Room-temperature Spintronic Devices Research Articles

Two-Dimensional Manganese Nitride Monolayer with Room Temperature Rigid Ferromagnetism under Strain

Developing low-dimensional spintronic materials with room temperature magnetic ordering and large spin polarization is the key for the fabrication of practical spintronic devices with a high circuit integration density and speed. Here, first-principles calculations were performed to systematically investigate a two-dimensional hexagonal MnN monolayer with room temperature magnetic ordering and 100% spin polarization. The MnN monolayer is thermally, dynamically, and mechanically stable, and intrinsically half-metallic with a very wide band gap. The Curie temperature of the MnN monolayer is estimated to be ∼368 K, which is higher than room temperature and insensitive to strain. The MnN monolayer shows half-metallic and excellent magnetic stability upon the external strain from −10 to 10%. Our calculations indicate that the MnN monolayer could be a promising material for room temperature spintronic devices.

Magnetic Behaviors of 3d Transition Metal-Doped Silicane: a First-Principle Study

We perform a first-principle computation on the magnetic properties of 3d transition metal (TM)-doped silicane. All the substituted systems are energetically stable. Robust half-metallic properties are found in Ti-, V- and Mn-substituted silicane. At the dopant concentration of 12.5%, we evaluate that the Curie temperature of Ti- and Mn-substituted silicane is at 340 and 666 K respectively in the mean-field approximation. Consequently, room-temperature ferromagnetism is easily achievable in Ti- and Mn-substituted silicane. Our work demonstrates potential application of Ti and Mn-substituted silicane for room-temperature spintronic devices.

Realization of zero-field skyrmions with high-density via electromagnetic manipulation in Pt/Co/Ta multilayers

Taking advantage of the electron-current ability to generate, stabilize, and manipulate skyrmions prompts the application of skyrmion multilayers in room-temperature spintronic devices. In this study, the robust high-density skyrmions are electromagnetically generated from Pt/Co/Ta multilayers using Lorentz transmission electron microscopy. The skyrmion density is tunable and can be significantly enhanced. Remarkably, these generated skyrmions after optimized manipulation sustain at zero field with both the in-plane current and perpendicular magnetic field being switched off. The skyrmion generation and manipulation method demonstrated in this study opens up an alternative way to engineer skyrmion-based devices. The results also provide key data for further theoretical study to discover the nature of the interaction between the electric current and different spin configurations.

Ferromagnetism and Half-Metallicity in Atomically Thin Holey Nitrogenated Graphene Based Systems.

Metal-free half-metallicity has been the subject of immense research focus in the field of spintronic devices. By using density functional theoretical (DFT) calculations, atomically thin holey nitrogenated graphene (C2 N) based systems are studied for possible spintronic applications. Ferromagnetism is observed in all the C-doped holey nitrogenated graphene. Interestingly, the holey nitrogenated graphene (C2 N) based system shows strong half-metallicity with a Curie temperature of approximately 297 K when a particular C-doping concentration is reached. It shows a strong half-metallicity compared with any metal-free systems studied to date. Thus, such carbon nitride based systems can be used for a 100 % spin polarized current. Furthermore, such C-doped systems show excellent dynamical, thermal, and mechanical properties. Thus, we predict a metal-free planar ferromagnetic half-metallic holey nitrogenated graphene based system for room-temperature spintronic devices.

Atomic-scale structure and formation of antiphase boundaries in α-Li0.5Fe2.5O4 thin films on MgAl2O4(001) substrates

The occurrence of antiferromagnetic coupling at antiphase domain boundaries (APBs) of ferromagnetic materials holds potential applications for room-temperature spintronic devices. Here, we report formation mechanism and atomic-scale structure properties of APBs in α-Li0.5Fe2.5O4 thin films on MgAl2O4 (001) substrates investigated by means of aberration-corrected scanning transmission electron microscopy. The APBs in the α-Li0.5Fe2.5O4 films are either conservative or non-conservative. Across the APBs the oxygen sublattice in α-Li0.5Fe2.5O4 is maintained, while the stacking sequence of the cation sublattice is interrupted. The propagation of APBs is found to occur in a complex way within the ferromagnetic films, including the dissociation of APBs and the formation of kinks. Importantly, the density of APBs can be tuned by controlling the thickness of the α-Li0.5Fe2.5O4 films since the APBs bound interfacial dislocations contributing to film-substrate strain relaxation. Our results evidence that the nano-scale APBs in the α-Li0.5Fe2.5O4 films are controllable and stable, which could be promising candidates for applications in nano-spintronic devices.

