Two‐band ferromagnetic Kondo lattice model on a ladder with quantum S = 3/2 core spins

Neuber, Danilo R.; Daghofer, Maria; Oleś, Andrzej M.; Linden, Wolfgang von der

doi:10.1002/pssc.200562404

Cited by 4 publications

(5 citation statements)

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“…A common large negative contribution to the above values comes from T x i T x j = −0.1854 correlation -it decreases further when the angle θ is varied towards θ = π/2, where the orbital correlations reach a minimal value, T ij (π/2) = T x i T x j = −0.2472. Thus, in agreement with earlier findings, 37,41 the quantum correction to the classical value −0.25 is very small indeed due to the gap which opens in orbital excitations in the present 2D case. This means that robust AO order with orbitals of the form (|x ± |z )/ √ 2 is realized in an undoped monolayer without crystal field splitting, similar to the OO in the 3D model, 32 if this monolayer has FM spin order.…”

Section: Numerical Results For Monolayer Manganites a Undoped 2d Clus...supporting

confidence: 93%

“…2. This coexistence of the AO order with the FM spin correlations is generic -it confirms the trend observed before in the 1D model 20 and on ladders, 41 and agrees with the Goodenough-Kanamori rules. 42 When robust AO state develops at the orbital degeneracy (E z = 0), the FM phase extends to a broader range of J ′ 0 than at |E z | > 0.…”

Section: Numerical Results For Monolayer Manganites a Undoped 2supporting

confidence: 90%

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Doping dependence of spin and orbital correlations in layered manganites

et al. 2006

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We investigate the interplay between spin and orbital correlations in monolayer and bilayer manganites using an effective spin-orbital t-J model which treats explicitly the eg orbital degrees of freedom coupled to classical t2g spins. Using finite clusters with periodic boundary conditions, the orbital many-body problem is solved by exact diagonalization, either by optimizing spin configuration at zero temperature, or by using classical Monte-Carlo for the spin subsystem at finite temperature. In undoped two-dimensional clusters, a complementary behavior of orbital and spin correlations is found -the ferromagnetic spin order coexists with alternating orbital order, while the antiferromagnetic spin order, triggered by t2g spin superexchange, coexists with ferro-orbital order. With finite crystal field term, we introduce a realistic model for La1−xSr1+xMnO4, describing a gradual change from predominantly out-of-plane 3z 2 − r 2 to in-plane x 2 − y 2 orbital occupation under increasing doping. The present electronic model is sufficient to explain the stability of the CE phase in monolayer manganites at doping x = 0.5, and also yields the C-type antiferromagnetic phase found in Nd1−xSr1+xMnO4 at high doping. Also in bilayer manganites magnetic phases and the accompanying orbital order change with increasing doping. Here the model predicts C-AF and G-AF phases at high doping x > 0.75, as found experimentally in La2−2xSr1+2xMn2O7.

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Section: Numerical Results For Monolayer Manganites a Undoped 2d Clus...supporting

confidence: 93%

Section: Numerical Results For Monolayer Manganites a Undoped 2supporting

confidence: 90%

Doping dependence of spin and orbital correlations in layered manganites

et al. 2006

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“…Whereas these results are to a large extent not surprising given the similarities with the manganites, the magnetic excitation spectra so far have been calculated only for a ladder system. 66 For the manganites, the DDEX model is usually simplified [62][63][64] by treating the core spins as classical and by taking the limit of large or infinite Hund's coupling J H which is not justified for the pnictides. Here, we instead focus on the regime of small and intermediate J H and develop the tools to calculate the magnetic excitation spectra in the presence of both, super-and double-exchange to linear-spin-wave order.…”

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confidence: 99%

Orbital ordering and unfrustrated(π,0)magnetism from degenerate double exchange in the iron pnictides

2010

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The magnetic excitations of the iron pnictides are explained within a degenerate double-exchange model. The local-moment spins are coupled by superexchanges J1 and J2 between nearest and next-nearest neighbors, respectively, and interact with the itinerant electrons of the degenerate dxz and dyz orbitals via a ferromagnetic Hund exchange. The latter stabilizes (π, 0) stripe antiferromagnetism due to emergent ferro-orbital order and the resulting kinetic energy gain by hopping preferably along the ferromagnetic spin direction. Taking the quantum nature of the spins into account, we calculate the magnetic excitation spectra in the presence of both, super-and doubleexchange. A dramatic increase of the spin-wave energies at the competing Néel ordering wave vector is found, in agreement with recent neutron scattering data. The spectra are fitted to a spin-only model with a strong spatial anisotropy and additional longer ranged couplings along the ferromagnetic chains. Over a realistic parameter range, the effective couplings along the chains are negative corresponding to unfrustrated stripe antiferromagnetism.

