Structural distortions of frustrated quantum spin lattices in high magnetic fields

Abstract

We study the stability of some strongly frustrated antiferromagnetic spin lattices in high magnetic fields against lattice distortions. In particular, we consider a spin-s anisotropic Heisenberg antiferromagnet on the square-kagomé and kagomé lattices. The independent localized magnons embedded in a ferromagnetic environment, which are the ground state at the saturation field, imply lattice instabilities for appropriate lattice distortions fitting to the structure of the localized magnons. We discuss in detail the scenario of this spin-Peierls instability in high magnetic fields which essentially depends on the values of the exchange interaction anisotropy ∆ and spin s. PACS number(s): 75.10. Jm, 75.45.+j

Structural instability of two- and three-dimensional pyrochlore spin lattices in high magnetic fields

“…In contrast to the above mentioned zero-field studies on the effects of magnetoelastic couplings in the pyrochlore lattice, high magnetic fields are essential in our consideration since only in a high magnetic field the independent localized magnons may become relevant for the ground-state properties of the considered systems. The present study extends our earlier results referring to the square-kagomé and kagomé lattices [24,25].…”

“…Since we know e.g. from the triangular lattice [32,33] and the square-kagomé and kagomé lattices [24,25], that the plateau width depends on the spin quantum number s we have also calculated the plateau width ∆h for the spin-s isotropic Heisenberg system on the 2D pyrochlore lattice with N = 24 sites for the values of s = 1/2, 1, 3/2, 2, 5/2.…”

Universal properties of highly frustrated quantum magnets in strong magnetic fields

“…Recently, it has been recognized that many geometrically frustrated lattices (including the kagomé lattice, the checkerboard lattice and the pyrochlore lattice) admit a simple class of exact eigenstates christened localized magnons [7,8]. These states become the ground states in strong magnetic fields and they are relevant for many physical properties of a wide class of highly frustrated quantum antiferromagnets in the low-temperature strong-field regime [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. In particular, the localizedmagnon states are responsible for magnetization jumps which the ground-state magnetization curve exhibits at the saturation field [7,8,10,15,16,17,23], may lead to a high-field spin-Peierls lattice instability [11,18,19], and imply a residual ground-state entropy at the saturation field [12,13,14].…”

“…These states become the ground states in strong magnetic fields and they are relevant for many physical properties of a wide class of highly frustrated quantum antiferromagnets in the low-temperature strong-field regime [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. In particular, the localizedmagnon states are responsible for magnetization jumps which the ground-state magnetization curve exhibits at the saturation field [7,8,10,15,16,17,23], may lead to a high-field spin-Peierls lattice instability [11,18,19], and imply a residual ground-state entropy at the saturation field [12,13,14]. Moreover, these states dominate the low-temperature thermodynamics in the vicinity of the saturation field [12,13,14,20,22,24] and may lead to an order-disorder phase transition of purely geometrical origin [13,22,24].…”

New Phase of MnSb2O6 Prepared by Ion Exchange: Structural, Magnetic, and Thermodynamic Properties

“…Layered oxides of transition metals have attracted much attention since they provide a playground for studying strong electronic correlation effects. − In a low-dimensional magnetic sublattice made up of magnetic-ion triangles, geometrical spin frustration arises when the spin exchanges between adjacent magnetic ions are antiferromagnetic (AFM). A large number of fascinating phenomena emerge from such geometrically spin frustrated systems; they include re-entrant phase transitions, , magnetization plateaus in the magnetization process, − localized magnons in close vicinity of the saturation field, ,, magnetic-field-induced spin-Peierls instability, − and enhanced magnetocaloric effects. − Competing interactions in spin-frustrated systems often result in an unusual critical behavior near the transitions − toward novel phases such as spin ice or quantum spin liquid ground states. ,,, Low-dimensional spin-frustrated systems frequently adopt noncollinear incommensurate spin arrangements to reduce the extent of their spin frustration. Such spin states may remove the inversion symmetry and hence induce finite ferroelectric polarization, , as found for the multiferroics TbMnO 3 , and CoCr 2 O 4 with cycloidal magnetic structures as well as for the delafossite family AMO 2 (A = Cu, Ag; M = Fe, Cr) − with helical magnetic order.…”