Gapless Semiconductor Research Articles

VTaNbAl: A class of spin gapless semiconductors with topological nontrivial features

We report a class of spin gapless semiconductors (SGSs) hosting topological nontrivial features along with a fully compensated ferrimagnetic behavior in VTaNbAl, a quaternary Heusler alloy. Unlike conventional SGSs, this class of compounds acquires a unique band structure with opposite spin characters in the valence and conduction band edges, making them potential candidates for spin valves and a large anomalous Nernst effect. Interestingly, despite compensated ferrimagnetic (CF) behavior, VTaNbAl shows a reasonably large anomalous Hall effect possibly arising from the intrinsic nonvanishing Berry curvature. The CF state breaks the time-reversal symmetry and hence opens the possibility of Weyl nodes. We found four pairs of Weyl nodes located near the Fermi level leading to the nonvanishing Berry curvature, and hence a large anomalous Hall conductivity ($\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$). Our experimental synthesis confirms VTaNbAl to crystallize in a cubic Heusler structure with $A2$-type disorder. A magnetization measurement shows a very small saturation moment ($\ensuremath{\sim}{10}^{\ensuremath{-}3}{\textmu{}}_{B}/\text{f.u.}$), which agrees fairly well with our theoretical findings of fully compensated ferrimagnetism in the alloy. Resistivity shows a metalliclike nature, with the signature of disorder-induced weak localization in the low-temperature limit. The overall variation with varying temperature, however, is extremely weak.

A new superhard material C5N2 assembled from diamane: a first-principles study

Due to the shortage of diamond and cubic boron nitride (BN) and the lack of other potential rivals, searching for suitable superhard materials is still attracting tremendous research interests, especially those with special properties except for semiconducting and insulating characteristics. Beyond previous synthetic methods, here we give a new approach of designing superhard materials (i.e. stacking diamane layers through chemical adsorption of molecules at the interface) via first-principles calculations. As a result, a superhard carbon-rich C5N2 compound with monoclinic C 2 symmetry is designed by inserting CN4 molecule between diamane layers, and it exhibits dynamical and mechanical stability at ambient environment. The hardness is estimated as 74.9 GPa, showing superhard nature. Different from indirect band gap insulators of diamond and cubic BN, C5N2 behaves as a direct band gap semiconductor with an energy gap of ∼2.10 eV. Besides, the properties of C5N2 can be effectively regulated by controlling the adsorbed molecules, for instance, it would turn into ferromagnetic phase with introduction of sp 3 hybridized three-folded C atoms and sp 2 hybridized two-fold coordinated N atoms. The estimated Curie temperatures of some ferromagnetic superhard phases are preferably above room temperature. Additionally, these ferromagnetic phases show diverse electronic properties, such as spin gapless semiconductor, bipolar magnetic semiconductor, metal, etc. This work opens a potential way to design superhard materials and tailor their physical properties, and can arouse their applications in spintronic field.

Which crystal structure is present on the surface of Ti[formula omitted]CrAl compound - a deduction from electronic structure measurements and calculations

In this report, we study the Ti2CrAl compound, a Heusler compound that was believed to exhibit half-metallic ferromagnet (HMF) or even spin gapless semiconductor (SGS) properties. Here, we present our investigations of electronic structure by means of X-ray Photoelectron Spectrosocopy (XPS), X-ray Absorption Spectroscopy (XAS) and band structure calculations. Our results show that the surface has the same regular Heusler structure as the bulk and not the inverted Heusler structure as it was assumed before. We noted that the sample is very hard, therefore we present here measurements of microhardness and elastic modulus using microindentation technique. In addition, thermopower calculated from the band structure for both structural models using Boltzmann equation is compared with our experimental measurements.

