Canted antiferromagnetism in an insulating lightly dopedLa1−xSr

Abstract

We have investigated the magnetic structure of an insulating lightly doped La 1Ϫx Sr x MnO 3 with xϭ0.04,0.125, and 0.17 with neutron scattering technique and bulk magnetization measurements. The magnetic structure of the xϭ0.04 sample at 5 K is a commensurate layer-type (A-type͒ antiferromagnetism with the propagation vector ͓010͔ and the moment of 3.7Ϯ0.2 B /M n, being parallel to the ͓100͔ axis in the orthorhombic Pnma symmetry. In addition, a spontaneous magnetization of 0.28Ϯ0.02 B /M n is observed at 8 K by magnetization measurement. By contrast, the xϭ0.125 sample exhibits a large ferromagnetic moment of 3.7Ϯ0.2 B /Mn and a small A-type antiferromagnetic component of 0.23Ϯ0.1 B /M n, while the xϭ0.17 sample exhibits only a ferromagnetic component of 3.6Ϯ0.2 B /Mn. These results are consistent with a spin structure derived from the conventional double exchange mechanism, but rule out the possibility of a recently suggested spiral spin structure for the insulating La 1Ϫx Sr x MnO 3 system.Distorted perovskite manganese oxides such as La 1Ϫx Sr x MnO 3 and La 1Ϫx Ca x MnO 3 transform from an antiferromagnetic insulator to a ferromagnetic metal as substitution of La ions by alkaline-earth ions. 1-4 Such behavior has been long known as metallic transport phenomena mediated by a double exchange mechanism. 5-7 The recent discovery of a gigantic magnetoresistance, 8-15 lattice-structure switching by an external field 16 as well as field-induced insulator-metal transitions 17-19 has renewed interest in these perovskite-type manganese oxide systems. Manganese ions in the parent material LaMnO 3 have a 3d 4 configuration where three electrons occupy the t 2g orbitals, while one electron occupies the e g orbital. The number of e g electrons in LaMnO 3 corresponds to half filling, and makes the parent LaMnO 3 a Motttype antiferromagnetic insulator. The substitution of La ions by divalent ions leads to doping of holes to the e g orbitals, introducing an itinerant character as well as ferromagnetism to well-doped samples. For a lightly doped insulating regime of the solid solution system La 1Ϫx Sr x MnO 3 , however, the double exchange model suggests a canted antiferromagnetism as the magnetic structure. 7 On the other hand, based on a mean field treatment of localized t 2g electrons and itinerant e g electrons with a strong Hund coupling, Inoue and Maekawa 20 recently proposed that a spiral state can be energetically more favorable than a canted antiferromagnetic state for a nearly half-doped insulating regime. This theory suggests that the spiral state continuously changes to the ferromagnetic state as a function of hole doping from half filling.In a pioneering work by Wollan and Koehler in 1955, the magnetic structures of the LaMnO 3ϩ␦ system as well as the La 1Ϫx Ca x MnO 3 system were studied by the neutron diffraction technique. 2 The spin structure of the LaMnO 3ϩ␦ system was reported to be a canted antiferromagnet where a layer type ͑a so-called A-type͒ antiferromagnetic ͑AF͒ structure coexists with a ferromagnet...

Magnon damping by magnon-phonon coupling in manganese perovskites

“…This result strongly suggests that magneto-elastic coupling is important to the understanding of the low temperature spin dynamics of A 0.7 B 0.3 MnO 3 . In the lower doping canted ferromagnet La 0.85 Sr 0.15 MnO 3 [27], much larger spin-wave broadening and damping have been found at low temperatures [28]. Although the magnon dispersion relation in that system appears to be consistent with the simple nearest-neighbor Heisen- …”

Changeover from glassy ferromagnetism of the orbital domain state to long-range ferromagnetic ordering inLa0.9Sr0.1MnO3

“…The nature of this low temperature phase previously has been interpreted in terms of canted antiferromagnetic phase 1 . Successive structural phase transition from a high temperature pseudocubic phase to intermediate Jahn-Teller distorted orthorhombic phase and to low temperature pseudocubic phase reported in this low doped regime 23,24 might be a cause of the observed behaviour. The nature of low temperature state is also reported in terms of charge localization, which is accompanied by ordering of polarons 2 .…”

Microscopically homogeneous magnetic structure ofLa1−xSrxMnOKumagai1, Iwai2, Tomioka3 et al. 1999Phys. Rev. B427501View full textAdd to dashboardCite

“…Keeping in mind that the samples used in Ref. 5 were not completely identical to ours this small quantitative discrepancy looks quite acceptable.…”

“…5 we would like to emphasize the very sharp changeover of the AFM and FM components despite a linear variation of the hole density. Due to our NMR data this changeover looks probably even more sharp with its central point close to xϭ0.05.…”

“…Recent neutron 5 and NMR ͑Refs. 6 and 7͒ studies came to very different conclusions about the doping range for coexistence of AFM and FM phases in manganites.…”