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Linear field demagnetization of artificial magnetic square ice
Jason P. Morgan,Aaron Stein,Sean Langridge,Christopher H. Marrows
Frontiers in Physics , 2013, DOI: 10.3389/fphy.2013.00028
Abstract: We have studied experimentally the states formed in artificial square ice nanomagnet systems following demagnetization in a rotating in-plane applied magnetic field that reduces to zero in a manner that is linear in time. The final states are found to be controlled via the system's lattice constant, which determines the strength of the magnetostatic interactions between the elements, as well as the field ramping rate. We understand these effects as a requirement that the system undergoes a sufficiently large number of active rotations within the critical field window in which elements may be reversed, such that the interactions are allowed to locally exert their influence if the ground state is to be approached. On the other hand, if quenched disorder is too strong when compared to the interaction strength, any close approach to the ground state is impossible. These results show that it is not necessary for there to be any ac component to the field amplitude that is applied to the system during demagnetization, which is the method almost exclusively employed in field protocols reported to date. Furthermore, by optimizing the parameters of our linear demagnetization protocol, the largest field-generated ground state domains yet reported are found.
Magnetic Roughness and Domain Correlations in Antiferromagnetically Coupled Multilayers
Sean Langridge,Joerg Schmalian,C. H. Marrows,D. T. Dekadjevi,B. J. Hickey
Physics , 1999, DOI: 10.1103/PhysRevLett.85.4964
Abstract: The in-plane correlation lengths and magnetic disorder of magnetic domains in a transition metal multilayer have been studied using neutron scattering techniques. A new theoretical framework is presented connecting the observed scattering to the in-plane correlation length and the dispersion of the local magnetization vector about the mean macroscopic direction. The results unambiguously show the highly correlated nature of the antiferromagnetically coupled domain structure vertically throughout the multilayer. We are easily able to relate the neutron determined magnetic dispersion and domain correlations to magnetization and magnetotransport experiments.
Manipulation of the spin helix in FeGe thin films and FeGe/Fe multilayers
Nicholas A. Porter,Charles S. Spencer,Rowan C. Temple,Christian J. Kinane,Timothy R. Charlton,Sean Langridge,Christopher H. Marrows
Physics , 2015, DOI: 10.1103/PhysRevB.92.144402
Abstract: Magnetic materials without structural inversion symmetry can display the Dzyaloshinskii-Moriya interaction, which manifests itself as chiral magnetic ground states. These chiral states can interact in complex ways with applied fields and boundary conditions provided by finite sample sizes that are of the order of the lengthscale of the chiral states. Here we study epitaxial thin films of FeGe with a thickness close to the helix pitch of the helimagnetic ground state, which is about 70 nm, by conventional magnetometry and polarized neutron reflectometry. We show that the helix in an FeGe film reverses under the application of a field by deforming into a helicoidal form, with twists in the helicoid being forced out of the film surfaces on the way to saturation. An additional boundary condition was imposed by exchange coupling a ferromagnetic Fe layer to one of the interfaces of an FeGe layer. This forces the FeGe spins at the interface to point in the same direction as the Fe, preventing node expulsion and giving a handle by which the reversal of the helical magnet may be controlled.
Agronomy—A Multidisciplinary and Open Access Journal
Peter Langridge
Agronomy , 2011, DOI: 10.3390/agronomy1010001
Abstract: Agronomy is a highly multidisciplinary area of science. It includes all aspects of science and technology related to the production and utilization of plants for food, feed, fuel, fiber and even land reclamation. In many respects, agronomy represents the integration of activities and disciplines ranging from genetics, chemistry and biotechnology to ecology, soil science and meteorology. [...]
Sean Leneghan, The Varieties of Ecstasy Experience: An Exploration of Person, Mind and Body in Sydney’s Club Culture (Saarbrücken: Lambert Academic Publishing, 2011)
Adam Langridge
Nordicum-Mediterraneum , 2013,
Abstract: A review of the book: The Varieties of Ecstasy Experience: An Exploration of Person, Mind and Body in Sydney’s Club Culture, by Sean Leneghan. Lambert Academic Publishing: Saarbrücken, Germany, 2011. ISBN: 978-3-8454-1634-2. 286 pp. (Paperback) $112 U.S.
William C. Prevette, Child, Church and Compassion: Towards Child Theology in Romania (Oxford: Regnum, 2012)
Adam Langridge
Nordicum-Mediterraneum , 2013,
Abstract: Review of the book: Child, Church and Compassion: Towards Child Theology in Romania, by William C. (Bill) Prevette. Regnum Studies in Mission Series. Regnum: Oxford, 2012. ISBN: 978-1-908355-03-4. Xvii + 377 pp. & index. (Paperback) $48.00 U.S.
