Room Temperature Ferromagnetism Research Articles

2D nature of magnetic states at SnO2 surfaces: a combined experimental and theoretical study.

For undoped SnO2, room temperature ferromagnetism could be seen uniquely in 2-dimensional configurations, particularly in ultra-thin films (whose thickness is ideally below 100 nm). Both bulk samples and nano-powders of pristine SnO2 are diamagnetic, indicating that a 2D surface is a key point in shaping up the magnetic properties in SnO2. As a complement to our experiments, we have performed a series of quantum-mechanical calculations for the bulk rutile-structure SnO2 as well as its (001) and (101) surfaces. The calculations included several atomic configurations with and without vacancies in/under the studied surfaces. The stability of the non-magnetic ground state of rutile SnO2 bulk was cross-checked and confirmed by its phonon spectrum computed within the harmonic approximation. Regarding the surfaces, the bulk-like (001) surface containing Sn vacancies has turned out to be ferromagnetic, while the shift of Sn vacancies under the surface resulted in a more complex ferrimagnetic state. The bulk-like (001) surface without vacancies and that with the O vacancies are predicted to be non-magnetic. Regarding the (101) surfaces, those terminated by a single layer of oxygen atoms and those terminated by tin atoms are non-magnetic, while a surface terminated by two layers of oxygen has turned out to be ferromagnetic.

Room-temperature ferromagnetism, half-metallicity and spin transport in monolayer CrSc2Te4-based magnetic tunnel junction devices.

The discovery of novel two-dimensional (2D) half-metallic materials with a robust ferromagnetic (FM) order and a high Curie temperature (Tc) is attractive for the advancement of next-generation spintronic devices. Here, we propose a monolayer with stable 2D intrinsic FM half-metallicity, i.e., the CrSc2Te4 monolayer, which was constructed by intercalating a monolayer of 1T-CrTe2-type sandwiched between two layers of 2H-ScTe2 monolayers. Our calculations reveal that it exhibits exceptional dynamical, thermal, and mechanical stabilities accompanied by a robust half-metallicity characterized by a wide bandgap of 1.02 eV and FM ordering with a high Tc of 326 K. Notably, these properties remain intact in almost the entire range of the biaxial strain from -5% to 5%. Furthermore, our investigations demonstrate excellent spin transport capabilities, including an outstanding spin-filtering effect, and a remarkably high tunneling magnetoresistance ratio peaking at 6087.07%. The remarkable magnetic features of the 2D CrSc2Te4 monolayer with room temperature FM, intrinsic half-metallicity, and 100% spin-polarization make it a promising candidate for the next-generation high-performance spintronic nanodevices as well as high-density magnetic recording and sensors.

Ferroelectrically controlled electromagnetic and transport properties of VN2H2/Al2O3 van der Waals multiferroic heterostructures.

The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductors owing to the lack of intrinsic single-phase multiferroic materials in nature. In this study, we propose a VN2H2/Al2O3 van der Waals magnetoelectric multiferroic heterostructure and investigate its electronic, magnetic, and transport properties using density functional theory combined with the Boltzmann transport theory. The VN2H2 monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the Al2O3 monolayer is a ferroelectric semiconductor with a polarization value of 0.11 C m-2. In the VN2H2/Al2O3 van der Waals heterostructures, the conversion between the metal and the semiconductor can be controlled by altering the polarization of the Al2O3 layer. The VN2H2/Al2O3 van der Waals heterostructure retains room-temperature ferromagnetism, and the reverse of polarization is accompanied with a change in the direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructures, which have potential applications in next-generation low-power logic and memory devices.

Stable room-temperature ferromagnetism and gate-tunable quantum anomalous Hall effect of two-dimensional 5d transition-metal trihalide OsX3 (X = Cl, Br, I) monolayers.

5d transition-metal compounds are usually not expected to exhibit distinct magnetic ordering owing to their substantial binding energy associated with 5d electrons. In this study, we demonstrate that two-dimensional (2D) 5d transition-metal Os trihalide OsX3 monolayers can exhibit room-temperature ferromagnetism and quantum anomalous Hall effect (QAHE) by utilizing density functional theory and Monte Carlo simulation. Our calculation results of coexisting Raman and infrared activities of lattice vibration reveal the structural stability of 2D OsX3 (X = Cl, Br, I) and structural instability of 2D OsX3 (X = F). Furthermore, all 2D OsX3 trihalides (X = Cl, Br, I) are half-metals, and their ferromagnetism remains stable under ambient temperature, where 2D OsCl3 and OsBr3 have an in-plane easy axis while 2D OsI3 has an out-of-plane easy axis. Notably, when spin-orbit coupling is included, the gate-tunable QAHE could emerge in ferromagnetic 2D OsI3, while 2D OsCl3 and OsBr3 are topologically trivial. Additionally, the magnon bands of 2D OsX3 (X = Cl, Br, I) possess two spin-wave branches with dispersion similar to that of the Dirac cone in the electronic structure of graphene, which are attributed to the unique ferromagnetic honeycomb sublattice of osmium atoms.

