Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl semimetal candidate, Co3Sn2S2, with a quasi-two-dimensional crystal structure consisting of stacked Kagomé lattices. This lattice provides an excellent platform for hosting exotic topological quantum states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl nodes close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 Ω−1 cm−1 and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagomé-lattice structure and the out-of-plane ferromagnetic order of Co3Sn2S2, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit.

We present a theory of the spin Hall magnetoresistance (SMR) in multilayers made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is induced by the simultaneous action of spin Hall and inverse spin Hall effects and therefore a nonequilibrium proximity phenomenon. We compute the SMR in F|N and F|N|F layered systems, treating N by spin-diffusion theory with quantum mechanical boundary conditions at the interfaces in terms of the spin-mixing conductance. Our results explain the experimentally observed spin Hall magnetoresistance in N|F bilayers. For F|N|F spin valves we predict an enhanced SMR amplitude when magnetizations are collinear. The SMR and the spin-transfer torques in these trilayers can be controlled by the magnetic configuration.

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In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur if spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental set-up is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet pairs to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions.

We report the observation of strong coupling between the exchange-coupled spins in a gallium-doped yttrium iron garnet and a superconducting coplanar microwave resonator made from Nb. The measured coupling rate of 450 MHz is proportional to the square root of the number of exchange-coupled spins and well exceeds the loss rate of 50 MHz of the spin system. This demonstrates that exchange-coupled systems are suitable for cavity quantum electrodynamics experiments, while allowing high integration densities due to their spin densities of the order of one Bohr magneton per atom. Our results furthermore show, that experiments with multiple exchange-coupled spin systems interacting via a single resonator are within reach.

We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or magnetite and for the nonferromagnet, copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin-mixing conductance of 4 × 10 14 −1 m −2 , we obtain a spin Hall angle of 0.11 ± 0.08 and a spin diffusion length of (1.5 ± 0.5) nm for Pt in our thin-film samples.

Surface acoustic waves (SAWs) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic-ferroelectric (Ni/LiNbO(3)) hybrid device. We measure the SAW magnetotransmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.

We perform a quantitative, comparative study of the spin pumping, spin Seebeck and spin Hall magnetoresistance effects, all detected via the inverse spin Hall effect in a series of over 20 yttrium iron garnet/Pt samples. Our experimental results fully support present, exclusively spin currentbased, theoretical models using a single set of plausible parameters for spin mixing conductance, spin Hall angle and spin diffusion length. Our findings establish the purely spintronic nature of the aforementioned effects and provide a quantitative description in particular of the spin Seebeck effect.Pure spin currents present a new paradigm in spintronics [1, 2] and spin caloritronics [3]. In particular, spin currents are the origin of spin pumping [4,5], the spin Seebeck effect [6,7] and the spin Hall magnetoresistance (SMR) [8][9][10]. Taken alone, all these effects have been extensively studied, both experimentally [6-9, 11-13] and theoretically [4,[14][15][16][17][18]. From a theoretical point of view, all these effects are governed by the generation of a current of angular momentum via a non-equilibrium process. The flow of this spin current across a ferromagnet/normal metal interface can then be detected. The relevant interface property that determines the spin current transport thereby is the spin mixing conductance. Nevertheless, there has been an ongoing debate regarding the physical origin of the measurement data acquired in spin Seebeck and SMR experiments due to possible contamination with anomalous Nernst effect [19][20][21] or anisotropic magnetoresistance [22,23] caused by static proximity polarization of the normal metal [23]. To settle this issue, a rigorous check of the consistency of the spin-current based physical models across all three effects is needed. If possible contamination effects are absent, according to the spin mixing conductance concept [24], there should exist a generalized Ohm's law between the interfacial spin current and the energy associated with the corresponding non-equilibrium process. This relation should invariably hold for the spin pumping, spin Seebeck and spin Hall magnetoresistance effects, as they are all based on the generation and detection of interfacial, nonequilibrium spin currents. We here put forward heuristic arguments that are strongly supported by experimental evidence for a scaling law that links all aforementioned spin(calori)tronic effects on a fundamental level and allows to trace back their origin to pure spin currents. (c) The spin Hall magnetoresistance is due to the torque exerted on M by an appropriately polarized Js which yields a change in the reflected spin current J r s . The interconversion between Js (J r s ) and the charge currents Jc (J r c ) are due to the (inverse) spin Hall effect in the normal metal.[schematically depicted in Fig. 1(a)], we place YIG / Pt bilayers in a microwave cavity operated at ν = 9.85 GHz to resonantly excite magnetization dynamics. The emission of a spin current density J s across the bilayer interface into the Pt provides...