Huge deformations of the crystal lattice can be achieved in materials with inherent structural instability by epitaxial straining. By coherent growth on seven different substrates the in-plane lattice constants of 50 nm thick Fe70Pd30 films are conti
nuously varied. The maximum epitaxial strain reaches 8,3 % relative to the fcc lattice. The in-plane lattice strain results in a remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering most of the Bain transformation path from fcc to bcc crystal structure. This has dramatic consequences for the magnetic key properties. Magnetometry and X-ray circular dichroism (XMCD) measurements show that Curie temperature, orbital magnetic moment, and magnetocrystalline anisotropy are tuned over broad ranges.
We have investigated the low-energy electronic structure of the heavy fermion superconductor CeCoIn5 by angle-resolved photoemission and band structure calculations. We measured the Fermi surface and energy distribution maps along the high-symmetry d
irections at hn = 100 eV and T = 25 K. The compound has quasi two-dimensional Fermi surface sheets centered at the M-A line of the Brillouin zone. The band structure calculations have been carried out within the local density approximation where the 4f electrons have been treated either localized or itinerant. We discuss the comparison to the experimental data and the implications for the nature of the 4f electrons at the given temperature.
We investigate the effect of external pressure on the Fe magnetic moment in undoped LaOFeAs within the framework of density functional theory and show that this system is close to a magnetic instability: The Fe moment is found to drop by nearly a fac
tor of 3 within a pressure range of $pm$ 5 GPa around the calculated equilibrium volume. While the Fe moments show an unusually strong sensitivity to the spin arrangement (type of anti-ferromagnetic structure), the low temperature structural distortion is found to have only a minor influence on them. Analysis of the Fermi surface topology and nesting features shows that these properties change very little up to pressures of at least 10 GPa. We discuss the magnetic instability in terms of the itinerancy of this system.
