We report on the structure, magnetization, magnetic anisotropy, and domain morphology of ultrathin yttrium iron garnet (YIG)/Pt films with thickness ranging from 3 to 90 nm. We find that the saturation magnetization is close to the bulk value in the thickest films and decreases towards low thickness with a strong reduction below 10 nm. We characterize the magnetic anisotropy by measuring the transverse spin Hall magnetoresistance as a function of applied field. Our results reveal strong easy plane anisotropy fields of the order of 50-100 mT, which add to the demagnetizing field, as well as weaker in-plane uniaxial anisotropy ranging from 10 to 100 μT. The in-plane easy axis direction changes with thickness, but presents also significant fluctuations among samples with the same thickness grown on the same substrate. X-ray photoelectron emission microscopy reveals the formation of zigzag magnetic domains in YIG films thicker than 10 nm, which have dimensions larger than several 100 μm and are separated by achiral Néel-type domain walls. Smaller domains characterized by interspersed elongated features are found in YIG films thinner than 10 nm.

We report on the switching of the in-plane magnetization of thin yttrium iron garnet (YIG)/Pt bilayers induced by an electrical current. The switching is either field-induced and assisted by a dc current, or currentinduced and assisted by a static magnetic field. The reversal of the magnetization occurs at a current density as low as 10 5 A/cm 2 and magnetic fields of ∼ 40 µT, two orders of magnitude smaller than in ferromagnetic metals, consistently with the weak uniaxial anisotropy of the YIG layers. We use the transverse component of the spin Hall magnetoresistance to sense the magnetic orientation of YIG while sweeping the current. Our measurements and simulations reveal that the current-induced effective field responsible for switching is due to the Oersted field generated by the current flowing in the Pt layer rather than by spin-orbit torques, and that the switching efficiency is influenced by pinning of the magnetic domains.The possibility of manipulating the magnetization of planar structures using electrical currents opens exciting perspectives in spintronics. Electrical currents can affect the magnetization of thin films through the Oersted magnetic field, 1-5 spin transfer torques, 6 and spinorbit torques. 7 Previous work has focused on magnetization switching and domain wall dynamics induced by spin-orbit torques in metallic ferromagnets adjacent to a heavy metal layer. [8][9][10][11][12][13][14][15] Recently, investigations extended towards insulating ferrimagnetic garnets, which, owing to the low magnetic damping, are particularly appealing for generating and transmitting spin waves 16-19 as well as for magnetization switching. [20][21][22] The most prominent exponent of this material class is yttrium iron garnet (YIG). Extensive work on the interplay of current-induced effects and magnetization dynamics in YIG/Pt bilayers demonstrated efficient spin-wave excitations, 23-27 spinwave amplification, 28,29 and the control of magnetization damping. 30 So far, however, no attempt at currentinduced magnetization switching of YIG has been reported. Two plausible reasons for the scarcity of results in this area are the extreme sensitivity of YIG to magnetic fields, which makes it difficult to control the intermediate magnetization states, as well as to the need to utilize YIG films with uniaxial in-plane anisotropy, which is required to achieve binary switching. Indeed, the electrical switching of garnet insulators has been reported only for thin films with relatively large perpendicular anisotropy, such as thulium iron garnet layers in combination with either Pt or W. [20][21][22] In this paper, we investigate the reciprocal effects of current and magnetic field on the switching of YIG/Pt bilayers with in-plane magnetic anisotropy. We demonstrate field-induced switching assisted by a dc current as well as current-induced switching assisted by a static magnetic field at extremely low current density (∼ 10 5 A/cm 2 ) and bias fields (40 − 60 µT). We further show that the magnetization reversal can be sensed...