Materials For Spintronic Devices Research Articles

Modulation of electronic and magnetic properties of monolayer chromium trihalides by alloy and strain engineering

Monolayer CrI3 is a rare ferromagnetic semiconductor with intrinsic long-range magnetic order, which makes it a great potential material in spintronic devices [Song et al., Science 360, 1214 (2018)]. To extend the applications of monolayer CrI3 in flexible devices, the modulation of its electronic and magnetic properties is important. Here, we investigated the combined effect of strain and alloy on the properties of monolayer CrI3 by first-principles calculations. Br is chosen as the alloyed element due to the similar atomic configuration and property of CrX3 (X = Br, I), and the strain is applied by simultaneously changing the in-plane lattice constants (a and b). We find that the bandgap of monolayer Cr2I6−xBrx can be tuned greatly, while the magnetic moment of monolayer Cr2I6−xBrx is regulated very little under different strain and Br concentration. This unique property of monolayer Cr2I6−xBrx under strain makes it a good candidate for the flexible spintronic devices.

Disordered exchange is biased

The magnetic properties of intercalated metal dichalcogenides are dramatically affected by small crystal imperfections, potentially providing design principles and materials for spintronic devices.

Tunable electronic structure and magnetic properties of two-dimensional g-C3N4/Cr2Ge2Te6 van der Waals heterostructures

Recently, it has been proven that the strain, electric field and interlayer distance can effectively modulate the electronic structure and magnetic properties of two-dimensional (2D) van der Waals (vdW) heterostructures, which can facilitate the applications of 2D materials in spintronic devices. Here, the electronic structure and magnetic properties of 2D g-C3N4/Cr2Ge2Te6 vdW heterostructures are investigated by first-principles calculations. The combination of these two monolayers significantly affects their lattice structures. With the increase of biaxial compressive strain ε, the band gap of the heterostructures gradually decreases, where the band gap is 61.4 meV at ε = −2%. At ε = −4% and −6%, the g-C3N4/Cr2Ge2Te6 heterostructures are metallic. At a biaxial compressive strain, the heterostructures show the in-plane magnetic anisotropy (IMA), but the system shows the perpendicular magnetic anisotropy at a biaxial tensile strain. By applying the electric field, the heterostructures show IMA. The band gap of the heterostructures hardly changes by changing the interlayer distance, but the magnetic anisotropy is changed. The spin channel of g-C3N4 inverses at valence band maximum as the interlayer distance increases by 0.75 Å. These results are significant to developing the low-dimensional spintronic devices.

Prediction of giant and ideal Rashba-type splitting in ordered alloy monolayers grown on a polar surface.

A large and ideal Rashba-type spin-orbit splitting is desired for the applications of materials in spintronic devices and the detection of Majorana fermions in solids. Here, we propose an approach to achieve giant and ideal spin-orbit splittings through a combination of ordered surface alloying and interface engineering, that is, growing alloy monolayers on an insulating polar surface. We illustrate this unique strategy by means of first-principle calculations of buckled hexagonal monolayers of SbBi and PbBi supported on Al2O3(0001). Both systems display ideal Rashba-type states with giant spin-orbit splittings, characterized with energy offsets over 600 meV and momentum offsets over 0.3 Å−1, respectively. Our study thus points to an effective way of tuning spin-orbit splitting in low-dimensional materials to draw immediate experimental interest.

Theoretical study of enhanced ferromagnetism and tunable magnetic anisotropy of monolayer CrI3 by surface adsorption

Magnetic anisotropy energy (MAE) plays a key role for 2D magnetic materials, which have attracted significant attention for their promising applications in spintronic devices. Based on first-principles calculations, we have investigated the influence of surface adsorption on the ferromagnetism and MAE of monolayer CrI3. We find that Li adsorption can dramatically enhance its ferromagnetism, and tune its easy magnetization axis to the in-plane direction from original out-of-plane at certain coverage of Li. The monotonic enhancement of in-plane magnetism in CrI3 as the coverage of Li increases are attributed to electrostatic doping induced by charge transfer between Li atoms and I atoms, as supported by the charge doping simulation. The tunable robust magnetic anisotropy may open new promising applications of CrI3–based materials in spintronic devices.

