Search for high temperature memory effects in magnetic nanoparticles M. Perovic a, * , M. Boskovic a , V. Kusigerski a , Z. Jaglicic b , J. Blanusa a , V. Spasojevic a , N. Pizurova c , O. Schneeweiss c a Institute of Nuclear Sciences Vinca, University of Belgrade, P.O.Box 522,11001, Belgrade, Serbia b Institute of Mathematics, Physics and Mechanics & Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia c Institute of Physics of Materials, Czech Academy of Science, Zizkova 22, 616 62, Brno, Czech Republic article info Article history: Received 13 August 2020 Received in revised form 24 September 2020 Accepted 8 October 2020 Keywords: Super spin glass nanoparticles Magnetite. Magnetic properties Magnetic memory effect Thermal memory cell abstract Nanoparticle materials have become a promising candidate for a new kind of storage media based on thermally induced memory effects due to the possibility to tailor their magnetic properties and behaviour. In this study, we have investigated whether the magnetic memory effects could appear at high, industry accessible temperatures including the possibility of thermal data inscription. Investigated iron oxide nanoparticles were synthesized by poliol method, which has been modified in order to allow control of particle agglomeration and consequently magnetic properties. Structure, morphology and the degree of nanoparticle agglomeration were studied by X-Ray diffraction, Transmission Electron Micro- scopy and Dynamic Light Scattering techniques, while magnetic properties as well as memory effects were measured on a commercial SQUID-based magnetometer. Results of the study confirmed that in super spin glass magnetite nanoparticles, magnetic memory effects can be observed up to 200 K which represents much higher temperatures in comparison to those achieved in spin glasses and other glassy materials. Procedures of writing and reading (inscribing and retrieving) of digital information in such a material were demonstrated and discussed in details. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Thermally induced memory effect represents one of the most fascinating magnetic phenomena that appear in the systems with nonequilibrium spin dynamics. The most challenging aspect of the related research studies is the possibility of digital information inscription into memorizing medium, as it can be done by pure thermal manipulation in contrast to the current magneto-storage devices where writing and erasing processes are controlled by application of magnetic or electric field [1]. Thermal memory effect was firstly observed by Nordblad and coworkers in cannonical Cu:Mn and CdCr 1.7 In 0.3 S 4 spin glasses [2,3] where below freezing temperature T f , randomly oriented atomic spins cooperatively freeze as a consequence of mixed and/or competing interactions or site/bond disorder. In the original experiment, the system was cooled down to T w < T f in zero field, and left to age for time t w at the waiting temperature T w . Afterwards, the cooling was continued down to the lowest temperature, and susceptibility was measured during the reheating. Measured susceptibility curve showed memory dip at T w , i.e. at the exact temperature of the previous aging. In the succeeding studies, similar experimental procedures including application of small amplitude DC or AC fields were employed in the measurements of magnetic memory effects in different glassy materials. Beside memory effects, in the low tem- perature disordered state, spin glass like systems exhibit plethora of nonequilibrium magnetic phenomena such as slow magnetic relaxation, aging or rejuvenation, each of them playing significant role in the inscription process [4,5]. Nonequilibrium magnetic phenomena also appear in materials such as polymers, gels, structural glasses, magnetic quasicrystals, complex metallic alloys or magnetic nanoparticles [6e11] which are similar to canonical spin glasses, often structurally or magnet- ically frustrated. Among the most comprehensive studies of the memory effects were those conducted on complex metallic alloys Taylor phase Al 3 (Mn, Fe), as well as on polycrystalline multiferroic * Corresponding author. E-mail address: mara.perovic@vinca.rs (M. Perovic). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2020.157523 0925-8388/© 2020 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 855 (2021) 157523