Key Words:Spin glass; Spintronics; Single crystals; Coercivity

Abstract:In this study, room-temperature spin-glass behaviors were observed in flake-like oriented attached hematite (alpha-Fe2O3) and iron phosphate hydroxide hydrate (Fe-5(PO4)(4)(OH)(3)center dot 2H2O) single crystals. Remarkably, their coercivity (H-c) values were found to be almost invariable at various given temperatures from 5 to 300 K. The spin topographic map in these flakes was assumed as superparamagnetic (SPM) "islands" isolated by spin glass (SG)-like "bridges". A spin-glass model was then proposed to demonstrate the spin frustration within these "bridges", which were formed by the staggered atomic planes in the uneven surfaces belonging to different attached nanoparticles. Under the spatial limitation and coupling shield of these "bridges", the SPM "islands" were found to be collectively frozen to form a superspin glass (SSG) state below 80 K in weak applied magnetic fields; whereas, when strong magnetic fields were applied, the magnetic coupling of these "islands" would become superferromagnetic (SFM) through tunneling superexchange, so that, these SFM spins could antiferromagnetically couple with the SG -like "bridges" to yield pronounced exchange bias (EB) effect. (C) 2015 Elsevier B.V. All rights reserved.

Volume:406

Translation or Not:no