Nature of the magnetic order in the charge-ordered cuprate La1.48Nd0.4Sr0.12CuO4

Using polarized neutron scattering we establish that the magnetic order in La1.48Nd0.4Sr0.12CuO4 is either (i) one dimensionally modulated and collinear, consistent with the stripe model or (ii) two dimensionally modulated with a novel noncollinear structure. The measurements rule out a number of alternative models characterized by 2D electronic order or 1D helical spin order. The low-energy spin excitations are found to be primarily transversely polarized relative to the stripe ordered state, consistent with conventional spin waves

Magnetic Excitations of Undoped Iron Oxypnictides

We study the magnetic excitations of undoped iron oxypnictides using a three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms of the spin wave dispersion, velocities, and structure factor are given. Aside from quantitative comparisons which can be made to inelastic neutron scattering experiments, we also give qualitative criteria which can distinguish various regimes of coupling strength. The magnetization reduction due to quantum zero point fluctuations shows clear dependence on the c-axis coupling.Comment: 4 pages, 5 figures, to appear in Frontiers of Physics in China: a special issue on Iron-based superconductor

An x-ray resonant diffraction study of multiferroic DyMn2O5

X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40K in multiferroic DyMn$_{2}$O$_{5}$. The magnetic order has a complex behaviour. There are several different ordering wavevectors, both incommensurate and commensurate, as the temperature is varied. In addition a non-magnetic signal at twice the wavevector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarisation. Some of the results, which bear resemblence to the behaviour of other members of the RMn$_{2}$O$_{5}$ family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.Comment: 8 pages, 8 figure

Normal State Spin Dynamics of Five-band Model for Iron-pnictides

Normal state spin dynamics of the recently discovered iron-pnictide superconductors is discussed by calculating spin structure factor S(q, omega) in an itinerant five-band model within RPA approximation. Due to the characteristic Fermi surface structure of iron-pnictide, column like response is found at (pi, 0) in extended Brillouin zone in the undoped case, which is consistent with the recent neutron scattering experiment. This indicates that the localized spin model is not necessary to explain the spin dynamics of this system. Furthermore, we show that the temperature dependence of inelastic neutron scattering intensity can be well reproduced in the itinerant model. We also study NMR 1/T_1T in the same footing calculation and show that the itinerant model can capture the magnetic property of iron-pnictide superconductors.Comment: 4 page

Antiferromagnetic fluctuations in Fe(Se1-xTex)0.92 (x = 0.75, 1) observed by inelastic neutron scattering

Motivated by the discovery of superconductivity in F-doped LaFeAsO, we investigated the magnetic fluctuations in a related compound Fe(Se1-xTex)0.92 (x = 0.75, 1) using neutron scattering techniques. Non-superconducting FeTe0.92 shows antiferromagnetic (AF) ordering with the ordering vector |Q| = 0.97 A-1 (Q = (0.5,0,0.5)) at TN ~ 70 K and a structural transition between tetragonal and monoclinic phases. In the AF monoclinic phase, the low-energy spectral weight is suppressed, indicating a possible gap formation. On the other hand, in the paramagnetic tetragonal phase, we observed a pronounced magnetic fluctuation around at |Q| ~ 0.92 A-1, which is slightly smaller than the commensurate value. In Fe(Se0.25Te0.75)0.92, which does not show magnetic ordering and shows superconductivity at Tc ~ 8 K, we observed that a magnetic fluctuation is located at |Q| ~ 0.9 A-1 at low energies and shifts to a higher value of |Q| ~ 1.2 A-1 at higher energies. The latter value is close to a reciprocal lattice vector Q = (0.5,0.5,0.5) or (0.5,0.5,0), where the AF fluctuations are observed in other FeAs-based materials. The existence of this common characteristic in different Fe-based superconductors suggests that the AF fluctuations may play a important role in superconductivity.Comment: 4 pages, 4 figure

