Haldane gap

The nickelates R2BaNi05 with RY, Nd-Gd, Dy-Tm feature antiferromagnetic S=1 Ni2+ chains interconnected by either nonmagnetic (R=Y) or magnetic (R=RE) ions. Recently, they attracted a considerable attention as model systems to study the ID magnetism, ID to 3D crossover, and the behavior of the Haldane-gap excitations through this crossover, as... 

Novel Theoretical Prediction Method of the Haldane Gap among the Azido-Bridged Compounds by DV-Xa Molecular Orbital Calculation Tomohiko Ishii, Yukikazu Fuke, Naoko Aizawa and Masahiro Yamashita ... 

Therefore in the present paper, we report that the energy difference between the singlet ground state and the triplet excited state is more important than the differences among the overlap populations mentioned above. Therefore a new theoretical way to predict the value of the Haldane gap using the DV-Xa method should be discussed. 

Table 4.1 Intra-chain exchange energy, J, and the Haldane gap, g, of several Haldane gap compounds with particular in-plane and bridging ligands and counteranions...

The crystallographic data of NINAZ, NDMAZ, and NDMAP we have obtained are completely consistent with those reported previously [2]. The cluster model of each compound we have used for the DV-Xa calculation is extracted from the X-ray structural data of the single crystal. Cluster models of the same formula N3-Ni(AA)2-N3-Ni(AA)2-N3 are used in the DV-Xa calculation in order to compare both the electronic structure and the Haldane gap directly. 

In the N3 bridged compounds, there is a stronger electron-electron interaction through the N/ bridging molecule between two adjacent Ni spins, than between the NO2 bridged compounds. A cluster model constructed on the basis of the accurate structure determined by X-ray diffraction is used in the DV-Xa calculation for NINAZ, NDMAZ, and NDMAP. These are typical Haldane gap materials, which include the N3-bridging ligand. 

Figure 4.5 Schematic expression of the singlet (left) and the triplet (right) spin states between two adjacent Ni2 ions having S=1 spin in the ID metal complex chain of the Haldane gap compound. The energy barrier of the spin inversion from the anti-parallel singlet to the parallel triplet state has the relationship with the energy difference between them.

K. Katsumata, H. Tasaki, Haldane Gap - Macroscopic Quantum Phenomena in Spin Systems, Selected Papers in Physics VIII, The Physical Society of Japan (1997). 

In order to test such a hypothesis, highly ideal model one-dimensional materials are required, since any interaction between chains must be minimised to enable Haldane Gap behaviour to be observed and studied. The molecular magnetic material [Ni(jU-N3)(l,3-diamino-... 

As said, the majority of these cases involve transition metal magnetism outside the scope of this review. Numerous classes of materials showing such behavior have been given special names and most were at least sampled by p.SR, such as Haldane gap (e.g.. 

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