Transport, Magnetic, and Memristive Properties of a Nanogranular (CoFeB)x(LiNbOy)100–x Composite Material

• Published in: Journal of experimental and theoretical physics Vol. 126; no. 3; pp. 353 - 367
• Main Authors: Rylkov, V. V., Nikolaev, S. N., Demin, V. A., Emelyanov, A. V., Sitnikov, A. V., Nikiruy, K. E., Levanov, V. A., Presnyakov, M. Yu, Taldenkov, A. N., Vasiliev, A. L., Chernoglazov, K. Yu, Vedeneev, A. S., Kalinin, Yu. E., Granovsky, A. B., Tugushev, V. V., Bugaev, A. S.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.03.2018; Springer Nature B.V
• Subjects: Classical and Quantum Gravitation; Cobalt; Composite materials; Disorder; Electrical resistivity; Elementary Particles; Elongation; Ferromagnetic materials; Granular materials; Hall effect; Magnetic properties; Magnetization; Metal-insulator transition; Nanocomposites; Order; Particle and Nuclear Physics; Phase Transition in Condensed System; Physics; Physics and Astronomy; Quantum Field Theory; Relativity Theory; Solid State Physics; Temperature dependence; Vacancies
• ISSN: 1063-7761; 1090-6509
• DOI: 10.1134/S1063776118020152

The properties of (CoFeB) x (LiNbO y ) 100– x nanocomposite films with a ferromagnetic alloy content x = 6–48 at % are comprehensively studied. The films are shown to consist of ensembles of CoFe granules 2–4 nm in size, which are strongly elongated (up to 10–15 nm) in the nanocomposite growth direction and are located in an LiNbO y matrix with a high content of Fe 2+ and Co 2+ magnetic ions (up to 3 × 1022 cm –3 ). At T ≤ 25 K, a paramagnetic component of the magnetization of nanocomposites is detected along with a ferromagnetic component, and the contribution of the former component is threefold that of the latter. A hysteresis of the magnetization is observed below the percolation threshold up to x ≈ 33 at %, which indicates the appearance of a superferromagnetic order in the nanocomposites. The temperature dependence of the electrical conductivity of the nanocomposites in the range T ≈ 10–200 K on the metallic side of the metal–insulator transition (44 at % < x < 48 at %) is described by a logarithmic law σ( T ) ∝ ln T . This law changes into the law of “1/2” at x ≤ 40 at %. The tunneling anomalous Hall effect is strongly suppressed and the longitudinal conductivity turns out to be lower than in a (CoFeB) x (AlO y ) 100– x composite material by an order of magnitude. The capacitor structures based on (CoFeB) x (LiNbO y ) 100– x films exhibit resistive switching effects. They are related to (i) the formation of isolated chains of elongated granules and an anomalously strong decrease in the resistance in fields E > 10 4 V/cm because of the suppression of Coulomb blockage effects and the generation of oxygen vacancies V O and (ii) the injection (or extraction) of V O vacancies (depending on the sign of voltage) into a strongly oxidized layer in the nanocomposites, which is located near an electrode of the structure and controls its resistance. The number of stable resistive switchings exceeds 10 5 at a resistance ratio R off / R on ~ 50.