Abstract
Muon spin relaxation studies on La
1 −
x
Ca
x
MnO
3 (
x = 0.33 and 0.67) powders show that the muon dynamic relaxation function changes from exponential above the magnetic transition temperature to stretched exponential below the critical temperature (
T
C = 274 K for
x = 0.33,
T
N = 150 K for
x = 0.67). This suggests a spatially inhomogeneous distribution of very slow Mn-ion correlation times. An anomalously small applied field destrroys the dynamical signature of the ferromagnetic transition for
x = 0.3, but not the antiferromagnetic transition for
x = 0.67. The
x = 0.67 system also shows the evidence of a change in the magnetic phase in zero field near
T = 75 K.