Magnetic properties of Mn-doped InSb nanowires from first principles

Room-temperature ferromagnetism (RTFM) has been achieved in Mn-doped InSb nanowires (NWs) through experiment. However, the underlying cause of RTFM remains unclear. In this paper, using first-principles calculations, the distribution of Mn ions and magnetic properties of Mn-doped wurtzite and zinc blend InSb NWs have been investigated. Our results indicate that wurtzite (In,Mn)Sb NWs can exhibit superior ferromagnetic behavior compared to zinc blend (In,Mn)Sb NWs. The distribution of Mn ions and magnetic properties in the (In,Mn)Sb NWs is influenced by their size, surface passivation and crystal structure. Furthermore, the ferromagnetic coupling is short-range in passivated (In,Mn)Sb NWs, and as the size of the NW decreases, the Mn-3d level becomes a deep acceptor in the band gap, resulting in an enhancement of ferromagnetism.

Introduction of the -B(OH)2 group into a graphene motif for pz orbital removal and ferromagnetic modulation.

Room-temperature ferromagnetism in graphene has attracted considerable attention due to its potential application as spintronics. Theoretically, magnetic moment of graphene can be generated by removing a single pz orbital from the π system, which introduces an unpaired electron into the graphene motif for magnetic coupling. In this work, pz orbital of graphene is experimentally removed by cleaving the π bond of graphene using H3BO3 with the assistance of supercritical CO2 (SC CO2), which simultaneously introduces -B(OH)2 groups and unpaired electrons. As a result, ferromagnetic coupling between unpaired electrons substantially enhances the magnetic properties of the 2D graphene motif, leading to room-temperature ferromagnetism. Overall, unpaired electrons were introduced into a 2D graphene motif through π bond cleavage, which provides a novel approach for magnetic manipulation of 2D materials with conjugated structures.

Cationic and oxygen defect modulation for tailoring the bandgap and room temperature ferromagnetism of CuO via multiple d-block cations

The potential of oxide-based dilute magnetic semiconductors (DMSs) for use in spintronics and magneto-optic devices has garnered a lot of attention over the years.

Room temperature ferromagnetism of graphite: Impurity induced vs intrinsic origin

Room temperature ferromagnetism of graphite: Impurity induced vs intrinsic origin

Two-dimensional Cr2GaX4 (X = S, Se, Te) monolayers: half-metallic intrinsic room temperature ferromagnets with large magnetic anisotropy

Based on first-principles calculations, we predict a series of Cr2GaX4 (X = S, Se, Te) monolayers, which exhibit intrinsic ferromagnetic ordering, large magnetic anisotropy energy, and high Curie temperatures above room temperature.

Impact of magnetic, thermal, structural, morphological and optical characteristics on room temperature ferromagnetism of pristine and cerium doped ZnO nanocomposites

An excellent fit between the theoretical and experimental studies of the related to structure, optics, and magnetism features of pristine and cerium-modified Zn-O NPs prepared through the wet chemical technique. Refining the XR-D pattern using the Rietveld-method reveals that the samples have a hexagonal Wurtzite structure. Absorption spectra reveal a shrinking bandwidth gap as cerium doping increases, substantiating ce2+ ion's essential function in ZnO's spectral qualities. The narrowing of the bandwidth gap due to the presence of impurity states was also verified by first-principles calculations. The residual magnetization increases with Cerium doping, and magnetic tests show roomtemperature weak-ferromagnetism (RTFM). In addition, ferromagnetism for cerium doping is confirmed by both first-principles calculations and experiments. Theoretical calculations imply that the cerium atoms may agglomerate to generate metallicantiferromagnetic chromium oxide when cerium doping reaches 8%. At ambient temperature, however, ferromagnetic behaviour is feasible since both ferromagnetic and antiferromagnetic behaviour are degraded when cerium is widely disseminated throughout the lattice as revealed by XRD studies

Spin-degree manipulation for one-dimensional room-temperature ferromagnetism in a haldane system.

