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Phase Transition from Antiferromagnetic Insulator to Ferromagnetic Metal in La 2- x Sr x CoO 4 –Magnetization and NMR Studies–

1993; Physical Society of Japan; Volume: 62; Issue: 4 Linguagem: Inglês

10.1143/jpsj.62.1127

1347-4073

Yuji Furukawa, Shinji Wada, Yoshihiro Yamada,

Advanced Condensed Matter Physics

Magnetic and zero-field nuclear magnetic resonance investigations have been made on the La 2- x Sr x CoO 4 system ( x =0–1.4), one of the isomorphous compounds of the superconducting cuprates. In the La-rich region ( x ≤0.5), the antiferromagnetic (AF) ordering persists and the internal magnetic field at 1.4 K remains almost constant ( H int ( Co)≃200 kOe), though the Néel temperature shows an initial strong decrease with a small amount of Sr substitution. When x increases further ( x ≥0.6), the AF state suddenly transforms to a ferromagnetic state and the Curie temperature shows a maximum ( T C =220 K) at x =0.9. Spontaneous magnetizations at T =4.2 K are, however, non-zero (2.2–1.6 µ B ) only in the range of x =0.7–0.9, and H int ( Co) strongly decreases from 190 kOe ( x =0.6) to below 40 kOe ( x =1.1). 59 Co spin-lattice relaxation time T 1 for x =0.7 and 0.9 follows the relation T 1 T =const., suggesting it is in a metallic state.