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Discovery of two dimensional (2D) magnets, showing intrinsic ferromagnetic (FM) or antiferromagnetic (AFM) orders, has accelerated development of novel 2D spintronics, in which all the key components are made of van der Waals (vdW) materials and their heterostructures. High-performing and energy-efficient spin functionalities have been proposed, often relying on current-driven manipulation and detection of the spin states. In this regard, metallic vdW magnets are expected to have several advantages over the widely-studied insulating counterparts, but have not been much explored due to the lack of suitable materials. Here, we report tunable itinerant ferro- and antiferromagnetism in Co-doped Fe4GeTe2 utilizing the vdW interlayer coupling, extremely sensitive to the material composition. This leads to high TN antiferromagnetism of TN ~ 226 K in a bulk and ~210 K in 8 nm-thick nanoflakes, together with tunable magnetic anisotropy. The resulting spin configurations and orientations are sensitively controlled by doping, magnetic field, and thickness, which are effectively read out by electrical conduction. These findings manifest strong merits of metallic vdW magnets as an active component of vdW spintronic applications.

Based on the detailed Mn L(2,3)-edge x-ray resonant scattering results, we report a new complexity in the magnetic order of multiferroic orthomangnites, which has been considered as the simple A-type cycloid order inducing ferroelectricity. The Dzyaloshinskii-Moriya interaction involved in the orthorhombic distortion brings on F-type canting from the A type, and the ordering type becomes the off-phase synchronized bc cycloid in TbMnO(3) or the tilted antiphase ab cycloid in Eu(3/4)Y(1/4)MnO(3). The F-type canting is responsible for the magnetic field-driven multiferroicity to weak ferromagnetism transition.

We investigated the electronic structures of ultrathin SrRuO3 (SRO) films with n = 1, 2, 3, 4, and 8 monolayers (MLs) on SrTiO3 substrates using O K-edge X-ray absorption spectroscopy (XAS). The intensities of the low-energy features reflect the strengths of the Ru 4d-O 2p orbital hybridization. The Ru 4d orbital state evolves with the increasing SRO thickness, exhibiting a crossover at approximately n = 2. For thick SRO films (n ≥ 3), this constitutes a metallic band, while for the 1 or 2 ML film, the band features shift to a higher energy to form a bandgap (> 0.2 eV), reflecting the emergent insulating nature. The polarization dependence of the peak intensities further shows that in the metallic films (n ≥ 3), Ru t2g - O 2p hybridizations are strong and anisotropic with stronger (weaker) equatorial (apical) hybridizations, possibly owing to compressive strain effects from the SrTiO3 substrate, while in thinner films (n ≤ 2), the hybridization effects become weak and rather isotropic because of the localization of Ru 4d orbitals. Thus, the evolution of anisotropic hybridizations in SRO films in the vicinity of the thickness-driven metal-insulator transition was substantiated.

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