ONSET OF FERROMAGNETISM IN EUXSR1-XS NEAR X=0.5

In a neutron-diffraction study of insulating EuxSr1-xS with x=0.40,A 0.50,A 0.52,A andA 0.54, the critical concentration for the spin-glass-to-ferromagnetism transition is determined to be as high as xc=0.51. For x just above xc, magnetic microdomains coexist with longrange ferromagnetic order, decoupled from one another by competing antiferromagnetic bonds. For the first time the breakdown of ferromagnetic order into microdomains is directly observed by decreasing the temperature, and it is interpreted as a ferromagnetism-to-spin-glass transition. © 1979 The American Physical Society.