B. Srinivasan et al., SPIN POPULATIONS IN ONE-DIMENSIONAL ALTERNANT SPIN SYSTEMS - A THEORETICAL APPROACH, The Journal of chemical physics, 109(14), 1998, pp. 5770-5777
Spin-density maps, deduced from polarized neutron diffraction experime
nts, for both the pair and chain compounds of the system Mn2+Cu2+ have
been reported recently. These results have motivated us to investigat
e theoretically the spin populations in such alternant mixed-spin syst
ems. In this paper, we report our studies on the one-dimensional ferri
magnetic systems (S-A,S-B)(N) where hi is the number of AB pairs. We h
ave considered all cases in which the spin Sri takes on allowed values
in the range I to 7/2 while the spin S-B is held fixed at 1/2. The th
eoretical studies have been carried out on the isotropic Heisenberg mo
del, using the density matrix renormalization group method. The effect
of the magnitude of the larger spin SA On the quantum fluctuations in
both A and B sublattices has been studied as a function of the system
size N. We have investigated systems with both periodic and open boun
dary conditions, the latter with a view to understanding end-of-chain
effects. The spin populations have been followed as a function of temp
erature as well as an applied magnetic held. High-magnetic fields are
found to lead to interesting re-entrant behavior. The ratio of spin po
pulations \P-A/P-B\ is not sensitive to temperature at low temperature
s. (C) 1998 American Institute as Physics.