Coordination Frameworks : New routes to functional and low dimensional magnetic properties

CCMMP Seminars
Dr Paul Saines
Martin Dove
October 24th, 2017 at 14:00
GO Jones Room 610

Materials that respond to an electric or magnetic signal are crucial to many modern technologies, including data storage, ultrasound sensors and low temperature cooling. They also exhibit fascinating fundamental phenomena as seen by the awarding of the 2016 Nobel Prize for theoretical understanding of topological phases Most materials of interest for these applications are complex metal oxides but, after decades of research, they still struggle to incorporate all features required to optimise complex functional properties or exhibit purely low dimensional behaviour. Recently new classes of materials that contain both inorganic and organic building blocks have attracted attention for their ability to exhibit such magnetic and electronic functionalities. These include coordination frameworks where transition metal or lanthanide cations are connected together by organic ligands to make extended structures. The tremendous choice of building blocks for such materials provide enormous flexibility to tailor their properties for particular applications, while the unique structures they adopt allow properties to be varied in ways not possible in conventional ferroic materials. This includes well-isolated low dimensional structures well suited to low dimensional magnetism. The origins of these properties in the atomic level structure and dynamics of frameworks is, however, currently obscured. Our group’s focus is to develop a fundamental understanding of the microscopic origins of these properties in frameworks and use this to develop design rules for improved properties. Recent examples of this include probing the magnetic and ferroelectric ordering of ternary transition metal frameworks that exhibit both ferroelectric and magnetic order to uncover unique trends in their magnetic structure and unusual origins for relaxor ferroelectric type behaviour. We will also discuss low dimensional magnetism in a terbium framework, whose magnetocaloric cooling effect is larger than its gadolinium analogue due to the 1D ferromagnetic coupling in its paramagnetic phase. This compound also undergoes a transition to a state that appears to have 1D long-range magnetic order, albeit incomplete, supported by the short-range antiferromagnetic coupling between chains on a frustrated triangular lattice.