The implementation and control of room temperature ferromagnetism (RTFM) by adding magnetic atoms to a semiconductor's lattice has been one of the most important problems in solid state state physics in the last decade. Herein we report for the first time, to our knowledge, on the mechanism that allows RTFM to be tuned by the inclusion of \emph{non-magnetic} aluminum in nickel ferrite. This material, NiFe$_{2-x}$Al$_x$O$_4$ (x=0, 0.5, 1.5), has already shown much promise for magnetic semiconductor technologies, and we are able to add to its versatility technological viability with our results. The site occupancies and valencies of Fe atoms (Fe$^{3+}$ T$_d$, Fe$^{2+}$ O$_h$, and Fe$^{3+}$ O$_h$) can be methodically controlled by including aluminum. Using the fact that aluminum strongly prefers a 3+ octahedral environment, we can selectively fill iron sites with aluminum atoms, and hence specifically tune the magnetic contributions for each of the iron sites, and therefore the bulk material as well. Interestingly, the influence of the aluminum is weak on the electronic structure (supplemental material), allowing one to retain the desirable electronic properties while achieving desirable magnetic properties.
Recent progress in understanding and controlling spintronic properties of (Ga,Mn)As and related compounds is contrasted to diverging experimental and theoretical results concerning the origin of high temperature ferromagnetism discovered in an ample class of magnetically doped wide-band-gap semiconductors.
We study the electronic correlation effects in armchair nanoribbon and nanotube using weak-coupling approach and non-Abelian density-matrix renormalization-group method. We show that upon appropriate doping, the system exhibits a new type of flat-band ferromagnetism, different from the well-known Milke-Tasaki one. The strongly correlated ground state consists of intrinsic magnetic moments of flat-band states and itinerant carriers of dispersive bands, and the exchange coupling between them yields a ferromagnetism. The resultant ferromagnetic state with metallic conductivity has a potential in …
Spin-based electronics in topological insulators (TIs) is favored by the long spin coherence1,2 and consequently fault-tolerant information storage. Magnetically doped TIs are ferromagnetic up to 13 K,3 well below any practical operating condition. Here we demonstrate that the long range ferromagnetism at ambient temperature can be induced in Bi2-xMnxTe3 by the magnetic proximity effect through deposited Fe overlayer. This result opens a new path to interface-controlled ferromagnetism in TI-based spintronic devices.
A ferromagnetic semiconductor, rutile (Ti,Co)O2, exhibits anomalous Hall effect at room temperature. Strong dependence of the anomalous Hall effect, as well as the magneto-optic response, on the carrier concentration suggests carrier induced ferromagnetism in this compound. Both ferromagnetic responses are caused by the charge carriers at the band edge of host semiconductor, indicating possibilities of spintronics devices operable at room temperature.
Two-dimensional (2D) Van der Waals ferromagnets carry the promise of ultimately miniature spintronics and information storage devices. Among the newly discovered 2D ferromagnets all inherit the magnetic ordering from their bulk ancestors. Here we report a new 2D ferromagnetic semiconductor at room temperature, 2H phase vanadium diselenide (VSe2) which show ferromagnetic at 2D form only. This unique 2D ferromagnetic semiconductor manifests an enhanced magnetic ordering owing to structural anisotropy at 2D limit.
