Cecilia I. Ventura

Magnetic excitations of perovskite rare-earth nickelates: RNiO3

Abstract To gain insight into the ground state of perovskite nickelates RNiO 3 (R: rare-earth), in particular charge disproportionation of the Ni ions and the magnetic configuration, we studied the magnetic excitations of the collinear, orthogonal and intermediate phases proposed for these materials. We used a localized spin model, including two kinds of Ni-spin magnitudes to describe an eventual charge disproportionation. For the magnetic couplings, we considered Heisenberg-like interactions up to next-nearest-neighbors, for the ferromagnetic and antiferromagnetic couplings present in the collinear phases. To describe the non-collinear phases, as proposed for other multiferroics, we considered Dzyaloshinskii–Moriya-type couplings to allow for the possibility of a relative angle θ , between nearest-neighbor spins in the two different magnetic sublattices. Using a simplified spin chain model for these compounds, we first analysed the stability of the collinear, orthogonal, and intermediate phases in the classical case. We then explored the quantum ground state indirectly, calculating the spin excitations obtained for each phase, using the Holstein–Primakoff transformation and the linear spin-wave approximation. For the collinear and orthogonal ( θ = π / 2 ) phases we predict differences in the magnon spectra, concretely in the number of magnon branches or the magnitude of the magnon gap, which would allow to distinguish between these phases, and in particular probe the charge disproportionation, in future experiments such as inelastic neutron scattering or resonant inelastic X-ray scattering.

Quantum Magnons of the Intermediate Phase of Half-Doped Manganite Oxides

At half doping, the ground state of three-dimensional manganite perovskite oxides like R1-xCaxMnO3, where R is a trivalent ion such as La, Pr, etc., is still unclear. Many experimental findings agree better with the combined magnetic, charge, and orbital order characteristic of the “intermediate phase”, introduced by Efremov in 2004 [Nat. Mater., 3, 853]. This phase consists of spin dimers (thus incorporating aspects of the Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine [Phys. Rev. Lett., 89, 097205]), though formed by a pair of parallel Mn spins of different magnitude, in principle (thereby allowing for a degree of Mn charge disproportionation: not necessarily as large as that of Mn3+-Mn4+ in Goodenoughs original CE phase [Phys. Rev. 100, 564 (1955)]). In the intermediate phase, consecutive spin dimers localed along the planar zig-zag chains are oriented at a constant relative angle φ between them. Varying Mn-charge disproportionation and φ, the intermediate phase should allow to continuously interpolate between the two limiting cases of the CE phase and the dimer phase denoted as “orthogonal intermediate π/2-phase”. It is not easy to find a microscopic model able to describe the phenomenological intermediate phase adequately for the spin, charge, and orbital degrees of freedom simultaneously. Here, we study the quantum spin excitations of a planar model of interacting localized spins, which we found can stabilize the intermediate phase classically. We compare the quantum magnons of the intermediate phase with those of the CE and orthogonal π/2 phases, in the context of recent experimental results.

Spin Excitations in Half-Doped Manganites

We investigate magnetic excitations in half-doped colossal magnetoresistance manganites. In particular, we focus on spin excitations in the CE phase originally proposed by Goodenough (Phys. Rev. 100:564, 1955). Using a localized spin model, we calculated magnons for 3D-perovskite compounds such as La1−xMxMnO3, where M=Ca, Sr, Ba, and for their 2D-laminar counterparts. We compared them with predictions for the spin excitations corresponding to other phases proposed. For the laminar half-doped manganite La0.5Sr1.5MnO4, for which magnon measurements by inelastic neutron scattering exist, as well as an estimation of the magnetic couplings, our calculations agree well with the experimental data.

Phase diagram description of the CaCu3Fe4O12 double perovskite

CaCu

Spectral properties of the one-dimensional two-channel Kondo lattice model

_3

Erratum to “Quantum Magnons of the Intermediate Phase of Half-Doped Manganite Oxides” [Aug 13 4691-4694]

Fe

Phase diagram description of the CaCu

_4

_3

O

Fe

_{12}

_4

exhibits a temperature-induced transition from a ferrimagnetic-insulating phase, in which Fe appears charge disproportionated, as Fe