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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 TB 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. Index Terms--Antiferromagnetism, blocking temperature, CuO nanoparticles, superparamagnetism.

Cupric oxide (CuO) nanoparticles with different morphologies are prepared by thermal annealing of the copper hydroxide at various temperatures. The magnetic measurements have shown the presence of weak ferromagnetic interaction and the blocking behavior in the nanoparticles and the surface spins are responsible for the anomalous magnetic properties of CuO.

Mn-doped CuO nanoparticles are synthesized by using a coprecipitation method and the magnetic behavior of [Cu.sub.0.9][Mn.sub.0.1]O nanoparticles is examined. It is shown that the spin-glass behavior is because of the enhanced surface effects of the CuO shell, while the ferromagnetic (FM) behavior is attributed to the coexistence of [Mn.sup.2+] and [Mn.sup.3+] ions.

Mn-doped CuO nanoparticles were synthesized using a coprecipitation method. Powder x-ray analysis reveals that all the samples crystallize into a monoclinic-type structure. Significant changes occur in both the microstructure and particle size with calcination temperature TA. The average particle size d increases from 11 to 85 nm as the TA increases from 250 to 850 °C. For particles of size d≤22 nm, energy dispersive spectroscopy indicates the existence of a crystalline Cu1-xMnxO core surrounded by an amorphous CuO shell. M(T) curves reveal a spin-glass behavior for the 11 and 22 nm particles and a ferromagnetic behavior for particles of size d>=35 nm. The observed ferromagnetic behavior is attributed to the coexistence of Mn2+ and Mn3+ ions. [ABSTRACT FROM AUTHOR]

Large size (~2 cm) single crystals of layered MoTe2 in both 2 H- and 1 T ′-types were synthsized using TeBr4 as the source of Br2 transport agent in chemical vapor transport growth. The crystal structures of the as-grown single crystals were fully characterized by X-ray diffraction, Raman spectroscopy, scanning transmission electron microscopy, scanning tunneling microscopy (STM), and electrical resistivity (ρ) measurements. The resistivity ρ( T ), magnetic susceptibility χ( T ), and heat capacity C p( T ) measurement results reveal a first order structural phase transition near ~240 K for 1 T ′-MoTe2, which has been identified to be the orthorhombic T d-phase of MoTe2 as a candidate of Weyl semimetal. The STM study revealed different local defect geometries found on the surface of 2H - and T d-types of MoTe6 units in trigonal prismatic and distorted octahedral coordination, respectively. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic ordering of the RCrTeO6 (R=Y, La, Tb and Er) samples comprising Cr3+ (S=3/2). The X-ray diffraction structure analysis revealed that all samples are a hexagonal structure with the space group P 3-. The magnetic susceptibility χ(T) and heat capacity CP(T) measurement results reveal that both short range and long range antiferromagnetic (AFM) orderings exist in non-magnetic rare earth R=Y and La compounds. For isostructural compounds of R=Tb and Er, CP(T) curves show long range ordering at the same temperature as non-magnetic R=Y, which indicates that the super-super exchange of Cr spins dominates. For R elements of Tb and Er with large spins sitting between honeycomb sublattices composed of CrO6-TeO6 octahedra, the two sublattices of R and Cr appear to be independently magnetic. [ABSTRACT FROM AUTHOR]

EPR investigations on La[sub 0.7]Ca[sub 0.3]MnO[sub 3] were carried out in the temperature range from 14 K to 300 K. The important observations are: (i) a coincidence of resistivity maxima with the disappearance of paramagnetic EPR line I, which suggests that there exists a strong electron-phonon interaction, (ii) the appearance of an "out of phase" line near the Curie temperature T[sub c] due to the formation of spin clusters consisting of Mn[sup 3+] and Mn[sup 4+] ions, and (iii) the appearance of an intense EPR line III and the splitting of FC and ZFC magnetization curves below 160 K, ascribed to local magnetic frustrations. The above EPR observations provide experimental evidence for the co-existence of spin fluctuations and magnetic disorders in this sample, which leads to the formation of spin-glass features below T[sub c]. [ABSTRACT FROM AUTHOR]

The effects of partial substitution of La by a smaller Lanthanide element (R) in La[sub 0.7-x]R[sub x]Ca[sub 0.3]MnO[sub 3] (R = Ce, Pr, Nd Sm, Gd, Dy with x = 0 and 0.1) ceramic pellets on the electron paramagnetic resonance has been investigated. The line width increased with decrease in ionic radius of the A site 〈r[sub A]〉 in paramagnetic phase, which is explained on the basis of tolerance factor. The observed increase in g-value and line width with increase in 〈r[sub A]〉 in ferromagnetic phase explained qualitatively by Mn-O-Mn bond angle distortion and Mn-O orbital overlap which in turn is governed by the size of the substitution ion. [ABSTRACT FROM AUTHOR]