Investigation of the Quenching Rate Effect on the Ferromagnetic Properties of CuO Nanoparticles
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https://doi.org/10.1007/s11837-020-04221-5 2020 The Minerals, Metals & Materials Society
NANOMECHANICS OF LOW-DIMENSIONAL MATERIALS
Investigation of the Quenching Rate Effect on the Ferromagnetic Properties of CuO Nanoparticles I.V. KARPOV,2 A.V. USHAKOV and A.A. SHAIHADINOV2
,1,2,3 V.G. DEMIN,2 E.A. GONCHAROVA,2
1.—Federal Research Center Krasnoyarsk Scientific Center, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia 660036. 2.—Siberian Federal University, Krasnoyarsk, Russia 660041. 3.—e-mail: [email protected]
We studied the effect of pressure in a plasma-chemical reactor on the magnetic properties of copper oxide nanoparticles. Plasma-chemical synthesis of copper oxide nanopowders was carried out using an oxygen plasma of an arc discharge at pressures of 40 Pa and 200 Pa. Transmission electron microscopy showed that the obtained samples were made up of highly agglomerated particles with average particle sizes of 31 nm and 27 nm, respectively. X-ray diffraction showed the presence of a single crystalline phase of CuO. Despite the insignificant difference in the average sizes, the nanoparticles exhibited radically different magnetic behavior. Using a vibrating superconducting quantum interference device magnetometer, it was shown that the magnetic properties of nanoparticles obtained at 40 Pa were close to the bulk material and exhibited weak ferromagnetism. The nanoparticles obtained at 200 Pa demonstrated a significant deviation from the properties of the bulk material, showed magnetic hardness, and shifts in the hysteresis loops.
INTRODUCTION Copper oxide nanoparticles have attracted the attention of researchers due to their unusual magnetic properties,1,2 which can be widely used in copper-based superconductors,3 highly sensitive sensors,4 as solid electrolytes,5 etc.6 CuO is a semiconductor with antiferromagnetic (AFM) ordering. The transition to the paramagnetic state occurs at a Ne´el temperature TN = 230 K. A detailed study of CuO nanoparticles obtained by various methods showed that, with a decrease in size, properties such as ferromagnetism (FM) at room temperature (RT),7 and the effect of exchange bias (EB),8 and temperature, change AFM ordering.8 Several models have been proposed to explain these effects. The FM has been explained by uncompensated spins on the surfaces of nanoparticles,9 or oxygen vacancies causing variable valency. EB has been explained by the interaction between the AFM core and the FM shell of uncompensated surface spins. Moreover, the FM shell exhibits spin-glass behavior. A similar effect is also present in CuO films and nanowires. Initially, the EB effect was studied
exclusively as an interesting phenomenon, but in the last decade, the AFM-FM binary system has found its applications in the spin valve and tunnel devices.10 For a detailed study of this phenomenon, it is necessary to solve one of the most difficult problems—the correct determination of the Ne´el temperature for CuO nanoparticles, determined by the behavior of the thermal dependence of
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