The room temperature deposition of high-quality epitaxial yttrium iron garnet thin film via RF sputtering

Highlights

• Epitaxial YIG films were successfully grown on GGG substrate at room temperature.

• The strain states of YIG thin films were analysed by RSM.

• These YIG films show excellent magnetic properties and narrow linewidth.

Abstract

Yttrium iron garnet (YIG) has great potential in the application of microwave devices and spintronics. However, the extremely high temperature for the growth of single crystalline YIG thin film on garnet substrate has being a barrier hindering its massive production and wide application, especially for some integrated devices which cannot bear high temperature for a long time. In this work, epitaxial single crystalline YIG thin films were successfully obtained by deposition on (111)-oriented gadolinium gallium garnet (GGG) at room temperature via RF sputtering followed by a short-time post-annealing treatment. Their structural and physical properties were carefully studied and compared with that of YIG/GGG(111) thin films deposited at high temperatures. The relatively large saturated magnetization (∼120 emu/cc) and a comparable linewidth (∼55 Oe) of those room-temperature-deposited YIG thin films can be achieved. This provides a viable alternative for growing YIG thin films on GGG or other garnet substrates.

Introduction

Ferrimagnetic yttrium iron garnet (Y₃Fe₅O₁₂, YIG) has attracted researchers' decades of attention for application in microwave devices and spintronics due to its relatively high Curie temperature (T_C ∼ 550 K), excellent magneto-optic Kerr effect [1], [2] and low magnetic loss [3], [4], [5]. Various techniques have been used to fabricate YIG thin films, such as Liquid Phase Epitaxy (LPE) [2], [6], Pulsed Laser Deposition (PLD) [7], [8], [9] and Radio Frequency (RF) magnetron sputtering [10], [11], [12]. Although LPE and PLD are wellknown for growing single-crystalline thick film with high quality and high deposition rate, respectively, RF magnetron sputtering is better at producing thin film with smooth sample surface and stable stoichiometric ratio, which is more recognized by industries and suit for massive production. Previous study indicates epitaxial growth of YIG films with high quality using sputtering requires high processing temperature (above 750 °C), which hinders its wide application [13], [14]. Although other growth method was applied to solve this problem, such as post-annealing process after deposition at low temperature, especially on some non-garget substrates such as silicon or quartz which could be widely used in large-scale practical production [10], [12], [15], there is few study to comprehensively analyze the effect of post-annealing process on YIG thin film grown on garnet substrates. It will be very important for industrial community if epitaxial YIG thin films could be massively produced on garnet substrates after being deposited at room temperature then annealed at high temperature. In this case, it will not be so critical for the choice of film-growth facility, especially for those without heater. And it will be quite efficient once large batches of films could be annealed in a furnace at the same time. Most importantly, this technique will benefit many devices which cannot stand for a long period at a relatively high temperature. In this work, epitaxial YIG thin films were grown on (111)-oriented gadolinium gallium garnet (Gd₃Ga₅O₁₂, GGG) substrates at room temperature by RF sputtering then annealed at high temperatures. By a series of systematical analysis of both structural and physical properties of YIG thin films prepared via different routes, we found that the physical properties of those films are comparable with that grown under high temperatures, presenting a proper way to obtain engineering desired ferrites through carefully tuning their growth conditions.