Magnetism in transition metal-substituted germanane: A search for room temperature spintronic devices

Using first-principles calculations, we investigated the geometric structure, binding energy, and magnetic behavior of monolayer germanane substitutional doped with transition metals. Our work demonstrates that germanane with single vacancy forms strong bonds with all studied impurity atoms. Magnetism is observed for Ti, V, Cr, Mn, Fe, and Ni doping. Doping of Ti and Mn atoms results in half-metallic properties, while doping of Cr results in dilute magnetic semiconducting state. We estimate a Curie temperature of about 735 K for Mn-substituted system in the mean-field approximation at impurity concentration 5.56%. Furthermore, when increasing the impurity concentration to 12.5%, Curie temperatures of Ti and Mn-substituted systems are 290 and 1120 K, respectively. Our studies demonstrate the potential of Ti and Mn-substituted germanane for room temperature spintronic devices.

Spin-orbit-induced gap modification in buckled honeycomb XBi and XBi3 (X = B, Al, Ga, and In) sheets

The band structure and stability of XBi and XBi3 (X = B, Al, Ga, and In) single sheets are predicted using first-principles calculations. It is demonstrated that the band gap values of these new classes of two-dimensional (2D) materials depend on both the spin-orbit coupling (SOC) and type of group-III elements in these hetero-sheets. Thus, topological properties can be achieved, allowing for viable applications based on coherent spin transport at room temperature. The spin-orbit effects are proved to be essential to explain the tunability by group-III atoms. A clear effect of including SOC in the calculations is lifting the spin degeneracy of the bands at the Γ point of the Brillouin zone. The nature of the band gaps, direct or indirect, is also tuned by SOC, and by the appropriate X element involved. It is observed that, in the case of XBi single sheets, band inversions naturally occur for GaBi and InBi, which exhibit band gap values around 172 meV. This indicates that these 2D materials are potential candidates for topological insulators. On the contrary, a similar type of band inversion, as obtained for the XBi, was not observed in the XBi3 band structure. In general, the calculations, taking into account SOC, reveal that some of these buckled sheets exhibit sizable gaps, making them suitable for applications in room-temperature spintronic devices.

Two-dimensional inversion-asymmetric topological insulators in functionalized III-Bi bilayers

The search for inversion asymmetric topological insulators (IATIs) persists as an effect for realizing new topological phenomena. However, so for only a few IATIs have been discovered and there is no IATI exhibiting a large band gap exceeding 0.6 eV. Using first-principles calculations, we predict a series of new IATIs in saturated Group III-Bi bilayers. We show that all these IATIs preserve extraordinary large bulk band gaps which are well above room-temperature, allowing for viable applications in room-temperature spintronic devices. More importantly, most of these systems display large bulk band gaps that far exceed 0.6 eV and, part of them even are up to ~1 eV, which are larger than any IATIs ever reported. The nontrivial topological situation in these systems is confirmed by the identified band inversion of the band structures and an explicit demonstration of the topological edge states. Interestingly, the nontrivial band order characteristics are intrinsic to most of these materials and are not subject to spin-orbit coupling. Owning to their asymmetric structures, remarkable Rashba spin splitting is produced in both the valence and conduction bands of these systems. These predictions strongly revive these new systems as excellent candidates for IATI-based novel applications.

Valley and spin dynamics in MoSe2 two-dimensional crystals.

We study valley and spin dynamics in monolayer molybdenum diselenide by polarization-resolved femtosecond transient absorption spectroscopy. Valley- and spin-polarized excitons are injected by a circularly polarized laser pulse, with an excess energy of 120 meV. Relaxation of the valley polarization is time-resolved by measuring dynamical circular dichroism of a linearly polarized probe pulse tuned to 790 nm, the peak of the exciton resonance of monolayer MoSe2. We obtain a valley relaxation time of 9 ± 3 ps at room temperature, which is at least one order of magnitude shorter than the simultaneously measured exciton lifetime. The results illustrate potential applications of MoSe2 in room-temperature valleytronic and spintronic devices.

