sensor are characterized in the parallel state and at 0 mT. We observe that the sensitivity shows a strong voltage dependence and the noise presents an unexpected decrease, not anticipated by the Hooge's law. Moreover, surprisingly, an almost stable detectivity (140-200 nT/sqrt(Hz) at 10 Hz and 15-20 nT/sqrt(Hz) at 1 kHz) as a function of the bias voltage is observed, tending to highlight that the variation of sensitivity and noise are correlated. Even if the I-V curves are strongly non-linear and reflect the different symmetries of the conduction bands channels, the variations in sensitivity and noise seems to depend mainly on the distortion of the MgO barrier due to bias voltage. With a simple model where the normal noise and sensitivity of the TMR sensors are modified by an element having no noise and a parabolic conductance with voltage, we describe the behavior of noise and sensitivity from mV to V.

In this manuscript we propose a calculation method where the magneto-resistive elements are modelled as fluctuating resistances to correct the output voltage noise of magnetic tunnel junction (MTJ) from standard electronic circuits. This method is validated on single elements, partial and full Wheatstone bridge circuits, giving rise to a correction factor affecting the output voltage noise as well as sensitivity values. Combining the correction factor and a normalization by the number of MTJs pillars and the pillar surface, we show that the performances extracted by this method allow universal comparison between any results from literature.

Experiments and theory are reexamining how the laws of thermodynamics are expressed in a quantum world. Most quantum thermodynamics research is performed at sub-Kelvin temperatures to prevent thermal fluctuations from smearing the quantum engine's discrete energy levels that mediate the asymmetric shuffling of electrons between the electrodes. Meanwhile, several groups report that building an electron-spin based implementation by placing the discrete spin states of paramagnetic centers between ferromagnetic electrodes can not only overcome this drawback, but also induce a net electrical power output despite an apparent thermal equilibrium. We illustrate this thermodynamics conundrum through measurements on several devices of large output power, which endures beyond room temperature. We've inserted the Co paramagnetic center in Co phthalocyanine molecules between electron spin-selecting Fe/C60 interfaces within vertical molecular nanojunctions. We observe output power as high as 450nW(24nW) at 40K(360K), which leapfrogs previous results, as well as classical spintronic energy harvesting strategies involving a thermal gradient. Our data links magnetic correlations between the fluctuating paramagnetic centers and output power. This device class also behaves as a spintronically controlled switch of current flow, and of its direction. We discuss the conceptual challenges raised by these measurements. Better understanding the phenomenon and further developing this technology could help accelerate the transition to clean energy. Abstract (150 words) Several experiments have suggested that building a quantum engine using the electron spin enables the harvesting of thermal fluctuations on paramagnetic centers even though the device is at thermal equilibrium. We illustrate this thermodynamics conundrum through measurements on several devices of large output power, which endures beyond room temperature. We've inserted the Co paramagnetic center in Co phthalocyanine molecules between electron spin-selecting Fe/C60 interfaces within vertical molecular nanojunctions. We observe output power as high as 450nW(24nW) at 40K(360K), which leapfrogs previous results, as well as classical spintronic energy harvesting strategies involving a thermal gradient. Our data links magnetic correlations between the fluctuating paramagnetic centers and output power. This device class also behaves as a spintronically controlled switch of current flow, and of its direction. We discuss the

Experiments and theory are reexamining how the laws of thermodynamics are expressed in a quantum world. Most quantum thermodynamics research is performed at sub-Kelvin temperatures to prevent thermal fluctuations from smearing the mesoscopic quantum engine's discrete energy levels that mediate the asymmetric shuffling of electrons between the electrodes. Meanwhile, several groups report that building an electron-spin based implementation by placing the discrete spin states of paramagnetic centers between ferromagnetic electrodes can not only overcome this drawback, but also induce a net electrical power output despite an apparent thermal equilibrium. We illustrate this apparent thermodynamics conundrum through measurements on several devices of large output power, which endures beyond room temperature. We've inserted the Co paramagnetic center in Co phthalocyanine molecules between electron spin-selecting Fe/C60 interfaces within vertical molecular nanojunctions. This device class behaves as a spintronically controlled switch of current flow, and of its direction. We observe dc current output over several hours, and output power as high as 450nW(24nW) at 40K(360K). This leapfrogs previous results, as well as other energy harvesting strategies involving a thermal gradient. Our data indicates that the output power is strongly altered when the partly fluctuating paramagnetic centers undergo a magnetic phase transition. This new conceptual ingredient in the spin engine can account for the device's operation beyond the boundaries of classical thermodynamics. Further clarifying the phenomenon and developing this technology could help accelerate the transition to clean energy.

