Study of magnetic and specific heat measurements at low temperatures in Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3

The magnetization at low temperatures for Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3 samples showed a rapid increase with decreasing temperatures, contrary to a La0.5Ca0.5MnO3 sample. Specific heat measurement at low temperatures showed a Schottky-like anomaly for the first two samples. However, there is not a straight forward correlation between the intrinsic magnetic moment of the Nd3+ ions and the Schottky-like anomaly.Comment: To be presented in the 1 Joint European Magnetic Symposia, Grenoble,France (2001). Also submitted to Journal of Magnetism and Magnetic Material

Magnetic relaxation and magnetization field dependence measurements in La0.5Ca0.5MnO3

We reported a systematic change in the average magnetic relaxation rate, after the application and removal of a 5 T magnetic field, in a polycrystalline sample of La0.5Ca0.5MnO3. Magnetic relaxation measurements and magnetization versus field curves were taken from 10 K to 160 K. The long time behavior of the relaxation curves was approximately logarithmic in all cases. Keywords: Charge Ordering, Relaxation, Magnetic measurementsComment: 2 figures, accepted to be presented in the International Conference on Magnetism 2000 in Recife, also submitted to Journal of Magnetism and Magnetic Material

Vortices in superconductors with a columnar defect: finite size effects

In the present work we investigate the behavior of a vortex in a long superconducting cylinder near to a columnar defect at the center. The derivations of the local magnetic field distribution and the Gibbs free energy will be carried out for a cylinder and a cavity of arbitrary sizes. From the general expressions, it considered two particular limits: one in which the radius of the cavity is very small but the radius of the superconducting cylinder is kept finite; and one in which the radius of the superconducting cylinder is taken very large (infinite) but the radius of the cavity is kept finite. In both cases the maximum number of vortices which are allowed in the cavity is determined. In addition, the surface barrier field for flux entrance into the cavity is calculated.Comment: 13 pages, 1 figur

Specific heat and magnetic measurements in Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 samples

We studied the magnetization as a function of temperature and magnetic field in the compounds Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3. It allowed us to identify the ferromagnetic, antiferromagnetic and charge ordering phases in each case. The intrinsic magnetic moments of Nd3+ and Ho3+ ions experienced a short range order at low temperatures. We also did specific heat measurements with applied magnetic fields between 0 and 9 T and temperatures between 2 and 300 K in all three samples. Close to the charge ordering and ferromagnetic transition temperatures the specific heat curves showed peaks superposed to the characteristic response of the lattice oscillations. Below 10 K the specific heat measurements evidenced a Schottky-like anomaly for all samples. However, we could not successfully fit the curves to either a two level nor a distribution of two-level Schottky anomaly. Our results indicated that the peak temperature of the Schottky anomaly was higher in the compounds with narrower conduction band.Comment: submitted to PR

Intrinsic magnetic properties of BixCo2−xMnO4 spinels obtained by short-time etching

International audienceThe structural and magnetic properties of the cubic spinel oxide Co2MnO4 (Fd3m space group) doped with different concentrations of bismuth, were investigated by X-ray diffraction and SQUID magnetometry. The Bi3+ ions entering into the CoIII octahedral sites do not alter the effective moment, μeff ∼8.2 μB, whereas both the magnetization M50 kOe at the highest field (50 kOe) and the field-cooled MFC magnetizations increased when increasing the Bi content. The ferrimagnetic character of the parent compound, Co2MnO4, is maintained for all materials although the antiferromagnetic interactions Co2+–Co2+ are affected, resulting in higher values of the Curie–Weiss temperature. Due to the large ionic radius of Bi, octahedra distortions occur as well as valence fluctuations of the Mn ions, giving rise to Jahn-Teller effects and enhancing the exchange interactions. The off-center Bi3+ ion is responsible of non-centrosymmetric charge ordering and should lead to multiferroïsme conditions for the BixCo2−xMnO4 material

TiO2 thin film growth using the MOCVD method

Titanium oxide (TiO2) thin films were obtained using the MOCVD method. In this report we discuss the properties of a film, produced using a ordinary deposition apparatus, as a function of the deposition time, with constant deposition temperature (90 °C), oxygen flow (7,0 L/min) and substrate temperature (400 °C). The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and visible and ultra-violet region spectroscopy (UV-Vis). The films deposited on Si (100) substrates showed the anatase polycrystalline phase, while the films grown on glass substrates showed no crystallinity. Film thickness increased with deposition time as expected, while the transmittance varied from 72 to 91% and the refractive index remained close to 2.6

Spin reversal and magnetization jumps in ErMexMn1-xO3 perovskites (Me = Ni, Co)

J. Magn. Magn. Mat., 2007, 312, 78-9

Modeling the crystallographic structure of Ho(Ni,Co,Mn)O3±δ perovskite-type manganite

International audienceCrystallographic and microstructural properties of Ho(Ni,Co,Mn)O3±* perovskite-type multiferroic material are reported. Samples were synthesized with a modified polymeric precursor method. The synchrotron X-ray powder diffraction (SXRPD) technique associated to Rietveld refinement method was used to perform structural characterization. The crystallographic structures, as well as microstructural properties, were studied to determine unit cell parameters and volume, angles and atomic positions, crystallite size and strain. X-ray energies below the absorption edges of the transition metals helped to determine the mean preferred atomic occupancy for the substituent atoms. Furthermore, analyzing the degree of distortion of the polyhedra centered at the transitions metal atoms led to understanding the structural model of the synthesized phase. X-ray photoelectron spectroscopy (XPS) was performed to evaluate the valence states of the elements, and the tolerance factor and oxygen content. The obtained results indicated a small decrease distortion in structure, close to the HoMnO3 basis compound. In addition, the substituent atoms showed the same distribution and, on average, preferentially occupied the center of the unit cell

