Structural origin of the pseudo-two-dimensional metallic state in theA-type antiferromagnetic manganites

Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors

“…In the manganites there are numerous vivid examples of the workings of orbital ordering 15,16,17 . Under the right circumstances one can find a transition from a high temperature cubic phase to a low temperature tetragonal phase accompanied by a quite moderate change in the lattice, but with a change in the electron system that is as drastic as a 'dimensional transmutation': this system changes from an isotropic 3D metal at high temperature to a quasi 2D electron system at low temperatures where the in-plane resistivity is orders of magntitude lower than the c-axis resistivity 18,19,20 .…”

“…We now set out to compute the magnetic excitation spectra, treating the orbital pseudospins as classical and static variables. Fixing the orbital degrees of freedom for a given set of parameters by the corresponding groundstate configuration we are left with an S = 1 Heisenberg model written in (18). The exchange couplings are plotted in Fig.…”

“…On a classical level, the magnetic transitions are easily understood in the spin-only model (18) as discussed before. The transition from the stripe-AF to the (π, π) AF at η ≈ 0.14 occurs exactly at the point where J y = 2J d whereas the transition from (π, π) to ferromagnetic order at η ≈ 0.3 corresponds to the point J x = −J y .…”

55Mn NMR study of the A‐type antiferromagnetic and metallic manganites La1–xSrxMnO3 (0.5 ≤ x ≤ 0.6)

“…Such properties are presumably due to the equivalent density of Mn 3+ and Mn 4+ ions and the resulting competition between the FM double exchange and the AFM superexchange interactions [7]. The A-type AFM spin structure with in-plane FM and out-of-plane AFM spin orderings has been observed in Sr-doped samples such as Pr 0.5 Sr 0.5 MnO 3 , Nd 0.45 Sr 0.55 MnO 3 , and La 0.46 Sr 0.54 MnO 3 [3][4][5]. Interestingly, a pseudo-2D metallic state was observed in the A-type AFM manganites as well as the d x^2-y^2 orbital ordering [8].…”

“…Heavily doped manganites with x ~ 0.5 have shown interesting physical properties, such as a charge-ordered CE-type antiferromagnetic (AFM) state, an orbital ordered A-type AFM state, and phase separation [2][3][4][5][6]. Such properties are presumably due to the equivalent density of Mn 3+ and Mn 4+ ions and the resulting competition between the FM double exchange and the AFM superexchange interactions [7].…”