Jahn–Teller distortions and the magnetic order in the perovskite manganites

Abstract

We introduce an effective model for e(g) electrons to describe three-dimensional perovskite (La(1 - x)Sr(x)MnO(3) and La(1 - x)Ca(x)MnO(3)) manganites and study the magnetic and orbital order on a 4 × 4 × 4 cluster using correlated wavefunctions. The model includes the kinetic energy, and on-site Coulomb interactions for e(g) electrons, antiferromagnetic superexchange interaction between S = 3/2 core spins, and the coupling between e(g) electrons and Jahn-Teller modes. The model reproduces the experimentally observed magnetic order: (i) an A-type antiferromagnetic phase in the undoped insulator LaMnO(3), with alternating e(g) orbitals and with small Jahn-Teller distortions, changing to a conducting phase at 32 GPa pressure, and (ii) ferromagnetic order in one-eighth-doped La(7/8)Sr(1/8)MnO(3) and in quarter-doped La(3/4)Sr(1/4)MnO(3) compounds. For half-doped La(1/2)Ca(1/2)MnO(3) one finds a competition between a ferromagnetic conductor and the CE insulating phase; the latter is stabilized by the Jahn-Teller coupling being two times larger than for the strontium-doped compound. Altogether, there is a subtle balance between all Hamiltonian parameters and the phase diagram is quite sensitive to the precise values they take.

Strong coupling of Jahn-Teller distortion to oxygen-octahedron rotation and functional properties in epitaxially strained orthorhombic LaMnO3

“…[1][2][3][4] As a result, there have been many experimental [5][6][7][8] and theoretical [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] studies of the end-member compound LaMnO 3 (LaMnO 3 ). The observed sequence of phases with decreasing temperature is as follows: 8,26 At very high temperature (above 1010 K), LaMnO 3 has a rhombohedral R3c structure, produced by rotation of the oxygen octahedron network of the ideal perovskite structure.…”

Orbital and spin ordering physics of the Mn3O4 spinel

“…However, the microscopic mechanism that relieves the geometric frustration inherent in the spinel structure and leads to the ferrimagnetic Yafet-Kittel ordering of spins at low temperatures remain unknown 24 . Further, the superexchange mechanism for electronic correlations in the Mn 3 O 4 spinel is likely different from the other well-studied transition-metal(TM) perovskite systems 25,26 . The active orbitals on the nearest-neighbour TM sites in the former are orthogonally directed with respect to one another, while they are aligned in the latter.…”

Onset and melting of local orbital order

“…Although long-range orbital order will be susceptible to orbital fluctuations at finite doping in the same way as for the staggered spin ordering in the doped antiferromagnet, 33 this HF result does provide a measure of the local orbital order. phase was studied at half doping using cooperative phonons with large electron-phonon coupling, [34][35][36][37] and recently at hole density x = 1/4 using Monte Carlo investigations, 38 and at several fractional hole densities using numerical simulations on finite 3d clusters, 39 the doping and temperature dependence of CE-type orbital correlations within an interacting electron model has not been investigated in the ferromagnetic phase.…”