  Zero field muon spin relaxation (ZF-{\mu}SR) has been used to study the
magnetic properties of the underdoped giant magnetoresistive ruthenocuprates
(GMR) RuSr2Nd1.8-xY0.2CexCu2O10-d (x = 0.95, 0.80). The results show a gradual
loss of initial asymmetry A0 at the ruthenium spin transition temperature, TRu.
At the same time the electronic relaxation rate, lambda shows a gradual
increase with decreasing temperature below TRu. These results have been
interpreted as evidence for Cu spin cluster formation below TRu. These
magnetically ordered clusters grow as the temperature is decreased thus causing
the initial asymmetry to decrease slowly. GMR is observed over a wide
temperature range in the materials studied and the magnitude increases as the
temperature is reduced from TRu to 4 K which suggests a relation between Cu
spin cluster size and -MR.
