252 research outputs found
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 NdCaMnO thin films
Thin films of NdCaMnO manganites with colossal
magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser
Deposition technique on (100)-SrTiO. The lattice parameters of these
manganites and correlatively their CMR properties can be controlled by the
substrate temperature . The maximum CMR effect at 75K, calculated as the
ratio is 10 for a deposition temperature of
degC. Structural studies show that the
NdCaMnO film is single phase, [010]-oriented and has a
pseudocubic symmetry of the perovskite subcell with a=3.77 at room
temperature. We suggest that correlation between lattice parameters, CMR and
substrate temperature 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 PrCaMnO 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
PrCaMnO 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 PrCaMnO thin films
Thin films of the charge-ordered (CO) compound PrCaMnO
have been deposited onto (100)-oriented SrTiO 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.
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