These authors contributed equally to this work. The introduction and control of ferromagnetism in graphene opens up a range of new directions for fundamental and applied studies. Several approaches have been pursued so far, such as introduction of defects, functionalization with adatoms, and shaping of graphene into nanoribbons with well-defined zigzag edges. 1-6 A more robust and less invasive method utilizes the introduction of an exchange interaction by a ferromagnetic insulator (FMI) in proximity with graphene. 7-14Here we present a direct measurement of the exchange interaction in room temperature ferromagnetic graphene. We study the spin transport in exfoliated graphene on a yttriumiron-garnet (YIG) substrate where the observed spin precession clearly indicates the presence and strength of an exchange field that is an unambiguous evidence of induced ferromagnetism. We describe the results with a modified Bloch diffusion equation and extract an average exchange field of the order of 0.2 T. Further, we demonstrate that a proximity induced 2D ferromagnet can efficiently modulate a spin current by controlling the direction of the exchange field. These results can create a building block for magneticgate tuneable spin transport in one-atom-thick spintronic devices. 8,9

We report the first observation of a large spin lifetime anisotropy in bilayer graphene (BLG) fully encapsulated between hexagonal boron nitride. We characterize the out-of-plane (τ ⊥ ) and in-plane (τ ) spin lifetimes by oblique Hanle spin precession. At 75 K and the charge neutrality point (CNP) we observe a strong anisotropy of τ ⊥ /τ = 8 ± 2. This value is comparable to graphene/TMD heterostructures, whereas our high quality BLG provides with τ ⊥ up to 9 ns, a more than two orders of magnitude larger spin lifetime. The anisotropy decreases to 3.5 ± 1 at a carrier density of n = 6 × 10 11 cm −2 . Temperature dependent measurements show above 75 K a decrease of τ ⊥ /τ with increasing temperature, reaching the isotropic case close to room temperature. We explain our findings with electric field induced spin-valley coupling arising from the small intrinsic spin orbit fields in BLG of 12 µeV at the CNP.

Thermal spin-transfer torque describes the manipulation of the magnetization by the application of a heat flow. The effect has been calculated theoretically by Jia et al. in 2011. It is found to require large temperature gradients in the order of Kelvins across an ultra thin MgO barrier. In this paper, we present results on the fabrication and the characterization of magnetic tunnel junctions with 3 monolayer thin MgO barriers.The quality of the interfaces at different growth conditions is studied quantitatively via high-resolution transmission electron microscopy imaging. We demonstrate tunneling magneto resistance ratios of up to 55% to 64% for 3 to 4 monolayer barrier thickness. Magnetic tunnel junctions with perpendicular magnetization anisotropy show spin-transfer torque switching with a critical current of 0.2 MA/cm 2 . The thermally generated torque is calculated ab initio using the Korringa-Kohn-Rostoker and non-equilibrium Green's function method. Temperature gradients generated from femtosecond laser pulses were simulated using COMSOL, revealing gradients of 20 K enabling thermal spin-transfer-torque switching.

Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction varies as the magnetic configuration changes from a parallel (P) to an anti-parallel (AP) configuration. Here we report the study on its as-yet-unexplored reciprocal effect, the magnetoPeltier effect, where the heat flow carried by the tunneling electrons is altered by changing the magnetic configuration of the MTJ. The magneto-Peltier signal that reflects the change in the temperature difference across the junction between the P and AP configurations scales linearly with the applied current in the small bias but is greatly enhanced in the large bias regime, due to higher-order Joule heating mechanisms. By carefully extracting the linear response which reflects the magneto-Peltier effect, and comparing it with the magneto-Seebeck measurements performed on the same device, we observe results consistent with Onsager reciprocity. We estimate a magnetoPeltier coefficient of 13.4 mV in the linear regime using a three-dimensional thermoelectric model. Our result opens up the possibility of programmable thermoelectric devices based on the Peltier effect in MTJs.The electrical resistance of a magnetic tunnel junction (MTJ), a stack of two ferromagnetic layers separated by an insulating tunnel barrier, depends on the relative magnetic orientation of the two magnetic layers [1][2][3]. This tunnel magnetoresistance (TMR) effect puts MTJs at the forefront of the applications in the field of spintronics [4]. Spin caloritronics [5][6][7] is an emerging field that couples thermoelectric effects with spintronics. Many interesting physical phenomena were discovered such as the spin (-dependent) Seebeck effect in magnetic metal [8], magnetic semiconductor [9] and magnetic insulator [10]. Particularly, in spin tunneling devices, the magneto-Seebeck effect was theoretically studied [11][12][13][14] and experimentally observed [15][16][17][18][19] in MTJs, where the Seebeck coefficient of the junction can be varied by changing the magnetic configuration. More recently, the spin (-dependent) Peltier effect that is driven by spin (polarized) currents has been experimentally observed in metallic [20,21] and insulating ferromagnets [22], which are shown to obey the Thomson-Onsager reciprocity relation [23][24][25] to the spin (-dependent) Seebeck effect. From this relation, the reciprocal effect of the magneto-Seebeck effect, which can be named as magneto-Peltier effect, is also expected in MTJs (see Fig. 1(a)(b)).However, experimental studies of the magneto-Peltier effect have not been reported so far. Its small effect compared to the often-dominant Joule heating effects has left the experimental observation elusive. In this work, we report the first experimental study of the magneto-Peltier effect as well as higher order heating effects, and...

The recently reported magnetic ordering in insulating two-dimensional (2D) materials, such as chromium triiodide (CrI 3 ) and chromium tribromide (CrBr 3 ), opens new possibilities for the fabrication of magnetoelectronic devices based on 2D systems. Inevitably, the magnetization and spin dynamics in 2D magnets are strongly linked to Joule heating. Therefore, understanding the coupling between spin, charge, and heat, i.e., spin caloritronic effects, is crucial. However, spin caloritronics in 2D ferromagnets remains mostly unexplored, due to their instability in air. Here we develop a fabrication method that integrates spin-active contacts with 2D magnets through hBN encapsulation, allowing us to explore the spin caloritronic effects in these materials. The angular dependence of the thermal spin signal of the CrBr 3 /Pt system is studied, for different conditions of magnetic field and heating current. We highlight the presence of a significant magnetic proximity effect from CrBr 3 on Pt revealed by an anomalous Nernst effect in Pt, and suggest the contribution of the spin Seebeck effect from CrBr 3 . These results pave the way for future magnonic devices using air-sensitive 2D magnetic insulators.