Using the electron beam of a scanning electron microscope as an external current source with tunable energy, we investigate the transport properties of high-energy electrons injected from vacuum into the metal layer of Pt/Cu/Si Schottky junctions. When the injection energy is varied between 1 and 30 keV, the current transmitted into the semiconductor increases by several orders of magnitude and reaches values orders of magnitude larger than the current injected from vacuum. Inspecting the energy dependence of the transmitted current we identify two transport regimes. In the limit of low injection energies and thick metal films, the transport is dominated by the formation and propagation of a secondary electron distribution in the metal layer. However, when the injection energy is sufficiently large and the metal layer sufficiently thin, electrons are transmitted into the semiconductor with negligible energy loss, i.e., the metal layer becomes essentially transparent. The transmitted current is then dominated by impact ionization in the semiconductor. When the metal layer of the Schottky junction is relatively thick and the injection energy of a few keV typically, the transmitted current increases abruptly. The origin of this abrupt change is interpreted as a combined effect of a quasiballistic electron transport in the metal layer and a sudden variation of the density of states in the semiconductor substrate.

The field of tunnelling spintronics has flourished through the study of magnetic tunnel junctions (MTJs) with MgO barriers. The combination of high spintronic performance and low effective barrier heights has enabled new technologies, ranging from next-generation memories to bio-inspired computing. This combination is made possible by structural defects such as oxygen vacancies. So far, experiments have pegged an energy separation between these localized states and the Fermi level, while theory has predicted that these are in fact occupied states. To rationalize the defect-mediated potential tunnelling landscape, we have performed experiments in which we tune the MTJ's Fermi level by altering one electrode's work function. We find that switching the top electrode from FeCoB to FeB increases the amplitude of defect-mediated barrier heights. Ab initio theory attributes this increase to an increased energy separation between the localized states of single and double oxygen vacancies and the Fermi level. We thus extract a rationalized potential landscape of tunnelling across oxygen vacancies in MgO involving occupied states. In junctions with high R.A. product such as ours, this leads to a picture of hole tunnelling.

En este artículo se presentan los resultados de aplicar la técnica de separación electrostática a minerales que contienen tierras raras. Se verificó la presencia de La, Ce, Sm, Pr y Nd en la muestra inicial mediante análisis de ICP-MS. Por medio de la separación electrostática se concentraron minerales conductores la hematita y no conductores como dolomita y feldespato-K. Por otro lado, mediante SEM-EDS se comprobó que los elementos de tierras raras pertenecen al mineral monacita (La, Ce, Nd)PO4 y que éste se encuentra asociado al Feldespato-K.

•The optimization of the pick-up coils via numerical simulations.•The implementation of a home-made vibrating sample magnetometer with enhanced sensitivity ∼2 × 10−4 emu.•The observation of in-plane magnetic anisotropies of thin films with a home-made VSM.

The influence of dynamic interlayer interactions on the spin-torque-driven and damped excitations are illustrated for a three layermacrospin model system that corresponds to a standard spin-torque oscillator. The free layer and a synthetic antiferromagnetic (SyF) pinned layer of the spin-torque oscillator are in-plane magnetized. In order to understand experimental results, numerical simulations have been performed considering three types of interlayer interactions: exchange interaction between the two magnetic layers of the SyF, mutual spin torque between the top layer of the SyF and the free layer and dipolar interaction between all three magnetic layers. It will be shown that the dynamic dipolar coupling plays a predominant role. First, it leads to a hybridization of the free layer and the SyF linear modes and through this gives rise to a strong field dependence of the critical current. In particular, there is a field range of enhanced damping in which much higher current is required to drive the modes into steady state. This results in a gap in the excitation spectrum. Second, the dynamic dipolar interaction is also responsible for the non-linear interaction between the current driven steady state mode and the damped modes of the system. Here one can distinguish: (i) a resonant interaction that leads to a kink in the frequency-field and frequency-current dispersions accompanied by a small hysteresis and a reduction of the linewidth of the steady state mode and (ii) a non-resonant interaction that leads to a strong frequency redshift of the damped mode. The results underline the strong impact of interlayer coupling on the excitation spectra of spin-torque oscillators and illustrate in a simple three mode model system how in the non-linear regime the steady state and damped modes influence each other.

Tunneling spintronic devices are foreseen to play an important role in emerging technologies, from data read‐out and storage to processing, including neuromorphic computing. A counterintuitive suspicion is that double oxygen vacancies within the commonly used MgO barrier underscore the high spintronic performance. Here, how the peculiar electronic properties of these nanoscale objects experimentally enhance spintronic performance is demonstrated. The vacancy's ground state near the Fermi level theoretically promotes enhanced transmission across the barrier of electrons with the Δ1 electronic symmetry that drives high spintronic performance. Annealing the MgO barrier experimentally increases the ratio of double to single oxygen vacancies. This promotes a lower Δ1 barrier height, reduces the Δ5 transmission, and enhances spintronic performance, in agreement with theory. This novel nanoscale paradigm of tunneling spintronics should affect all research that utilizes this low barrier height (e.g., spin transfer torque), help establish an ultimate limit on laterally downscaling these devices, and promote new nanoscale quantum computing concepts.

