Publications by Franz Lang

Spin Jahn-Teller antiferromagnetism in CoTi2O5

PHYSICAL REVIEW B 99 (2019) ARTN 064403

FKK Kirschner, RD Johnson, F Lang, DD Khalyavin, P Manuel, T Lancaster, D Prabhakaran, SJ Blundell

FeTi$_2$O$_5$: a spin Jahn-Teller transition tuned by cation substitution

Physical Review B American Physical Society (0)

F Lang, L Jowitt, D Prabhakaran, RD Johnson, SJ Blundell

We have used muon-spin rotation, heat capacity and x-ray diffraction measurements in combination with density functional theory and dipole field calculations to investigate the crystal and magnetic structure of FeTi$_2$O$_5$. We observe a long range ordered state below 41.8(5) K with indications of significant correlations existing above this temperature. We determine candidate muon stopping sites in this compound, and find that our data are consistent with the spin Jahn-Teller driven antiferromagnetic ground state with $\boldsymbol{k}$=(1/2,1/2,0) reported for CoTi$_2$O$_5$. By comparing our data with calculated dipolar fields we can restrict the possible moment size and directions of the Fe$^{2+}$ ions.

Static and Fluctuating Magnetic Moments in the Ferroelectric Metal LiOsO3

Proceedings of the 14th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2017) Journal of the Physical Society of Japan (2018)

FKK Kirschner, F Lang, FL Pratt, T Lancaster, Y Shi, Y Guo, AT Boothroyd, SJ Blundell

Nodal multigap superconductivity in KCa2Fe4As4F2

PHYSICAL REVIEW B 97 (2018) ARTN 060509

M Smidman, FKK Kirschner, DT Adroja, AD Hillier, F Lang, ZC Wang, GH Cao, SJ Blundell

LaSr3 NiRuO4 H4 : A 4d Transition-Metal Oxide-Hydride Containing Metal Hydride Sheets.

Angewandte Chemie (International ed. in English) 57 (2018) 5025-5028

L Jin, M Lane, D Zeng, FKK Kirschner, F Lang, P Manuel, SJ Blundell, JE McGrady, MA Hayward

The synthesis of the first 4d transition metal oxide-hydride, LaSr3 NiRuO4 H4 , is prepared via topochemical anion exchange. Neutron diffraction data show that the hydride ions occupy the equatorial anion sites in the host lattice and as a result the Ru and Ni cations are located in a plane containing only hydride ligands, a unique structural feature with obvious parallels to the CuO2 sheets present in the superconducting cuprates. DFT calculations confirm the presence of S=1/2  Ni+ and S=0, Ru2+ centers, but neutron diffraction and μSR data show no evidence for long-range magnetic order between the Ni centers down to 1.8 K. The observed weak inter-cation magnetic coupling can be attributed to poor overlap between Ni 3dz2 and H 1s in the super-exchange pathways.

Comparative study of the magnetic properties of La3Ni2B ' O-9 for B ' = Nb, Ta or Sb


C-M Chin, PD Battle, SJ Blundell, E Hunter, F Lang, M Hendrickx, RP Sena, J Hadermann

Two-gap superconductivity with line nodes in CsCa2Fe4As4F2

PHYSICAL REVIEW B 97 (2018) ARTN 060506

FKK Kirschner, DT Adroja, Z-C Wang, F Lang, M Smidman, PJ Baker, G-H Cao, SJ Blundell

Multigap Superconductivity in RbCa2Fe4As4F2 Investigated Using mu SR Measurements


DT Adroja, FKK Kirschner, F Lang, M Smidman, AD Hillier, Z-C Wang, G-H Cao, GBG Stenning, SJ Blundell

Comparative study of the magnetic properties of La<inf>3</inf>Ni<inf>2</inf>B′O<inf>9</inf> for B′ = Nb, Taor Sb

Journal of Solid State Chemistry 258 (2018) 825-834

CM Chin, PD Battle, SJ Blundell, E Hunter, F Lang, M Hendrickx, R Paria Sena, J Hadermann

© 2017 Elsevier Inc. Polycrystalline samples of La3Ni2NbO9 and La3Ni2TaO9 have been characterised by X-ray and neutron diffraction, electron microscopy, magnetometry and muon spin relaxation (µSR); the latter technique was also applied to La3Ni2SbO9. On the length scale of a neutron diffraction experiment, the six-coordinate sites of the monoclinic perovskite structure are occupied in a 1:1 ordered manner by Ni and a random ⅓Ni/⅔B′ mixture. Electron microscopy demonstrated that this 1:1 ordering is maintained over microscopic distances, although diffuse scattering indicative of short-range ordering on the mixed site was observed. No magnetic Bragg scattering was observed in neutron diffraction patterns collected from La3Ni2B′O9 (B′ = Nb or Ta) at 5 K although in each case µSR identified the presence of static spins below 30 K. Magnetometry showed that La3Ni2NbO9 behaves as a spin glass below 29 K but significant short-range interactions are present in La3Ni2TaO9 below 85 K. The contrasting properties of these compounds are discussed in terms of their microstructure.

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

Fourier space derivation of the demagnetization tensor for uniformly magnetized objects of cylindrical symmetry


F Lang, 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

The serum and glucocorticoid-inducible kinase SGK1 and the Na+/H+ exchange regulating factor NHERF2 synergize to stimulate the renal outer medullary K+ channel ROMK1.

Journal of the American Society of Nephrology : JASN 13 (2002) 2823-2830

CC Yun, M Palmada, HM Embark, O Fedorenko, Y Feng, G Henke, I Setiawan, C Boehmer, EJ Weinman, S Sandrasagra, C Korbmacher, P Cohen, D Pearce, F Lang

Mineralocorticoids stimulate Na(+) reabsorption and K(+) secretion in principal cells of connecting tubule and collecting duct. The involved ion channels are ENaC and ROMK1, respectively. In Xenopus oocytes, the serum and glucocorticoid-sensitive kinase SGK1 has been shown to increase ENaC activity by enhancing its abundance in the plasma membrane. With the same method, ROMK1 appeared to be insensitive to regulation by SGK1. On the other hand, ROMK1 has been shown to colocalize with NHERF2, a protein mediating targeting and trafficking of transport proteins into the cell membrane. The present study has been performed to test whether NHERF2 is required for regulation of ROMK1 by SGK1. Coexpression of neither NHERF2 nor SGK1 with ROMK1 increases ROMK1 activity. However, coexpression of NHERF2 and SGK1 together with ROMK1 markedly increases K(+) channel activity. The combined effect of SGK1 and NHERF2 does not significantly alter the I/V relation of the channel but increases the abundance of the channel in the membrane and decreases the decay of channel activity after inhibition of vesicle insertion with brefeldin. Coexpression of NHERF2 and SGK1 does not modify cytosolic pH but leads to a slight shift of pK(a) of ROMK1 to more acidic values. In conclusion, NHERF2 and SGK1 interact to enhance ROMK1 activity in large part by enhancing the abundance of channel protein within the cell membrane. This interaction allows the integration of genomic regulation and activation of SGK1 and NHERF2 in the control of ROMK1 activity and renal K(+) excretion.