205 research outputs found
Frustration effects in magnetic molecules
Besides being a fascinating class of new materials, magnetic molecules
provide the opportunity to study concepts of condensed matter physics in zero
dimensions. This contribution will exemplify the impact of molecular magnetism
on concepts of frustrated spin systems. We will discuss spin rings and the
unexpected rules that govern their low-energy behavior. Rotational bands, which
are experimentally observed in various molecular magnets, provide a useful,
simplified framework for characterizing the energy spectrum, but there are also
deviations thereof with far-reaching consequences. It will be shown that
localized independent magnons on certain frustrated spin systems lead to giant
magnetization jumps, a new macroscopic quantum effect. In addition a
frustration-induced metamagnetic phase transitions will be discussed, which
demonstrates that hysteresis can exist without anisotropy. Finally, it is
demonstrated that frustrated magnetic molecules could give rise to an enhanced
magnetocaloric effect.Comment: 6 pages, 4 figures; submitted to J. Low. Temp. Phys.; proceedings of
the Sixth International Symposium on Crystalline Organic Metals,
Superconductors, and Ferromagnets (ISCOM
Aging and memory properties of topologically frustrated magnets
The model 2d kagome system (H3O)Fe3(SO4)2(OH)6 and the 3d pyrochlore Y2Mo2O7
are two well characterized examples of low-disordered frustrated
antiferromagnets which rather then condensing into spin liquid have been found
to undergo a freezing transition with spin glass-like properties. We explore
more deeply the comparison of their properties with those of spin glasses, by
the study of characteristic rejuvenation and memory effects in the
non-stationary susceptibility. While the pyrochlore shows clear evidence for
these non-trivial effects, implying temperature selective aging, that is
characteristic of a wide hierarchical distribution of equilibration processes,
the kagome system does n not show clearly these effects. Rather, it seems to
evolve towards the same final state independently of temperature.Comment: submitted for the proceedings of the 46th MMM conference (Seattle,
2001
- …