The quantum mechanical tunnelling process conserves the quantum properties of the particle considered. As applied to solid-state tunnelling (SST), this physical law was verified, within the field of spintronics, regarding the electron spin in early experiments across Ge tunnel barriers, and in the 90s across Al2O3 barriers. The conservation of the quantum parameter of orbital occupancy, as grouped into electronic symmetries, was observed in the u002700s across MgO barriers, followed by SrTiO3 (STO). In the solid-state, an additional subtlety is the sign of the charge carrier: are holes or electrons involved in transport? We demonstrate that SST across MgO magnetic tunnel junctions (MTJs) involves holes by examining how shifting the MTJu0027s Fermi level alters the ensuing barrier heights defined by the barrieru0027s oxygen vacancies. In the process, we consolidate the description of tunnel barrier heights induced by specific oxygen-vacancy induced localized states. This should provide important insight into spin transfer torque physics across MgO.

A comprehensive numerical study of the spin toque driven dynamic states is presented for a synthetic ferrimagnet. For this, the Landau-Lifshitz-Gilbert equation has been solved simultaneously for the two coupled layers of the synthetic ferrimagnet in a macrospin approach including the spin transfer torque term from an external polarizer for one of them. It is shown that a large variety of dynamic modes (in-plane precession (IPP) and out-of-plane precession) can be established, upon varying the strength of the exchange bias field that pins one of the layers of the SyF as well as the Ruderman-Kittel-Kasuya-Yosida interlayer coupling strength. The current—field state diagrams are presented as well as the frequency current dependencies of the most important mode which is the IPP mode. A characteristic feature of the IPP mode for the coupled system (as compared to single layer excitations) is the change, increase or decrease of the frequency, with current upon increasing field. It is shown that this strongly depends on the asymmetry of the internal fields that the two layers experience, upon varying either their thickness or the exchange bias field.

The quantum mechanical tunnelling process conserves the quantum properties of the particle considered. As applied to solid-state tunnelling (SST), this physical law was verified, within the field of spintronics, regarding the electron spin in early experiments across Ge tunnel barriers, and in the 90s across Al2O3 barriers. The conservation of the quantum parameter of orbital occupancy, as grouped into electronic symmetries, was observed in the '00s across MgO barriers, followed by SrTiO3 (STO). Barrier defects, such as oxygen vacancies, partly conserve this electronic symmetry. In the solid-state, an additional subtlety is the sign of the charge carrier: are holes or electrons involved in transport? We demonstrate that SST across MgO magnetic tunnel junctions (MTJs) with a large resistance-area (RA) product involves holes by examining how shifting the MTJ's Fermi level alters the ensuing barrier heights defined by the barrier's oxygen vacancies. In the process, we consolidate the description of tunnel barrier heights induced by specific oxygen-vacancy induced localized states. Our work opens prospects to understand the concurrent observation of high TMR and spin transfer torque across MgO-based nanopillars.

Materials science and device studies have, when implemented jointly as “operando” studies, better revealed the causal link between the properties of the device's materials and its operation, with applications ranging from gas sensing to information and energy technologies. Here, as a further step that maximizes this causal link, the paper focuses on the electronic properties of those atoms that drive a device's operation by using it to read out the materials property. It is demonstrated how this method can reveal insight into the operation of a macroscale, industrial‐grade microelectronic device on the atomic level. A magnetic tunnel junction's (MTJ's) current, which involves charge transport across different atomic species and interfaces, is measured while these atoms absorb soft X‐rays with synchrotron‐grade brilliance. X‐ray absorption is found to affect magnetotransport when the photon energy and linear polarization are tuned to excite FeO bonds parallel to the MTJ's interfaces. This explicit link between the device's spintronic performance and these FeO bonds, although predicted, challenges conventional wisdom on their detrimental spintronic impact. The technique opens interdisciplinary possibilities to directly probe the role of different atomic species on device operation, and shall considerably simplify the materials science iterations within device research.

Este artículo describe la implementación y una optimización detallada de un magnetómetro de muestra vibrante (VSM) para un laboratorio de licenciatura en física. Los parámetros de operación de VSM se discutieron ampliamente usando la configuración de bobinas de Foner y Mallison. Se discutió la influencia de los parámetros implicados (por ejemplo, frecuencia de oscilación, amplitud de oscilación, cambio de velocidad del campo magnético externo, configuración de bobinas, etc.) sobre la tensión inducida en las bobinas de captación. Se utilizó un disco de níquel de 6 mm de diámetro para la calibración del magnetómetro, comparando el bucle de histéresis medido con nuestro magnetómetro con el obtenido utilizando un VSM comercial. Se obtuvieron curvas de magnetización de dos muestras diferentes para probar la sensibilidad del magnetómetro. El magnetómetro de muestra vibrante implementado en el presente trabajo es capaz de detectar cambios en el momento magnético total hasta 10-3 emu. La optimización detallada del VSM descrita en el presente trabajo es un ejemplo de cómo resolver un problema real en materia condensada, relacionado con la determinación del valor de magnetización de una muestra magnética.