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Magnetismus Poster: Do., 13:00–15:30 D-P239
Search for S = 1 Haldane chains in metallo-supramolecular assemblies
M. Lommel 1 , Y. Bodenthin 1 , U. Pietsch 1 , G. Schwarz 2 , W. Haase 3 , Z.
Tomkowicz 3,4 , D. G. Kurth 2
1 University Siegen, FB7 Solid State Physics, D-57068 Siegen (Germany) – 2 Max
Planck Institute of Colloids and Interfaces, D-14424 Potsdam (Germany) – 3 Institute
of Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, D-
64287(Germany), – 4 Institute of Physics, Jagellonian University, Reymonta 4, 30-059
Kraków (Poland)
The physics of antiferromagnetic Heisenberg chains is an area of high interest since
even at zero temperature quantum fluctuations suppress long range order. In 1983
Haldane concluded that for all integer spin values even a spin liquid ground state with
a finite excitation gap is realized. [1] Since this time several Ni(II) metallo-organic
systems have been clearly identified. Our aim was to elucidate the magnetic properties
of metallo-supramolecular polyelectrolyte-amphiphile complexes (PAC) with Ni(II) as
metal ion. [2] In PAC metal ions are coupled in a one-dimensional chain via metallosupramolecular
coordination polyelectrolytes (MEPE), whereas amphiphile molecules
serve as spacers between the MEPE chains. Ni(II)-PAC could be an molecular system
realizing a Haldane quantum spin chain with S = 1. From the topology of the Ni(II)-
PAC compound one may expect that Ni(II) S = 1 spins coupled via MEPE fragments
in a chain can interact with each other antiferromagnetical. First magnetization results
reveal a Curie-Weiss behaviour with a small antiferromagnetic Weiss temperature of
1.3 K. These observations imply that one can realize the quantum Haldane situation
by chemically engineering of the coupling strength between Ni-spins in a chain via
increase of the antiferromagentic exchange interaction.
Experiments on Fe(II)-PAC reveal the possibility to tune the magnetic properties
of PAC by changing length of the ligand and amount of amphiphiles. Additionally
previous element selective XMCD investigation elucidate an antiparallel oriented spinpolarization
between iron and its sourrounding ligand leading to a magnetic coupling
between neighbouring metal centres due to a superexchange interaction.
The intention was to investigate the superexchange coupling between two Ni(II)-metal
centres in PAC using x-ray magnetic linear dichroism (XMLD). We investigated a series
of four different samples containing two different ligands each with two different metal
to amphiphile ratios (1:6 and 1:2 metal to amphiphile ratios) at low temperature. The
evaluation of the data was treated in terms of Zak’s formalism.
All experiments were performed using the ALICE diffractometer of group Zabel, Uni-
Bochum at BESSY II. This project is supported by DFG Priority program 1137 Molecular
Magnetism.
[1] F. D.M. Haldane, Phys. Rev. Lett. 50 (1983) 1153
[2] D. G. Kurth, P. Lehmann, M. Schütte, Proc. Natl. Acad. Sci., USA, 97 (2000)
5704-5707