Unconventional gapless semiconductor in an extended martini lattice in covalent honeycomb materials

We study characteristic electronic structures in an extended martini lattice model and propose its materialization in $\ensuremath{\pi}$-electron networks constructed by designated chemisorption on graphene and silicene. By investigating the minimal tight-binding model, we reveal rich electronic structures tuned by the ratio of hopping parameters, ranging from the band insulator to the unconventional gapless semiconductor. Remarkably, the unconventional gapless semiconductor is characterized by a flat band at the Fermi level. Further, the density functional theory calculations for candidate materials reveal that the characteristic electronic structures can be realized by designated chemisorption or chemical substitution on graphene and silicene, and that the electronic structure near the Fermi level is tunable by the choice of the atomic species of adsorbed atoms. Our results open the way to search exotic electronic structures and their functionalities induced by an extended martini lattice.

Experimental demonstration of electrical spin injection into semiconductor employing conventional three-terminal and non-local Hanle devices using spin gapless semiconductor as ferromagnetic injector

Here, the deposition of a polycrystalline thin film of a noble promising alloy Ti2CoSi (TCS) on a p-Si substrate has been reported, and its spin gapless semiconducting characteristics have been investigated experimentally. The structural, magnetic, and electronic transport features of the TCS film have been investigated in detail followed by its implementation as a ferromagnetic tunnel contact for proficient spin accumulation into a semiconductor employing both conventional three-terminal and non-local (NL) Hanle measurements. As we can avoid noticing erroneous effects like anisotropic magnetoresistance of the ferromagnetic electrodes, the NL-Hanle experiment has been established to be the most effective method for demonstrating true spin transport in semiconductors.

Large magnetoresistance and spin-polarized photocurrent in Mn2.25Co0.75Ga0.5Sn0.5/MgO/Mn2.25Co0.75Ga0.5Sn0.5 magnetic tunnel junctions

With the development of information storage devices with high density, low power consumption and multi-means regulation, magnetic tunnel junctions (MTJs) with completely spin polarized materials as electrodes have attracted much attention. Heusler alloy Mn2.25Co0.75Ga0.5Sn0.5(MCGS) is a recently fabricated spin gapless semiconductor with 100 % spin polarization and high Curie temperature of 725 K. Here, the spin-dependent electronic transport and photoelectric properties of MCGS/MgO/MCGS MTJs are investigated systematically by density functional theory and non-equilibrium Green's function method. It is found that the MCGS/MgO/MCGS MTJs with four different terminations all present high tunnel magnetoresistance (TMR) and the maximum TMR is up to 6.51 × 106 %. The TMR value can be reduced and switched between positive and negative values by applying bias voltage, which can be used to designed magnetic logic devices. Furthermore, perfect spin injection efficiency can be obtained in the MCGS/MgO/MCGS MTJs and the switch of the spin channel can be controlled by the magnetization configuration of the ferromagnetic electrodes. Moreover, nearly 100 % spin-polarized photocurrent can be obtained by tailoring the polarization angle and photon energy of polarized light. The linearly polarized light is more favorable than circularly polarized light to generate high spin-polarized photocurrent. These results provide a theoretical guidance for designing the spin and optical tunable spintronic devices.

Kinetic arrest of atomic diffusion-induced spin gapless semiconductor in Ti2MnAl Heusler compound

The metastable spin gapless semiconductor Ti2MnAl results from the kinetic arrest of atomic diffusion during sample preparation from the high-temperature relatively low-symmetric phase to the low-temperature high-symmetric phase.

Disordered spin gapless semiconducting CoFeCrGa Heusler alloy thin films on Si (100): experiment and theory.

