34 research outputs found
Magnetic polarons in Ca_(1-x)Y_xMnO_3
Experimental evidence show that in the magnetoresistive manganite Ca_(1-x)
Y_xMnO_3, ferromagnetic (FM) polarons arises in an antiferromagnetic (AF)
background, as a result of the doping with Yttrium. This hypothesis is
supported in this work by classical Monte Carlo (MC) calculations performed on
a model where FM Double Exchange (DE) and AF Superexhange (SE) compite.Comment: 3 pages, 3 figs, submitted to LAW3M conferenc
Influence of Nd on the magnetic properties of Nd1-xCaxMnO3
The role played by the Nd ions in the magnetic properties of Nd0.5Ca0.5MnO3
and Nd0.7Ca0.3MnO3 is studied using static magnetization, neutron diffraction
and high frequency (9.4-475GHz) Electron Spin Resonance. We show that the Nd
ions are weakly coupled to the Mn ions via ferromagnetic exchange and are
responsible for the peculiar ferromagnetic resonance observed in the FM phase
of both compounds (ground state below 120K for x=0.3, high field state for
x=0.5). We then use ESR to look for magnetic phase separation in the low field,
CO phase of Nd0.5Ca0.5MnO3. We show that there is no trace of the FM phase
imbedded in the CO phase, contrary to what is observed in La0.5Ca0.5MnO3 or
Pr0.5Sr0.5MnO3.Comment: to be published in phys.Rev.B as a Rapid Com
Charge disproportionation in YNiO : ESR and susceptibility study
We present a study of the magnetic properties of YNiO in the
paramagnetic range, above and below the metal-insulator (MI) transition. The dc
susceptibility, (measured up to 1000 K) is a decreasing function of
T for 150 K (the N\'{e}el temperature) and we observe two different
Curie-Weiss regimes corresponding to the metallic and insulator phases. In the
metallic phase, this behaviour seems to be associated with the small ionic
radius of Y% . The value of the Curie constant for T T allows
us to discard the possibility of Ni localization. An electron spin
resonance (ESR) spectrum is visible in the insulator phase and only a fraction
of the Ni ions contributes to this resonance. We explain the ESR and behaviour for T T in terms of charge disproportionation of
the type 2Ni Ni+Ni that is compatible with the
previously observed structural transition across T.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
Interplay of superexchange and orbital degeneracy in Cr-doped LaMnO3
We report on structural, magnetic and Electron Spin Resonance (ESR)
investigations in the manganite system LaMn_{1-x}Cr_{x}O_{3} (x<=0.5). Upon
Cr-doping we observe a reduction of the Jahn-Teller distortion yielding less
distorted orthorhombic structures. A transition from the Jahn-Teller distorted
O' to the pseudocubic O phase occurs between 0.3<x<0.4. A clear connection
between this transition and the doping dependence of the magnetic and ESR
properties has been observed. The effective moments determined by ESR seem
reduced with respect to the spin-only value of both Mn^{3+} and Cr^{3+} ions
Spin Dynamics In Perovskites, Pyrochlores, And Layered Manganites
High temperature electron spin resonance (ESR) and magnetic susceptibility (Ï) are analyzed for manganites related with colossal magnetoresistance (CMR). The properties of compounds with different crystalline structures: three-dimensional (3D) perovskites, pyrochlore, and La1.2Sr1.8Mn2O7, a two-dimensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature dependence of the ESR linewidth presents a universal behavior dominated by the variations of Ï(T), ÎHpp(T) = [C/TÏ(T)]ÎHpp(â). The high temperature limit of the linewidth, ÎHpp(â), is related to the parameters of the Hamiltonian describing the interactions of the spin system. The role played by magnetic anisotropy, isotropic superexchange, and double exchange is revealed and discussed in the analysis of the experimental data. In CMR and non-CMR pyrochlores, ÎHpp(â)âÏ2 p/J where J is proportional to the Curie-Weiss temperature, including the hybridization mechanism producing CMR. Instead, ÎHpp(â) of CMR perovskites seems not to be affected by the double-exchange interaction. In