Complex critical magnetic behaviour in three dimensions (original) (raw)

Critical Phenomena Study of 3D Heisenberg Magnet

arXiv (Cornell University), 2023

Recent discovery of several van der waals magnetic material and moire magnet introduce to us an extremely challenging and revolutionary era of 2D magnetism and correlated phenomena for low dimensional material[

Critical behavior of low dimensional magnetic systems

Journal of Magnetism and Magnetic Materials, 2017

In this study, critical behavior of low dimensional magnetic systems as cyano-bridged Tb(III)-Cr(III) bimetallic assembly was investigated with the mixed spin 3-spin 3/2 Ising model. The mixed spin Ising model is simulated with Cellular Automaton cooling and heating algorithms on one-dimensional lattices in periodic boundary conditions. The Ising model Hamiltonian includes only antiferromagnetic nearest-neighbor interaction (J > 0). The mixed spin system behaves like the isolated one-dimensional chain for zero magnetic field (h = H J = 0). In the presence of the magnetic field, the magnetization is calculated using zero-field cooling (ZF C) and field cooling (F C) processes. The one-dimensional Ising model results are compatible with the cyano-bridged Tb(III)-Cr(III) bimetallic quasi-one dimensional assembly ((Tb(H 2 O) 2 (DMF) 4 Cr(CN) 6 •H2O(DMF= dimethylformamide)) results.

Magnetic Systems at Criticality: Different Signatures of Scaling

Acta Physica Polonica A, 2013

Dierent aspects of critical behaviour of magnetic materials are presented and discussed. The scaling ideas are shown to arise in the context of purely magnetic properties as well as in that of thermal properties as demonstrated by magnetocaloric eect or combined scaling of excess entropy and order parameter. Two non-standard approaches to scaling phenomena are described. The presented concepts are exemplied by experimental data gathered on four representatives of molecular magnets.

Magnetic-field induced quantum phase transition and critical behavior in a gapped spin system

Journal of Magnetism and Magnetic Materials, 2007

Magnetization measurements were performed on TlCuCl 3 with gapped ground state. The critical density and the magnetic phase diagram were obtained. The interacting constant was obtained as U=k B ¼ 313 K. The experimental phase boundary for To5 K agrees perfectly with the magnon BEC theory based on the Hartree-Fock approximation with realistic dispersion relations and U=k B ¼ 320 K. The exponent f obtained with all the data points for To5 K is f ¼ 1:99, which is somewhat larger than theoretical exponent f BEC ¼ 3 2. However, it was found that the exponent converges at f BEC ¼ 3 2 with decreasing fitting window.

Critical phenomena near the final ordering phase transition point in double magnetic systems

Physics Letters A, 1993

Magnetic crystals containing two subsystems ofdifferent types ofmagnetic ions are considered. Itis assumed that the subsystem of the first type of ions isalready ordered ata relatively high temperature, while the ordering temperature of the second subsystem T 02 is much lower. We carry out the analysis of the critical behavior of such double magnetic systems in the vicinity of the temperature T~2. We find quite different critical behavior for different symmetries of the subsystem coupling. 450 0375-9601 /93/S 06.00

Dimensional crossover in quantum critical metallic magnets

Physical Review B, 2008

Nearly magnetic metals often have layered lattice structures, consisting of coupled planes. In such a situation, physical properties will display, upon decreasing temperature or energy, a dimensional crossover from two-dimensional (2d) to three-dimensional (3d) behavior, which is particularly interesting near quantum criticality. Here we study this crossover in thermodynamics using a suitably generalized Landau-Ginzburg-Wilson approach to the critical behavior, combined with renormalization group techniques. We focus on two experimentally relevant cases: the crossover from a 2d to a 3d antiferromagnet, and the crossover from a 2d ferromagnet to a 3d antiferromagnet. As naive scaling does not apply at and above the upper critical dimension, two crossover scales arise which can be associated with separate dimensional crossovers of classical and quantum fluctuations, respectively. In particular, we find an intermediate regime with novel power laws where the quantum fluctuations still have a 2d and the classical fluctuations already have a 3d character. For the ferromagnet-to-antiferromagnet crossover, the mismatch of the dynamical exponents between the 2d and 3d regimes leads to an even richer crossover structure, with an interesting 2d non-critical regime sandwiched between two critical regimes. For all cases, we find that thermal expansion and compressibility are particularly sensitive probes of the dimensional crossover. Finally, we relate our results to experiments on the quantum critical heavy-fermion metals CeCu6−xAux, YbRh2Si2, and CeCoIn5.

Effective and asymptotic criticality of structurally disordered magnets

arXiv (Cornell University), 2022

Changes in magnetic critical behaviour of quenched structurally-disordered magnets are usually exemplified in experiments and in MC simulations by diluted systems consisting of magnetic and non-magnetic components. By our study we aim to show, that similar effects can be observed not only for diluted magnets with non-magnetic impurities, but may be implemented, e.g., by presence of two (and more) chemically different magnetic components as well. To this end, we consider a model of the structurally-disordered quenched magnet where all lattice sites are occupied by Ising-like spins of different length L. In such random spin length Ising model the length L of each spin is a random variable governed by the distribution function p(L). We show that this model belongs to the universality class of the site-diluted Ising model. This proves that both models are described by the same values of asymptotic critical exponents. However, their effective critical behaviour differs. As a case study we consider a quenched mixture of two different magnets, with values of elementary magnetic moments L 1 = 1 and L 2 = s, and of concentration c and 1 − c, correspondingly. We apply field-theoretical renormalization group approach to analyze the renormalization group flow for different initial conditions, triggered by s and c, and to calculate effective critical exponents further away from the fixed points of the renormalization group transformation. We show how the effective exponents are governed by difference in properties of the magnetic components.

Critical hysteresis for n-component magnets

Arxiv preprint cond-mat/9807188

Earlier work on dynamical critical phenomena in the context of magnetic hysteresis for uniaxial (scalar) spins, is extended to the case of a multicomponent (vector) field. From symmetry arguments and a perturbative ...