Spin gapless semiconductors (SGSs) are an intriguing class of quantum materials that bridge the gap between half-metallic ferromagnets and semiconductors. The presence of a semiconducting bandgap for one spin channel and zero band gap for other spin channels, together with the possibility of four different band structure configurations, makes them one of the most desirable candidates to be used in tunable spin transport based spintronics devices. Here, we have performed various structural, magnetic and transport measurements on an optimized CoFeCrGa (CFCG) Heusler alloy thin film (∼50 nm) grown over a Si(100) substrate using an industry-viable magnetron sputtering technique. The grown film showed B2-ordering under the given set of X-ray diffraction measurement conditions with a saturation magnetization (Ms) of 1.86μB per f.u. (at 5 K) and a Curie temperature of ∼595 K. Nearly linearly varying longitudinal resistivity with a negative temperature coefficient was observed. A fitted longitudinal conductivity curve through a "two-carrier model" shows a slight band overlap in the gapless channel for one spin channel and a small energy gap (ΔE) of 167 meV for other spin channels. A negative and linear out-of-plane magnetoresistance response was observed in these films. The temperature dependent anomalous Hall effect measurement gives nearly temperature independent carrier concentration (and/or) mobility with an anomalous Hall conductivity of 91.35 S cm-1 at 5 K. The first principles calculations have also been performed for bulk and (220) CFCG surfaces to correlate the various structural, electronics and magnetic properties of the optimized CFCG Heusler alloy thin film. The DFT derived results, viz. lattice parameter and MS exhibit a good match with the experimentally observed results. All these properties collectively imply that the grown film possesses disordered-SGS like behaviour. It is remarkable to note that CFCG films with the (022) surface possess a very high electronic spin polarization of 91%. The results of the study suggest that CFCG is a potential candidate to be used in spintronics-based devices such as spin-injectors.

Antisite disorder and Berry curvature driven anomalous Hall effect in the spin gapless semiconducting Mn2CoAl Heusler compound

Spin gapless semiconductors exhibit a finite band gap for one spin channel and a closed gap for another spin channel, and they have emerged as a new state of magnetic materials with a great potential for spintronic applications. The first experimental evidence for spin gapless semiconducting behavior was observed in an inverse Heusler compound ${\mathrm{Mn}}_{2}\mathrm{CoAl}$. Here, we report a detailed investigation of the crystal structure and anomalous Hall effect in ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ using experimental and theoretical studies. The analysis of the high-resolution synchrotron x-ray diffraction data shows antisite disorder between Mn and Al atoms within the inverse Heusler structure. The temperature-dependent resistivity shows semiconducting behavior and follows Mooij's criteria for disordered metal. The scaling behavior of the anomalous Hall resistivity suggests that the anomalous Hall effect in ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ is primarily governed by an intrinsic mechanism due to the Berry curvature in momentum space. The experimental intrinsic anomalous Hall conductivity (AHC) is found to be $\ensuremath{\sim}35$ S/cm, which is considerably larger than the theoretically predicted value for ordered ${\mathrm{Mn}}_{2}\mathrm{CoAl}$. Our first-principles calculations conclude that the antisite disorder between Mn and Al atoms enhances the Berry curvature and hence the value of intrinsic AHC, which is in very good agreement with the experiment.

Emergence of asymmetric skew-scattering dominated anomalous Nernst effect in the spin gapless semiconductors Co1+xFe1−xCrGa

Heusler alloy-based spin gapless semiconductors (SGSs) with very high Curie temperatures $({T}_{C})$ have recently gained enormous attention because of their unconventional electronic structures. They exhibit a nonzero band gap in one of the spin channels and a zero band gap in the other spin channel, making them an important class of materials for tunable spin transport. Here, we report the experimental observation of anomalous Nernst effect (ANE) in ${\mathrm{Co}}_{1+x}{\mathrm{Fe}}_{1\ensuremath{-}x}\mathrm{CrGa}$ ($x=0$, 0.2, 0.4, and 0.5), which are the emerging quaternary Heusler alloy-based SGSs. While the electron-electron elastic scattering and the disorder-mediated weak localization effect play the major roles in electrical transport for all the samples at low temperatures, the magnon-drag effect was found to dominate the longitudinal thermoelectric transport. The ANE coefficient at room temperature increases from $\ensuremath{\approx}0.018\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for $x=0$ to $\ensuremath{\approx}0.063\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for $x=0.5$, which is higher than that for ${\mathrm{Ni}}_{81}\phantom{\rule{0.16em}{0ex}}{\mathrm{Fe}}_{19}$ and compressively strained $\mathrm{SrRu}{\mathrm{O}}_{3}$ films. Our analysis indicates that the observed ANE in these samples originates from asymmetric skew scattering of charge carriers.

