Publications by Franz Lang

La2SrCr2O7: Controlling the Tilting Distortions of n = 2 Ruddlesden-Popper Phases through A-Site Cation Order.

Inorganic chemistry 55 (2016) 8951-8960

R Zhang, BM Abbett, G Read, F Lang, T Lancaster, TT Tran, PS Halasyamani, SJ Blundell, NA Benedek, MA Hayward

Structural characterization by neutron diffraction, supported by magnetic, SHG, and μ(+)SR data, reveals that the n = 2 Ruddlesden-Popper phase La2SrCr2O7 adopts a highly unusual structural configuration in which the cooperative rotations of the CrO6 octahedra are out of phase in all three Cartesian directions (ΦΦΦz/ΦΦΦz; a(-)a(-)c(-)/a(-)a(-)c(-)) as described in space group A2/a. First-principles DFT calculations indicate that this unusual structural arrangement can be attributed to coupling between the La/Sr A-site distribution and the rotations of the CrO6 units, which combine to relieve the local deformations of the chromium-oxygen octahedra. This coupling suggests new chemical "handles" by which the rotational distortions or A-site cation order of Ruddlesden-Popper phases can be directed to optimize physical behavior. Low-temperature neutron diffraction data and μ(+)SR data indicate La2SrCr2O7 adopts a G-type antiferromagnetically ordered state below TN ∼ 260 K.

Robustness of superconductivity to competing magnetic phases in tetragonal FeS

PHYSICAL REVIEW B 94 (2016) ARTN 134509

FKK Kirschner, F Lang, CV Topping, PJ Baker, FL Pratt, SE Wright, DN Woodruff, SJ Clarke, SJ Blundell

La2SrCr2O7F2: A Ruddlesden-Popper Oxyfluoride Containing Octahedrally Coordinated Cr(4+) Centers.

Inorganic chemistry 55 (2016) 3169-3174

R Zhang, G Read, F Lang, T Lancaster, SJ Blundell, MA Hayward

The low-temperature fluorination of the n = 2 Ruddlesden-Popper phase La2SrCr2O7 yields La2SrCr2O7F2 via a topochemical fluorine insertion reaction. The structure-conserving nature of the fluorination reaction means that the chromium centers of the initial oxide phase retain an octahedral coordination environment in the fluorinated product, resulting in a material containing an extended array of apex-linked Cr(4+)O6 units. Typically materials containing networks of octahedrally coordinated Cr(4+) centers can only be prepared at high pressure; thus, the preparation of La2SrCr2O7F2 demonstrates that low-temperature topochemical reactions offer an alternative synthesis route to materials of this type. Neutron diffraction, magnetization, and μ(+)SR data indicate that La2SrCr2O7F2 undergoes a transition to an antiferromagnetic state below TN ≈ 140 K. The structure-property relations of this phase and other Cr(4+) oxide phases are discussed.

Unconventional magnetism on a honeycomb lattice in alpha-RuCl3 studied by muon spin rotation

PHYSICAL REVIEW B 94 (2016) ARTN 020407

F Lang, PJ Baker, AA Haghighirad, Y Li, D Prabhakaran, R Valenti, SJ Blundell

Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory.

Physical review letters 114 (2015) 017602-

FR Foronda, F Lang, JS Möller, T Lancaster, AT Boothroyd, FL Pratt, SR Giblin, D Prabhakaran, SJ Blundell

Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials.

The effect of the demagnetizing field in cylindrical samples in high transverse field mu+SR experiments


F Lang, SJ Blundell