We report a novel spin injection and detection mechanism via the anomalous Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE) refers to the transverse spin current generated within the ferromagnet. We utilize the ASHE and its reciprocal effect to electrically inject and detect magnons in a magnetic insulator in a non-local geometry. Our experiments reveal that permalloy can have a higher spin injection and detection efficiency to that of platinum, owing to the ASHE. We also demonstrate the tunability of the ASHE via the orientation of the permalloy magnetization, thus creating new possibilities for spintronic applications.In non-magnetic metals with high spin-orbit coupling, a charge current generates a transverse spin current via the spin Hall effect (SHE) [1,2]. This type of spin current generation perpendicular to a charge current has a significant technological relevance for spin transfer torque devices [3,4] and also for the electrical injection of magnons (quantized spin waves) in magnetic insulators [5][6][7]. The electrical injection and detection of magnons offer a distinct technological advantage for the integration of magnon spintronics into solid state devices, over other magnon generation mechanisms such as spin pumping by radiofrequency fields [8] or the spin Seebeck effect due to a temperature gradient [9]. In this regard Platinum (Pt), a normal metal with a large spin-orbit coupling, is the most commonly used material for the electrical generation (and detection) of magnons via SHE. Recent studies showed that ferromagnets can also be utilized for electrical detection of magnons via the inverse spin Hall effect (ISHE) [10][11][12][13]. In particular, Tian et. al. [13] reported that ISHE in a ferromagnetic cobalt was independent of its magnetization direction.In a ferromagnetic metal the presence of the magnetization order parameter leads to the anomalous Hall effect (AHE) [14]. Here, we report a novel mechanism of spin current generation in a ferromagnet related to the AHE. The AHE generates a transverse electric potential, mutually orthogonal to the applied charge current (I) in a FM and its magnetization (M ) direction. Due to a finite spin polarization in a FM, we expect that AHE can also result in a transverse spin accumulation. We call this effect the anomalous spin Hall effect (ASHE) in a ferromagnet. In addition to this new ASHE, the regular SHE due to the spin-orbit coupling in the ferromagnetic material will also be present and contribute to a spin accumulation perpendicular to I. The spin accumulation due to SHE in the FM will be independent of M , since the inverse process (ISHE) in a FM was shown to be independent of its magnetization by Tian et. al. [13]. To demonstrate this mechanism we realize for the first time non-local magnon transport in a ferrimagnetic insulator, yttrium iron garnet(Y 3 Fe 5 O 12 , YIG), with allelectrical injection and detection using a ferromagnetic metal, permalloy (Ni 80 Fe 20 , Py). The insulating spin transport channel (YIG) facil...

We report a novel mechanism for the electrical injection and detection of out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where the direction of the spin accumulation can be controlled by manipulating the magnetization of the ferromagnet. This mechanism is distinct from the spin Hall effect (SHE), where the spin accumulation is created along a fixed direction parallel to an interface. We demonstrate this unique property of the ASHE in nanowires made of permalloy (Py) to inject and detect out-of-plane spin accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that the efficiency for the injection/detection of out-of-plane spins can be up to 50% of that of in-plane spins. We further report the possibility to detect spin currents parallel to the Py/YIG interface for spins fully oriented in the out-of-plane direction, resulting in a sign reversal of the nonlocal magnon spin signal. The new mechanisms that we have demonstrated are highly relevant for spin torque devices and applications.

