Theory
Colossal Magnetoresistance
Magnetoresistance is the relative change in electrical resistance of a
material on the application of magnetic field. The magnetoresistance
of conventional materials is quite small; but materials with large magnetoresistance
have been synthesized now. Depending on the magnitude, it is called either
as Giant magnetoresistance(GMR) or Colossal magnetoresistance(CMR).
Magnetoresistance has aroused great interest recently
because of possible application in devices such as read/write heads
in computer discs and in sensors.
Colossal Magnetoresistance has been predominantly discovered in manganese-based
perovskite oxides. This arises because of strong mutual coupling of spin,
charge and lattice degrees of freedom. Hence not only high temperature
superconductivity, but also new magnetoelectronic properties
are increasingly discovered in materials with perovskite
structures.
Most of the perovskite oxides exhibit the following types of ordering.They
are,
Charge ordering,
Orbital
ordering and Spin
ordering
Our work on charge, orbital and spin
ordering....
We have recently carried out density functional calculations using FPLMTO
method on YBaMn2O5 which
is built-up of MnO5 square pyramids.
From our study of total, site and orbital projected DOS, we found that
YBaMn2O5 possesses
checker-board
type charge ordering and F-type
orbital-ordering. This compound also possesses
G-type
ferrimagnetic (spin) ordering in addition
to charge ordering and orbital ordering. The nature of charge and
orbital ordering is well illustrated in the two figures.
The
G-type ferrimagnetic spin ordering can be seen from the spin
density of Mn-electrons in 001 and 110 plane.
The
theoretically investigated charge, orbital and spin ordering and
magnetic moments of Mn are found to be in excellent agreement with
the experimental findings. As YBaMn2O5contains finite
magnetic moment in addition to insulating behavior it may be technologically
usefuland hence we have calculated the optical properties.
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