High‐Quality Magnetically Hard ε‐Fe<sub>2</sub>O<sub>3</sub> Thin Films through Atomic Layer Deposition for Room‐Temperature Applications
Topias Jussila, Anish Philip, J. Lindén, Maarit Karppinen
Abstract
The critical‐element‐free ε‐Fe 2 O 3 ferrimagnet exhibits giant magnetic coercivity even at room temperature. It is thus highly attractive material for advanced applications in fields such as spintronics, high‐density data storage, and wireless communication. However, a serious obstacle to overcome is the notoriously challenging synthesis of ε‐Fe 2 O 3 due to its metastable nature. Atomic layer deposition (ALD) is the state‐of‐the‐art thin‐film technology in microelectronics. Herein, it is demonstrated that it has also true potential for the fabrication of amazingly stable in situ crystalline and high‐performance ε‐Fe 2 O 3 thin films from simple (FeCl 3 and H 2 O) chemical precursors at a moderately low deposition temperature (280 °C). Standard X‐ray diffraction and Fourier transfer infrared spectroscopy characterization indicates that the films are of high level of phase purity. Most importantly, precise temperature‐dependent 57 Fe Mössbauer spectroscopy measurements verify that the hematite (α‐Fe 2 O 3 ) trace in the films is below 2.5%, and reveal the characteristic low‐ and high‐temperature transitions at 208–228 K and ≈480 K, respectively, while magnetization measurements confirm the symmetric hysteresis loops expected for essentially phase‐pure ε‐Fe 2 O 3 films. Excitingly, the highly c ‐axis oriented film growth, the overall film quality, and the unique magnetic properties remain the same, independently of the substrate material used.