Features of the Pulsed Magnetization Switching in a High-Coercivity Material Based on ε-Fe2O3 Nanoparticles

• Published in: Physics of the solid state 2020-03, Vol.62 (3), p.445-453
• Main Authors: Popkov, S. I., Krasikov, A. A., Semenov, S. V., Dubrovskii, A. A., Yakushkin, S. S., Kirillov, V. L., Mart’yanov, O. N., Balaev, D. A.
• Format: Article
• Language: English
• Subjects: Capacitor banks; Coercivity; Ferrimagnetism; Hysteresis loops; Iron oxides; Low temperature; Magnetic induction; Magnetic moments; Magnetic structure; Magnetic switching; Magnetic transitions; Magnetism; Magnetization; Nanoparticles; Parameters; Particle spin; Physics; Physics and Astronomy; Room temperature; Silicon dioxide; Solenoids; Solid State Physics; Spin dynamics; Xerogels
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783420030166

The magnetic structure of the ε-Fe 2 O 3 iron oxide polymorphic modification is collinear ferrimagnetic in the range from room temperature to ~150 K. As the temperature decreases, ε-Fe 2 O 3 undergoes a magnetic transition accompanied by a significant decrease in the coercivity H c and, in the low-temperature range, the compound has a complex incommensurate magnetic structure. We experimentally investigated the dynamic magnetization switching of the ε-Fe 2 O 3 nanoparticles with an average size of 8 nm in the temperature range of 80–300 K, which covers different types of the magnetic structure of this iron oxide. A bulk material consisting of xerogel SiO 2 with the ε-Fe 2 O 3 nanoparticles embedded in its pores was examined. The magnetic hysteresis loops under dynamic magnetization switching were measured using pulsed magnetic fields H max of up to 130 kOe by discharging a capacitor bank through a solenoid. The coercivity Н с upon the dynamic magnetization switching noticeably exceeds the Н с value under the quasi-static conditions. This is caused by the superparamagnetic relaxation of magnetic moments of particles upon the pulsed magnetization switching. In the range from room temperature to ~ 150 K, the external field variation rate dH / dt is the main parameter that determines the behavior of the coercivity under the dynamic magnetization switching. It is the behavior that is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K) when the ε-Fe 2 O 3 magnetic structure is incommensurate, the coercivity during the pulsed magnetization switching depends already on the parameter dH / dt and is determined, to a great extent, by the maximum applied field H max . Such a behavior atypical of systems of ferrimagnetic particles is caused already by the dynamic spin processes inside the ε-Fe 2 O 3 particles during fast magnetization switching.