Exploitable Magnetic Anisotropy of Magnetic CrBr3 Monolayer

We investigated the influence of Li and F adsorption on the ferromagnetism and magnetic anisotropy energy of CrBr3 monolayer based on the first-principles calculations. It is observed that Li adsorption can dramatically enhance its ferromagnetism, and tune its easy magnetization axis to the in-plane direction from original out-of-plane. The monotonic enhancement of in-plane magnetism in CrBr3 as the coverage of Li increases is attributed to electrostatic doping induced by charge transfer between Li atoms and Br atoms. By contrast, the F adsorption reduces the out-of-plane magnetism in CrBr3 as the coverage of F increases, but keeps the original easy magnetization. Our results may open new promising applications of CrBr3-based materials in spintronic devices.

Light-Enhanced Spin Diffusion in Hybrid Perovskite Thin Films and Single Crystals.

Organolead trihalide perovskites have attracted substantial interest with regard to applications in charge-based photovoltaic and optoelectronic devices because of their low processing costs and remarkable light absorption and charge transport properties. Although spin is an intrinsic quantum descriptor of a particle and spintronics has been a central research theme in condensed matter physics, few studies have explored the spin degree of freedom in the emerging hybrid perovskites. Here, we report the characterization of a spin valve that uses hybrid perovskite films as the spin-transporting medium between two ferromagnetic electrodes. Because of the light-responsive nature of the hybrid perovskite, a high magnetoresistance of 97% and a large spin-diffusion length of 81 nm were achieved at 10 K under light illumination in polycrystalline films. Furthermore, by using thin perovskite single crystals, we discovered that the spin-diffusion length was able to reach 1 μm at low temperatures. Our results indicate that the spin relaxation is not significant as previously expected in such lead-containing materials and demonstrate the potential of low-temperature-processed hybrid perovskites as new active materials in spintronic devices.

Cu-doping impact on the electronic and magnetic properties of Co[formula omitted]ZrSn

The electronic and magnetic properties of Cu-doped Full-Heusler Co2ZrSn compound are investigated using first-principles calculations. The Cu-doping at Co-site (Cu@Co) exhibits a substantial impact on the physical properties of Co2ZrSn system. Half-metallic ferromagnetism is evident within the GGA method for the undoped system, while the GGA+U scheme diminishes the half-metallicity. Our calculations show that as Cu-concentration increases, the total magnetic moment of the system decrease and become non-magnetic for 75% and 100% Cu-doping within GGA and GGA+U methods, respectively. Furthermore, spin-polarization is computed, which is an important parameter for the utilization of magnetic materials in spintronic devices. Finally, the doped structure’s stability is analyzed by calculating the formation energies.

Electronic structure and magnetic properties of 3d transition-metal atom adsorbed SnO monolayers

Monolayer SnO has attracted extensive attention due to the unique electronic properties, which have potential applications in nanoelectronic and optoelectronic devices. Transition metal (TM) atoms are often used to modulate electronic structures and magnetic properties of two dimensional (2D) materials, which can facilitate the application of these materials in spintronic devices. The electronic structure and magnetic characteristics of 3d TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) adsorbed SnO monolayer are predicted by first-principle calculations. The n-type doping in the SnO monolayer appears when Sc, Ti, V, Cr, Mn, Fe and Zn atoms are adsorbed. Co, Ni and Cu adsorptions induce the p-type doping in the SnO monolayer. In addition, the magnetic moments of SnO in the adsorption systems are in the range from −0.038 to 0.414 μB, and that reach the maximum at the case of Ni-absorbed. It is also found that Fe, Co and Ni adsorbed SnO monolayers have a perpendicular magnetic anisotropy (PMA), while Ti, V, Cr and Mn adsorbed SnO monolayers have an in-plane magnetic anisotropy (IMA). Our results indicate that TM adsorbed SnO monolayers have the potential applications in spintronic devices.