Two-dimensional intrinsic ferrovalley Janus 2H-VSeS monolayer with high Curie temperature and robust valley polarization

Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain ($-$8%<$\varepsilon$<8%) can effectively tune the magnetic moments of V atom, valley splitting $\Delta$E, T$_{c}$ and MAE of Janus 2H-VSeS monolayer. The corresponding $\Delta$E and T$_{c}$ are adjusted from 72meV to 106.8meV and from 180K to 340K, respectively. The electronic phase transition from bipolar magnetic semiconductor (BMS) to half-semiconductor (HSC), spin gapless semiconductor (SGS), and half-metal (HM) is also observed due to the change of V 3d-orbital occupation. Due to the broken space- and time-reversal symmetry, the opposite valley charge carriers carry opposite Berry curvature, which leads to prominent anomalous Hall conductivity at the K and K$^{\prime}$ valleys. The maximum modulation of Berry curvature can reach to 45% and 9.5% by applying the biaxial strain and charge carrier doping, respectively. The stable in-plane magnetocrystalline anisotropy and large spontaneous valley polarization make the ferromagnetic Janus 2H-VSeS monolayer a promising material for achieving the spintronics and valleytronics devices.

Tunable magnetocrystalline anisotropy and valley polarization in an intrinsic ferromagnetic Janus 2H -VTeSe monolayer

Two-dimensional Janus monolayers with specular asymmetry exhibit excellent physicochemical properties and are a good candidate for optoelectronic, valley electronic, and nanoelectronics devices. Based on the density functional theory, the Janus $2H$-VTeSe monolayer is an intrinsic ferromagnetic semiconductor with an indirect band gap of 0.324 eV and exhibits a good thermodynamic and kinetic stability, in-plane magnetocrystal anisotropy, large spontaneous valley polarization of 155 meV, and high Curie temperature (${T}_{c}$) of 380 K. The biaxial strain ($\ensuremath{-}6%&lt;\ensuremath{\varepsilon}&lt;6%$) can effectively tune the Janus $2H$-VTeSe monolayer from the bipolar magnetic semiconductor phase to half-semiconductor, spin gapless semiconductor, and half-metallic phases. Moreover, the magnetocrystal anisotropy energy (MAE) is modulated by the strain from 0.54 meV ($\ensuremath{\varepsilon}=\ensuremath{-}6%$) to 1.32 meV ($\ensuremath{\varepsilon}=\ensuremath{-}2%$), and the easy [100] and hard [001] magnetic axes could be switched from each other by charge carrier doping. The calculated valley optical response of the Janus $2H$-VTeSe monolayer exhibits a valley-selective circular dichroism. Due to the broken inversion and time-reversal symmetry, the valley polarization and Berry curvature can be continuously tuned by applying biaxial strains (modulation range 24.2%), external electric field (modulation range 2%), and varying the magnetization angle (0 to 180 degrees). The Janus $2H$-VTeSe monolayer possesses intrinsic ferromagnetic ordering, large spontaneous valley polarization, high ${T}_{c}$ of 380 K, and considerable MAE of 1.15 meV, giving it a potential application in the two-dimensional spintronic devices.

Unusual Kinetic Properties of Usual Heusler Alloys

The review considers various groups of Heusler compounds, which can have the properties of a semiconductor, a half-metallic ferromagnet, a spin gapless semiconductor, a topological semimetal, and a non-collinear antiferromagnet. In these Heusler compounds, “conventional” from the point of view of the crystal structure, unusual kinetic and magnetic properties can be observed, which are caused by the features of their electronic structure (e.g., presence of an energy gap for one spin projection) and magnetic state (e.g., strong ferromagnetism, compensated ferrimagnetism). Their magnetic and kinetic characteristics are very sensitive to external influences. Depending on the alloy composition and external parameters, transitions between the considered states can be realized. All this opens up further prospects for controlling the electronic and magnetic characteristics of such compounds and their practical application.