contrast with the 3D perovskites, the ESR linewidth and resonance field of La1.2Sr1.8Mn2O7, a bilayer compound, although isotropic at high temperatures, becomes anisotropic for Tc= 125 K<T<Tpâ450 K. © 2000 American Institute of Physics.879 II58105812Causa, M.T., (1998) Phys. Rev. B, 58, p. 3233Lofland, (1997) Phys. Lett. A, 233, p. 476Causa, M.T., Alejandro, G., Tovar, M., Pagliuso, P.G., Rettori, C., Oseroff, S.B., Subramanian, M.A., (1999) J. Appl. Phys., 85, p. 5408Anderson, P.W., Weiss, P.R., (1953) Rev. Mod. Phys., 25, p. 269Zener, C., (1951) Phys. Rev., 82, p. 403Shimakawa, Y., Kubo, Y., Hamada, N., Jorgensen, J.D., Hu, Z., Short, S., Nohara, M., Takagi, H., (1999) Phys. Rev. B, 59, p. 1249. , and references thereinVentura, C., Alascio, B., (1997) Phys. Rev. B, 56, p. 14533Huber, D.L., Alejandro, G., Caneiro, A., Causa, M.T., Prado, F., Tovar, M., Oseroff, S.B., (1999) Phys. Rev. B, 60, p. 12155Chauvet, O., Goglio, G., Molinie, P., Corraze, B., Brohan, L., (1998) Phys. Rev. Lett., 81, p. 1102. , and references thereinMoreno, N.O., Pagliuso, P.G., Rettori, C., Gardner, J.S., Sarrao, J.L., Thompson, J.D., GarcĂa-Flores, A., Oseroff, S.B., unpublishe
EPR and Magnetic Properties of the CanFe2Mnn-2O3n-1 Perovskite Related Series
We present EPR and Susceptibility measurements performed on the perovskite-like family CanFe2Mnn-2O3n-1. On going from n=2 to n=3 Fe3+ is progressively replaced by Mn4+. As a consequence the ordering temperature is depressed and frustrations in the magnetic interactions were found. The measurements are compared with the previously studied system CanFe2Tin-2O3n-1, where magnetic Mn4+ were replaced by non magnetic Ti4+. We discuss the results in terms of cationic ordering and super exchange interactions
Pyrochlore Manganites Spin Dynamics In The Paramagnetic Regime
We report electron spin resonance (ESR) and dc magnetic susceptibility in polycrystalline pyrochlores A2Mn2O7 (A=Y, Tl) measured in the paramagnetic phase up to 600 K. It is shown that the ESR linewidth has a universal behavior given by ÎHpp(T) = ÎHpp(Tââ)[C/TÏdc(T)], where C is the single-ion Curie constant. The high-temperature limit for the linewidth, given by ÎHpp(Tââ)â(Ïp)2/J, is determined by the superexchange constant J for each material. A value of (Ïp/Îł) = 6300 G was found for all pyrochlores, including In2Mn2O7. Different broadening mechanisms are discussed. © 1999 American Institute of Physics.858 II B54085410Jin, S., Tiefeid, T.H., McCormack, M., Fastnach, R.A., Ramesh, R., Chen, L.H., (1994) Science, 264, p. 413Millis, A.J., Littlewood, P.B., Shraiman, B.I., (1995) Phys. Rev. Lett., 74, p. 5144Allub, R., Alascio, B., (1997) Phys. Rev. B, 55, p. 14113Rettori, C., Rao, D., Singley, J., Kidwell, D., Oseroff, S.B., Causa, M.T., Neumeier, J.J., Schultz, S., (1997) Phys. Rev. B, 55, p. 3083Granado, E., Pagliuso, P.G., Sanjurjo, J.A., Rettori, C., Oseroff, S.B., Causa, M.T., Butera, A., Rivas, J., (1998) Non-Crystalline and Nanoscale Materials, pp. 105-115. , edited by J. Rivas and M. A. LĂłpez-Quintela World Scientific, SingaporeCausa, M.T., (1998) Phys. Rev. B, 58, p. 3233Tovar, M., (1998) J. Appl. Phys., 83, p. 7201Rosenfeld, H.D., Subramanian, M.A., (1996) J. Solid State Chem., 125, p. 278Subramanian, M.A., Torardi, C.C., Johnson, D.C., Pannetier, J., Sleight, A.W., (1988) J. Solid State Chem., 72, p. 24Reimers, J.N., Greedan, J.E., Kremer, R.K., Gmelin, E., Subramanian, M.A., (1991) Phys. Rev. B, 43, p. 3387Raju, N.P., Greedan, J.E., Subramanian, M.A., (1994) Phys. Rev. B, 49, p. 1086Hwang, H.Y., Cheong, S.-W., (1997) Nature (London), 389, p. 942Ventura, C., Alascio, B., (1997) Phys. Rev. B, 56, p. 14533Kennedy, B.J., (1998) Physica B, 241-243, p. 303Cox, D., private communicationSeehra, M.S., (1968) Rev. Sci. Instrum., 39, p. 1044Anderson, P.W., Weiss, P.R., (1953) Rev. Mod. Phys., 25, p. 269Huber, D.L., (1998) J. Appl. Phys., 83, p. 6949Huber, D.L., Causa, M.T., Tovar, M., private communicationCausa, M.T., Alejandro, G., Zysler, R., Prado, F., Caneiro, A., Tovar, M., J. Magn. Magn. Mater., , in pres