Structural phase transition and spontaneous exchange bias in NiCr1.9Fe0.1O4 nanoparticles: XRD, EXAFS and magnetic measurements

Abstract Here, we report structural and magnetic phase transitions in NiCr1.9Fe0.1O4 nanoparticles of size ∼60 nm synthesized through cost-effective co-precipitation route. X-ray diffraction pattern shows a stable cubic phase at RT in contrast to tetragonal phase in bulk NiCr2O4. Decreasing the temperature, a complete tetragonal symmetry is observed at 50 K, while a coexistence of cubic and tetragonal phases in the intermediate temperature range. Interestingly, no tetragonal to orthorhombic phase transformation has been observed down to 12 K as observed in NiCr2O4 at 70 K. The local structure examined from temperature dependent EXAFS demonstrates that although no change in distribution of cations among tetrahedral (A) and octahedral (B) sites down to 10 K has been observed, Fe3+ ions occupy A site replacing equivalent amount of Ni2+ towards B site which is contradicting to the bulk NiCr2O4 where Ni2+ occupies only A site. Magnetic studies demonstrate a two-fold increase in para to long-range ferrimagnetic transition, TC, due to increase in A-B exchange interaction and no change in spiral ordering temperature, TS indicates strong B-B interaction. In addition, these nanoparticles exhibit unusually high spontaneous exchange bias of ∼1.265 kOe at 60 K. We discuss the temperature dependent exchange bias on the basis of competition between uncompensated B site moments and ferromagnetically ordered spins at A site. The tunable exchange bias without field highlight the potential applications of these materials in spintronics devices.

Half metallic ferromagnetism of Mn-doped indium nitride nanoparticles

Herein, Mn3+ doped InN nanoparticles (InN:Mn NPs) with room-temperature ferromagnetism were successfully synthesized via a vapor – solid phase nitriding reaction. The content of doped Mn3+ can effectively change the ferromagnetic properties of the as-synthesized samples. The saturation magnetization value of InN nanoparicles with various Mn3+ doping concentrations display a parabolic-like change as the Mn3+ doped content increase and reaches the top value of 0.2998 emu g−1 corresponding to the Mn3+ doped content of 0.91 at.% at room temperature. Magnetic properties originate from the coupling between N 2p orbital and Mn 3d orbital in the conduction bands. Compared with pure InN nanoparticles, half metallic ferromagnetic InN:Mn nanoparticles have smaller electric resistivity, larger hall coefficient and hall mobility, which will be a promising material in spintronic devices.

The metal-free magnetism and ferromagnetic narrow gap semiconductor properties in graphene-like carbon nitride

In spintronics, if a two-dimensional (2D) organic metal-free material has stable magnetism and narrow gap semiconductor properties, it will have a very bright application prospect. A graphene-like carbon nitride (g-C13N13) that we design just meets these requirements. As a new structure, firstly the stability of the g-C13N13 has been verified. It has stable electron spin polarization and the magnetic moment of each primitive cell is 1μB. It exhibits ferromagnetic narrow gap semiconductor properties through our analysis of energy band structure and charge density. Ferromagnetic ordering between two adjacent primitive cells is stable. The Monte Carlo simulation using the Ising model shows the Curie temperature material is 204 K. Our research is an inspiration for the applications of this kind of materials in spintronics devices.

Giant Inverse Spin Hall Effect in Bi Doped PtBi Alloy

AbstractFor generating or detecting spin currents without ferromagnetic materials in spintronic devices, nonmagnetic materials with large spin Hall angles would elicit extreme interest. A giant inverse spin Hall effect (ISHE) generating in Pt doped with 8% Bi by composition is demonstrated. From a combination of ferromagnetic resonance, spin pumping, and ISHE experiments, a large spin current is found induced in an yttrium iron garnet/Pt0.92Bi0.08 bilayer. The spin diffusion length and spin Hall angle of the Pt0.92Bi0.08 alloy are λSD = 3.3 ± 0.1 nm and θSH = 0.106 ± 0.005, respectively. In the experiments, the spin–charge conversion of this alloy is twice that of Pt and is larger than most reported heavy metals. Such enhancement can be attributed to the skew scattering from the high atomic number of Bi impurities via the spin–orbit interaction.