Unexpected band gap evolution and high carrier mobility sparked by the orbital variation in two-dimensional GaGeX (X = S, Se, Te)

As elemental group material, germanium, enjoys a high status in the field of two-dimensional (2D) materials. However, 2D germanene is a gapless semiconductor, which greatly limits its application in optoelectronic devices. Herein, we found an interesting class of 2D materials, named GaGeX (X = S, Se, Te), consisting of two outer GaX layers and an inner germanene, a sandwich structure stacked together by interlayer Ga-Ge bonds. Compared with known 2D materials (such as MoX2), the band gaps gradually decrease in the order of sulfide, selenide, and telluride, the electronic calculations show that they have a unique band gaps reversely enlarging trend of 0.03, 0.46 and 0.72 eV from GaGeS to GaGeTe, respectively. Moreover, GaGeX is predicted to have superior mobility, especially with a hole mobility of up to 5510 cm2 V−1 s−1 in GaGeTe. These novel phenomena are found closely related to the orbital variation. Our findings render these 2D materials potential candidates for future optoelectronic devices.

Voltage-Controlled Switching of Magnetic Anisotropy in Ambipolar Mn2CoAl/Pd Bilayers

An ultrahigh electric field induced by ionic liquid gating (ILG) can be employed to manipulate ferromagnetism with low Joule heating dissipation, showing great potential for spintronics applications. In ferromagnetic/heavy metal thin films, however, typical materials used in both layers are electron-carrier dominant, which significantly suppresses the ILG effect due to the short electrostatic screening length in metal. Here, we employ ${\mathrm{Mn}}_{2}\mathrm{Co}\mathrm{Al}$, a spin gapless semiconductor with hole carriers, as the ferromagnetic layer and investigate the ILG effect in $\mathrm{Mg}\mathrm{O}/{\mathrm{Mn}}_{2}\mathrm{CoAl/Pd}$ ultrathin films with perpendicular magnetic anisotropy. Reversible change of the magnetic anisotropy from the out-of-plane to the in-plane direction is achieved, induced by electrostatic charge accumulation. Moreover, ambipolar transport behavior has been observed and explained by a two-carrier model. Finally, we find that skew scattering is the mechanism of the anomalous Hall effect and can be enhanced at a positive gate voltage in our system. Our results strongly demonstrate that a significant ILG effect on magnetism can be easily achieved in two-carrier dominant ultrathin films.

Electronic phase transition, spin filtering effect, and spin Seebeck effect in 2D high-spin-polarized VSi2X4 (X = N, P, As)

Spin gapless semiconductors (SGSs) and bipolar magnetic semiconductors (BMSs) are highly desirable for advanced spintronic applications due to their unique electronic and magnetic properties. Being inspired by the recent synthesis of the 2D MA2X4 family with various electronic properties, including nontrivial topological properties, 2D ferromagnetism, Ising superconductivity, and robust valley polarization, we systematically studied the electron structure, magnetism, and spin transport properties for VSi2X4 (X = N, P, As) monolayers by the density functional theory combined with the nonequilibrium Green's function method. The results show that VSi2X4 monolayers are ferromagnetic type-II SGS and BMS with high Curie temperatures 230–250 K. The interesting electronic phase transitions of type-II-SGS-to-metal-to-type-I-SGS for VSi2P4 and BMS-to-type-I-SGS-to-type-II-SGS for VSi2As4 can be achieved by applying the biaxial strain. Furthermore, the VSi2P4 monolayer exhibits the bias-dependent spin filtering effect and the temperature-driven spin Seebeck effect. The high Curie temperature, the versatile strain-tuned electronic phase transitions, and the excellent spin transport characteristics make 2D VSi2X4 the promising candidate for spintronic applications and will stimulate intensive studies on this class of high-spin-polarized 2D systems.

Demonstration of reconfigurable magnetic tunnel diode and giant tunnel magnetoresistance in magnetic tunnel junctions made with spin gapless semiconductor and half-metallic Heusler alloy

