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Influence of Cu-Zn substitution on magnetic behaviour of multiferroic CuO

Magnetic behaviour of Cu(1-x)ZnxO, x=0, 0.0125, 0.025, was investigated in order to study the influence of substitution of Cu with Zn on magnetic properties. Copper(II) oxide attracted attention of the scientific community because it exhibits ferroelectricity driven by magnetic order at temperature as high as 230 K [1]. It was shown that disorder in the form of impurities can stabilize the ferroelectric phase [2]. In pure CuO the multiferroic phase is present above the first order phase transition at TN1 = 213 K and exists up to the subsequent first order phase transition TN2 = 230 K[1, 2]. Pyroelectric measurements showed that the multiferroic temperature window widen with doping [2]. Motivated with this, we performed syntheses of undoped and Zn-doped CuO powders by pyrolytical method. Precursors Cu(CH3COO)2·H2O, NaHCO3 and Zn(CH3COO)2·2H2O were homogenized in agate mortar and the mixtures were subjected to thermal treatment on 180 °C during 2 h and 200 °C during 16 h. XRD analysis showed that the rinsed and dried powders were single-phase CuO. Obtained powders consisted of very small sized nanocrystalline particles in the range of 10–15 nm, that was confirmed by TEM analysis. Measurements of magnetization of the pelleted samples were performed using the MPMS SQUID magnetometer in the sweep temperature mode in order to collect the changes of magnetization very densely. With careful analysis we observed the two phase transition temperatures in accordance with previous results, even though the samples are not the monocrystals, but are in the ceramic polycrystalline form. From the magnetic measurements, we confirmed that the Cu-Zn substitution successfully influences the temperatures of the phase transitions and enlarges the temperature window between those transitions. Therefore, doping can enhance multiferroic properties of CuO what makes it very interesting for future investigations [3]. [1] T. Kimura, Y. Sekio, H. Nakamura, T. Siegrist, A.P. Ramires, Nature Mater., 7 (2008) 291. [2] J. Hellsvik, M. Balestieri, T. Usui, A. Stroppa, A. Bergman, L. Berqvist, D. Pabhakaran, O. Eriksson, S. Picozzi, T. Kimura, J. Lorenzana, Phys. Rev. B, 90 (2014) 014437. [3] Project FerMaEl (UIP- 2014-09-8276) financed by the Croatian Science Foundation

CuO, doped with ZnO, magnetism

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