Spin-lasers: From threshold reduction to large-signal analysis

Lasers in which spin-polarized carriers are injected provide paths to different practical room temperature spintronic devices, not limited to magnetoresistive effects. Unlike the conventional understanding of spintronic devices, an optimal performance of such spin-lasers can arise for finite, not infinite, spin relaxation time. By considering spin-relaxation times of both electrons and holes, we elucidate advantages of spin-lasers over their conventional (spin-unpolarized) counterparts. In addition to the steady-state threshold reduction, spin-lasers can improve transient operation leading to shorter turn-on delay times, reduced ringing of emitted light, and an enhanced bandwidth.

Growth of Sr2FeMoO6 Based Tri-layer Structure for Room Temperature Magnetoresistive Applications

Tunnel magnetoresistance in Sr2FeMoO6 based tri-layered structure was studied at room temperature. The Sr2FeMoO6/SrTiO3/Sr2FeMoO6 tri-layered structure was grown by pulse laser deposition on STO buffered Si(100) substrate. The X-ray diffraction and Micro Raman studies confirm the polycrystalline phase formation of SFMO thin films without any impurity phases. The single layer SFMO thin film shows the good ferromagnetic behavior with saturation magnetization of ∼1.48 μB/ f.u. at room temperature. The high value of tunneling magnetoresistance of ∼7% of tri-layer structure at room temperature was attributed to spin dependent tunneling through uniform STO barrier layer. The room temperature tunneling magnetoresistance in SFMO tri-layer structure open the future prospect for their possible integration to room temperature spintronic devices.

Antiferromagnetic/ferromagnetic nanostructures for multidigit storage units

The pursuit of higher densities in binary storage media is facing serious operating limitations. In order to overcome these constraints, several multistate techniques have been investigated as alternatives. Here, we report on an approach to define multistate switching memory units based on magnetic nanostructures exhibiting exchange bias. Writing and reading conditions were studied in patterned antiferromagnetic/ferromagnetic thin films. We establish the necessary and sufficient requirements for this multidigit memory concept that might open up new possibilities for the exploration and design of suitable room temperature spintronic devices.

Ferromagnetic Interfacial Interaction and the Proximity Effect in aCo2FeAl/(Ga,Mn)AsBilayer

The magnetic properties of a Co2FeAl/(Ga,Mn)As bilayer epitaxied on GaAs (001) are studied both experimentally and theoretically. Unlike the common antiferromagnetic interfacial interaction existing in most ferromagnet-magnetic semiconductor bilayers, a ferromagnetic interfacial interaction in the Co2FeAl/(Ga,Mn)As bilayer is observed from measurements of magnetic hysteresis and x-ray magnetic circular dichroism. The Mn ions in a 1.36 nm thick (Ga,Mn)As layer remain spin polarized up to 400 K due to the magnetic proximity effect. The minor loops of the Co2FeAl/(Ga,Mn)As bilayer shift with a small ferromagnetic interaction field of +24 Oe and -23 Oe at 15 K. The observed ferromagnetic interfacial coupling is supported by ab initio density functional calculations. These findings may provide a viable pathway for designing room-temperature semiconductor spintronic devices through magnetic proximity effect.

Direct evidence for significant spin-polarization of EuS in Co/EuS multilayers at room temperature

The new era of spintronics promises the development of nanodevices, where the electron spin will be used to store information and charge currents will be replaced by spin currents. For this, ferromagnetic semiconductors at room temperature are needed. We report on significant room-temperature spin polarization of EuS in Co/EuS multilayers recorded by x-ray magnetic circular dichroism (XMCD). The films were found to contain a mixture of divalent and trivalent europium, but only Eu++ is responsible for the ferromagnetic behavior of EuS. The magnetic XMCD signal of Eu at room temperature could unambiguously be assigned to magnetic ordering of EuS and was found to be only one order of magnitude smaller than that at 2.5 K. The room temperature magnetic moment of EuS is as large as the one of bulk ferromagnetic Ni. Our findings pave the path for fabrication of room–temperature spintronic devices using spin polarized EuS layers.

