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O Waldmann

Publications and source records attributed to O Waldmann.

12 recordsLinked to original sources
PubMed2006

Field-induced magnetoelastic instabilities in antiferromagnetic molecular wheels.

The magnetic torque of the antiferromagnetic molecular wheel CsFe8 was studied down to 50 mK and up to 28 T. Below about 0.5 K phase transitions were observed at the field-induced level crossings (LCs). Intermolecular magnetic interactions are very weak excluding field-induced magnetic ordering. A magnetoelastic coupling was considered. A generic model shows that the wheel structure is unconditionally unstable at the LCs, and the predicted torque curves explain the essential features of the data well.

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PubMed2004

Quantum magneto-oscillations in a supramolecular Mn(II)-[3 x 3] grid.

The magnetic grid molecule Mn(II)-[3 x 3] has been studied by high-field torque magnetometry at 3He temperatures. At fields above 5 T, the torque versus field curves exhibit an unprecedented oscillatory behavior. A model is proposed which describes these magneto-oscillations well.

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PubMed2003

Elementary excitations in the cyclic molecular nanomagnet Cr8.

Combining recent and new inelastic neutron scattering data for the molecular cyclic cluster Cr8 produces a deep understanding of the low lying excitations in bipartite antiferromagnetic Heisenberg rings. The existence of the L band, the lowest rotational band, and the E band, essentially spin wave excitations, is confirmed spectroscopically. The different significance of these excitations and their physical nature is clearly established by high-energy and Q-dependence data.

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PubMed2002

Butterfly hysteresis loop at nonzero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization.

At low temperatures, the magnetization of the molecular ferric wheel NaFe6 exhibits a step at a critical field B(c) due to a field-induced level crossing. By means of high-field torque magnetometry we observed a hysteretic behavior at the level crossing with a characteristic butterfly shape which is analyzed in terms of a dissipative two-level model. Several unusual features were found. The nonzero bias field of the level crossing suggests the possibility of cooling by adiabatic magnetization.

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PubMed2002

Field-dependent anisotropy change in a supramolecular Mn(II)- [3 x 3] grid.

The magnetic anisotropy of a novel Mn(II)- [3x3] grid complex was investigated by means of high-field torque magnetometry. Torque vs field curves at low temperatures demonstrates a ground state with S>0 and exhibits a torque step due to a field-induced level crossing at B(*) approximately 7.5 T, accompanied by an abrupt change of magnetic anisotropy from easy-axis to hard-axis types. These observations are discussed in terms of a spin Hamiltonian formalism.

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PubMed2001

Magnetic anisotropy of a cyclic octanuclear Fe(III) cluster and magneto-structural correlations in molecular ferric wheels.

The magnetic anisotropy of the cyclic octanuclear Fe(III) cluster [Cs subsetFe(8)[N(CH(2)CH(2)O)(3)](8)]Cl was investigated. Based on a spin Hamiltonian formalism and the consequent use of all symmetries, the magnetic anisotropy could be calculated exactly to first order, i.e., in the strong exchange limit. Experimentally, the magnetic anisotropy was investigated by magnetic susceptibility and high-field torque magnetometry of single crystals. The field and angle dependence of the torque at 1.7 K could be accurately reproduced by the calculations with one single parameter set, providing accurate results for the coupling constant and single-ion zero-field-splitting. These magnetic parameters are compared to those of several related hexanuclear ferric wheels and are discussed with respect to magneto-structural correlations for both coupling constant and single-ion anisotropy.

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