652 research outputs found
Magnetic-history-dependent nanostructural and resistivity changes in Pr0.5Ca0.5Mn0.98Cr0.02O3
We show that nanostructure and resistivity of Pr0.5Ca0.5Mn0.98Cr0.02O3 are
sensitive to whether the sample is zero-field-cooled (ZFC) of field-cooled (FC)
either in the 'self magnetic field (H = 2 T)' of the electron microscope or
under the external magnetic field of 2 T. FC resistivity at H = 2 T is lower
than ZFC values below 140 K. The average value of the chare-orbital modulation
vector (q = 0.44) of the FC crystallites is lower than that of the ZFC
cystallites (q = 0.48) and the FC crystallites exhibit numerous defects like
discommensuration, dislocations and regios with loss of superstructures
compared to the ZFC crystallites.Comment: 7 pages, 3 figure
Adatom incorporation and step crossing at the edges of 2D nanoislands
Adatom incorporation into the ``faceted'' steps bordering the 2D nanoislands
is analyzed. The step permeability and incorporation coefficients are derived
for some typical growth situations. It is shown that the step consisting of
equivalent straight segments can be permeable even in the case of fast egde
migration if there exist factors delaying creation of new kinks. The step
consisting of alternating rough and straight segments may be permeable if there
is no adatom transport between neighboring segments through the corner
diffusion.Comment: 3 pages, one figur
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
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.
- …