25 research outputs found
Magnetic phase transitions and unusual antiferromagnetic states in the Hubbard model
Ground state magnetic phase diagrams of the square and simple cubic lattices
are investigated for the narrow band Hubbard model within the slave-boson
approach by Kotliar and Ruckenstein. The transitions between saturated
(half-metallic) and non-saturated ferromagnetic phases as well as similar
transition in antiferromagnetic (AFM) state are considered in the
three-dimensional case. Two types of saturated antiferromagnetic state with
different concentration dependences of sublattice magnetization are found in
the two-dimensional case in the vicinity of half-filling: the state with a gap
between AFM subbands and AFM state with large electron mass. The latter state
is hidden by the phase separation in the finite-U case.Comment: Invited Report on the Moscow International Symposium on Magnetism
MISM-2017, 7 pages, J. Magn. Magn. Mater., in pres
Magnetic States, Correlation Effects and Metal-Insulator Transition in FCC Lattice
The ground-state magnetic phase diagram (including collinear and spiral
states) of the single-band Hubbard model for the face-centered cubic lattice
and related metal-insulator transition (MIT) are investigated within the
slave-boson approach by Kotliar and Ruckenstein. The correlation induced
electronic spectrum narrowing and a comparison with a generalized Hartree-Fock
approximation allow one to estimate the strength of correlation effects. This,
as well as the MIT scenario, depends dramatically on the ratio of the
next-nearest and nearest electron hopping integrals . In contrast with
metallic state, possessing strong band narrowing, insulator one is only weakly
correlated. The magnetic (Slater) scenario of MIT is found to be superior over
the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first
order transition for most . The insulator state is type-II or type-III
antiferromagnet, and the metallic state is spin-spiral, collinear
antiferromagnet or paramagnet depending on . The picture of magnetic
ordering is compared with that in the standard localized-electron (Heisenberg)
model.Comment: 10 pages, final version, Journal of Physics: Condensed Matte
Correlation Effects and Non-Collinear Magnetism in the Doped Hubbard Model
The ground--state magnetic phase diagram is investigated for the two-- and
three--dimensional -- Hubbard model. We take into account commensurate
ferro--, antiferromagnetic, and incommensurate (spiral) magnetic phases, as
well as phase separation into magnetic phases of different types, which was
often missed in previous investigations. We trace the influence of correlation
effects on the stability of both spiral and collinear magnetic order by
comparing the results of employing both the generalized non-correlated
mean--field (Hartree--Fock) approximation and generalized slave boson approach
by Kotliar and Ruckenstein with correlation effects included. We found that the
spiral states and especially ferromagnetism are generally strongly suppressed
up to non-realistic large Hubbard , if the correlation effects are taken
into account. The electronic phase separation plays an important role in the
formation of magnetic states and corresponding regions are wide, especially in
the vicinity of half--filling. The details of magnetic ordering for different
cubic lattices are discussed.Comment: Invited Report on the Moscow International Symposium on Magnetism
MISM-2014, 6 pages, final versio
Incommensurate magnetic order and phase separation in the two-dimensional Hubbard model with nearest and next-nearest neighbor hopping
We consider the ground state magnetic phase diagram of the two-dimensional
Hubbard model with nearest and next-nearest neighbor hopping in terms of
electronic density and interaction. We treat commensurate ferro- and
antiferromagnetic, as well as incommensurate (spiral) magnetic phases. The
first-order magnetic transitions with changing chemical potential, resulting in
a phase separation (PS) in terms of density, are found between ferromagnetic,
antiferromagnetic and spiral magnetic phases. We argue that the account of PS
has a dramatic influence on the phase diagram in the vicinity of half-filling.
The results imply possible interpretation of the unusual behavior of magnetic
properties of one-layer cuprates in terms of PS between collinear and spiral
magnetic phases. The relation of the results obtained to the magnetic
properties of ruthenates is also discussed.Comment: 19 pages, 7 figure
Effect of electron correlations on the formation of spiral magnetic states in the two-dimensional t-t′ Hubbard model
The formation of the spiral magnetic order in the ground state of the Hubbard model for a square lattice has been studied within the slave-boson method in a wide range of the parameters of the carrier density and Coulomb interaction. Next-nearest-neighbor electron hopping, as well as the magnetic phase separation, has been taken into account. It has been shown that the electron correlations lead to the suppression of the ferromagnetic and spiral phases in comparison with the Hartree-Fock approximation. The application of the results to the explanation of the experimental data, in particular, to the description of the magnetic state of the high-temperature superconductors of the cuprate-based systems has been discussed. © 2013 Pleiades Publishing, Inc