The intricate correlation between lattice geometry, topological behavior and charge degrees of freedom plays a key role in determining the physical and chemical properties of a quantum-magnetic system. Herein, we investigate the introduction of the unusual oxidation state as an alternative pathway to modulate the magnetic ground state in the well-known S = 1 Haldane system nickelate Y2BaNiO5 (YBNO). YBNO is topologically reduced to incorporate d9-Ni+ (S = 1/2) in the one-dimensional Haldane chain system. The random distribution of Ni+ for the first time results in the emergence of a one-dimensional ferromagnetic phase with a transition temperature far above room temperature. Theoretical calculations reveal that the antiferromagnetic interplay can evolve into ferromagnetic interactions with the presence of oxygen vacancies, which promotes the formation of ferromagnetic order within one-dimensional nickel chains. The unusual electronic instabilities in the nickel-based Haldane system may offer new possibilities towards unconventional physical and chemical properties from quantum interactions.

Prediction of intrinsic room-temperature ferromagnetism in two-dimensional CrInX2 (X = S, Se, Te) monolayers.

Herein, using density functional theory, novel two-dimensional (2D) CrInX2 (X = S, Se, Te) structures are predicted to be practical ferromagnetic (FM) semiconductors. Phonon vibrations and molecular dynamics simulations verified their structural and thermodynamic stability. Sizable fully spin-polarized band gaps of 1.03 and 0.69 eV are found for CrInS2 and CrInSe2, while CrInTe2 exhibits half-metallic band nature (at 0 K with a perfect lattice). The high magnetic anisotropy energies are responsible for their long-range spin polarization. The Curie temperatures (Tc) are estimated to be 347, 397 and 447 K for CrInS2, CrInSe2 and CrInTe2, respectively, all well above the room-temperature. The high Tc originates from unusual FM direct exchange, the efficient super-exchange coupling between neighboring Cr eg-orbitals with zero virtual exchange gaps and the presence of dual Cr-X-Cr super-exchange channels. Our systematic study of the CrInX2 monolayer suggests that it could be a promising material for spintronics applications.

Structure-dependent spin-polarized electron transport in twin-crystal Cu1-xEuxO semiconductors.

In this work, Eu-doped twin copper oxide (twin Cu1-xEuxO) was synthesized using the gas-liquid phase chemical deposition method in combination with high-temperature oxidation. The incorporation of Eu3+ ions was affected by their diffusivity and the related charge trapping mechanisms. The twin Cu1-xEuxO configuration exhibited significant room-temperature ferromagnetism. From our analysis, it was demonstrated that as the Eu3+ doping concentration increased, the saturation magnetization first increased and then gradually decreased, reaching a peak at 0.82 at%. A p-type to an n-type semiconducting transition was also recorded as the doping concentration increased. A significant anomalous Hall effect characterized by a maximum anomalous Hall coefficient of 1.65, and a maximum Hall conductivity mobility of 16.50 Ohm-1 cm-1 and 250.59 cm2 v-1 s-1, respectively, were derived for the twin Cu1-xEuxO, doped with 0.82 at% at room temperature. First-principles computational simulations were also conducted to elucidate the underlying mechanisms of the magnetic properties, the p-type to n-type transition, and the interplay between the spin-polarized states associated with 4f and carriers. In twin Cu1-xEuxO, the anomalous Hall effect originated from the contribution of the edge-to-jump scattering mechanism. The latter can be significantly enhanced by doping with Eu atoms, which yields the manifestation of the oblique scattering mechanism. Our work paves the way for the development of twin Cu1-xEuxO material structures, which emerge as an ideal candidate for future spintronic applications.

First-principles predictions of room-temperature ferromagnetism in orthorhombic MnX2 (X = O, S) monolayers.

Two-dimensional ferromagnets with high spin-polarization at ambient temperature are of considerable interest because they might be useful for making nanoscale spintronic devices. We report that even though bulk phases of MnO2 are generally antiferromagnetic with low ordering temperatures, the corresponding MnO2 and MnS2 monolayers are ferromagnetic, and MnS2 is a high temperature half metallic ferromagnet. Based on first-principles calculations, we find that the MnO2 monolayer is an intrinsic ferromagnetic semiconductor with a Curie temperature TC of ∼300 K, while the half-metallic MnS2 monolayer has a remarkably high TC of ∼1150 K. Both compounds have substantial magnetocrystalline anisotropy, out of plane in the case of MnO2 monolayers, and in plane along the b-axis of orthorhombic MnS2 monolayer. Interestingly, a metal-insulator phase transition occurs in the MnS2 monolayer when the applied biaxial strain is beyond -2%. Tuning near this metal-insulator transition offers additional possibilities for devices. The present work shows that MnX2 (X = O, S) monolayers have the properties required for ultrathin nano-spintronic devices.