High - Temperature Superconductivity in Iron Based Layered Compounds

We present a review of basic experimental facts on the new class of high - temperature superconductors - iron based layered compounds like REOFeAs (RE=La,Ce,Nd,Pr,Sm...), AFe_2As_2 (A=Ba,Sr...), AFeAs (A=Li,...) and FeSe(Te). We discuss electronic structure, including the role of correlations, spectrum and role of collective excitations (phonons, spin waves), as well as the main models, describing possible types of magnetic ordering and Cooper pairing in these compounds.Comment: 43 pages, 30 figures, review talk on 90th anniversary of Physics Uspekh

Magnetism and its microscopic origin in iron-based high-temperature superconductors

High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising since these undoped states display dramatically different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el temperatures. Although there is general consensus that magnetic interactions are important for superconductivity, much is still unknown concerning the microscopic origin of the magnetic states. In this review, progress in this area is summarized, focusing on recent experimental and theoretical results and discussing their microscopic implications. It is concluded that the parent compounds are in a state that is more complex than implied by a simple Fermi surface nesting scenario, and a dual description including both itinerant and localized degrees of freedom is needed to properly describe these fascinating materials.Comment: 14 pages, 4 figures, Review article, accepted for publication in Nature Physic

Ibrutinib for Relapsed / Refractory CLL: A UK and Ireland Analysis of Outcomes in 315 patients

In 2014, ibrutinib was made available for relapsed/refractory chronic lymphocytic leukaemia (CLL) patients. The UK CLL Forum collected data from UK/Ireland patients with a minimum of 1 year follow-up with pre-planned primary endpoints; the number of patients still on therapy at 1 year (Discontinuation Free Survival; DFS) and 1 year overall survival (OS). With a median 16 months follow-up, data on 315 patients demonstrated 1 year DFS of 73.7% and 1 year OS of 83.8%. Patients with better pre-treatment performance status (PS 0/1 vs 2+) had superior DFS (77.5% vs 61.3%;p14 days and had OS of 89.7%, while 26% of patients had dose reductions and 13% had temporary treatment breaks >14 days. We could not demonstrate a detrimental effect of dose reductions alone (1 year OS: 91.7%), but patients who had first year treatment breaks > 14 days, particularly permanent cessation of ibrutinib had both reduced 1 year OS (68.5%) and also a statistically significant excess mortality rate beyond one year. Although outcomes appear inferior to the RESONATE trial (1 year OS;90%: PFS;84%), this may partly reflect the inclusion of PS 2+ patients and that 17.5% of patients permanently discontinued ibrutinib due to an event other than disease progression

Lipocalin 2 modulates the cellular response to amyloid beta

The production, accumulation and aggregation of amyloid beta (Aß) peptides in Alzheimer's disease (AD) are influenced by different modulators. Among these are iron and iron-related proteins, given their ability to modulate the expression of the amyloid precursor protein and to drive Aß aggregation. Herein, we describe that lipocalin 2 (LCN2), a mammalian acute-phase protein involved in iron homeostasis, is highly produced in response to Aß1-42 by choroid plexus epithelial cells and astrocytes, but not by microglia or neurons. Although Aß1-42 stimulation decreases the dehydrogenase activity and survival of wild-type astrocytes, astrocytes lacking the expression of Lcn2 are not affected. This protection results from a lower expression of the proapoptotic gene Bim and a decreased inflammatory response. Altogether, these findings show that Aß toxicity to astrocytes requires LCN2, which represents a novel mechanism to target when addressing AD.Cell Death and Differentiation advance online publication, 23 May 2014; doi:10.1038/cdd.2014.68.We thank Dr. Ioannis Sotiropoulos for reagents and comments. Sandro Da Mesquita and Ana Catarina Ferreira are recipients of PhD fellowships and Fernanda Marques is recipient of a postdoctoral fellowship by the Fundacao para a Ciencia e Tecnologia (FCT, Portugal)/FEDER. This work was supported by a grant from FCT/FEDER (EXPL/NEUOSD/2196/2013)