On the magnetic susceptibility of CuOx
TL;DR: The magnetic susceptibility measurements were performed on CuO before and after quenching from high temperature as discussed by the authors, and it was argued that the large rise in the magnetization at temperatures much below the Neel temperature observed in certain samples may not be of impurity origin.
Abstract: The magnetic susceptibility measurements were performed on CuO before and after quenching from high temperature A large increase in the magnetic susceptibility is observed by quenching or consequent decrease in the oxygen content It is argued that the large rise in the magnetization at temperatures much below the Neel temperature observed in certain samples may not be of impurity origin but results from the random freezing of isolated Cu 2+ ions near the oxygen defects
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TL;DR: In this paper, the formation of these morphologies is explained in terms of the variation in the interplanar H-bonds breaking rate with different temperatures, and magnetic measurements reveal the presence of weak ferromagnetic interaction and the blocking behavior in these nanoparticles.
Abstract: Cupric oxide (CuO) nanoparticles with different morphologies were synthesized by thermal annealing of the copper hydroxide at various temperatures. Significant changes in both the particle size and the morphology with the annealing temperature (TA) were observed. The average particle size (d) increases from 13 to 33 nm and the morphology varies from ellipsoidal to rodlike as TA increases from 150 to 550 °C. The formation of these morphologies is explained in terms of the variation in the interplanar H-bonds breaking rate with different temperatures. The magnetic measurements reveal the presence of weak ferromagnetic interaction and the blocking behavior in these nanoparticles. The magnetic field dependence of the superparamagnetic blocking temperature (TB) follows the Brown equation. In addition, the linear variation in zero field cooled susceptibility with particle size is consistent with the predictions of Neel model for the uncompensated spins. These surface spins are responsible for the observed anoma...
78 citations
TL;DR: In this paper, the magnetic properties of CuO nanoparticles prepared by the sol-gel method were reported. And the presence of superparamagnetism and net magnetic moments of the nanoparticles were attributed to uncompensated Cu/sup 2+/ions at the surface of the particles.
Abstract: We report on the magnetic properties of CuO nanoparticles prepared by the sol-gel method. M (T) curves show a blocking temperature at T/sub B/=135 K and 160 K for 13 nm and 17 nm size particles, respectively, in measuring field H=100 Oe. The M-H data for both the samples show a reversal magnetization at 300 K, whereas below T/sub B/ it exhibit symmetrical hysteresis loops with a coercive field of 200 Oe (155 Oe) and a remanence 0.306 emu/mole (0.171 emu/mole) for 13 nm (17 nm) at 5 K. Presence of superparamagnetism and net magnetic moments of CuO nanoparticles are attributed to the uncompensated Cu/sup 2+/ions at the surface of the particles.
66 citations
TL;DR: In this article, the grain size is highly dependent on the nature of non-polar solvent, 25-30 and 80-90 nm sized nanoparticles with isooctane and n-octane, respectively.
Abstract: Copper oxide nanoparticles were synthesized by water-in-oil microemulsions with two different apolar solvents (isooctane and n -octane). Our studies on the samples show that the grain size is highly dependent on the nature of non-polar solvent, 25–30 and 80–90 nm sized nanoparticles with isooctane and n -octane, respectively. The Neel temperature of CuO nanoparticles obtained from isooctane is about 80 K. For the larger particles obtained from n -octane, the transition temperature shifts to higher temperature ( ∼ 220 K ) near that of the bulk.
58 citations
TL;DR: The effect of the particle size and ball-mill induced defects on the magnetic properties of cupric oxide has been assessed by magnetic measurements as discussed by the authors, showing that up to room temperature, instead of the increasing susceptibility found in bulk samples, a Curie-Weiss-like behavior is observed above the ordering temperature of ca. 230 K.
Abstract: The effect of the particle size and ball-mill-induced defects on the magnetic properties of cupric oxide has been assessed by magnetic measurements. Nanoparticles with an average strain e =0.035 and average crystallite size D =9 nm show a susceptibility one order of magnitude higher than the starting material. Up to room temperature, instead of the increasing susceptibility found in bulk samples, a Curie–Weiss-like behavior is observed above the ordering temperature of ca. 230 K.
49 citations
TL;DR: In this article, 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.
Abstract: 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+.
45 citations
References
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TL;DR: In this article, a structure consisting of ferromagnetic sheets of Cu spins alternating along the [100] orthorhombic axis was deduced from the magnetic peak intensities.
Abstract: Powder neutron diffraction studies of undoped ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$ have revealed new superlattice peaks below \ensuremath{\sim}220 K. The absence of corresponding x-ray superlattice lines and an observed susceptibility anomaly near 220 K suggest the occurrence of antiferromagnetism. From the magnetic peak intensities we deduce a structure consisting of ferromagnetic sheets of Cu spins alternating along the [100] orthorhombic axis, with the spins aligned along the [001] orthorhombic axis, The low-temperature magnetic moment is approximately 0.5${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$/(Cu atom). The tetragonal-orthorhombic transition at 505 K has also been studied.
729 citations
TL;DR: In this paper, the spin precession of positive muons has been observed in the antiferromagnetic state of La2CuO(4y), and the long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Neel temperature.
Abstract: Zero-field spin precession of positive muons has been observed in the antiferromagnetic state of La2CuO(4-y). Sharp onsets of the sublattice magnetization are found at temperatures close to those of the susceptibility maxima of different specimens. The long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Neel temperature. A combination of the present results and neutron-scattering studies indicates the ordered moment per Cu atom to be significantly less than 1 mu(B).
161 citations
TL;DR: In this paper, the magnetic susceptibility of high purity cupric oxide has been measured from 14°K to 1100°K, and the results were interpreted in terms of antiferromagnetic super-exchange, characterized by a Neel temperature of 230°K and a direct spin coupling with an energy of 730 cm −1.
Abstract: The magnetic susceptibility of high purity cupric oxide has been measured from 14°K to 1100°K. The gramme susceptibility is constant within 1 per cent at 2.00 × 10 −6 c.g.s. units below 130°K, and rises to a broad maximum of 3.38 × 10 −6 at 540°K. The results are interpreted in terms of antiferromagnetic super-exchange, characterized by a Neel temperature of 230°K, and a direct spin coupling with an energy of 730 cm −1 .
144 citations
TL;DR: In this paper, the symmetry requirements of the monoclinic system were shown to be satisfied by Story-Iaskelyne's drawings of melaconite with cuprite and chrysocolla.
Abstract: The goniometrical measurements of N. Story-l\\laskelyne ) on crystals of tenorite (also called melaconite) found with cuprite and chrysocolla in a chloritic veinstone from Lostwithiel, Cornwall, satisfy the symmetry requirements of the monoclinic system, and the crystal habit illustrated in the drawing of Story-l\\1askelyne is clearly that of the holohedral class of the monoclinic system. ~Ioreover, as A. Scacchi) has pointed out, the goniometrical measurements of J. J enzsch ) on artificial crystals of cupric oxide formed near a flue in a smelterhearth during roasting of copper matte with sodium chloride at Freiberg, yield calculated elements agreeing with those of Story-1\\Iaskelyne, and the crystals drawn by J enzsch exhibited the same habit and twinlaw as those of Story-·Maskelyne. J enzsch interpretE
72 citations