The use of magnetic insulators is attracting a lot of interest due to a rich variety of spindependent phenomena with potential applications to spintronic devices. Here we report ultrathin yttrium iron garnet (YIG) / gadolinium iron garnet (GdIG) insulating bilayers on gadolinium iron garnet (GGG). From spin Hall magnetoresistance (SMR) and X-ray magnetic circular dichroism measurements, we show that the YIG and GdIG magnetically couple antiparallel even in moderate in-plane magnetic fields. The results demonstrate an allinsulating equivalent of a synthetic antiferromagnet in a garnet-based thin film heterostructure and could open new venues for insulators in magnetic devices. As an example, we demonstrate a memory element with orthogonal magnetization switching that can be read by SMR.

Recent experiments on strongly coupled microwave and ferromagnetic resonance modes have focused on large volume bulk crystals such as yttrium iron garnet, typically of millimeter-scale dimensions. We extend these experiments to lower volumes of magnetic material by exploiting low-impedance lumped-element microwave resonators. The low impedance equates to a smaller magnetic mode volume, which allows us to couple to a smaller number of spins in the ferromagnet. Compared to previous experiments, we reduce the number of participating spins by two orders of magnitude, while maintaining the strength of the coupling rate. Strongly coupled devices with small volumes of magnetic material may allow the use of spin orbit torques, which require high current densities incompatible with existing structures.

We present measurements of ferromagnetic-resonance -driven spin pumping and inverse spin-Hall effect in NbN/Y3Fe5O12 (YIG) bilayers. A clear enhancement of the (effective) Gilbert damping constant of the thin-film YIG was observed due to the presence of the NbN spin sink.By varying the NbN thickness and employing spin-diffusion theory, we have estimated the room temperature values of the spin diffusion length and the spin Hall angle in NbN to be 14 nm and -1.1×10 -2 , respectively. Furthermore, we have determined the spin-mixing conductance of the NbN/YIG interface to be 10 nm -2 . The experimental quantification of these spin transport parameters is an important step towards the development of superconducting spintronic devices involving NbN thin films.

No abstract

The ν = 0 quantum Hall state in graphene has attracted experimental [1][2][3][4][5][6][7][8][9][10][11] and theoretical [12][13][14][15][16][17][18] interest.Graphene supports four zero-energy Landau levels which are described by spin and valley degeneracies.These lead to a number of approximately degenerate symmetry-broken states 12,14 . Electron-electron and electron-phonon interactions break valley-symmetry and determine the ground state of the ν = 0 state. The consensus emerging from theory [16][17][18] and experiment 3,8,9,11 is that these interactions favour an antiferromagnetic insulating state which supports long-range spin-polarized edge transport 3,11 . Here we report a competition between canted antiferromagnetic and ferromagnetic quantum Hall states in graphene placed on a ferrimagnetic insulator Y3Fe5O12 (YIG), which induces a uniform magnetic exchange field in graphene of the order 60 T. The magnetic order and energy gap of the edge modes in graphene are tunable with an 8 T out-of-plane magnetic field at 2.7 K.A magnetic field parallel (B∥) to the plane of graphene can promote a ferromagnetic (F-) state 9 . In general, however a competition between antiferromagnetic (AF-) and F-states leads to a canted antiferromagnetic (CAF-) state in which the spins are tilted parallel (as preferred by the Zeeman field) and perpendicular (as preferred by the interactions that favour AF order) to the magnetic field, pointing in opposite directions in the two sublattices as schematically illustrated in Fig. 1. The CAF-state continuously interpolates between the AF-(θ = π/2) and F-states (θ = 0), where θ is the angle between the spins and magnetic field. In the AF-state, charged edge excitations are gapped, but the F-state supports gapless counterpropagating edge modes 15,17 . Therefore, in the CAF-state the energy gap of the edge modes is tunable with a magnetic field with a gap at θ = π/2 which vanishes at θ = 0 (Ref. 17), and a competition between the CAF-and F-states can be detected by transport measurements 9 . Although a tunable energy