Rhodium Doped Manganites : Ferromagnetism and Metallicity

The possibility to induce ferromagnetism and insulator to metal transitions in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown for the first time. Colossal magnetoresistance (CMR) properties are evidenced for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to induce such properties is compared to the results obtained by chromium and ruthenium doping. Models are proposed to explain this behavior.Comment: 11 pages, 8 figure

Control of the colossal magnetoresistance by strain effect in Nd0.5_{0.5}Ca0.5_{0.5}MnO3_{3} thin films

Thin films of Nd$_{0.5}$Ca$_{0.5}$MnO$_{3}$ manganites with colossal magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser Deposition technique on (100)-SrTiO$_{3}$. The lattice parameters of these manganites and correlatively their CMR properties can be controlled by the substrate temperature $T_{S}$. The maximum CMR effect at 75K, calculated as the ratio $\rho (H=0T)/\rho (H=7T)$ is 10$^4$ for a deposition temperature of $T_{S}=680$ degC. Structural studies show that the Nd$_{0.5}$Ca$_{0.5}$MnO$_{3}$ film is single phase, [010]-oriented and has a pseudocubic symmetry of the perovskite subcell with a=3.77$\AA$ at room temperature. We suggest that correlation between lattice parameters, CMR and substrate temperature $T_{S}$ result mainly from substrate-induced strains which can weaken the charge-ordered state at low temperature.Comment: 9 pages, 4 figures. To be published in Applied Physics Letter

Comment on ''the controlled charge ordering and evidence of the metallic state in Pr0.65_{0.65}Ca0.35_{0.35}MnO3_{3} films''

In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12} L133) Lee \QTR{it}{et al.} have studied the transport properties of Pr$_{0.65}$Ca$_{0.35}$MnO$_{3}$ thin films. They claimed that they are able to controlled the charge-ordered (CO) state by the lattice strains. We propose herein another alternative since another indexation of the orientation of the film can be found leading to almost no distortion of the cell, as compared to the bulk compound.Comment: 2 page

Incoherent Effect of Fe and Ni Substitutions in the Ferromagnetic-Insulator La0.6Bi0.4MnO3+d

A comparative study of the effect of Fe and Ni doping on the bismuth based perovskite La0.6Bi0.4MnO3.1, a projected spintronics magnetic semiconductor has been carried out. The doped systems show an expressive change in magnetic ordering temperature. However, the shifts in ferromagnetic transition (TC) of these doped phases are in opposite direction with respect to the parent phase TC of 115 K. The Ni-doped phase shows an increase in TC ~200 K, whereas the Fe-doped phase exhibits a downward shift to TC~95 K. Moreover, the Fe-doped is hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is observed that the materials are semiconducting in the ferromagnetic phase with activation energies of 77 & 82 meV for Fe & Ni-doped phases respectively. In the presence of external magnetic field of 7 Tesla, they exhibit minor changes in the resistivity behaviours and the maximum isothermal magnetoresistance is around -20 % at 125 K for the Ni-phase. The results are explained on the basis of electronic phase separation and competing ferromagnetic and antiferromagnetic interactions between the various mixed valence cations.Comment: 18 pages including figure

Competition between ferromagnetism and spin glass: the key for large magnetoresistance in oxygen deficient perovskites SrCo1-xMxO3-d (M = Nb, Ru)

The magnetic and magnetotransport properties of the oxygen deficient perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and Ru-substituted cobaltites are weak ferromagnets, with transition temperatures Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass behavior at temperatures below Tf = 80-90 K. It is demonstrated that there exists a strong competition between ferromagnetism and spin glass state, where Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites induces magnetic disorder, and this particular magnetic behavior is the origin of large negative magnetoresistance of these oxides, reaching up to 30% at 5 K in 7 T. The differences between Nb- and Ru-substituted cobaltites are discussed on the basis of the different electronic configuration of niobium and ruthenium cations.Comment: 32 pages, 9 figures, to appear in Phys. Rev.

Ferromagnetism and magneto-dielectric effect in insulating LaBiMn4/3Co2/3O6 thin films

High quality epitaxial thin films of LaBiMn4/3Co2/3O6 perovskite were fabricated on (001)-oriented SrTiO3 and LaAlO3 substrates by the pulsed laser deposition technique. Magnetization measurements reveal a strong magnetic anisotropy and a ferromagnetic behavior that is in agreement with a super-exchange interaction between Mn4+ and Co2+ ions, which are randomly distributed in the B-site. A distinct anomaly is observed in the dielectric measurements at 130K corresponding to the onset of the magnetic ordering, suggesting a coupling. Above this temperature, the extrinsic Maxwell-Wagner effect is dominating. Theses results are explained using the Raman spectroscopic studies indicating a weak spin-lattice interaction around this magnetic transition.Comment: Submitted to Appl. Phys. Lett. (2008

Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario

Field-induced magnetization jumps with similar characteristics are observed at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even the existence- of these jumps depends critically on the magnetic field sweep rate used to record the data. It is proposed that, for both compounds, the martensitic character of their antiferromagnetic-to-ferromagnetic transitions is at the origin of the magnetization steps.Comment: 4 pages,4 figure

Instability of metal-insulator transition against thermal cycling in phase separated Cr-doped manganites

We show that metal-insulator transition in Pr0.5Ca0.5Mn1-xCrxO3 (x = 0.015-0.025) is unstable against thermal cycling. Insulator-metal transition shifts down and low temperature resistivity increases each time when the sample is cycled between a starting temperature TS and a final temperature TF. The effect is dramatic lower is x. Insulator-metal transition in x = 0.015 can be completely destroyed by thermal cycling in absence of magnetic field as well as under H = 2 T. Magnetic measurements suggest that ferromagnetic phase fraction decreases with thermal cycling. We suggest that increase in strains in ferromagnetic- charge ordered interface could be a possible origin of the observed effect.Comment: 14 pages, 5 figures and 2 tables (revised

Thickness dependence of the stability of the charge-ordered state in Pr0.5_{0.5}Ca0.5_{0.5}MnO3_{3} thin films

Thin films of the charge-ordered (CO) compound Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$ have been deposited onto (100)-oriented SrTiO$_{3}$ substrates using the Pulsed Laser Deposition technique. Magnetization and transport properties are measured when the thickness of the film is varied. While the thinner films do not exhibit any temperature induced insulator-metal transition under an applied magnetic field up to 9T, for thickness larger than 1100\UNICODE{0xc5} a 5T magnetic field is sufficient to melt the CO state. For this latest film, we have measured the temperature-field phase diagram. Compared to the bulk material, it indicates that the robustness of the CO state in thin films is strongly depending on the strains and the thickness. We proposed an explanation based on the distortion of the cell of the film.Comment: 9 pages, 6 figures, submitted to Phys. Rev.