Spatially homogeneous ferromagnetism below the enhanced Curie temperature in EuO_{1-x} thin films
Pedro M. S. Monteiro,Peter J. Baker,Adrian Ionescu,Crispin H. W. Barnes,Zaher Salman,Andreas Suter,Thomas Prokscha,Sean Langridge
Physics , 2013, DOI: 10.1103/PhysRevLett.110.217208
Abstract: We have used low energy implanted muons as a volume sensitive probe of the magnetic properties of EuO_{1-x} thin films. We find that static and homogeneous magnetic order persists up to the elevated T_C in the doped samples and the muon signal displays the double dome feature also observed in the sample magnetization. Our results appear incompatible with either the magnetic phase separation or bound magnetic polaron descriptions previously suggested to explain the elevated T_C, but are compatible with an RKKY-like interaction mediating magnetic interactions above 69 K.
Distinct magnetic phase transition at the surface of an antiferromagnet
Sean Langridge,Gavin M. Watson,Doon Gibbs,Joseph J. Betouras,Nikitas I. Gidopoulos,Frank Pollmann,Martin W. Long,Christian Vettier,Gerry H. Lander
Physics , 2013, DOI: 10.1103/PhysRevLett.112.167201
Abstract: In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present study, we report a distinct and unexpected surface magnetic phase transition, uniquely at a lower temperature than the N\'eel temperature. Employing grazing incidence X-ray resonant magnetic scattering we have observed the near surface behavior of uranium dioxide. UO$_2$ is a non-collinear, triple-q, antiferromagnet with the U ions on an face-centered-cubic lattice. Theoretical investigations establish that at the surface the energy increase, due to the lost bonds, reduces when the spins near the surface rotate, gradually losing their normal to the surface component. At the surface the lowest-energy spin configuration has a double-q (planar) structure. With increasing temperature, thermal fluctuations saturate the in-plane crystal field anisotropy at the surface, leading to soft excitations that have ferromagnetic $XY$ character and are decoupled from the bulk. The structure factor of a finite two-dimensional $XY$ model, fits the experimental data well for several orders of magnitude of the scattered intensity. Our results support a distinct magnetic transition at the surface in the Kosterlitz-Thouless universality class.
Unfashionable crop species flourish in the 21st century
Wayne Powell, Peter Langridge
Genome Biology , 2004, DOI: 10.1186/gb-2004-5-7-233
Abstract: The genomic era was founded on the study of a limited number of model organisms [1] that were chosen for their small genome size and experimental tractability. The use of model organisms can be powerful because a community of scientists can work collectively on a single organism, but it also encourages a reductionist approach. Intriguingly, the study of diversity and organism complexity is now gaining more prominence, often at the expense of research on model organisms. The mapping of a large number of wheat expressed sequence tags (ESTs) [2], physical mapping of the wheat genome [3], studies of synteny between related parts of the wheat genome [4,5] and between wheat and other cereals [6], and studies of the organization of sequence polymorphism into haplotypes [7] are big steps forward. These developments in crop genomics vividly illustrate how, although model organisms provide good starting points, their significance may decline as accessibility to genome technologies improves and the social and biological relevance of crop science to the public continues to gain prominence.Before the emergence of molecular biology, crop plants such as bread wheat (Triticum aestivum L.) were considered to be good models for cytogenetic investigations and research into polyploidy. Wheat has one of the largest and most complex genomes known: it is an allopolyploid, containing three different ancestral genomes (designated A, B and D), each of which contains seven pairs of homologous chromosomes. The number of chromosomes in the diploid genome (2n) is therefore 42; this number is also referred to as 6x, as each of the six ancestral genomes has seven chromosomes. The homologous chromosomes and genes in different ancestral genomes are referred to as 'homoeologous'. Although the ancestral genomes are very similar in gene content and gene order, chromosome pairing at meiosis is under genetic control and is restricted to homologous chromosomes. This results in disomic inheritance, as if t
Giant topological Hall effect in strained Fe$_{0.7}$Co$_{0.3}$Si epilayers
Nicholas A. Porter,Priyasmita Sinha,Michael B. Ward,Alexey N. Dobrynin,Rik M. D. Brydson,Timothy R. Charlton,Christian J. Kinane,Michael D. Robertson,Sean Langridge,Christopher H. Marrows
Physics , 2013,
Abstract: The coupling of electron spin to real-space magnetic textures leads to a variety of interesting magnetotransport effects. The skyrmionic spin textures often found in chiral B20-lattice magnets give rise, via real-space Berry phases, to the topological Hall effect, but it is typically rather small. Here, B20-ordered Fe$_{0.7}$Co$_{0.3}$Si epilayers display a giant topological Hall effect due to the combination of three favourable properties: they have a high spin-polarisation, a large ordinary Hall coefficient, and dense chiral spin textures. The topological Hall resistivity is as large as 820 n$\Omega$cm at helium temperatures. Moreover, we observed a drop in the longitudinal resistivity of 100 n$\Omega$cm at low temperatures in the same field range, suggesting that it is also of topological origin. That such strong effects can be found in material grown in thin film form on commercial silicon wafer bodes well for skyrmion-based spintronics.
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