A Possible Correlation Between Suppression Of Superconductivity, Magnetic Ordering And Normal State Resistivity Parameters In The Yb1-χprχba2cu3 O7-δ System

Polycrystalline samples of the Pr doped Yb1-PrχBa2Cu3 O7-δ (i.e. Yb(Pr)-123) system for 0 ≤ χ ≤ 1 have been investigated for resistivity ρ and magnetization M as a function of temperature in normal and superconducting states. The gradual decrease in superconducting critical temperature Tc(χ) is found to be correlated with the χ-dependent ratio of resistivity slope (dρ/dT)cc (corresponding to the linear ρ(T) region) and residual resistivity ρ0. In particular, the observed difference of critical Pr concentration where superconductivity is destroyed (χc) in Yb(Pr)-123 (χc ≈ 0.65) and Y(Pr)-123 (χc ≈ 0.55) matches with the difference in the value of Pr concentration where the ratio (dρ/dT)cc/ρ0 tends to go to zero in them. The M(T) data of the Yb(Pr)-123 samples show magnetic ordering for χ > χc at characteristic temperatures, Tn, that increase with χ. Interestingly, the Yb(Pr)-123 sample with Pr content (χ = 0.6) near χc reveals several anomalous features like transition from metallic to semiconducting-like ρ(T), an excessive broadening of the diamagnetic transition and weakening of the M(T) signal related to antiferromagnetic ordering of Pr ions. These observations can be consistently interpreted by assuming the presence of dynamically fluctuating striped phase in these systems.168261273Soderholm, L., Zhang, K., Hinks, D.G., Beno, M.A., Jorgensen, J.D., Segree, C.V., Schuller, I.K., (1987) Nature, 328, p. 604Felner, I., Yaron, U., Nowik, I., Bauminger, E.R., Wolfus, Y., Yacoby, E.R., Hilscher, G., Pillmayer, N., (1989) Phys. Rev., B40, p. 6739Cooke, D.W., Kwok, R.S., Lichti, R.L., Adams, T.R., Bockema, C., Dawson, W.K., Kebede, A., Mihalisin, T., (1990) Phys. Rev., B41, p. 4801Xu, Y., Guan, W., (1991) Solid State Commun., 80, p. 105Malik, S.K., Tomy, C.V., Bhargava, P., (1991) Phys. Rev., B44, p. 7042Radousky, H.B., (1992) J. Mat. Res., 7, p. 1917Jhans, H., Malik, S.K., Dhar, S.K., Vijayaraghavan, R., (1993) Physica, C207, p. 247Guan, W., Xu, Y., Sheen, S.R., Chen, Y.C., Wei, J.Y.T., Lai, H.F., Wu, M.K., Ho, J.C., (1993) Phys. Rev., B49, p. 15993Fehrenbacher, Rice, T.M., (1993) Phys. Rev. Lett., 70, p. 3471Liechtenstein, A.I., Mazin, I.I., (1995) Phys. Rev. Lett., 74, p. 1000Mazin, I.I., (1999) Phys. Rev., B60, p. 92Zou, Z., Ye, J., Oka, K., Nishihara, Y., (1998) Phys. Rev. Lett., 80, pp. L074Liu, G.D., Zhao, Z.X., Che, G.C., (1999) Solid State Commun., 109, p. 495Zhou, J.S., Goodenough, J.B., Sato, H., Naito, M., (1999) Phys. Rev., B59, p. 3827Service, R.F., (1999) Science, 283, p. 1106Hasselmann, N., Castro Neto, A.H., Morair Smith, C., Dimashko, Y., (1999) Phys. Rev. Lett., 82, p. 2135Emery, V.J., Kivelson, S.A., (1999) J. Low Temp. Phys., 117, p. 189Gupta, A., Lal, R., Sedky, A., Narlikar, A.V., Awana, V.P.S., (2000) Phys. Rev., B61, p. 11752Gupta, A., Sedky, A., Narlikar, A.V., to be publishedJia, Y.X., Liu, J.Z., Matsushita, A., Lan, M.D., Klavins, P., Shelton, R.N., (1992) Phys. Rev., B46, p. 11745Cava, R.J., Batlogg, B., Rabe, K.M., Rietman, E.A., Gallagher, P.K., Rupp L.W., Jr., (1988) Physica, C156, p. 523Bottger, G., Magetschots, I., Kaldis, E., Fischer, P., Kruger, Ch., Fauth, F., (1996) J. Phys. Condens. Matter, 8, p. 8896Phillips, J.C., (1997) Proc. Natl. Acad. Sci. (USA), 94, p. 12774Takenaka, K., Mizuhashi, K., Takagi, H., Uchida, S., (1994) Phys. Rev., B50, p. 6534Chien, T.R., Datars, W.R., Liu, J.Z., Lan, M.D., Shelton, R.N., (1994) Physica, C221, p. 428Blackstead, H.A., Dow, J.D., Chrisey, D.B., Horwitz, J.S., Black, M.A., McGinn, P.J., Klunzinger, A.E., Pulling, D.B., (1996) Phys. Rev., B54, p. 6122Narlikar, A.V., Gupta, A., Samanta, S.B., Chen, C., Hu, Y., Wandre, F., Wanklyn, B.M., Hodby, J.W., (1999) Phil. Mag., B79, p. 71