R. A. Borzi

Effect of ion doping on CuO magnetism

We have investigated the magnetism of 0.5 at. % Fe3+-doped CuO samples by Mossbauer spectroscopy and magnetization studies. The Curie–Weiss-type behavior observed for low-field-magnetization measurements at temperatures higher than 220 K is interpreted as an uncompensation of moments enhanced by the doping. The results are compared with 1.2 at. % Zn2+-doped CuO magnetization results and previous ones for samples doped with divalent ions. Trivalent ion doping produces an increase in the susceptibility with a peak at TN. The magnetic coupling of Fe2+ ions to the magnetic lattice is found to be about four times stronger than that of Fe3+.

History-dependent magnetic properties in pure and Zn-doped cupric oxide

Abstract Magnetization curves taken in zero-field-cooling and field-cooling regimes on pure CuO and Zn-doped CuO samples demonstrate thermal irreversibility. For the Zn-doped sample, this is present above the Neel temperature ( T N ) and is reinforced below T N . Hysteresis is related to inherent frustration of the magnetic structure of CuO.

Magnetic and hyperfine interactions in systems of antiferromagnetic oxide nanoparticles with industrial applications

We report characterizations of systems of antiferromagnetic iron oxide particles of importance in catalysis where Mossbauer spectroscopy has played an essential role. We show that signals contributing to the Mossbauer spectra that arise from the surface or from non-crystalline environments still find difficulty in their assignment in spite of the large amount of research already done on hematite and similar antiferromagnetic systems.

Surface Phase Transformations Induced on Fe0.86Mn0.14 by Carbon Ion-Irradiation

Conversion electron Mössbauer spectroscopy and X-ray diffraction have been used to investigate the modifications induced by room-temperature irradiation with 360 keV C− ions on a Fe0.86Mn0.14 alloy. The data show that the irradiation produces γ-FeMn along with an increase in the amount of α-FeMn at the expense of ∈-FeMn, both originally present. The initial distribution of Mn atoms in the α-FeMn martensitic phase is observed to change after irradiation.

Magnetic disorder in cupric oxide

Investigations of the abnormal magnetic properties of cupric oxide reveal discrepancies between both experimental results and theoretical explanations. Through iron-doping cupric oxide by ball-milling and thermal treatments we have been able to obtain Mössbauer results that are an experimental evidence of semi-disorder. The magnetic hyperfine field of the Cu0.995Fe0.005O solid solution displays a spin-glass-like thermal dependence that undergoes two transitions, one at about 150 K, that can be assigned to the long-range ordering of the cupric oxide spins, and the second one at some temperature between 4.2 and 15 K, that exposes either the freezing of the Fe3+ spins into a local canted state or of magnetic clusters in the CuO matrix.