Magnetic van der Waals (vdW) materials have emerged as promising candidates for spintronics applications, especially after the recent discovery of intrinsic ferromagnetism in monolayer vdW materials. There has been a critical need for tunable ferromagnetic vdW materials beyond room temperature. Here, we report a real-space imaging study of itinerant ferromagnet FeGeTe and the enhancement of its Curie temperature well above ambient temperature. We find that the magnetic long-range order in FeGeTe is characterized by an unconventional out-of-plane stripe-domain phase. In FeGeTe microstructures patterned by a focused ion beam, the out-of-plane stripe domain phase undergoes a surprising transition at 230 K to an in-plane vortex phase that persists beyond room temperature. The discovery of tunable ferromagnetism in FeGeTe materials opens up vast opportunities for utilizing vdW magnets in room-temperature spintronics devices.

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co8Zn9Mn3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? Utilizing winding number conservation, we develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. By observing the created meron pair directly within a magnetic field, we determine its topological structure unambiguously and explore the topological effect in its creation and annihilation processes. Our work opens a pathway towards developing and controlling topological structures in general magnetic systems without the restriction of perpendicular anisotropy and Dzyaloshinskii–Moriya interaction.

Gorenstein derived categories are defined, and the relation with the usual derived categories is given. The bounded Gorenstein derived categories of Gorenstein rings and of finite-dimensional algebras are explicitly described via the homotopy categories of Gorenstein-projective modules, and some applications are obtained. Gorenstein derived equivalences between CM-finite Gorenstein algebras are discussed.