Influence of adding manganese chromium-layered double oxide on the optical, magnetic and dielectric properties of cobalt spinel ferrite nanoparticles

Hydrotalcite-like materials such as layered double oxides (LDOs) are promising materials for many technological applications. Linking the multilayer structure of LDOs with the exceptional optical, magnetic, and dielectric properties of spinel ferrites could result in advanced nanocomposites for photovoltaic, magneto-recording, and high-frequency applications. For that purpose, nanocomposites of type manganese chromium-layered double oxide/cobalt spinel ferrite, (MnCr)-LDOx/CoFe2O4 (x = 1, 3, and 5 wt%), were produced by the co-precipitation route. X-ray diffraction (XRD) analysis showed the successful incorporation of MnCr-LDO in CoFe2O4 lattice. After a 5 wt% addition of MnCr-LDO, the lattice parameter of pure CoFe2O4 increased from 8.3832 Å to 8.4136 Å, the crystallite size increased from 18.7 nm to 21.7 nm, and the strain dropped from 2.15 to 2.04. Transmission electron microscopy (TEM) revealed cubic morphologies for (MnCr)-LDOx/CoFe2O4 nanocomposites. Two strong absorbance peaks appeared in the Ultraviolet- visible (UV-vis) spectra (at ∼270 and ∼370 cm−1). The energy band gap and Urbach energy were estimated for the prepared samples. The composite sample (MnCr)-LDO1 wt%/CoFe2O4 recorded the highest band gap values (Eg1 = 3.39 eV, Eg2 = 4.46 eV, and Eg3 = 5.89 eV), while the (MnCr)-LDO3 wt%/CoFe2O4 sample had a relatively high Urbach energy value (1.35 eV). Vibrating sample magnetometer (VSM) analysis showed room temperature ferromagnetic (RTFM) behavior for the prepared composites. The saturation magnetization (Ms) value declined as the MnCr-LDO addition to CoFe2O4 increased, and the (MnCr)-LDO3 wt%/CoFe2O4 sample acquired the highest Ms (64.428 emu g−1) among all the produced composites. Pure CoFe2O4 had a much higher coercivity (Hc = 1158.1 Oe) than (MnCr)-LDOx/CoFe2O4 (x = 1, 3, and 5 wt%) nanocomposites (Hc = 1119.8, 978.48, and 984.16 Oe). Moreover, complex impedance spectroscopy measurements were performed in frequency range of 50 Hz- 5 MHz using Nyquist plots and electric modulus analysis. Nyquist plots were fitted to an analogous electric circuit consisting of a resistor R1 connected in series to two parallel constant phase element- resistor circuits (CPE-R). On the other hand, a different circuit comprises of two CPE, capacitor (C1), and resistor all connected in parallel was used to model CoFe2O4.

Above-Room-Temperature Ferromagnetism in Copper-Doped Two-Dimensional Chromium-Based Nanosheets.

Two-dimensional ferromagnetic materials (2D-FMs) are expected to become ideal candidates for low-power, high-density information storage in next-generation spintronics devices due to their atomically ultrathin and intriguing magnetic properties. However, 2D-FMs with room-temperature Curie temperatures (Tc) are still rarely reported, which greatly hinders their research progress and practical applications. Herein, ultrathin Cu-doped Cr7Te8 FMs were successfully prepared and can achieve above-room-temperature ferromagnetism with perpendicular magnetic anisotropy via a facile chemical vapor deposition (CVD) method, which can be controlled down to an atomic thin layer of ∼3.4 nm. STEM-EDX quantitative analysis shows that the proportion of Cu to metal atoms is ∼5%. Moreover, based on the anomalous Hall effect (AHE) measurements in a six-terminal Hall bar device without any encapsulation as well as an out-of-plane magnetic field, the maximum Tc achieved ∼315 K when the thickness of the sample is ∼28.8 nm; even the ultrathin 7.6 nm sample possessed a near-room-temperature Tc of ∼275 K. Meanwhile, theoretical calculations elucidated the mechanism of the ferromagnetic enhancement of Cu-doped Cr7Te8 nanosheets. More importantly, the ferromagnetism of CVD-synthesized Cu-doped CrSe nanosheets can also be maintained above room temperature. Our work broadens the scope on room-temperature ferromagnets and their heterojunctions, promoting fundamental research and practical applications in next-generation spintronics.

