Magnetic coupling at rare earth ferromagnet/transition metal ferromagnet interfaces: A comprehensive study of Gd/Ni.

Thin film magnetic heterostructures with competing interfacial coupling and Zeeman energy provide a fertile ground to study phase transition between different equilibrium states as a function of external magnetic field and temperature. A rare-earth (RE)/transition metal (TM) ferromagnetic multilayer is a classic example where the magnetic state is determined by a competition between the Zeeman energy and antiferromagnetic interfacial exchange coupling energy. Technologically, such structures offer the possibility to engineer the macroscopic magnetic response by tuning the microscopic interactions between the layers. We have performed an exhaustive study of nickel/gadolinium as a model system for understanding RE/TM multilayers using the element-specific measurement technique x-ray magnetic circular dichroism, and determined the full magnetic state diagrams as a function of temperature and magnetic layer thickness. We compare our results to a modified Stoner-Wohlfarth-based model and provide evidence of a thickness-dependent transition to a magnetic fan state which is critical in understanding magnetoresistance effects in RE/TM systems. The results provide important insight for spintronics and superconducting spintronics where engineering tunable magnetic inhomogeneity is key for certain applications.T.D.C.H. and J.W.A.R. acknowledge funding from the EPSRC [EP/I038047/1], the EPSRC Programme grant “Superconducting Spintronics” [EP/N017242/1] and the Leverhulme Trust [IN-2013-033]. S.B. acknowledges support from the Knut and Alice Wallenberg Foundation. X.L.W. and J.H.Z. acknowledge support from the MOST of China [2015CB921500]. Research at SLAC and Stanford was supported through the Stanford Institute for Materials and Energy Sciences (SIMES) which like the SSRL user facility and the scanning SQUID microscopy is funded by the Office of Basic Energy Sciences of the U.S. Department of Energy.This is the final version of the article. It first appeared from Nature Publishing Group at http://dx.doi.org/10.1038/srep30092

An explanation for a universality of transition temperatures in families of copper oxide superconductors

A remarkable mystery of the copper oxide high-transition-temperature (Tc) superconductors is the dependence of Tc on the number of CuO2 layers, n, in the unit cell of a crystal. In a given family of these superconductors, Tc rises with the number of layers, reaching a peak at n=3, and then declines: the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers and the latest notion of a competing order nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, Tc can be raised further.Comment: 15 pages, 3 figures. The version published in Natur

Optical Magnetometry

Some of the most sensitive methods of measuring magnetic fields utilize interactions of resonant light with atomic vapor. Recent developments in this vibrant field are improving magnetometers in many traditional areas such as measurement of geomagnetic anomalies and magnetic fields in space, and are opening the door to new ones, including, dynamical measurements of bio-magnetic fields, detection of nuclear magnetic resonance (NMR), magnetic-resonance imaging (MRI), inertial-rotation sensing, magnetic microscopy with cold atoms, and tests of fundamental symmetries of Nature.Comment: 11 pages; 4 figures; submitted to Nature Physic

Phylogeographic uniformity in mitochondrial DNA of the snapping turtle (Chelydra serpentina)

Previous studies have revealed considerable genetic variation, geographic localization, and genealogical depth for mitochondrial DNA (mtDNA) haplotypes within each of several species of freshwater turtles in the south-eastern United States of America. Here we report a notable exception to such phylogeographic patterns. In control-region sequences of 66 snapping turtles (Chelydra serpentina) collected from 10 south-eastern states, a single mtDNA haplotype predominated and the two rare variants detected were nearly identical to the common genotype. This pattern of low mtDNA variation and a lack of appreciable geographic population structure is extremely unusual for a widely distributed animal species. For purposes of taxonomy and conservation, these findings suggest the presence of only one 'evolutionarily significant unit' for C. serpentina in this otherwise phylogeographically rich region of the country. Possible explanations for this phylogeographic pattern in the snapping turtle are considered

South Asians making Britain: timeline

A timeline 'South Asians Making Britain', arising from project research and authored by Florian Stadtler, Rozina Visram, Susheila Nasta, Sheila Pulham, and Lisa Villani, was published on the Guardian website, 10 September 2010. The timeline made a signifcant impact on publication and provides a visual and textual history of South Asians in Britain