Superior room-temperature magnetic field-dependent magnetoelectric effect in BiFeO3-based multiferroic

Multiferroics that exhibit simultaneous electric and magnetic orders have attracted a great deal of interests both in fundamental science and practical applications. In general, high-performance single-phase multiferroics are extremely rare, owing to the incompatibility between ferroelectricity and magnetism. The most interesting property that makes multiferroics useful in device applications is the direct and significant magnetoelectric coupling at room temperature, resulting in a hysteretic magnetoelectric response. However, it still remains a great challenge to realize such a cross-coupling hysteresis loop between the ferroelectric and magnetic orders, i.e. an effective magnetic command of polarization, or an electric-field command of magnetization in a single-phase bulk material. Here we report the multiferroic behavior of chemically modified bismuth ferrite, Bi0.88Dy0.12Fe0.97Ti0.03O3+δ, which exhibits simultaneous (weak) ferromagnetism and ferroelectricity. More interestingly, this solid solution shows an evident magnetoelectric effect at a low magnetic field by demonstrating a hysteretic loop that characterizes the electric voltage signal as a function of bias magnetic field. Moreover, the room-temperature magnetoelectric effect with the saturated magnetoelectric coefficient up to ±0.23 mV/cm•Oe at ±250 Oe is obtained. The observed properties are attributed to the combination of linear magnetoelectric effect and domain wall motion. This result points to potential new applications of single-phase multiferroic materials in spintronic devices in which electric dipoles can be effectively tuned by a magnetic field.

First-principles study of the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube

By using first-principles calculations based on density-functional theory, the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube are systematically investigated. The binding energies of the hybrid structures are remarkably higher than those of corresponding freestanding TM chains, indicating the TM chains are significantly stabilized after encapsulating into copper nanotube. The formed bonds between outer Cu and inner TM atoms show some degree of covalent bonding character. The magnetic ground states of Fe@CuNW and Co@CuNW hybrid structures are ferromagnetic, and both spin and orbital magnetic moments of inner TM atoms have been calculated. The magnetocrystalline anisotropy energies (MAE) of the hybrid structures are enhanced by nearly fourfold compared to those of corresponding freestanding TM chains, indicating that the hybrid structures can be used in ultrahigh density magnetic storage. Furthermore, the easy magnetization axis switches from that along the axis in freestanding Fe chain to that perpendicular to the axis in Fe@CuNT hybrid structure. The large spin polarization at the Fermi level also makes the hybrid systems interesting as good potential materials for spintronic devices.

Magnetization and Spin Polarization of Heusler Alloys Co $_{2}$TiSn and Co$_{2}$ TiGa$_{0.5}$Sn $_{0.5}$

The substitution effect on half-metallicity for Co-based Heusler alloys Co 2 TiGa 1-x Sn x was investigated by experimental measurements and first-principles band calculations. The synthesized alloys crystalized in the ordered L2 1 crystal structure. The spontaneous magnetization obeyed the Slater-Pauling rule, indicating the possibility that Co 2 TiSn and Co 2 TiGa 0.5 Sn 0.5 are half-metals. The first-principles band calculations revealed that Co 2 TiSn is half-metal and Co 2 TiGa 0.5 Sn 0.5 is nearly half-metal. The spin polarization P was determined by the Andreev reflection technique. The intrinsic P values were 58.9% for Co 2 TiSn and 58.2% for Co 2 TiGa 0.5 Sn 0.5 , respectively. The P values of Co 2 TiGa 1-x Sn x were relatively higher than other Co-based Heusler alloys. Thus, Co-based Heusler alloys Co 2 TiGa 1-x Sn x are possible candidates for half-metallic electrode materials in spintronic devices.

