Yttrium iron garnet has a very high Verdet constant, is transparent in the infrared and is an insulating ferrimagnet leading to its use in optical and magneto-optical applications. Its high Q-factor has been exploited to make resonators and filters in microwave devices, but it also has the lowest magnetic damping of any known material. In this article we describe the structural and magnetic properties of single crystal thin-film YIG where the temperature dependence of the magnetisation reveals a decrease in the low temperature region. In order to understand this complex material we bring a large number of structural and magnetic techniques to bear on the same samples. Through a comprehensive analysis we show that at the substrate -YIG interface, an interdiffusion zone of only 4–6 nm exists. Due to the interdiffusion of Y from the YIG and Gd from the substrate, an addition magnetic layer is formed at the interface whose properties are crucially important in samples with a thickness of YIG less than 200 nm.

We report spin wave propagation experiments in thin yttrium iron garnet (YIG) films. Using time-resolved scanning Kerr microscopy we extract the mode structure of the spin waves. For quasi-single-mode excitation, the spin wave decay can be fitted with a damped harmonic oscillator function providing us with information about the attenuation length. We measure values of about 2.7 and 3.6 μm for the spin wave decay length of 38-and 49-nm-thick YIG samples, respectively. Micromagnetic simulations are performed to compare experimental and simulated modes. The data are in very good agreement with these simulations.

We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80 nm, with Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics.Introduction -Insulating magnetic materials have recently played an important role in spintronics, since they allow pure spin currents to flow without associated charge transport. Within the family of ferromagnetic insulators, yttrium iron garnet (YIG) holds a special place owing to several favourable properties, including ultra-low damping, high Curie temperature and chemical stability [1][2][3]. By growing an overlayer of heavy metal (HM), such as platinum or tantalum, several important spintronic phenomena have been explored in the YIG/HM bilayer system, including the magnetic proximity effect [4,5], spin pumping [6,7], spin Hall magnetoresistance (SMR) [8,9], spin Seebeck effect [10,11] and so on. Furthermore, the spin Hall effect in HM can convert a charge current into a transverse pure spin current, making it possible to manipulate the ferromagnetic insulator by spin transfer torque (STT). Recently, several groups have reported controlling the damping in YIG by applying a DC charge current in a Pt capping layer [12], by which spin-Hall autooscillation can be realized [13,14]. Replacing the DC current with a microwave current, the electrical signal in Pt can also be transmitted via spin waves in YIG [3]. In order to further explore the application of the YIG/HM system, it is necessary to understand the torque on YIG induced by the charge current in HM.

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