The Low-Temperature Magnetic State and Magnetic Ordering Temperature of ϵ-Fe2O3 Iron Oxide Nanoparticles

• Published in: IEEE magnetics letters Vol. 10; pp. 1 - 3
• Main Authors: Dubrovskiy, Andrey A., Semenov, Sergey V., Knyazev, Yuri V., Popkov, Sergey I., Yakushkin, Stas S., Kirillov, Viktor L., Martyanov, Oleg N., Balaev, Dmitry A.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Anomalies; Ferromagnetic resonance; Ferromagnetism; FMR spectra; Iron oxides; Low temperature; Magnetic hysteresis; Magnetic materials; Magnetic properties; Magnetic resonance; Magnetic structure; magnetic transition; Magnetic transitions; Magnetism; Magnetization; Nanomagnetics; Nanoparticles; Perpendicular magnetic anisotropy; Phase diagrams; Phase transitions; Saturation magnetization; Silicon dioxide; Temperature; Temperature dependence; Temperature distribution; Xerogels; ϵ-Fe<inline-formula xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <tex-math notation="LaTeX"> _{2}</tex-math> </inline-formula>O<inline-formula xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <tex-math notation="LaTeX"> _{3}</tex-math> </inline-formula> nanoparticles
• ISSN: 1949-307X; 1949-3088
• DOI: 10.1109/LMAG.2019.2956674

The ε-Fe 2 O 3 iron oxide polymorph is a well-known magnetic material with a complex magnetic structure, which undergoes a series of magnetic transitions in different temperature ranges. However, the ε-Fe 2 O 3 phase diagram is still unclear. We report on the magnetic properties of a sample consisting of ε-Fe 2 O 3 nanoparticles with an average size of 8 nm embedded in a SiO 2 xerogel matrix without an admixture of foreign phases. Along with the features typical of the well-known ε-Fe 2 O 3 magnetic transition in the temperature range 80-150 K, the temperature dependence of magnetization M(T) of ε-Fe 2 O 3 includes other low-temperature anomalies. In an external field of H = 70 kOe, there is a noticeable temperature hysteresis of magnetization at 50-90 K, and near T 50 K, the M(T) curves have a characteristic bending, which may be indicative of an additional magnetic transition. The ferromagnetic resonance spectra shows that, near 500 K, a magnetic phase transition occurs, which was previously thought to be a transition to the paramagnetic state. An analysis of the temperature dependence of the ferromagnetic resonance spectra shows that the magnetically ordered phase in ε-Fe 2 O 3 exists up to about 800 K.