We demonstrate a modulation of up to 18% in the magnon spin transport in a magnetic insulator (Y3Fe5O12, YIG) using a common ferromagnetic metal (permalloy, Py) as a magnetic control gate. A Py electrode, placed between two Pt injector and detector electrodes, acts as a magnetic gate in our prototypical magnon transistor device. By manipulating the magnetization direction of Py with respect to that of YIG, the transmission of magnons through the Py|YIG interface can be controlled, resulting in a modulation of the non-equilibrium magnon density in the YIG channel between the Pt injector and detector electrodes. This study opens up the possibility of using the magnetic gating effect for magnon-based spin logic applications.

We observe that an rf microwave field strongly influences the transport of incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in the nonlinear regime suppresses thermal magnon transport by 95%. The transport is also modulated at non-resonant conditions in two cases, both related to the magnon band minimum. Firstly, a strong enhancement of the nonlocal signal appears at a static magnetic field below the resonance condition. This increase only occurs at one field polarity and can be as large as 800%. We attribute this effect to magnon kinetic processes, which give rise to band-minimum magnons and high-energy chiral surface modes. Secondly, the signal increases at a static field above the resonance condition, where the rf frequency coincides with the magnon band minimum. Our study gives insight into the interplay between coherent and incoherent spin dynamics: The rf field modifies the occupation of relevant magnon states and, via kinetic processes, the magnon spin transport. arXiv:1810.11667v1 [cond-mat.mes-hall]

The van der Waals materials are a new platform to study two-dimensional systems, including magnetic order. Since the number of spins is relatively small, measuring the magnetization is challenging. Here, we report spin Hall magnetoresistance (SMR) up to room temperature caused by the magnetic surface texture of exfoliated flakes of magnetic van der Waals materials. For the antiferromagnet FePS 3 the SMR amounts to 0.1% for an applied magnetic field of 7 T at 5 K, which implies a substantial canting of the magnetic moments in a perpendicular antiferromagnetic order. The canting is substantial even for a magnetic field along the Néel vector, which illustrates the unique power of the SMR to detect magnetic surface textures in van der Waals magnets.

We report the control of the modulation efficiency of the magnon conductivity in yttrium iron garnet (YIG) using magnon spin injection from a ferromagnetic metal permalloy (Py) used as a modulator in a three-terminal magnon transistor geometry. The modulation efficiency is estimated by means of nonlocal spin-transport measurements between platinum injector and detector strips. A charge current is sent through the Py modulator to create a spin accumulation at the YIG-Py interface via the spin Hall effect and the anomalous spin Hall effect (ASHE). We observe an enhancement of the modulation efficiency for the electrically generated magnons from 2.5%/mA at 10 mT to 4.7%/mA for magnetic fields higher than 50 mT. That enhancement is attributed to the ASHE, which is maximized when the Py magnetization is perpendicular to the charge current. However, the modulation efficiency of the thermally generated magnons exhibits an opposite behavior, 12.0%/mA at 10 mT to 6.6%/mA at 50 mT, which disagrees with what we expect from the ASHE contribution to the modulation.

We present the detection of the spin-flop transition in the antiferromagnetic van der Waals material MnPS 3 via thermally generated nonlocal magnon transport using permalloy (Py) detector strips. Py detector strips possess the inverse anomalous spin Hall effect, which has the unique power to detect an out-of-plane spin accumulation [Das et al., Nano Lett. 18, 5633 (2018)]. This enables us to detect magnons with an out-of-plane spin polarization, in contrast to strips of high-spin-orbit materials such as Pt which possess only the spin Hall effect and are sensitive to only an in-plane spin polarization of the spin accumulation. We show that nonlocal magnon transport is able to measure the spin-flop transition in the absence of spurious magnetoresistance effects. Our measurements show the detection of magnons generated by the spin Seebeck effect before and after the spin-flop transition. We observe a signal reversal of the magnon spin accumulation which agrees with the out-of-plane spin polarization carried by magnon modes before and after the spin-flop transition.