Magnetic properties of quantum ferrimagnetic spin chains

Abstract

Magnetic susceptibilities of spin-(S, s) ferrimagnetic Heisenberg chains are numerically investigated. It is argued how the ferromagnetic and antiferromagnetic features of quantum ferrimagnets are exhibited as functions of (S, s). Spin-(S, s) ferrimagnetic chains behave like combinations of spin-(S − s) ferromagnetic and spin-(2s) antiferromagnetic chains provided S = 2s.PACS numbers: 75.10. Jm, 75.40.Mg, 65.50.+m Quantum behavior of mixed-spin systems is one of the hot topics and a recent progress in the theoretical understanding of it deserves special mention. In contrast with pioneering calculations [1] in the 1980s, the current vigorous argument might more or less be motivated by the Haldane conjecture [2] in that it covers not only ferrimagnetism but also mixed-spin antiferromagnetism. As coexistent spins of different kinds do not necessarily result in magnetic ground states, it remains a stimulative problem there whether the system is massive or massless. Actually various mixed-spin chains [3,4] and ladders [5] with singlet ground states have also been discussed extensively via the nonlinear-σ-model technique with particular emphasis on the competition between massive and massless phases. On the other hand, an arbitrary alignment of alternating spins S and s, which is described by the Hamiltonianshows ferrimagnetism instead of antiferromagnetism and thus has gapless excitations from the ground state. Chemical explorations into ferrimagnetic chain compounds have vigorously been reported so far. In an attempt to obtain bimetallic complexes including onedimensional systems, CuMn(S 2 C 2 O 2 ) 2 (H 2 O) 3 ·4.5H 2 O [6] was first synthesized. Since then numerous bimetallic chain compounds [7] were systematically synthesized and measured. In the series of investigations, the smaller spin s was fixed to 1/2 and the larger spin S was changed from 1/2 to 5/2 featuring several important concepts. One of their main interests was the achievement of a ferromagnetic interaction between nearest-neighbor metal ions, namely, the design of molecular-based ferromagnets. Therefore quantum ferrimagnetism was not necessarily the main subject there. Though there also appeared theoretical investigations [1,8] in close contact with experiments, the argument was restricted to the spin combinations (S, 1/2) and the larger spin S was sometimes treated as classical.In such circumstances, several renewed interests [9][10][11][12][13][14][15][16][17][18][19], have recently been introduced into the field. Alcaraz and Malvezzi [9] predicted the universal low-energy physics of anisotropic ferrimagnetic chains and the distinct behavior of isotropic ones. Kuramoto [16] discussed critical properties of the model in a field showing its magnetization curve with a plateau. Maisinger et al. [19] revealed the field-induced double-peak structure of the specific heat. Another noteworthy subject, which is the main interest here, is the coexistence of the ferromagnetic and antiferromagnetic features in quantum ferrimagnets. The author et al. pointe...

Intrinsic double-peak structure of the specific heat in low-dimensional quantum ferrimagnets

“…Although the T −1 -diverging χT at low temperatures is reminiscent of the ferromagnetic susceptibility, it turns into the high-temperature paramagnetic behavior showing the antiferromagnetic increase. Recently an explicit sum rule [2] for the ferrimagnetic susceptibility has been found: Spin-(S, s) ferrimagnetic chains behave similar to combinations of spin-(S − s) ferromagnetic and spin-(2s) antiferromagnetic chains provided S = 2s. An epochal argument [3] on the ground-state magnetization curves of low-D quantum magnets stimulated broad interest in ferrimagnetic chains [4,5] and ladders [6] in a field.…”

Ferro- and Antiferromagnetic Aspects of Alternating Spin Systems

“…Ferrimagnets are believed to have a combined effect of both behaviors [4,8,9,17,21,18], ferromagnetic and antiferromagnetic. Susceptibility times temperature decreases at low temperature showing a minimum and them starts to increase showing that the antiferromagnetic behavior is not smeared out after the minimum.…”

Thermodynamic properties of ferrimagnetic spin chains in the presence of a magnetic field

“…This behavior has been observed in the low and high temperature regime of quantum ferrimagnets 6 . There are many approaches to study the properties of the ferrimagnetic chains; The dual features of ferrimagnetic excitations can be illuminated by using the densitymatrix renormalization group (DMRG) 5,8 and quantum Monte Carlo (QMC) methods 7,9 . Numerical diagonalization, combined with Lanczos algorithm 10 and the scaling technique 11 , further have been applied to study the modern topics such as the phase transition 10,12 and the quantized magnetization plateau.…”