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“…Interestingly, our results indicate that as n → 2.5 the legs are FM aligned. However, as n → 3 a novel AFM ordering between the legs develop, while the FM islands involve three spins [54]. The latter may arise from competing double-exchange-FM vs AFM tendencies coming from the localized spins and Fermi instability k F , namely the energy of the large FM blocks as n → 3 is reduced by the rung AFM arrangement.…”

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Novel Magnetic Block States in Low-Dimensional Iron-Based Superconductors

et al. 2019

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Inelastic neutron scattering recently confirmed the theoretical prediction of a ↑↑↓↓-magnetic state along the legs of quasi-one-dimensional (quasi-1D) iron-based ladders in the orbital-selective Mott phase (OSMP). We show here that electron-doping of the OSMP induces a whole class of novel block-states with a variety of periodicities beyond the previously reported π/2 pattern. We discuss the magnetic phase diagram of the OSMP regime that could be tested by neutrons once appropriate quasi-1D quantum materials with the appropriate dopings are identified.Introduction. Competing interactions in strongly correlated electronic systems can induce novel and exotic effects. For example, in the iron-based superconductors [1][2][3][4] charge, spin, and orbital degrees of freedom combine phenomena known from cuprates with those found in manganites. Prominent among these novel effects is the orbital-selective Mott phase (OSMP) [5], where interactions acting on a multi-orbital Fermi surface cause the selective localization of electrons on one of the orbitals. As a consequence, the system is in a mixed state with coexisting metallic and Mott-insulating bands [ Fig. 1(a)]. Since the theoretical studies of the OSMP require the treatment of challenging multi-orbital models most of the investigations thus far were performed with approximations such as the the slave-particle mean field method [6][7][8][9] or dynamical mean-field theory [10][11][12]. Here, we present unambiguous numerical evidence of the OSMP within low-dimensional multi-orbital Hubbard models, unveiling a variety of new phases.The magnetic ordering associated with the OSMP could be significantly different from that observed in cuprates. The latter are described by single-band Hamiltonians and the parent compounds order in a staggered antiferromagnetic fashion. However, recent inelastic neutron scattering (INS) experiments [13] on quasi-1D ironbased materials of the 123 family (AFe 2 X 3 ; A alkali metals, X=Se,S chalcogenides) unveiled exotic π/2-block magnetic states where spins form antiferromagnetically (AFM) coupled ferromagnetic (FM) islands, in a ↑↑↓↓pattern [ Fig. 1(b)]. Similar patterns were also reported in two dimensions with iron vacancies, such as in Rb 0.89 Fe 1.58 Se 2 [14] and K 0.8 Fe 1.6 Se 2 [8,[15][16][17]. For the aforementioned compounds the OSMP state is believed to be relevant [8,13,[18][19][20].Recent theoretical investigations [21,22] showed that a multi-orbital Hubbard model in the OSMP state properly describes the INS spin spectra of π/2-block state of powder BaFe 2 Se 3 [13]. However, the origin of block magnetism and its relation to the OSMP is an intriguing and generic question that has been barely explored. We show that the block-OSMP magnetism can develop in various shapes and sizes depending on the electrondoping, far beyond the previously reported π/2-pattern. Moreover, here we develop effective Hamiltonians for the OSMP which allows for an intuitive understanding of the origin of block magnetism. Our simplified, yet accurate, model...

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Two‐band ferromagnetic Kondo lattice model on a ladder with quantum S = 3/2 core spins

Cited by 4 publications

References 9 publications

Doping dependence of spin and orbital correlations in layered manganites

Doping dependence of spin and orbital correlations in layered manganites

Orbital ordering and unfrustrated(π,0)magnetism from degenerate double exchange in the iron pnictides

Novel Magnetic Block States in Low-Dimensional Iron-Based Superconductors

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