Absence of actual plateaus in zero-temperature magnetization curves of quantum spin clusters and chains

Abstract

We examine the general features of the non-commutativity of the magnetization operator and Hamiltonian for the small quantum spin clusters. The source of this non-commutativity can be a difference in the Landé g-factors for different spins in the cluster, XY-anisotropy in the exchange interaction and the presence of the Dzyaloshinskii-Moriya term in the direction different from the direction of the magnetic field. As a result, zero-temperature magnetization curves for small spin clusters mimic those for the macroscopic systems with the band(s) of magnetic excitations, i.e. for the given eigenstate of the spin cluster the corresponding magnetic moment can be an explicit function of the external magnetic field yielding the non-constant (non-plateau) form of the magnetization curve within the given eigenstate. In addition, the XY-anisotropy makes the saturated magnetization (the eigenstate when all spins in cluster are aligned along the magnetic field) inaccessible for finite magnetic field magnitude (asymptotical saturation). We demonstrate all these features on three examples: spin-1/2 dimer, mixed spin-(1/2,1) dimer, spin-1/2 ring trimer. We consider also the simplest Ising-Heisenberg chain, the Ising-XYZ diamond chain with four different g-factors. In the chain model the magnetization curve has a more complicated and non trivial structure which that for clusters.

Magnetization plateau as a result of the uniform and gradual electron doping in a coupled spin-electron double-tetrahedral chain

“…It was confirmed that this striking phenomenon is not in conflict with the OYA criterion (1) and may be a direct result of different Landé g-factors of magnetic particles [39][40][41][42][43], quenched disorder [44][45][46] or doping by itinerant particles [47][48][49][50][51]. In the last case, a change of the particle concentration may allow one to tune the value and position of the magnetization plateau in a controlled way.…”

Breakdown of intermediate one-half magnetization plateau of spin-1/2 Ising-Heisenberg and Heisenberg branched chains at triple and Kosterlitz-Thouless critical points

“…The low-temperature asymptotes (k B T /J = 0.01) of the concurrence can be understood from the ground-state phase diagram [ Fig. 3(a)] and the formulas (24), which imply existence of three different ground states |I , |II and |III depending on a relative size of the magnetic field. It follows from Fig.…”

Non-conserved magnetization operator and ‘fire-and-ice’ ground states in the Ising-Heisenberg diamond chain

“…As a result the magnetic moment is not a good quantum number and the magnitude of magnetization could vary within the same eigenstate under the change of the magnetic field. Thus, the deviations form the horizoantal line is occur in the magnetization curve (quasi-plateaus) [4,13,20,50]. However, the deviation of the magnetization curve parts from the horizontal line due to difference in g-factors of the quantum spin from the three-spin linear cluster in the [(CuL) 2 DyMo(CN) 8 ] · 2CH 3 CN · H 2 O SCM is merely visible by eyes, as the difference of the values of g-factors is rather small [13].…”