Interfacial Origin of the Magnetisation Suppression of Thin Film Yttrium Iron Garnet

Abstract

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.

Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy

“…Therefore, we speculate, that the significant drop of 4πM eff for the 11 nm thin film can be explained by the observed reduction of 4πM s (see Table III). A similar behavior for 4πM s was reported for thin PLD or magnetron-sputtered YIG films, and different explanations were given [76,56,91]. One reason for a reduced saturation magnetization could be an intermixing of substrate and film elements at the GGG/YIG interface, whereby a gradual change of the film composition is assumed [75,77].…”

“…Using the 10%-to-90% edge response criterion, it shows a transition width of (1.9 ± 0.4) nm at the interface. This is lower than the observed 4-6 nm non-magnetic dead layer reported for YIG films deposited by RF magnetron sputtering [76], and the about 4 nm or the 5-7 nm deep Ga diffusion observed for PLD [77] or laser molecular beam epitaxy (MBE) [75], respectively. However, at some positions of the sample's cross-section we found a reduced YIG film thickness on a wavy GGG surface (not shown), which we attribute to a possible etch-back of the substrate at the beginning of film growth or an already existing wavy substrate surface.…”

Synthetic Antiferromagnetic Coupling Between Ultrathin Insulating Garnets

“…The magnetic properties of the ultra-thin magnetic garnet bilayer cannot be extracted using standard magnetometry, because the 500-m-thick GGG substrate shows a dominating paramagnetic background that masks the magnetic signal from the bilayer. We performed longitudinal SMR measurements, which only probe the top surface magnetization [17][18][19][20] , and thus the magnetization of the GdIG interlayer at the bottom interface is not expected to influence the SMR signal 52 . SMR depends on the relative angle of the surface magnetization in the FMI and the spin accumulation in the HM.…”

“…However, material quality in these cases is not as consistently high as seen in LPE-based YIG. For example, recent works report unusual magnetic anisotropy related to Fe 3+ vacancies in PLD-grown YIG 47,48 , and either exceptionally high magnetization 53 or a magnetization suppression 52 in sputtered films that could be related to the interface between YIG and the used substrate Gd 3 Ga 5 O 12 (GGG). The variety in the results and interpretations that can be found in the literature calls for an in-depth characterization of those thin YIG films.…”

Interfacial and Bulk Magnetic Properties of Stoichiometric Cerium Doped Terbium Iron Garnet Polycrystalline Thin Films

“…[ 18,19 ] More recently the interdiffusion claims were bolstered with scanning transmission electron microscopy that showed a 6 nm Gd, Ga‐doped YIG interlayer region that is paramagnetic at room temperature. [ 20 ] While significant research has been done on the single crystal YIG/GGG system for magnonics, very little work is available on polycrystalline garnets that have substantial implications in silicon photonics.…”