Search

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]

We report the structure, magnetic and dielectric properties of CuO nanoparticles synthesized by co-precipitation method. The magnetic measurements reveal the presence of a ferromagnetic (FM) component at room temperature with coercivity of 200 Oe and saturation magnetization of 0.004 emu/g. The observed FM may originate from different valence states of the copper ions due to the oxygen vacancies at the surface/or interface of the particles. In addition, these nanoparticles also exhibit a high dielectric permittivity (\varepsilon^\prime\sim 10^4) with weak temperature dependence in a wide range of temperature. Such a room temperature FM and giant dielectric permittivity without the presence of any transition metal could be a very good option for a class of spintronics. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of CuO nanoparticles prepared by the sol-gel method. M (T) curves show a blocking temperature at TB = 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 Cu2+ ions at the surface of the particles. [ABSTRACT FROM AUTHOR]

The polycrystalline NdCr 1-x Fe x O 3 (x = 0, 0.3, 0.5, 0.7, 1) perovskite ceramic compounds were made by sol-gel auto-combustion technique and characterized by using XRD and SEM spectroscopic techniques. X-ray studies of all samples noticed no trace of impurity and are single phase orthorhombic structure with Pbnm space group. Average crystallite size is in the order of 30–50 nm. Temperature and field dependent magnetic data were performed in the temperature range up to 300 K at 0.01T, 0.5T applied field, field range ±5T at 5 K, 300 K temperature respectively. M-T curve of x = 0, 0.3 samples at 0.01T field exhibited novel magnetic (diamagnetic like) behavior, with further increase in Fe content reversal magnetism disappeared. M-H hysteresis of all samples under ±5T (except x = 1 at 300 K) at 5 K and 300 K showed weak ferromagnetic behavior, and x = 1 sample at 300 K exhibited ferromagnetic nature. The antiferromagnetic ordering is observed at T N1 = 223 K, 190 K, 232 K, 192 K and 157 K for x = 0, 0.3, 0.5, 0.7 and 1 respectively. All samples (except x = 0.5, 0.7 at 0.01T and x = 0.7 at 0.5T) have shown negative paramagnetic Curie temperature (θ P) nature, due to antiferromagnetic exchange interactions. Figure Temperature dependent magnetization of x = 0 sample of NdCr 1-x Fe x O 3 at 0.01T field. Image 1 • Crystalline size found to be in the order of 30–50 nm. • x = 0 to x = 0.3 at 0.01T showed magnetic reversal behavior for T ≤ TN1. • All samples except x = 1 at 300 K showed weak ferromagnetic behavior. • Magnetization increased with rise in Fe content at 0.01T, 0.5T fields. • Frustration for x = 1 is more 2.8, 2.4 at 0.01T, 0.5T fields respectively. [ABSTRACT FROM AUTHOR]

Cupric oxide (CuO) nanoparticles with different crystallite sizes were synthesized by thermal annealing of the copper hydroxide at various temperatures. The monoclinic crystal structure and average crystallite size was determined by using X-ray diffraction (XRD). The average crystallite sizes were varies between 15 nm and 66 nm. The dielectric studies including electrical permittivity, modulus, AC and DC conductivity were measured in ranges of frequency 20 Hz - 1 MHz and temperature 80 K–300 K. These CuO nanoparticles exhibits high dielectric permittivity value is about ≈104 at room temperature as well as intrinsic dielectric constant also increases with particle size. The relaxation process related to the temperature-independent activation energy was deduced from the electric loss scaling. AC conduction obeys universal power law, and its conduction mechanism was explained by hooping model. Image 1 • Different size CuO nanoparticles are synthesized by thermal annealing. • The grain size has great influence on the dielectric behavior of these particles. • The M″ curves show strong grain peaks in all CuO nanoparticles. • σ ac follows Jonscher's power law for all CuO nanoparticles. [ABSTRACT FROM AUTHOR]