A. Mailhot

Theory of coexisting transverse-spin freezing and long-ranged antiferromagnetic order in lightly doped La2-xSrxCuO4.

We provide an explanation of the spin-freezing transition recently observed by Chou et al. [Phys. Rev. Lett. 71, 2323 (1993)] in

TRICRITICAL BEHAVIOR OF THE FRUSTRATED XY ANTIFERROMAGNET

{\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}

Comment on "Critical properties of highly frustrated pyrochlore antiferromagnets"

{\mathrm{Sr}}_{\mathit{x}}

Magnetic-field-induced first-order transition in the frustrated XY model on a stacked triangular lattice

{\mathrm{CuO}}_{4}

Histogram Monte Carlo study of multicritical behavior in the hexagonal easy-axis Heisenberg antiferromagnet

for x\ensuremath{\lesssim}0.02. We propose that topological excitations of the two-dimensional Heisenberg quantum antiferromagnet having noncoplanar transverse components have a pair-interaction energy that qualitatively and quantitatively agrees with the observed values of spin-freezing temperature as a function of doping.

Finite-size scaling of the frustrated Heisenberg model on a hexagonal lattice.

Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding their criticality.

Spin texture of weakly doped CuO2 planes

Critical properties of the Ising model on a stacked triangular lattice, with antiferromagnetic first and second-neighbor in-plane interactions, are studied by extensive histogram Monte Carlo simulations. The results, in conjunction with the recently determined phase diagram, strongly suggest that the transition from the period-3 ordered state to the paramagnetic phase remains in the xy universality class. This conclusion is in contrast with a previous suggestion of mean-field tricritical behavior.

Effect of biquadratic exchange on the axial Heisenberg model: Application to the magnetic phase transitions in UNi2Si2.

We argue that the analysis of Reimers et al. [Phys. Rev. B 45, 7295 (1992)] of their Monte Carlo data on the Heisenberg pyrochlore antiferromagnet, which suggests a new universality class, is not conclusive. By reanalysis of their data, we demonstrate asymptotic volume dependence in some thermodynamic quantities, which suggests the possibility that the transition may be first order