Curiale, J., R. D. Sánchez, H. E. Troiani, H. Pastoriza, P. Levy, and A. G. Leyva. "Morphological and magnetic characterization of manganites oxide based nanowires and nanotubes." Physica B 354, no. 1-4 (2004): 98–103.
Abstract: A morphological and magnetic study of sub-micrometric nanostructures of a manganese oxide-based compound La0.325Pr0.300Ca0.375MnO3 is presented. Nanowires of 50 and 100 nm and tubes with external diameters of 200 and 800 nm were synthesized. Scanning electron microscopy with EDS microanalysis (SEM) and transmission electron microscopy (TEM) allowed to characterize the morphology and microstructure of these nanostructures. The walls of the nanotubes are composed of on average 40 nm grain size particles, while in nanowires the grains are much smaller, in the range between 4 and 20 nm. In both situations, the small grains present a random crystalline orientation, as it is confirmed by TEM diffraction experiments. Magnetization measurements and hysteresis loops are presented and discussed based on magnetic interaction between the grains, anisotropy considerations and reversal magnetization mechanisms.
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Curiale, J., R. D. Sánchez, H. E. Troiani, C. A. Ramos, H. Pastoriza, A. G. Leyva, and P. Levy. "Magnetism of manganite nanotubes constituted by assembled nanoparticles." Phys. Rev. B 75 (2007): 224410.
Abstract: We present the study of the magnetic properties of manganite nanotubes with 800 nm of external diameter and 3-5 μm length. The study includes two ferromagnetic compounds, La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3, and one with ferromagnetic and charge ordered phase coexistence, La0.325Pr0.300Ca0.375MnO3. In this case, the walls are formed by grains and have approximately thickness of 150 nm and the most probable grain size is 70 nm. For the ferromagnetic nanotubes smaller values are observed, between 45 and 60 nm for the thickness and 25 nm for the grain size, respectively. In La0.325Pr0.300Ca0.375MnO3 we observe distinctive features comparing with the ferromagnetic nanotubes. After cooling below T$_C$ the samples at $H=0$, the first magnetization curve shows a gradual growth of the magnetization until reach a maximum value, which depends of H. After this, the material presents expected ferromagnetic hysteresis loops. Also, significant differences between the cooling and warming magnetization processes and large linewidth in the ferromagnetic resonances are observed. These experimental facts are explained in terms of the competition between the charge ordered and the ferromagnetic phases, including strong interaction among these last regions. Observations of dipolar interactions between the magnetic grains are evidenced by isothermal remanent magnetization and direct current demagnetization experiments.
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Franco, D. G., V. C. Fuertes, M. C. Blanco, M. T. Fernández-Díaz, R. D. Sánchez, and R. E. Carbonio. "Synthesis, structure and magnetic properties of La3Co2SbO9: A double perovskite with competing antiferromagnetic and ferromagnetic interactions." Journal of Solid State Chemistry 194 (2012): 385–391.
Abstract: The synthesis, structural characterization, and magnetic properties of La3Co2SbO9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P21/n. Co2+ and Sb5+ have the maximum order allowed for the La3Co2SbO9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) Å, b=5.6842(2) Å, c=7.9748(2) Å and β=89.999(3)°. Magnetization measurements indicate the presence of ferromagnetic correlations with TC=55 K attributed to the exchange interactions for non-linear Co2+–O–Sb5+–O–Co2+ paths. The effective magnetic moment obtained experimentally is μexp=4.38 μB (per mol Co2+), between the theoretical one for spin only (3.87 μB) and spin-orbit value (6.63 μB), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 μB/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration.
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Pomiro, F., D. M. Gil, V. Nassif, A. Paesano, M. I. Gómez, J. Guimpel, R. D. Sánchez, and R. E. Carbonio. "Weak ferromagnetism and superparamagnetic clusters coexistence in YFe1−xCoxO_3 (0 ≤ x ≤ 1) perovskites." Materials Letters 94 (2017): 472–482.
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