ChemInform Abstract: Perpendicular Magnetic Anisotropy in Co‐Based Full Heusler Alloy Thin Films

AbstractReview: 59 refs.

Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and their magnetic coupling with ferromagnetic surface: first-principles study

Using first-principles calculations, we have systematically investigated the structural, electronic, and magnetic properties of facial (fac-) and meridional (mer-) tris(8-hydroxyquinoline)iron(III) (Feq3) molecules and their interaction with ferromagnetic substrate. Our calculation results show that for the isolated Feq3, mer-Feq3 is more stable than the fac-Feq3; both Feq3 isomers have a high spin-state of 5 μB as the ground state when an on-site Hubbard-U term is included to treat the highly localized Fe 3d electrons; while the standard DFT calculations produce a low spin-state of 1 μB for mer-Feq3. These magnetic behaviors can be understood by the octahedral ligand field splitting theory. Furthermore, we found that fac-Feq3 has a stronger bonding to the Co surface than mer-Feq3 and an anti-ferromagnetic coupling was discovered between Fe and Co substrate, originating from the superexchange coupling between Fe and Co mediated by the interface oxygen and nitrogen atoms. These findings suggest that Feq3 molecular films may serve as a promising spin-filter material in spintronic devices.

Spin-Current and Spin-Splitting in Helicoidal Molecules Due to Spin-Orbit Coupling.

The use of organic materials in spintronic devices has been seriously considered after recent experimental works have shown unexpected spin-dependent electrical properties. The basis for the confection of any spintronic device is ability of selecting the appropriated spin polarization. In this direction, DNA has been pointed out as a potential candidate for spin selection due to the spin-orbit coupling originating from the electric field generated by accumulated electrical charges along the helix. Here, we demonstrate that spin-orbit coupling is the minimum ingredient necessary to promote a spatial spin separation and the generation of spin-current. We show that the up and down spin components have different velocities that give rise to a spin-current. By using a simple situation where spin-orbit coupling is present, we provide qualitative justifications to our results that clearly point to helicoidal molecules as serious candidates to integrate spintronic devices.

Phase Structure and Magnetic Properties of Mn70Ga30–xSnx ($x = 5$ –30) Alloy Ribbons

In recent years, much attention has been paid to new rare-earth-free magnetic materials to avoid using the expensive and limited availability of rare earths. The Mn-based alloys with high magnetic anisotropy and Curie temperature well above room temperature have been regard as good candidate materials in spintronic devices and rare-earth-free magnets. In which, Mn-Ga binary compounds are such materials that exhibit a combination of various technologically important properties including high spin polarization, high perpendicular anisotropy, and high Curie temperature, multiple structures, temperature-induced phase transitions. An important feature of this kind of materials is that their structural and magnetic properties can be tuned with the changes of elemental compositions and annealing conditions to fit a specific practical application [1]. On the other hand, the Mn 3 Ga compound has the hexagonal structure of Ni 3 Sn (D0 19 ) type similar to Mn 3 Ge and Mn 3 Sn, which are known to have the triangular antiferromagnetic spin structure with a small ferromagnetic moment in the c plane. In 1993, H. Niida reported the phase structure and magnetic properties of pseudobinary system Mn 3+δ Ga 1−x Ge x ingots [2]. It was found that the D0 19 -type structure is stable at 873 K in the whole composition range 0 ≤ x ≤ 1.0 with appropriate values of δ. In previous work, we reported the phase evolution, electric and magnetic properties of the annealed Mn 60+x Ga 40-x (x = 0−15) melt-spun ribbons [3]. In this work, Mn 70 Ga 30−x Sn x (x = 5, 10, 15, 20, 30) melt-spun ribbons were prepared by using melt-spinning and subsequently annealing. The effects of Sn substitution for Ga on phase structure, Curie temperature T C , magnetic properties of these annealed Mn-Ga-Sn ribbons have been investigated.