Room Temperature Magnetic Rare-Earth Iron Garnet Thin Films with Ordered Mesoporous Structure

Amphiphilic polymers are very attractive as porogens for the preparation of ordered mesoporous thin films and powders with pore sizes ranging from 40 down to a few nanometers in diameter because they are capable of both forming different superstructures and interacting with sol–gel precursors. In the present work, we report for the first time the synthesis of a series of highly crystalline rare-earth iron garnet (RE 3 Fe 5 O 12, RE = Y, Gd–Dy) thin films with cubic networks of interconnected pores averaging 17 nm in diameter through facile polymer templating of hydrated nitrate salts. Despite intricate crystallization pathways, e.g., Y 3 Fe 5 O 12 via Y 4 Fe 2 O 9 and h -YFeO 3, the nanoscale architecture of all these materials is only affected to a limited extent by solid–solid conversions at elevated temperatures. We specifically focus on the characterization of the morphology, microstructure, and magnetic properties of polymer-templated Y 3 Fe 5 O 12 . This novel mesoporous material is single phase after heating to 900 °C, free of major structural defects, and is also well-defined on the atomic level, as evidenced by a combination of in situ and ex situ scattering/diffraction techniques, electron microscopy, Raman and X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The high quality of the nanocrystalline Y 3 Fe 5 O 12 thin films with overall soft magnetic properties and moderate anisotropy is further confirmed by SQUID magnetometry measurements. The magnetization behavior in the temperature range 5–380 K describes Bloch’s T 3/2 law for a 3D Heisenberg-type ferromagnet well.