Muon spin relaxation and susceptibility measurements of an itinerant-electron system Sr 1-xCa xRuO 3: Quantum evolution from ferromagnet to paramagnet

Muon spin relaxation (\u3bcSR) and magnetic susceptibility measurements have been performed in the itinerant-electron magnet Sr 1-xCa xRuO 3, with x= 0.0, 0.3, 0.5, 0.65, 0.7, 0.75, 0.8, 0.9, and 1.0. SrRuO 3 is a ferromagnet with the critical temperature T c 3c160 K. Upon (Sr, Ca) substitution, T c decreases monotonically with increasing Ca concentration x and the ferromagnetic order disappears around x= 0.7. Very weak static magnetism is observed in the x= 0.75 and 0.8 systems, while the x= 0.9 and 1.0 systems remain paramagnetic in their full volume. Phase separation between volumes with and without static magnetism was observed in the x= 0.65, 0.7, 0.75, and 0.8 systems, near the magnetic crossover around x= 0.7. In this concentration region, \u3bcSR measurements revealed discontinuous evolution of magnetic properties in contrast to magnetization measurements, which exhibit seemingly continuous evolution. Unlike the volume-integrated magnetization measurements, \u3bcSR can separate the effects of the ordered moment size and the volume fraction of magnetically ordered regions. The muon spin relaxation rate 1/T 1 exhibits critical slowing down of spin fluctuations near T c in the ferromagnetic systems with x= 0.0-0.65, consistent with the behavior expected in the self-consistent renormalization theory of itinerant electron ferromagnets. The lack of maximum of 1/T 1 in the x= 0.7 system indicates the disappearance of critical slowing down. These results demonstrate a first-order quantum evolution in the ferromagnet to paramagnet crossover near x= 0.7. \ua9 2011 American Physical Society.Peer reviewed: YesNRC publication: Ye