Antiferromagnetic metallic state in the heavily doped region of perovskite manganites

Magnetic Phase Diagram for Bilayer Manganites

“…Such a small chemical pressure effect is considered to reflect the stability of the d x 2 −y 2 like orbital due to the released JT distortion (see Section 3a) over the concentration range (0 · 25≤ z ≤1 · 00 and x = 0·5). In fact, the averaged JT distortion is ∆ =1 · 01 even for NdSr 2 Mn 2 O 7 (z = 1·0), which is smaller than the value for La 1 · 2 Sr 1 · 8 Mn 2 O 7 (∆ = 1·02) (Moritomo et al 1998a(Moritomo et al , 1998b. Fig.…”

“…The appearance of the charge-ordered state in the limited z region around z = 1·0 can be ascribed to the released JT distortion. The ∆ value is 1 · 00 at z = 1·0 (Moritomo et al 1998a), but becomes larger with a decrease in z (∆ = 1·01 for z = 1·0). As Li et al (1998) proposed, the charge-ordered state in this system is considered to be stabilised by concomitant orbital ordering within the MnO 2 sheet.…”

“…Up to present, extensive studies on the lattice and magnetic structure were performed on La 2−2x Sr 1+2x Mn 2 O 7 (Mitchell et al 1997;Akimoto et al 1999;Moritomo et al 1999aMoritomo et al , 1999bKubota et al 1999). In this system, the hole-doping procedure not only decreases the nominal concentration of the e g carriers, but significantly releases the static Jahn-Teller (JT) distortion of the MnO 6 octahedra (Moritomo et al 1998a(Moritomo et al , 1998b: the averaged JT distortion ∆ defined by d Mn−O(out) /d Mn−O(in) decreases from ∆ = 1 · 03 at x = 0·3 to 1·00 at x = 0·5. Such a variation of the JT distortion should affect the orbital character of the e g electrons, and hence the magnetotransport properties.…”

“…Such a variation of the JT distortion should affect the orbital character of the e g electrons, and hence the magnetotransport properties. Moritomo et al (1998aMoritomo et al ( , 1998b have investigated the ground state properties for (La 1−z Nd z ) 2−2x Sr 1+2x Mn 2 O 7 (x = 0·4 − 0·5) by systematically changing z and x, and have found that the x ≥ 0 · 45 region is dominated by a layered AFM (A-type AFM) state. In this magnetic structure, an FM MnO 2 sheet alternates along the c-axis (intra-bilayer coupling is negative) (Moritomo et al 1989a(Moritomo et al , 1998b.…”

“…Kawano et al (1997) have performed neutron diffraction measurements on Nd 1−x Sr x MnO 3 and found that the low temperature spin structure changes from CE-type at x = 0·5 to A-type at x = 0·55. Recently, Akimoto et al (1998) and Moritomo et al (1998aMoritomo et al ( , 1998b have systematically investigated the ground state properties for cubic-type manganites as a function of x and W , and found that the phase diagram is dominated by the FM metallic state in the low-x region and an AFM metallic state in the high-x region.…”