Frustration & Magnetoelectrics
The quest for an improved control of the electric polarisation with an externally applied magnetic field (which for example can impact the engineering of novel RAM elements), is directed in a family of strongly interacting materials involving frustrated magnetic interactions. Within this topic we demonstrate fundamental modification of low-dimensional, triangular spin lattices, with anisotropic super-exchange interactions, when spin and/or orbital degrees of freedom are tuneable variables.
Frustration arises when a system cannot minimize all the pair-wise interactions simultaneously because of local geometric constraints. Competing or frustrated interactions extend beyond the condensed matter problems and into biological materials. In that respect, nature has the ability to "resolve" frustrated interactions in order to perform specific biological activity.
Macroscopic magnetic properties (i.e. SQUID magnetometery) unveil low-dimensional spin correlations in triangular spin lattice systems.
Frustration may give-rise to novel and complex phenomena that motivate us to (i) develop new class of materials (ii) study cooperative phenomena in magnetism that provide fertile ground for testing theories of interacting systems that possess different spatial dimensions, ranges, and sign of interactions, and that exhibit local anisotropy of the basic interacting unit, the spin.
Probing order at variable length & t-scales
Use of positive muons (μ+SR spectroscopy) has a great potential to uncover new and unexpected forms of magnetism owing to its high-sensitivity to very small magnetic fields and spatially inhomogeneous properties… a powerful tool in small-moment magnetism where complementary neutron scattering may fail!
Neutron inelastic scattering (diffraction) tells us where the atoms are in a lattice and what they do. This provides a unique insight in the nanoscopic world of interactions involving the electronic and lattice degrees of freedom of quantum complex, strongly correlated materials.
Understanding their crystal structure, the impact on the materials’ functionality can be uncovered and high-end applications are designed effectively.
Perspectives
Magneto-electrics
Competing phases (frustration) mediate the nanoscale domain magnetism and impact the underlined electric order.
Coupled magnetic and electric phenomena in frustrated mixed-valent oxides open new avenues in memory & sensor technologies.
For more information: in a pdf and at the "Selected Recent Publications"
keywords: Multiferroics, Strongly Interacting Systems, Neutron Scattering, Electronics