Related papers: Coupling of replicate order-parameters in incommen…
Starting from the irreducible representations of the group of the wave vector we construct the spin wave functions consistent with inversion symmetry, neglected in the usual representation analysis. We obtain the relation between the basis…
The magnetic phase transitions reported below 230 K in cupric oxide are analyzed theoretically at the macroscopic and microscopic levels. The incommensurate multiferroic and lock-in commensurate phases are shown to realize an inverted…
An effective model is developed to explain the phase diagram and the mechanism of magnetoelectric coupling in multiferroics, $RMn_2O_5$. We show that the nature of magnetoelectric coupling in $RMn_2O_5$ is a coupling between two Ising-type…
We study the existence of incommensurate phases in the phase diagram of the two orbital double exchange model coupled with Jahn-Teller phonons and with superexchange interactions. In agreement with experimental results, we find that undoped…
We review the phenomenology of coupled magnetic and electric order parameters for systems in which ferroelectric and incommensurate magnetic order occur simultaneously. We discuss the role that such materials might play in fabricating novel…
Within the framework of the $s$-$d(f)$ exchange model in the mean-field approximation for square, simple cubic, body-centered and face-centered cubic lattices, the formation of a ferromagnetic, spiral, and commensurate antiferromagnetic…
The study of improper phases in the context of multiferroic materials has a long history, but superconductivity has yet to be connected to the network of ferroic orders. In this work, we highlight an overlooked mechanism that couples…
We present the results of a theoretical analysis of two-dimensionally modulated incommensurate phases in crystals and define the space distribution of magnetization and polarization vector in the incommensurate phase and demonstrate that…
The double exchange model describing interactions of itinerant electrons with localized spins is usually used to explain ferromagnetism in metals. We show that for a variety of crystal lattices of different dimensionalities and for a wide…
We study planar ferromagnetic spin-chain systems with weak antiferromagnetic inter-chain interaction and dipole-dipole interaction. The ground state depends sensitively on the relative strengths of antiferromagnetic exchange and dipole…
The consequences of the opening of a phason gap in incommensurate systems are studied on a simple model, the discrete frustrated $\phi^4$-model. Analytical considerations and numerical results show that there is a very weak phase transition…
The generic magnetic phase diagram of multiferroic RMn$_2$O$_5$ (with R=Y, Ho, Tb, Er, Tm), which allows different sequences of ordered magnetic structures for different R's and different control parameters, is described using order…
Composite multiferroics are materials exhibiting the interplay of ferroelectricity, magnetism, and strong electron correlations. Typical example --- magnetic nano grains embedded in a ferroelectric matrix. Coupling of ferroelectric and…
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…
The formalism of composite and intertwined orders has been remarkably successful in discussing the complex phase diagrams of strongly correlated materials and high-$T_c$ superconductors. Here, we propose that composite orders are also…
The theory of a sequence of phase transitions of high-symmetry-incommensurate-commensurate phase controlled by competing order parameters is investigated. The temperature dependence of dielectric constant is derived. The comparison of the…
Neutron scattering studies of single-crystal LiNiPO$_4$ reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short- and long-range incommensurate phases are intermediate between the high temperature…
The underdoped phase diagram of the iron-based superconductors exemplifies the complexity common to many correlated materials. Indeed, multiple ordered states that break different symmetries but display comparable transition temperatures…
Inversion-asymmetric antiferromagnets (AFMs) with odd-parity spin-polarization pattern have been proposed as a new venue for spintronics. These AFMs require commensurate ordering to ensure an effective time-reversal symmetry, which…
We study Fermi liquid instabilities in spin-orbit-coupled metals with inversion symmetry. By introducing a canonical basis for the doubly degenerate Bloch bands in momentum space, we derive the general form of interaction functions. A…