Neutron scattering studies on magnetic structure of the double-layered manganite La2−2xSr1+2xMn2O7 (0.30≤x≤0.50)

Abstract

Systematic powder diffraction studies have been carried out to establish the magnetic phase diagram of La2−2xSr1+2xMn2O7 (LSMO327) in a wide hall concentration range (0.30 ≤ x ≤ 0.50), using the HERMES diffractometer. LSMO327 exhibits a planar ferromagnetic structure for 0.32 ≤ x ≤ 0.38 at low temperatures. A finite canting angle between planar magnetic moments on neighboring planes starts appearing around x ∼ 0.40 and reaches 180• (A-type antiferromagnet) at x = 0.48. At x = 0.30, on the other hand, the magnetic moments are aligned parallel to the c-axis.

The Jahn-Teller effect of layered perovskite manganites La2−2xSr1+2xMn2O7 studied by Mn K-edge XAFS

“…Since the colossal magnetoresistance (CMR) was discovered in perovskite manganites Ln 1Àx A x MnO 3 (Ln: rare-earth ions; A: alkalineearth ion) [1][2][3], the same effect was found in the bilayered perovskite manganites Ln 2À2x A 1+2x Mn 2 O 7 [4,5]. The two series of materials are similar in some aspects: they show the same ferromagnetic-paramagnetic and metal-insulator transitions at a certain doping range of x and they show the same CMR effect at temperatures close to curie temperature ðT c Þ; furthermore, the CMR effect is optimized for samples doped at about x ¼ 0:33: However, the bilayered Mn oxides has gained special interest, because they show much larger CMR than the perovskite manganites, and the CMR can be achieved at a lower magnetic field.…”

Low-temperature electrical transport in bilayer manganiteLa1.2Sr1.8Mn<

“…Its reduced dimensionality gives rise to anisotropic characteristics of charge transport and magnetic properties and also enhances the CMR effect near the magnetic transition temperature, although at the cost of reducing it to about 100 K. 7 The magnetic structure of heavily doped bilayer compounds always shows the coexistence of FM and antiferromagnetic (AFM) correlations. 9,10,11,12 The magnetic correlations are predominantly FM within the two-dimensional MnO 2 layers, while the magnetic coupling between the MnO 2 layers changes from FM for x ≤ 0.4 to canted AFM for x > 0.4. The interplay between FM double exchange and AFM superexchange interactions between Mn ions in these compounds becomes more subtle and is expected to be responsible for the unusual transport properties observed in the bilayer manganites.…”

Hole concentration dependence of Mn eg orbital state in bilayer manganites studied by magnetic Compton profile measurement

“…Bilayer manganite La 2K2x Sr 1C2x Mn 2 O 7 is particularly attractive, because it shows much larger CMR than the base compound La 1Kx Sr x MnO 3 [11]. Recent neutrondiffraction measurements have revealed a detailed magnetic phase diagram of bilayer manganite depending on the hole concentration, x, indicating that the Mn-3d orbital state, especially e g orbital state, is closely connected with the x dependence of magnetic structures, transition temperatures (T c and T N ), Mn-O bond lengths and so on [12,13]. According to the magnetic phase diagram, the magnetic moment is pointed along the c-axis in the range of 0.3!x!…”