Ma. Senarisrodriguez et Jb. Goodenough, MAGNETIC AND TRANSPORT-PROPERTIES OF THE SYSTEM LA1-XSRXCOO3-DELTA (0-LESS-THAN-X-LESS-THAN-OR-EQUAL-TO-0.50), Journal of solid state chemistry, 118(2), 1995, pp. 323-336
Magnetic and transport measurements on the system La1-xSrx CoO3-delta
(0 < x less than or equal to 0.50, delta = 0 for 0 less than or equal
to x < 0.30, and delta (x) less than or equal to 0.06 for 0.30 less th
an or equal to x less than or equal to 0.50) have led to a phase diagr
am for this system. Upon Sr doping, the material segregates into hole-
rich, metallic ferromagnetic regions and a hole-poor matrix similar to
LaCoO3. The Co ions of the ferromagnetic phase are in intermediate-sp
in configurations; the hole-poor matrix experiences a thermally induce
d low-spin to high-spin transition. For low Sr doping (x < 0.20), the
hole-rich regions are isolated from one another and show superparamagn
etic behavior below T-c approximate to 240 K; long-range magnetic orde
r via frustrated intercluster interactions occurs below a superparamag
netic freezing temperature T-g that increases with x. At x = 0.20, the
coupling between the intermediate-spin, metallic ferromagnetic cluste
rs within an interpenetrating matrix reaches a magnetic percolation th
reshold that orders the clusters ferromagnetically below T-c approxima
te to 250 K. However, the electrical conduction in the ferromagnetic r
egions is modulated by the matrix, which has a spin state that varies
with temperature. This causes a reentrant semiconductive behavior in t
he samples with 0.20 less than or equal to x less than or equal to 0.2
5. Metallic ferromagnetic behavior is found for 0.30 less than or equa
l to x less than or equal to 0.50 even though the presence of an inter
penetrating hole-poor matrix persists to x = 0.50. A ferromagnetic fra
ction less than unity leads to peculiar magnetic properties that have
been attributed in the literature to a magnetic ''cluster glass.'' (C)
1995 Academic Press, Inc.