arXiv subjects

M. L. Plumer

Publications and source records attributed to M. L. Plumer.

34 records · Page 2Linked to original sources

arXiv2007

Field induced tricritical behavior in the S=1/2 quasi one-dimensional frustrated Ising antiferromagnet

The results of extensive histogram cluster heat-bath Monte Carlo simulations on the critical behavior of the quasi-one dimensional Ising antiferromagnet on a stacked triangular lattice are presented. A small applied field is shown to induce a crossover from XY universality to mean-field tricritical behavior. Experimental estimates of critical exponents suggest that these two types of phase transitions are observed in S=1 CsNiCl$_3$ and $S=1/2$ CsCoBr$_3$, respectively. The present results demonstrate that this difference can be explained by an unusual staggered magnetic field arising from quantum exchange mixing previously proposed to account for spin excitations in $S=1/2$ quasi-one-dimensional Ising antiferromagnets.

cond-mat.str-el↗

arXiv2007

Surface spin dynamics of antiferromagnetically coupled frustrated triangular films

Results are presented for spin-wave dispersions in geometrically frustrated stacked triangular antiferromagnets with a thin film or semi-infinite geometry having either zero, easy-plane, or easy-axis anisotropy. Surface effects on the equilibrium spin configurations and excitation spectrum are investigated for the case of antiferromagnetically coupled films, serving to extend previous results on ferromagnetically coupled layers [E. Meloche et al., Phys. Rev. B 74, 094424 (2006)]. An operator equation of motion formalism is applied to systems which are quasi-one and quasi-two dimensional in character. In contrast to the case of ferromagnetically coupled films the new results show surface modes that are well separated in frequency from bulk excitations. Magnetic excitations in thin films with an even or an odd number of layers show qualitatively different behavior. These results are relevant for a wide variety of stacked triangular antiferromagnetics materials.

cond-mat.mtrl-sci↗

arXiv2006

First order phase transition in the frustrated triangular antiferromagnet CsNiCl3

By means of high-resolution ultrasonic velocity measurements, as a function of temperature and magnetic field, the nature of the different low temperatures magnetic phase transitions observed for the quasi-one-dimensional compound CsNiCl3 is established. Special attention has been devoted to the field-induced 120 degree phase transition above the multicritical point in the H-T phase diagram where the elastic constant C44 reveals a step-like variation and hysteresis effects. These results represent the first experimental evidence that the 120 degree phase transition is weakly first order and contradict the popular notion of new universality classes for chiral systems.

cond-mat.str-el↗

arXiv1996

Weak first-order transition in the quasi-one-dimensional frustrated XY antiferromagnet

The results of finite-size scaling analysis of histogram Monte-Carlo simulations on the stacked triangular XY antiferromagnet with anisotropic near-neighbor exchange interactions are presented. With ferromagnetic interplane coupling ten times stronger than the antiferromagnetic intraplane interaction ($J_\| / J_\bot = -10$), a weak first-order transition is revealed. These results represents the first simulational corroboration of a wide variety of renormalization-group calculations made over the past twenty years. As such, they shed light on recent controversy regarding the critical behavior in this and similar frustrated systems and have particular relevance to recently reported data on $CsCuCl_3$.

cond-mat↗

arXiv1995

Thermal phase diagram of a model Hamiltonian for columnar phases of liquid crystals

We present the phase diagram and critical properties of a coupled $XY$-Ising model on a triangular lattice using the mean-field approximation, the Migdal-Kadanoff scheme of renormalization group and Monte-Carlo simulations. The topology of the phase diagram is similar for the three techniques, with the appearance of a phase with $XY$ order and Ising disorder. The results suggest a line of transitions belonging to the 2D-Ising universality class in contrast with previous data indicating a new universality class. This model is relevant to the columnar phases of discotic liquid crystals [such as hexa(hexylthio)triphenylene (HHTT)] in the limit of weak intercolumn coupling.

cond-mat↗

arXiv1995

Phenomenological model of elastic distortions near the spin-Peierls transition in $CuGeO_3$

A phenomenological model of the Landau type forms the basis for a study of elastic distortions near the spin-Peierls transition $T_c$ in $CuGeO_3$. The atomic displacements proposed by Hirota {\it et al.} [Phys. Rev. Lett. {\bf 73}, 736 (1994)] are accounted for by the model which includes linear coupling between $Cu$ and $O$ distortions. $Cu$ displacements are seen to be responsible for anomalies in the elastic properties {\it at} $T_c$, whereas incipient $O$ distortions give rise to temperature dependence below $T_c$. A discussion of possible critical behavior is also made.

