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 YNiO3_{3} : ESR and susceptibility study

We present a study of the magnetic properties of YNiO$_{3}$ in the paramagnetic range, above and below the metal-insulator (MI) transition. The dc susceptibility, $\chi_{dc}$ (measured up to 1000 K) is a decreasing function of T for $T >$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% $^{3+}$. The value of the Curie constant for T$<$ T$_{MI}$ allows us to discard the possibility of Ni$^{3+}$ 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 $\chi _{dc}$ behaviour for T $<$ T$_{MI}$ in terms of charge disproportionation of the type 2Ni$$ Ni$^{2+}$+Ni$^{4+},$ that is compatible with the previously observed structural transition across T$_{MI}$.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 (χ) 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 χ(T), ΔHpp(T) = [C/Tχ(T)]ΔHpp(∞). The high temperature limit of the linewidth, ΔHpp(∞), 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, ΔHpp(∞)∝ω2 p/J where J is proportional to the Curie-Weiss temperature, including the hybridization mechanism producing CMR. Instead, ΔHpp(∞) 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&lt;T&lt;Tp≈450 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., García-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 ΔHpp(T) = ΔHpp(T→∞)[C/Tχdc(T)], where C is the single-ion Curie constant. The high-temperature limit for the linewidth, given by ΔHpp(T→∞)∝(ωp)2/J, is determined by the superexchange constant J for each material. A value of (ωp/γ) = 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. López-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