Here, we report fabrication of a high quality exchanged biased trilayer magnetic tunnel junction (MTJ) utilizing a magnetron sputtering system. The MTJ is composed of a type-II spin gapless semiconductor (SGS) Ti2CoSi inverse Heusler alloy (used as a lower electrode), a thin MgO layer (used as a tunnel barrier), and a half-metallic ferromagnet (HMF) Co2MnSi Heusler alloy (used as an upper electrode). Spin dependent transport properties reveal that the micro-fabricated MTJ can act as a reconfigurable magnetic tunnel diode, which lets the electric current to flow in either the forward or reverse path relying on the relative alignment of the magnetization direction of the upper and lower magnetic electrodes. A considerably high on/off current ratio (∼103) and a significantly low turn on voltage (VT) of 0.09 V have been achieved at 5 K for both parallel and antiparallel configurations. Another important characteristic shown by our fabricated MTJ is that it exhibits extremely large tunnel magnetoresistance ratios of 892% at 5 K and 197% at room temperature, which brings to light the utmost importance of using the combination of HMF and SGS materials as magnetic electrodes in a tunnel junction for potential applications in modern spintronic devices. All these exceptional features can undoubtedly nominate CMS/MgO/TCS MTJs as a promising candidate to serve as memory or logic elements in next generation ultra-high density magnetoresistive random access memories together with contemporary spin based electronic devices.

The Magnetic and Thermally-Induced Spin-Related Transport Features Using Germanene Nanoribbons With Zigzag and Klein Edges

The current work employs the first-principles computations and non-equilibrium Greens function to investigate the magnetic and thermally-induced spin-related transport features using germanene nanoribbons with zigzag and Klein edges (ZKGeNRs). It was demonstrated that the ZKGeNRs with various widths (N) are placed in various spin-resolved electronic states. By increasing the width parameter N from 4 to 9, the ZKGeNRs moves from an indirect-gap bipolar magnetic semiconducting state (BMS) to bipolar spin gapless semiconductor (BSGS), and finally to ferromagnetic metal (FM). Moreover, since the right and the left temperatures of the ZKGeNRs device are different, the spin-up and spin-down currents flow in reverse orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, the threshold temperature decreases as N increases and then disappears, while the spin currents increase as N increases. Simulation results indicated that the ZKGeNRs could be an appropriate choice for spin caloritronic devices and could be utilized in future low-power consumption applications.

Spontaneous spin magnetism of donor conduction electrons of hybridized states of a crystal formed by a system of 3d-elements impurity atoms of low concentration (&lt;1 at.%)

The given work is devoted to the experimental proof of existing the spontaneous spin polarization of the donor electron system of 3d-transition element impurity atoms of low concentration (&lt;1 at.%) in a mercury selenide crystal. For this purpose there have been measured the dependences of the magnetization on the magnetic field strength at low temperatures (T=5 K). As a result of the analysis of the obtained dependences, there were extracted the impurity contributions, which are described by the magnetization curves typical of the ferromagnets, and by the magnetic parameters conforming to the spontaneous magnetism of the systems under study, which are unambiguously related to the donor conduction electrons of the outer d-shells of impurity atoms. By its nature, according to the developed theoretical concepts, the spontaneous spin polarization manifests itself in exchange interaction, taking place in hybridizing the electronic states of the impurity atom and the conduction band ones of the crystal. Keywords: 3d-impurities of the low concentration, gapless semiconductors, hybridized electronic states, spontaneous spin polarization, low-temperature ferromagnetism

Robust Dirac spin gapless semiconductors in a two-dimensional oxalate based organic honeycomb-kagome lattice.

Two-dimensional (2D) ferromagnetic materials with intrinsic and robust spin-polarized Dirac cones are of great interest in exploring exciting physics and in realizing spintronic devices. Using comprehensive ab initio calculations, herein we reveal a family of 2D oxalate-based metal-organic frameworks (MOFs) that possess the desired characteristics. We propose that these 2D oxalate-based MOFs may be assembled by oxalate ions (C2O42-) and two homo-transition metal atoms. We demonstrate that 2D MOFs of Ni2(C2O4)3 and Re2(C2O4)3 are intrinsic Dirac spin gapless semiconductors with linear band dispersion, low energy dissipation and high electron carrier velocity. As robust ferromagnets, they also possess large magnetic moments, large perpendicular magnetic anisotropy, and high Curie temperatures, e.g. 208 K for Ni2(C2O4)3. In particular, spin-orbit coupling triggers a topologically nontrivial band gap of 143 meV in Re2(C2O4)3, which is promising to realize the quantum anomalous Hall effect at high temperatures.