cond-mat↗

arXiv1994

Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular Ising Antiferromagnet

Histogram Monte-Carlo simulation results are presented for the magnetic-field -- temperature phase diagram of the Ising model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions. Finite-size scaling results for this frustrated system at three points along the paramagnetic transition boundary are presented which strongly suggest a line of triciritcal points at low field and a first-order transition line at higher fields. These results are compared with the corresponding phase diagrams from conventional mean-field theory as well as from the Monte Carlo mean-field calculations of Netz and Berker [Phys. Rev. Lett. {\bf 66}, 377 (1991)].

cond-mat↗

arXiv1994

Mean-field transfer-matrix study of the magnetic phase diagram of CsNiF$_{\bf 3}$

A method for treating ferromagnetic chains coupled with antiferromagnetic interactions on an hexagonal lattice is presented in this paper. The solution of the $1D$ part of the problem is obtained by classical transfer-matrix while the coupling between the chains is processed by mean-field theory. This method is applied with success to the phase diagram and angular dependence of the critical field of CsNiF$_3$. Results concerning the general influence of single-ion anisotropy on the magnetic ordering of such systems are also presented.

cond-mat↗

arXiv1994

XY universality of the stacked triangular Ising antiferromagnet

Histogram analysis of Monte-Carlo simulation results of the Ising antiferromagnet on a stacked triangular lattice are reported. Finite-size scaling estimates for critical exponents suggest $XY$ universality. This result supports earlier predictions based on symmetry arguments and is in contrast with a recent suggestion of a new universality class by Bunker {\it et al.} [Phys. Rev. B {\bf 48}, 15861 (1993)].

cond-mat↗

arXiv1994

Mean-field phase diagrams of $AT_2X_2$ compounds

Magnetic-field -- temperature phase diagrams of the axial next-nearest-neighbor Ising model are calculated within the framework of a Landau-type expansion of the free energy derived from molecular-field theory. Good qualitative agreement is found with recently reported results on body-centered-tetragonal $UPd_2Si_2$. This work is expected to also be relevant for related compounds.

cond-mat↗

arXiv1994

Tricritical behavior of the frustrated XY antiferromagnet

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.

cond-mat↗

arXiv1993

Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular XY Antiferromagnet: A Finite-Size Scaling Study

Histogram Monte-Carlo simulation results are presented for the magnetic-field -- temperature phase diagram of the XY model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions. Finite-size scaling results at the various transition boundaries are consistent with expectations based on symmetry arguments. Although a molecular-field treatment of the Hamiltonian fails to reproduce the correct structure for the phase diagram, it is demonstrated that a phenomenological Landau-type free-energy model contains all the esstential features. These results serve to complement and extend our earlier work [Phys. Rev. B {\bf 48}, 3840 (1993)].

cond-mat↗

arXiv1993

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

The results of a detailed histogram Monte-Carlo study of critical-fluctuation effects on the magnetic-field temperature phase diagram associated with the hexagonal Heisenberg antiferromagnet with weak axial anisotropy are reported. The multiphase point where three lines of continuous transitions merge at the spin-flop boundary exhibits a structure consistent with scaling theory but without the usual umbilicus as found in the case of a bicritical point.

cond-mat↗

arXiv1993

Magnetic-Field Induced First-Order Transition in the Frustrated XY Model on a Stacked Triangular Lattice

The results of extensive Monte Carlo simulations of magnetic-field induced transitions in the xy model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions are discussed. A low-field transition from the paramagnetic to a 3-state (Potts) phase is found to be very weakly first order with behavior suggesting tricriticality at zero field. In addition to clarifying some long-standing ambiguity concerning the nature of this Potts-like transition, the present work also serves to further our understanding of the critical behavior at $T_N$, about which there has been much controversy.

cond-mat↗

arXiv1993

Histogram Monte Carlo study of next-nearest-neighbor Ising antiferromagnet on a stacked triangular lattice

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.

cond-mat↗

arXiv1993

Comment on "Critical properties of highly frustrated pyrochlore antiferromagnets"

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

cond-mat↗