ALFA II-HIFIELD Proyect #II0147FI

ALFA II-HIFIELD
Proyect #II0147FI
“Advanced Materials in H.M.F”
V.Sagredo A
L.M. De Chalbaud; L.Betancourt
Magnetism Group
ULA-Mérida
Mérida-VENEZUELA

Tentative research lines
• A) Colossal magneto-resistance
in chromium chalcogenide
compounds
• B) Variable range-hopping
conduction in semiconductors

MAGNETORESISTANCE IN
FeCr 2 S 4

MAGNETIZATION and M.S. in
FeCr 2 S 4

MAGNETORESISTANCE IN
MANGANITES

MAGNETIZATION IN
MANGANITES

A) Colossal Magneto-Resistance
The discovery of the colossal MR phenomenon
in perovskite Mn oxides of .R 1-x
B x
MnO 3
Where R: rare earth and B a divalent cation.
Has generated wide attention due a variety of
interesting physical properties and their potential
for technological applications.
In this type of materials is long known to exist
the metal-insulator transition.

Important property
It is important to note that CMR does not saturate
until applied fields at least of the order of 6 T where
the MR, when normalized to the high field resistance,
can exceed that of GMR by orders of magnitude. It
has been suggested that the field scale over which
CMR materials can be applied will be pushed to
lower values by field- amplification or spin-valve
techniques.

Chromium chalcogenides
A.P.Ramirez et. Al in Science (97) proposed
investigate spinel structure chalcogenide compounds
with composition AB 2
X 4
where A and B are
transition elements occupying tetrahedral and
octahedral sites respectively and X is a chalcogen.
FeCr 2 S 4

Differences from perovskite oxides
i) There are many ferromagnetic members of this
family, there is the possibility of varying both
anion as well cation species while maintained the
spinel structure.
ii
Unlike in the perovskite where the A-cation
acts mainly to donate charge and control the unit
cell volume, in the spinels it is common to have
A-cation derived states near the Fermi level.

B) Variable range hopping
conduction in semiconductors
Chromium diluted chalcogenide
compounds as FeCr 2-x Al x S 4 have
shown that Al favors the fluctuation
of Coulomb potential.
This effect produces an increase of
resistivity and the transport behavior
transits from MP transport to the
VRH process

Cr based chalcogenide
spinels
FeCr 2 S 4
CoCr 2 S 4
Diluted ACr 2-x III x S 4 compounds
Examples: CdCr 2-x Ga x Se 4
CdCr 2-x In x S 4