Abstract:The magnetic domains in 2D layered material Fe 3 GeTe 2 are studied by using variabletemperature scanning tunneling microscope with a magnetic tip after in situ cleaving of single crystals. A stripy domain structure is revealed in a zero-field cooled sample below the ferromagnetic transition temperature of 205 K, which is replaced by separate double-walled domains and bubble domains when cooling the sample under a magnetic field of a ferromagnetic 3 3 Ni tip. The Ni tip can further convert the double-walled do… Show more
“…Local atomic environment is also studied by the Mössbauer and X-ray absorption spectroscopies 14,15 . Partially filled Fe d orbitals results in an itinerant ferromagnetism in Fe 3− x GeTe 2 16 , which exhibits exotic physical phenomena such as nontrivial anomalous Hall effect 17–19 , Kondo lattice behavior 20 , strong electron correlations 21 , and unusual magnetic domain structures 22,23 . A second-step satellite transition T * is also observed just below T c , and is not fully understood 10,15 .Figure 1( a ) Crystal structure and ( b ) X-ray energy-dispersive spectrum of Fe 3− x GeTe 2 single crystal.…”
We present a comprehensive study on anisotropic magnetocaloric porperties of the van der Waals weak-itinerant ferromagnet Fe3−xGeTe2 that features gate-tunable room-temperature ferromagnetism in few-layer device. Intrinsic magnetocrystalline anisotropy is observed to be temperature-dependent and most likely favors the long-range magnetic order in thin Fe3−xGeTe2 crsytal. The magnetic entropy change ΔSM also reveals an anisotropic characteristic between H//ab and H//c, which could be well scaled into a universal curve. The peak value $$-\Delta {S}_{M}^{{\max }}$$−ΔSMmax of 1.20 J kg−1 K−1 and the corresponding adiabatic temperature change ΔTad of 0.66 K are deduced from heat capacity with out-of-plane field change of 5 T. By fitting of the field-dependent parameters of $$-\Delta {S}_{M}^{{\max }}$$−ΔSMmax and the relative cooling power RCP, it gives $$-{\rm{\triangle }}{S}_{M}^{{\max }}$$−∆SMmax ∝ Hn with n = 0.603(6) and RCP ∝ Hm with m = 1.20(1) when H//c. Given the high and tunable Tc, Fe3−xGeTe2 crystals are of interest for fabricating the heterostructure-based spintronics device.
“…Local atomic environment is also studied by the Mössbauer and X-ray absorption spectroscopies 14,15 . Partially filled Fe d orbitals results in an itinerant ferromagnetism in Fe 3− x GeTe 2 16 , which exhibits exotic physical phenomena such as nontrivial anomalous Hall effect 17–19 , Kondo lattice behavior 20 , strong electron correlations 21 , and unusual magnetic domain structures 22,23 . A second-step satellite transition T * is also observed just below T c , and is not fully understood 10,15 .Figure 1( a ) Crystal structure and ( b ) X-ray energy-dispersive spectrum of Fe 3− x GeTe 2 single crystal.…”
We present a comprehensive study on anisotropic magnetocaloric porperties of the van der Waals weak-itinerant ferromagnet Fe3−xGeTe2 that features gate-tunable room-temperature ferromagnetism in few-layer device. Intrinsic magnetocrystalline anisotropy is observed to be temperature-dependent and most likely favors the long-range magnetic order in thin Fe3−xGeTe2 crsytal. The magnetic entropy change ΔSM also reveals an anisotropic characteristic between H//ab and H//c, which could be well scaled into a universal curve. The peak value $$-\Delta {S}_{M}^{{\max }}$$−ΔSMmax of 1.20 J kg−1 K−1 and the corresponding adiabatic temperature change ΔTad of 0.66 K are deduced from heat capacity with out-of-plane field change of 5 T. By fitting of the field-dependent parameters of $$-\Delta {S}_{M}^{{\max }}$$−ΔSMmax and the relative cooling power RCP, it gives $$-{\rm{\triangle }}{S}_{M}^{{\max }}$$−∆SMmax ∝ Hn with n = 0.603(6) and RCP ∝ Hm with m = 1.20(1) when H//c. Given the high and tunable Tc, Fe3−xGeTe2 crystals are of interest for fabricating the heterostructure-based spintronics device.
“…A possible explanation for this behavior is the formation of domain structures that are unresolvable through our optical measurements. Bulk crystal FGT exhibits stripy and bubble-like domains 10,23,24 . On the other hand, Co/Pt multilayer films with low disorder 25 show similar hysteresis loops to those in Fig.…”
Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that FeGeTe (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (T) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces an atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant ferromagnetism and for engineering spintronic vdW heterostructures.
“…FGT is a vdW ferromagnetic (FM) metal with a layered hexagonal crystal structure, where the Fe 3 Ge slabs are sandwiched by Te layers (Figure 1a). [21,[28][29][30][31][32][33] The Curie temperature T c is relatively high, ranging from 150 to 220 K depending on the Fe occupancy, [34,35] and decreases sharply when the sample is thinned to 2D limit. [3,4] Together with the nearly square-shaped hysteresis loop, large coercivity and strong perpendicular magnetic anisotropy, FGT exhibits a potential for vdW heterostructure based spintronics.…”
Van der Waals (vdW) magnetic materials, including CrI 3 , Cr 2 Ge 2 Te 6 , and Fe 3 GeTe 2 , etc., have attracted much attention over the past few years for offering a platform to explore new fundamental physics and novel device applications. [1-8] Layered
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