Giant coercivity enhancement in a room-temperature van der Waals magnet through substitutional metal-doping

Low-temperature electron-electron interaction correction to the anomalous Hall effect in Fe3GaTe2single crystals

The electron-electron interaction (EEI), weak localization and Kondo effect are known to correct low-temperature (low-T) resistivity in metals and semimetals. However, the impact of EEI on the anomalous Hall effect (AHE) by EEI remains a subject of debate. In this study, we investigate the EEI corrections to both the low-Tlongitudinal and AH resistivities in van der Waals ferromagnetic Fe3GaTe2single crystals with a high Curie temperature. Our findings reveal that the longitudinal resistivity is well-described by the EEI theory developed by Altshuleret al,while the AH resistivity deviates from this theory. We found that the AH resistivity follows aTtemperature dependence, and its relative rate of change is 2.6 times that of the longitudinal resistivity. These results demonstrate that EEI significantly influences the low-TAH resistivity under intrinsic mechanism in Fe3GaTe2. This observation challenges the conventional understanding that EEI does not contribute to the AHE in systems with mirror symmetry, as suggested by skew scattering and side jump models. This work opens avenues for further exploration of EEI effect in disordered magnetic materials.

Persistent ferromagnetic ground state in pristine and Ni-doped Fe3GaTe2 flakes

Room-temperature magnetism and its stability upon miniaturization are essential characteristics required for materials for spintronic devices and information storage. Among various candidates, Fe3GaTe2 stands out due to its high Curie temperature and strong perpendicular magnetic anisotropy (PMA), recently gaining large attention as one of the promising candidate materials for spintronics applications. In this study, we measured the thickness-dependent ferromagnetic properties of Fe3GaTe2 and (Fe1 - xNix)3GaTe2 (with x = 0.1) flakes. We observed that both pristine and Ni-doped Fe3GaTe2 exhibit persistent ferromagnetism, with only a minor decrease in TC as the thickness is reduced to a few tens of nanometers. This capacity to retain robust ferromagnetic properties at reduced dimensions is highly advantageous for thin-film applications, which is crucial for the scaling of spintronic devices. Understanding and controlling thickness-dependent magnetic properties is fundamental to harnessing the full potential of Fe3GaTe2 in van der Waals magnetic heterostructures and advanced spintronic technologies.

Metamagnetic transition and meta-stable magnetic state in Co-doped Fe3GaTe2

The transition between the ferromagnetic (FM) and anti-ferromagnetic (AFM) phases in van der Waals (vdW) magnets has been extensively studied since the discovery of vdW magnets, due to the importance of both transitions within a single material. Recently, among vdW magnets, Fe3GaTe2 (FGaT) has garnered significant attention for its robust FM properties that remain stable above room temperature. Also, the FM to AFM phase transition in this material has been achieved through substitutional Co-atom doping at Fe sites. Here, we have reconfirmed the FM to AFM phase transition in FGaT and observed the metamagnetic transition between the two magnetic phases. Furthermore, the meta-stable magnetic state in 19-22% Co-doped FGaT in a certain field range was noted, which vanishes when the doping level increases further. Interestingly, when measuring the minor loop during the phase transition, its magnetization under a field-sweep reversing field is maintained in a meta-stable magnetic state region. The persistence of magnetization, which indicates the co-existence of AFM and FM domains in this meta-stable magnetic region, creates multi-level configurations that enable advanced applications in multi-level logic devices, neuromorphic computing, and applications involving magnetic domains. Our findings can expand the application scope and the utilization methods of vdW magnets.

Tuning the magnetic properties of van der Waals Fe3GaTe2 crystals by Co doping

Tuning the magnetic properties of two-dimensional van der Waals ferromagnets has special importance for their practical applications. Using first-principles calculations, we investigate the magnetic properties of Co-doped Fe3GaTe2 with different Co concentrations and different Co atomic sites. Calculation results show that Fe or Co atoms with relatively lower atomic concentrations preferentially occupy Fe1 sites with interlayer coupling, which is more energetically favorable. As the doping concentration of Co atoms increases, the total magnetic moment of the doped system decreases, while the average atomic magnetic moments of Fe1 and Fe2 increase and decrease, respectively, with Fe1 reaching ∼2.08μB. The spin polarization of the doped model 2Co-2 near the Fermi energy level is significantly reduced, while 4Co-3 exhibits an enhanced trend. At some doping level, a phase change from ferromagnetism to antiferromagnetism appears at high Co concentration. These results provide a theoretical basis for experimental studies and valuable information for the development of Fe3GaTe2-based spintronic devices.

Layer-Number-Dependent Magnetism in the Co-Doped van der Waals Ferromagnet Fe3GaTe2

Recently, van der Waals (vdW) antiferromagnets have been proposed to be crucial for spintronics due to their favorable properties compared to ferromagnets, including robustness against magnetic perturbation and high frequencies of spin dynamics. High-performance and energy-efficient spin functionalities often depend on the current-driven manipulation and detection of spin states, highlighting the significance of two-dimensional metallic antiferromagnets, which have not been much explored due to the lack of suitable materials. Here, we report a new metallic vdW antiferromagnet obtained from the ferromagnet Fe3GaTe2 by cobalt (Co) doping. Through the layer-number-dependent Hall resistance and magnetoresistance measurements, an evident odd-even layer-number effect has been observed in its few-layered flakes, suggesting that it could host an A-type antiferromagnetic structure. This peculiar layer-number-dependent magnetism in Co-doped Fe3GaTe2 helps unravel the complex magnetic structures in such doped vdW magnets, and our finding will enrich material candidates and spin functionalities for spintronic applications.

Electronic Structure of Above-Room-Temperature van der Waals Ferromagnet Fe3GaTe2

Fe3GaTe2, a recently discovered van der Waals ferromagnet, demonstrates intrinsic ferromagnetism above room temperature, necessitating a comprehensive investigation of the microscopic origins of its high Curie temperature (TC). In this study, we reveal the electronic structure of Fe3GaTe2 in its ferromagnetic ground state using angle-resolved photoemission spectroscopy and density functional theory calculations. Our results establish a consistent correspondence between the measured band structure and theoretical calculations, underscoring the significant contributions of the Heisenberg exchange interaction (Jex) and magnetic anisotropy energy to the development of the high-TC ferromagnetic ordering in Fe3GaTe2. Intriguingly, we observe substantial modifications to these crucial driving factors through doping, which we attribute to alterations in multiple spin-splitting bands near the Fermi level. These findings provide valuable insights into the underlying electronic structure and its correlation with the emergence of high-TC ferromagnetic ordering in Fe3GaTe2.