Spin excitations and quantum criticality in the quasi-one-dimensional Ising-like ferromagnetCoCl2·2D2Oin a transverse field

Abstract

. (2017). Spin excitations and quantum criticality in the quasi-one-dimensional Ising-like ferromagnet CoCl2·2D2O in a transverse field. Physical Review B, 96(17), [174424 ] We present experimental evidence for a quantum phase transition in the easy-axis S = 3/2 anisotropic quasione-dimensional ferromagnet CoCl 2 · 2D 2 O in a transverse field. Elastic neutron scattering shows that the magnetic order parameter vanishes at a transverse critical field μ 0 H c = 16.05(4) T, while inelastic neutron scattering shows that the gap in the magnetic excitation spectrum vanishes at the same field value, and reopens for H > H c . The field dependence of the order parameter and the gap are well described by critical exponents β = 0.45 ± 0.09 and zν close to 1/2, implying that the quantum phase transition in CoCl 2 · 2D 2 O differs significantly from the textbook version of a S = 1/2 Ising chain in a transverse field. We attribute the difference to weak but finite three-dimensionality of the magnetic interactions.

Comprehensive cluster-theory analysis of the magnetic structures and excitations inCoCl2·2H2O

“…CoCl 2 •2H 2 O has previously been considered to be a fair representation for a one-dimensional Ising system, however, as shown by Larsen et al [1], the quantum phase transition of the system in a transverse field is characterized by critical exponents equal to those derived for a three-dimensional, meanfield system. Here, we are going to present a comprehensive and realistic model for the magnetic properties of CoCl 2 •2H 2 O.…”

“…The most recent and most realistic analysis is the one presented by Shinkevich and Syljåsen [2]. Prior to their work, the possibility of observing Bloch oscillations in anisotropic spin- 1 2 chains was discussed by Kyriakidis and Loss [3]. Shinkevich and Syljåsen argue that the longitudinal field deriving from the interactions between spins on neighboring chains invalidates the single domain-wall picture of Kyriakidis and Loss by creating bound pairs of domain walls [2].…”

“…Of major importance for the development of the model is our investigation of the excited doublet by a neutron time-of-flight experiment. We also present measurements of the spin waves, where the moments are rotated away from the easy axis by applying a field of up to 170 kOe, with most focus on the soft mode behavior shown by the spin waves close to the quantum-phase transition, where the antiferromagnetic ordered is destroyed [1,6].…”

“…There are two Co sites with identical surroundings per monoclinic unit cell, at (0,0,0) and ( 1 2 , 1 2 ,0). More details and a figure illustrating the crystal structure may be found in our preceding publication [1]. A quite complete model for the magnetic properties of the bulk system has been established by Narath [8,9].…”

“…(1), B 0 4 , has cubic symmetry and accounts for the major bulk effects of the crystal field without making any distinction between an x, y, or z direction. Defining the main axes of the anisotropy tensor so that z is the easiest axis, i.e., the b axis, and y the hardest one [1], it may, effectively, be accounted for by the two quadrupolar terms in Eq. (1) with B 0 2 < 0 and B 2 2 < 0.…”