Hexagonal manganites
The hexagonal Manganites belong to the class of Multiferroic materials. These crystals present magnetic and electric properties that coexist; the dominant frustrated antiferromagnetic properties and high temperature ferroelectric distortion give way to rich phase diagrams. Their delicate magneto-structural interplay is yet to be fully understood. An understanding can be reached using Density Functional Theory first-principles based phenomenological models that try to describe the underlying mechanisms behind the crystal’s Multiferroic nature. Inputting these models into a Spin Dynamics code, the dynamic properties of spins as a function of temperature and across domain walls are simulated.
The magnetic order that minimises the energy of hexagonal YMnO3. Red, purple and green dots correspond to oxygen, manganese and yttrium sites, respectively. The arrows represent net magnetic moment per manganese site.
A schematic diagram of a frustrated trio of spins on a triangular lattice. Each pair of spins posses an antiferromagnetic exchange, through which an anti parallel alignment of the pair of spins minimises the energy. The geometry of the lattice makes this impossible and the system’s total energy is minimised by a 120º angle between neighbouring spins.
The magnetic order that minimises the energy of a trimer of MnO5 bipyramids in hexagonal YMnO3. Red, purple and green dots correspond to oxygen, manganese and yttrium sites, respectively. The arrows represent net magnetic moment per manganese site.
The low temperature crystal structure of hexagonal YMnO3. Red, purple and green dots correspond to oxygen, manganese and yttrium sites, respectively. The arrows represent net magnetic moment per manganese site.