We observe anisotropic Hanle lineshape with unequal in-plane and out-of-plane non-local signals for spin precession measurements carried out on lateral metallic spin valves with transparent interfaces. The conventional interpretation for this anisotropy corresponds to unequal spin relaxation times for in-plane and out-of-plane spin orientations as for the case of 2D materials like graphene, but it is unexpected in a polycrystalline metallic channel. Systematic measurements as a function of temperature and channel length, combined with both analytical and numerical thermoelectric transport models, demonstrate that the anisotropy in the Hanle lineshape is magneto-thermal in origin, caused by the anisotropic modulation of the Peltier and Seebeck coefficients of the ferromagnetic electrodes. Our results call for the consideration of such magnetothermoelectric effects in the study of anisotropic spin relaxation.Electrical spin injection and detection in non-local lateral spin valves have been used extensively to study pure spin currents in non-magnetic (NM) materials [1][2][3][4][5][6][7][8].Hanle measurements allow the manipulation of the spin accumulation in the NM via a perpendicular magnetic field, which induces spin precession as the carriers diffuse along the NM channel. From these experiments, we can extract the spin transport parameters of the channel, like the spin relaxation length and time, and hence get an insight about the nature of spin-orbit interaction (SOI) causing spin relaxation. This is particularly relevant for 2D materials like graphene, where the SOI acting along the in-plane and out-of-the plane directions can differ and lead to anisotropic spin relaxation, manifested by different signals for the in-plane and out-of-plane spin configurations in the Hanle experiments [9,10]. In contrast, for polycrystalline films, spin relaxation is expected to be isotropic [11].In this work we use metallic non-local spin valves (NLSVs), with aluminium (Al) as the NM material, to study spin precession as a function of temperature. Permalloy (Ni 80 Fe 20 , Py) has been used as the ferromagnetic (FM) electrodes to inject a spin-polarized current into Al across a transparent interface and to nonlocally detect the non-equilibrium spin accumulation in Al at a distance L from the injector. This model system with transparent FM/NM interfaces has been thoroughly studied via spin valve measurements. But curiously, corresponding spin precession studies in such systems are scarce. Only recently a few groups have demonstrated spin precession in NLSVs with transparent FM/NM interfaces [12,13], with the NM channel being either silver or copper. More importantly, these few experiments have been done only at low temperatures (T ≤ 10 K), with no reports on Hanle measurements at room temperature for transparent FM/NM interfaces.We demonstrate, through non-local spin precession experiments on Py/Al NLSVs with transparent interfaces, an anomalous Hanle lineshape for T > 150 K, in which the in-plane and out-of-plane spin signals ar...

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 report the temperature dependence of the effective spin-mixing conductance between a normal metal (aluminium, Al) and a magnetic insulator (Y 3 Fe 5 O 12 , YIG). Non-local spin valve devices, using Al as the spin transport channel, were fabricated on top of YIG and SiO 2 substrates. By comparing the spin relaxation lengths in the Al channel on the two different substrates, we calculate the effective spin-mixing conductance (G s ) to be 3.3 × 10 12 Ω −1 m −2 at 293 K for the Al/YIG interface. A decrease of up to 84% in G s is observed when the temperature (T ) is decreased from 293 K to 4.2 K, with G s scaling with (T /T c ) 3/2 . The real part of the spin-mixing conductance (G r ≈ 5.7 × 10 13 Ω −1 m −2 ), calculated from the experimentally obtained G s , is found to be approximately independent of the temperature. We evidence a hitherto unrecognized underestimation of G r extracted from the modulation of the spin signal by rotating the magnetization direction of YIG with respect to the spin accumulation direction in the Al channel, which is found to be 50 times smaller than the calculated value.The transfer of spin information between a normal metal (NM) and a magnetic insulator (MI) is the crux of electrical injection and detection of spins in the rapidly emerging fields of magnon spintronics 1 and antiferromagnetic spintronics 2,3 . The spin current flowing through the NM/MI interface is governed by the spin-mixing conductance 4-7 , G ↑↓ , which plays a crucial role in spin transfer torque 8-10 , spin pumping 11,12 , spin Hall magnetoresistance (SMR) 13,14 and spin Seebeck experiments 15 . In these experiments, the spinmixing conductance (G ↑↓ = G r + iG i ), composed of a real (G r ) and an imaginary part (G i ), determines the transfer of spin angular momentum between the spin accumulation ( µ s ) in the NM and the magnetization ( M ) of the MI in the non-collinear case. However, recent experiments on the spin Peltier effect 16 , spin sinking 17 and nonlocal magnon transport in magnetic insulators 18,19 necessitate the transfer of spin angular momentum through the NM/MI interface also in the collinear case ( µ s M ). This is taken into account by the effective spin-mixing conductance (G s ) concept, according to which the transfer of spin angular momentum across the NM/MI interface can occur, irrespective of the mutual orientation between µ s and M , via local thermal fluctuations of the equilibrium magnetization (thermal magnons 20 ) in the MI. The spin current density ( j s ) through the NM/MI interface can, therefore, be expressed as 17,21,22 :where,m is a unit vector pointing along the direction of M . While G r and G i have been extensively studied a) in spin torque and SMR experiments 23-25 , direct experimental studies on the temperature dependence of G s are lacking.In this letter, we report the first systematic study of G s versus temperature (T ) for a NM/MI interface. For this, we utilize the lateral non-local spin valve (NLSV) geometry, which provides an alternative way to study the spin-mixing...