Periodic oxygen-defective ZrO2−x films with room-temperature ferromagnetism produced by precisely controlling oxidation of metallic Zr foil

Ferromagnetism can be induced by introducing oxygen vacancies into metallic oxides. The oxygen deficiencies introduced into ZrO2 samples thus far have been present in unquantifiable concentrations and randomly scattered near the surface. We successfully produced room-temperature-ferromagnetic 9 μm-thick ZrO2−x films via a stepwise oxidation process consisting of annealing metallic Zr foil in air and under a controlled oxygen partial pressure. The ZrO2−x films are composed of a periodic structure with a spacing of 3–4 nm; this structure originated from the presence and absence of oxygen deficiencies. The unique structure in the ZrO2−x phase consisting of the periodic arrangements of oxygen deficiencies can be produced by the stepwise oxidation using Zr metal. Our proposed process should open the door for new applications of defect-driven ferromagnetic films of undoped magnetic oxides with a periodic oxygen-defective structure.

Hidden Valley Polarization, Piezoelectricity, and Dzyaloshinskii-Moriya Interactions of Janus Vanadium Dichalcogenides.

Due to the lack of inversion symmetry and the discovery of room-temperature ferromagnetism, two-dimensional semiconducting vanadium-based van der Waals transition-metal dichalcogenides (V-TMDs) are drawing attention for their possible application in spintronics and valleytronics. Here, we show the functional properties enriched by the broken inversion, out-of-plane mirror, and time-reversal symmetries of Janus H-VXY TMDs (X, Y = S, Se, Te). By first-principles calculations, we reveal the intrinsic xy easy-plane magnetism of the Janus vanadium-based TMD monolayers and systematically study their hidden valley polarization and giant magneto band structure. Their strong nearest-neighbor exchange strengths lead to near-room-temperature magnetic phase transitions. The Janus H-VXY system also exhibits piezoelectricity with nonzero e31 and e21. Interestingly, it is found that the right-handed Dzyaloshinskii-Moriya interaction has nonzero in-plane components in our Janus system, with fluctuating magnitudes determined by competence between relaxed bond-angle and atomic index of ligands.

Electronic structure and magnetic properties of CrI3 monolayer doped by rare earth metal atoms

CrI3 monolayer is a two-dimensional (2D) ferromagnetic (FM) semiconductor materials with broad application prospects in the field of spintronics due to its magnetic semiconductor feature and unique 2D structure. In this work, we employ first-principles calculations based on density functional theory to investigate the electronic structure and magnetic properties of CrI3 monolayer doped with rare earth (RE) metal atoms (RE = Sc, Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tm, and Lu). The results demonstrate that doping with RE atoms enables the control of total magnetic moments and a significantly enhancement of the Curie temperature of CrI3 monolayer. Especially, the Curie temperature of CrGdI6 monolayer reaches 347.58 K, which could be a promising candidate for realizing room temperature ferromagnetism. Furthermore, by applying strain and electric field, the CrREI6 monolayers exhibit metal, half-metal and spin gapless semiconductor properties. These findings not only provide valuable insights into the manipulation of electronic structure and magnetic properties in CrI3 monolayer but also establish RE doped CrI3 monolayer as a promising material for spintronic devices.

Efficient current-induced spin torques and field-free magnetization switching in a room-temperature van der Waals magnet

The discovery of magnetism in van der Waals (vdW) materials has established unique building blocks for the research of emergent spintronic phenomena. In particular, owing to their intrinsically clean surface without dangling bonds, the vdW magnets hold the potential to construct a superior interface that allows for efficient electrical manipulation of magnetism. Despite several attempts in this direction, it usually requires a cryogenic condition and the assistance of external magnetic fields, which is detrimental to the real application. Here, we fabricate heterostructures based on Fe 3 GaTe 2 flakes that have room-temperature ferromagnetism with excellent perpendicular magnetic anisotropy. The current-driven nonreciprocal modulation of coercive fields reveals a high spin-torque efficiency in the Fe 3 GaTe 2 /Pt heterostructures, which further leads to a full magnetization switching by current. Moreover, we demonstrate the field-free magnetization switching resulting from out-of-plane polarized spin currents by asymmetric geometry design. Our work could expedite the development of efficient vdW spintronic logic, memory, and neuromorphic computing devices.