U. K. Rößler

The quantum nature of skyrmions and half-skyrmions in Cu2OSeO3

The Skyrme-particle, the skyrmion, was introduced over half a century ago in the context of dense nuclear matter. But with skyrmions being mathematical objects--special types of topological solitons--they can emerge in much broader contexts. Recently skyrmions were observed in helimagnets, forming nanoscale spin-textures. Extending over length scales much larger than the interatomic spacing, they behave as large, classical objects, yet deep inside they are of quantum nature. Penetrating into their microscopic roots requires a multi-scale approach, spanning the full quantum to classical domain. Here, we achieve this for the first time in the skyrmionic Mott insulator Cu2OSeO3. We show that its magnetic building blocks are strongly fluctuating Cu4 tetrahedra, spawning a continuum theory that culminates in 51 nm large skyrmions, in striking agreement with experiment. One of the further predictions that ensues is the temperature-dependent decay of skyrmions into half-skyrmions.

Magnetically induced reorientation of martensite variants in constrained epitaxial Ni-Mn-Ga films grown on MgO(001)

Magnetically induced reorientation (MIR) is observed in epitaxial orthorhombic Ni-Mn-Ga films. Ni-Mn-Ga films have been grown epitaxially on heated MgO(001) substrates in the cubic austenite state. The unit cell is rotated by 45 relative to the MgO cell. The growth, structure texture and anisotropic magnetic properties of these films are described. The crystallographic analysis of the martensitic transition reveals variant selection dominated by the substrate constraint. The austenite state has low magnetocrystalline anisotropy. In the martensitic state, the magnetization curves reveal an orthorhombic symmetry having three magnetically non-equivalent axes. The existence of MIR is deduced from the typical hysteresis within the first quadrant in magnetization curves and independently by texture measurement without and in the presence of a magnetic field probing microstructural changes. An analytical model is presented, which describes MIR in films with constrained overall extension by the additional degree of freedom of an orthorhombic structure compared to the tetragonal structure used in the standard model.

Critical properties in single crystals of Pr1-xPbxMnO3

The critical properties at the ferromagnetic-paramagnetic transition have been analyzed from data of static magnetization measurements on single crystals of

Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets

Pr_{1-x}Pb_xMnO_3

Chiral Skyrmionic matter in non-centrosymmetric magnets

for x=0.23 and x=0.30. In

Spin-flop transition in uniaxial antiferromagnets: Magnetic phases, reorientation effects, and multidomain states

Pr_{1-x}Pb_xMnO_3

Twin boundary energy of hierarchically twinned magnetic shape memory alloys

, the ferromagnetic ordering and the metal-insulator transition do not coincide in parts of the phase diagram. The crystal with x=0.23 is a ferromagnetic insulator with Curie temperature

Strongly frustrated triangular spin lattice emerging from triplet dimer formation in honeycomb Li2IrO3

T_C

Magnetoelectric effects in single crystals of the cubic ferrimagnetic helimagnet Cu2OSeO3

=167 K, while the crystal with x =0.30 has

First-order structural transition in the magnetically ordered phase of Fe1.13Te

T_C