Room-temperature ferromagnetic behaviour of InMnAs films grown by laser ablation technique

InMnAs layers were fabricated by pulsed laser ablation of solid targets (Mn and InAs) in flow of hydrogen and arsine. The InMnAs layers with thickness ranging from 130 to 270 nm were deposited on semi-insulating GaAs (100) substrates at 320°C. The Mn quantity was controlled by changing ratio of sputtering time of Mn and InAs targets. The X-ray diffraction measurements identified the InMnAs as mosaic monocrystal with MnAs phase texture inclusions. Room temperature ferromagnetism of these InMnAs layers is evident from magnetometry and magneto-optical measurements. In addition, the InMnAs layers show anomalous Hall effect with the hysteresis loop and saturation magnetic field HS ≈ 2500 Oe at temperatures up to 300K depending on the Mn content. The Curie temperature higher than 300K allows using these magnetic semiconductor layers as a source of spin polarized carriers in room temperature spintronic devices.

Room-temperature ferromagnetism in self-assembled (In, Mn)As quantum dots

Self-assembled In1−xMnxAs quantum dots (0.19⩽x⩽0.45) have been grown on GaAs (100) substrates by low-temperature molecular beam epitaxy. The microstructure analysis revealed that the uniformly distributed In1−xMnxAs dots have a zinc blende structure as x⩽0.38. Furthermore, all samples exhibit ferromagnetic state at 5K, and their Curie temperatures range from 260to340K varying with x. These (In, Mn)As quantum dots are promising for room-temperature spintronic devices.

Ferromagnetism in Mn doped half-Heusler NiTiSn: Theory and experiment

In this letter, the authors show by ab initio density functional calculations and experiments that Mn doped semiconducting half-Heusler compound NiTiSn can exhibit room-temperature ferromagnetism. Curie temperatures were calculated by Monte Carlo simulations using calculated Heisenberg exchange parameters in an ab initio Green’s function approach. The calculated temperature exceeds room temperature for a Mn doping concentration of 22%. Magnetic measurements confirm the presence of possible intrinsic ferromagnetism in these systems. This brings up the possibility of considering this system as a potential candidate for use in room-temperature spintronic devices.

Structural, Optical, and Magnetic Behavior of in-situ Doped, MOCVD-Grown Ga1-xMnxN Epilayers and Heterostructures

AbstractDilute magnetic semiconductors (DMS) show promise as materials that can exhibit ferromagnetism at room temperature (RT). However, the nature of ferromagnetism in this material system must be well understood in order to allow intelligent design of RT spintronic devices. This work investigates the magnetic properties of the as-grown films and the effect of Mn incorporation on crystal integrity and device performance. Ga1-xMnxN films were grown by MOCVD on c-plane sapphire substrates with varying thickness and Mn concentration. Homogenous Mn incorporation throughout the films was verified with Secondary Ion MassSpectroscopy (SIMS), and no macroscopic second phases (MnxNy) were detected using X-ray diffraction (XRD). Superior crystalline quality in the MOCVD-grown films relative to Mn-implanted GaN epilayers was confirmed via Raman spectroscopy. Vibrating sample magnetometry measurements showed an apparent room temperature ferromagnetic hysteresis in the as-grown epiayers. Similarly, a marked decrease in the magnetization was observed with annealing and silicon doping, as well as in post-growth annealed Mg-codoped samples. The observed decrease in muB per Mn with increasing Mn concentration is explained by Raman spectroscopy results, which show a decrease in long-range lattice ordering and an increase in nitrogen vacancy concentration with increasing Mn concentration. Magnetic and electron-spin paramagnetic resonance (EPR) data also show that the position of the Fermi level relative to the Mn2+/3+ level is the determining factor in magnetization. Light emitting diodes (LEDs) containing a Mn-doped active region have also been produced. Devices were fabricated with different Mn-doped active layer thicknesses, and I-V characteristics show that the devices become more resistive as thickness of the Mn-doped active layer increases. The magnetic and structural properties observed in this work will be used in conjunction with characteristics and magneto-optical of the Mn-containing devices to discuss the theoretical models of ferromagnetism in Ga1-xMnxN