A review is given for the recent progress of research in the field of oxide-based diluted magnetic semiconductor (DMS), which was triggered by combinatorial discovery of transparent ferromagnet. The possible advantages of oxide semiconductor as a host of DMS are described in comparison with conventional compound semiconductors. Limits and problems for identifying novel ferromagnetic DMS are described in view of recent reports in this field. Several characterization techniques are proposed in order to eliminate unidentified ferromagnetism of oxide-based DMS (UFO). Perspectives and possible devi…
There are two competing views of itinerant ferromagnetism, the first viewing ferromagnetism as resulting from the indirect coupling between local moments via the itinerant carrier dynamics, the so-called RKKY mechanism, while in the alternative picture, ferromagnetism results from the spin polarization of itinerant carriers by the strong atomic Hund interaction - the so-called double exchange (DE) scenario. Which view describes the ferromagnetism in diluted magnetic semiconductors, materials with promise for spintronic applications, is still unclear. Here, we describe the detailed physical res…
The inherent susceptibility of low-dimensional materials to thermal fluctuations has long been expected to poses a major challenge to achieving intrinsic long-range ferromagnetic order in two-dimensional materials. The recent explosion of interest in atomically thin materials and their assembly into van der Waals heterostructures has renewed interest in two-dimensional ferromagnetism, which is interesting from a fundamental scientific point of view and also offers a missing ingredient necessary for the realization of spintronic functionality in van der Waals heterostructures. Recently several …
A report of progress in spintronics-related works involving group III nitrides is given emphasizing contradictory opinions concerning basics characteristics of these materials. The actual position of magnetic impurities in the GaN lattice as well as a possible role of magnetic precipitates is discussed. The question whether the hole introduce by the Mn impurities is localized tightly on the Mn d-levels or rather on the hybridized p-d bonding states is addressed. The nature of spin-spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined, and poss…
Employing the state-of-the-art Density Functional Theory with both GGA and hybrid HSE06 functional along with the incorporation of spin-orbit coupling, we have engineered stable room temperature ferromagnetism in non-magnetic LaH$_3$ through C substitution at octahedral and tetrahedral H sites where the induced magnetic moment is mostly contributed by 2p orbital of C atom. It is interesting that the magnetic signature is switched on with an impurity concentration as low as 1.04 at% with a magnetic moment of $\approx$ 1.0 $μ_B$ per impurity, where the localized behavior of the 2p states of C al…
Low-dimensional quantum materials that remain strongly ferromagnetic down to mono layer thickness are highly desired for spintronic applications. Although oxide materials are important candidates for next generation of spintronic, ferromagnetism decays severely when the thickness is scaled to the nano meter regime, leading to deterioration of device performance. Here we report a methodology for maintaining strong ferromagnetism in insulating LaCoO3 (LCO) layers down to the thickness of a single unit cell. We find that the magnetic and electronic states of LCO are linked intimately to the struc…
Novel 2D ferromagnets with high Curie temperature and large perpendicular magnetic anisotropy are especially attractive owing to the future promising application in modern spintronics, but meanwhile the 2D ferromagnetic materials with high Curie temperature and large perpendicular magnetic anisotropy are rarely reported. Based on density functional theory (DFT) calculations, we predict a new kind of 2D ferromagnetic materials - GdB2N2, which possesses large magnetic moment, high Curie temperature (335 K) and large perpendicular magnetic anisotropy (10.38 meV/f.u.). Biaxial strain ranging from …
The realization of semiconductors that are ferromagnetic above room temperature will potentially lead to a new generation of spintronic devices with revolutionary electrical and optical properties. Transition temperatures in doped ZnO are high but, particularly for Mn doping, the reported moments have been small. We show that by careful control of both oxygen deficiency and aluminium doping the ferromagnetic moments measured at room temperature in n-type ZnMnO and ZnCoO are close to the ideal values of 5mB and 3mB respectively. Furthermore a clear correlation between the magnetisation per tran…
Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces presents an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunction is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3 , the experiment reveals the evidence for magnetic phase separation in hole-doped Ti d1 t2g system resulting in …
Strain-enhanced edge ferromagnetism and bipolar magnetic semiconducting behavior in Janus graphene nanoribbons
School of Physics and Astronomy, and Key Laboratory of Multiscale Spin Physics (Ministry of Education), Beijing Normal University（北京师范大学物理与天文学院，多尺度自旋物理教育部重点实验室）；School of Physics and Electronics, Shandong Normal University（山东师范大学物理与电子科学学院）
Chiral antiferromagnets are currently considered for broad range of applications in spintronics, spin-orbitronics and magnonics. In contrast to the established approach relying on materials screening, the anisotropic and chiral responses of low-dimensional antifferromagnets can be tailored relying on the geometrical curvature. Here, we consider an achiral, anisotropic antiferromagnetic spin chain and demonstrate that these systems possess geometry-driven effects stemming not only from the exchange interaction but also from the anisotropy. Peculiarly, the anisotropy-driven effects are complemen…
Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO$_{3-δ}$, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-p…
For nearly a century, the Stoner model has dominated research in itinerant ferromagnetism, yet recent work on ultracold, optically trapped Fermi gases suggests that phase separation of spins occurs independent of long-range magnetic order. In this paper, we consider the breakdown of the Stoner criterion in a Landau-Fermi liquid with weak non-zero gauge field. Due to a process analogous to Kohn's theory of a metal-insulator transition, we find the stability of a Fermi liquid phase in the absence of non-quasiparticle contributions to the response is strongly dependent on Landau parameters of mix…
The seminal experimental discovery of the remarkably stable MoSi$_2$N$_4$ monolayer has led to a handful of predicted magnetic two-dimensional (2D) materials in the MA$_2$Z$_4$ family (M = transition metals, A = Si, Ge, and Z = N, P, As). These magnetic monolayers were predicted to be dynamically stable, but none of them has been synthesized to date. In this Research Letter, from first-principles thermodynamic stability analysis, we demonstrate that only the nitrides are thermodynamically stable and this occurs under N-rich conditions. Based on this finding, we propose two ferromagnetic, semic…
Two-dimensional (2D) van der Waals (vdW) magnets provide an ideal platform for exploring, on the fundamental side, new microscopic mechanisms and for developing, on the technological side, ultra-compact spintronic applications. So far, bilinear spin Hamiltonians have been commonly adopted to investigate the magnetic properties of 2D magnets, neglecting higher order magnetic interactions. However, we here provide quantitative evidence of giant biquadratic exchange interactions in monolayer NiX2 (X=Cl, Br and I), by combining first-principles calculations and the newly developed machine learning…
The chiral helimagnet, $Cr_{1/3}NbS_{2}$, hosts exotic spin textures, whose influence on the magneto-transport properties, make this material an ideal candidate for future spintronic applications. To date, the interplay between macroscopic magnetic and transport degrees of freedom is believed to result from a reduction in carrier scattering following spin order. Here, we present electronic structure measurements through the helimagnetic transition temperature, $T_{C}$ that challenges this view by showing a Fermi surface comprised of strongly hybridized Nb- and Cr- derived electronic states, an…
Here, we report the synthesis and physical properties of Co2FeGe (CFG) Heusler alloy (HA) nanoparticles (NPs). The NPs of size 23 nm are prepared using the co-precipitation method. X-ray and selected area electron diffraction patterns have confirmed the cubic Heusler phase of the NPs with the A2-disorder. These NPs are soft ferromagnetic, and exhibit a high saturation magnetization (Ms) along with a very high Curie temperature (Tc) of 1060 K. The observed Tc value matches closely with the theoretically calculated one following a model provided by Wurmehl et al. [1]. The high Ms and Tc make the…
Complex oxide systems have attracted considerable attention because of their fascinating properties, including the magnetic ordering at the conducting interface between two band insulators, such as LaAlO3 (LAO) and SrTiO3 (STO). However, the manipulation of the spin degree of freedom at the LAO/STO heterointerface has remained elusive. Here, we have fabricated hybrid magnetic tunnel junctions consisting of Co and LAO/STO ferromagnets with the insertion of a Ti layer in between, which clearly exhibit magnetic switching and the tunnelling magnetoresistance (TMR) effect below 10 K. The magnitude …
$μ$SR measurements of 3D Ising ferromagnetism in bulk Fe$_3$GeTe$_2$ crystals
Memorial University（纪念大学）；PSI Center for Neutron and Muon Sciences（瑞士保罗谢尔研究所中子与μ子科学中心）；Durham University（杜伦大学）；University of Warwick（华威大学）；Clarendon Laboratory, Department of Physics, University of Oxford（牛津大学物理系克拉伦登实验室）
Van der Waals (vdW) ferromagnets are an important class of materials for spintronics applications. The recent discovery of atomically vdW magnets CrI$_3$ and Cr$_2$Ge$_2$Te$_6$ has triggered a renaissance in the area of two-dimensional (2D) magnetism. Herein we systematically studied 2H-Mn$_{0.28}$TaS$_2$ single crystal, a 2D vdW ferromagnet with $T_c$ $\sim$ 82.3 K and a large in-plane magnetic anisotropy. Mn $K$-edge x-ray absorption spectroscopy was measured to provide information on its electronic state and local atomic environment. The detailed magnetic isotherms measured in the vicinity …
Using a positive semidefinite operator technique one deduces exact ground states for a zig-zag hexagon chain described by a non-integrable Hubbard model with on-site repulsion. Flat bands are not present in the bare band structure, and the operators $\hat B^{\dagger}_{μ,σ}$ introducing the electrons into the ground state, are all extended operators and confined in the quasi 1D chain structure of the system. Consequently, increasing the number of carriers, the $\hat B^{\dagger}_{μ,σ}$ operators become connected i.e. touch each other on several lattice sites. Hence the spin projection of the car…
Electrically induced ferromagnetism in an irradiated complex oxide
University of California, San Diego（加州大学圣迭戈分校）；University of Denver（丹佛大学）；University of California, Davis（加州大学戴维斯分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
