Magnetic properties of mechanically milled nanosized cupric oxide

Magnetic hardness features and loop shift in nanostructured CuO

“…5,6 EB has been explained in terms of interaction between an AFM core and a spin glass-like or FM shell of uncompensated surface spins. 7,9,11 EB has also been observed in CuO nanowires 13 and nanostructures. 14 Differences might appear when determining the ordering temperature in nanostructured CuO based only on magnetic measurements.…”

“…Previous results on milled CuO showed magnetic hysteresis at RT 10,11,20,21 and loop shifts that have been interpreted as EB effects. 10,11,14 In this work, we examine and compare the structural, microstructural, and magnetic properties of CuO nanostructures produced by controlled HEBM. The results show hysteresis at RT, splitting between zero-field-cooled (ZFC) and fieldcooled (FC) curves above RT, T N reduction as well as shifted hysteresis loops along both vertical and horizontal axes.…”

“…Indeed, it shows a change of slope at T N and a broad maximum near 550 K 2 which has been explained in terms of a strong linear chain antiferromagnetism, along [1 0 1] direction. 3,4 CuO nanoparticles exhibit atypical properties, such as ferromagnetic (FM) response at room temperature (RT), [5][6][7][8] exchange bias (EB) phenomenon, [9][10][11][12] and variation of AFM order temperature. 9, 10 Several models have been designed to explain those findings.…”

“…It has been proposed that in CuO nanoparticles, the accumulation of oxygen vacancies weakens the super-exchange Cu-O-Cu paths inducing a T N reduction. 7,8 Ferromagnetic behavior has been attributed to uncompensated surface spins 7,9,11 and to oxygen vacancies causing mixed valence systems. 5,6 EB has been explained in terms of interaction between an AFM core and a spin glass-like or FM shell of uncompensated surface spins.…”

“…In spite of this, a reduction of T N has been commonly reported to occur in nanostructured CuO. [9][10][11][12][13][14][15][16] For instance, based on muon spin relaxation and susceptibility measurements, Zheng et al 14 reported a T N % 30 K for 5 nm CuO obtained by ball milling a single crystal and a T N % 13 K for 2-3 nm nanorods. Punoose et al 9 found a T N ¼ 40 K for 6.6 nm CuO synthesized by sol-gel, which would account for the ordering of Cu 2þ ions in the core.…”