Multicritical points in the magnetic phase diagrams of axial and planar antiferromagnets

Magnetoelastic coupling and critical behavior of some strongly correlated magnetic systems

The strongly correlated magnetic systems are attracting continuous attention in current condensed matter research due to their very compelling physics and promising technological applications. Being a host to charge, spin, and lattice degrees of freedom, such materials exhibit a variety of phases, and investigation of their physical behavior near such a phase transition bears an immense possibility. This review summarizes the recent progress in elucidating the role of magnetoelastic coupling on the critical behavior of some technologically important class of strongly correlated magnetic systems such as perovskite magnetites, uranium ferromagnetic superconductors, and multiferroic hexagonal manganites. It begins with encapsulation of various experimental findings and then proceeds toward describing how such experiments motivate theories within the Ginzburg-Landau phenomenological picture in order to capture the physics near a magnetic phase transition of such systems. The theoretical results that are obtained by implementing Wilson's renormalization-group to nonlocal Ginzburg-Landau model Hamiltonians are also highlighted. A list of possible experimental realizations of the coupled model Hamiltonians elucidates the importance of spin-lattice coupling near a critical point of strongly correlated magnetic systems.

Successive spin orderings of tungstate-bridged Li2Ni(WO4)2 of spin 1

Magnetic, thermodynamic, and dielectric properties of Li2Ni(WO4)2 of S  =  1 system have been studied using magnetic susceptibility, specific heat, and dielectric constant measurements. The magnetic orderings can be identified in three stages, including a short range magnetic ordering indicated by the rounded χ(T) peak with maximum at  ∼20 K, and signatures of two successful antiferromagnetic long range orderings near T(N1) ~ 18 K and T(N2) ~ 13 K revealed by the d(χ(T)) /d(T) peaks. The successive long range magnetic orderings are related to the quasi triangular symmetry breaking in the ac- and bc-planes and to the change of the dielectric constant, suggesting the presence of spin-phonon coupling. The specific heat and magnetic entropy analysis for Li2Ni(WO4)2 shows the existence of a significant low dimensional magnetic correlations at high temperature and confirms the long range three-dimensional (3D) behavior of magnetic orderings below T(N1) and T(N2).

Phase diagram of pb(Zr,Ti)O3 solid solutions from first principles

A first-principles-derived scheme that incorporates ferroelectric and antiferrodistortive degrees of freedom is developed to study finite-temperature properties of Pb(Zr1-xTix)O3 solid solution near its morphotropic phase boundary. The use of this numerical technique (i) resolves controversies about the monoclinic ground state for some Ti compositions, (ii) leads to the discovery of an overlooked phase, and (iii) yields three multiphase points that are each associated with four phases. Additional neutron diffraction measurements strongly support some of these predictions.