Magnetic order of the disturbed spin-Peierls compound (Cu,Mg)GeO3

We have measured muon spin relaxation (μSR) in (Cu1−xMgx)GeO3, a spin-Peierls compound disturbed by the Mg (S=0) doping of the Cu (S=12) spin chain. Static magnetic order was observed in the zero-field μSR measurements below the Néel temperatures determined by the susceptibility measurements. The zero-field muon relaxation exhibits a characteristic line shape in disturbed spin-Peierls compounds; muon spin precession together with exponential static relaxation. The amplitude of the precession, which is a measure of spacial homogeneity of the ordered moment size, takes the maximum at Mg concentration x∼0.03, which is just above the phase boundary in the temperature–Mg concentration (T–x) phase diagram.