Magnetic structure in Dy/Sc superlattices

We have investigated magnetic order in superlattices of Dy and Sc grown along the hcp c axis by molecular beam epitaxy (MBE) techniques. Our neutron diffraction experiments reveal that individual Dy layers order ferromagnetically below Tc∼150 K. The magnetic coherence length along the growth direction is less than the Dy-layer thickness. Previous studies of rare-earth superlattices with Y or Lu as spacer layers have shown that magnetic coherence propagates through sufficiently thin nonmagnetic interlayers. This arises from the long-range exchange interaction that originates from nesting features in the Fermi surface of the spacer material. The lack of coupling in Dy/Sc superlattices reflects the very different Fermi surface of Sc, with much weaker nesting than Y and Lu

Anisotropic magnetic behavior in Dy/Y films and superlattices

By neutron diffraction we show that superlattices of Dy and Y grown by molecular-beam epitaxy along the hcp b axis exhibit little magnetic coupling between successive Dy layers, even for Y spacers as thin as 9 atomic planes (26). Previous studies of Dy/Y superlattices grown along the hcp c axis established that long-range three-dimensional helimagnetic ordering takes place even through Y spacer layers as thick as 120. This highly anisotropic coupling behavior is shown to have its origin in nearly-two-dimensional nesting features of the Y and Dy Fermi surfaces. Nesting along the c axis gives rise to sharp peaks along c in the wave-vector-dependent magnetic susceptibility, and causes the exchange coupling to exhibit long-range oscillations in real space. The lack of nesting features along the b axis leaves a rapid exponential decay of the exchange interaction with spin separation. From magnetic measurements by superconducting-quantum-interference-device magnetometry on b-axis superlattices and films, we deduce that the first-order ferromagnetic transition of Dy is suppressed, and that the critical field required to produce the ferromagnetic alignment is much higher than the c-axis counterpart. This difference arises from anisotropy of the energy balance of the system. The magnetic coherence in b-axis superlattices and films is anisotropic and exhibits an unusual temperature dependence

Correlating material-specific layers and magnetic distributions within onion-like Fe 3 O 4 /MnO/ γ- Mn2 O3 core/shell nanoparticles

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The magnetic responses of two nanoparticle systems comprised of Fe3 O 4/γ−Mn2O3 (soft ferrimagnetic, FM/hard FM) and Fe3O4/MnO/γ−Mn2 O3 (soft FM / antiferromagnetic, AFM/hard FM) are compared, where the MnO serves to physically decouple the FM layers. Variation in the temperature and applied field allows for Small Angle Neutron Scattering (SANS) measurements of the magnetic moments both parallel and perpendicular to an applied field. Data for the bilayer particle indicate that the graded ferrimagnetic layers are coupled and respond to the field as a single unit. For the trilayer nanoparticles, magnetometry suggests a Curie temperature (TC)≈ 40 K for the outer γ−Mn2O3 component, yet SANS reveals an increase in the magnetization associated with outer layer that is perpendicular to the applied field above TC during magnetic reversal. This result suggests that the γ−Mn2O3 magnetically reorients relative to the applied field as the temperature is increased above 40 K

Magnetic field frustration of the metal-insulator transition in V2 O3

Despite decades of efforts, the origin of metal-insulator transitions (MITs) in strongly correlated materials remains one of the main long-standing problems in condensed-matter physics. An archetypal example is V2O3, which undergoes simultaneous electronic, structural, and magnetic phase transitions. This remarkable feature highlights the many degrees of freedom at play in this material. In this work, acting solely on the magnetic degree of freedom, we reveal an anomalous feature in the electronic transport of V2O3: On cooling, the magnetoresistance changes from positive to negative values well above the MIT temperature, and shows divergent behavior at the transition. The effects are attributed to the magnetic field quenching antiferromagnetic fluctuations above the Néel temperature TN, and preventing long-range antiferromagnetic ordering below TN. In both cases, suppressing the antiferromagnetic ordering prevents the opening of the incipient electronic gap. This interpretation is supported by Hubbard model calculations which fully reproduce the experimental behavior. Our study sheds light on this classic problem providing a clear and physical interpretation of the nature of the metal-insulator transition.Fil: Trastoy, J.. University of California at San Diego; Estados UnidosFil: Camjayi, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Del Valle, J.. University of California at San Diego; Estados UnidosFil: Kalcheim, Y.. University of California at San Diego; Estados UnidosFil: Crocombette, J. P.. Université Paris-Saclay; FranciaFil: Gilbert, D.A.. University of Tennessee; Estados UnidosFil: Borchers, J.A.. Nist Center For Neutron Research; Estados UnidosFil: Villegas, J.E.. Université Paris-Saclay; FranciaFil: Ravelosona, D.. Center For Nanoscience And Nanotechnology; FranciaFil: Rozenberg, M.J.. Université Paris-Saclay; FranciaFil: Schuller, Ivan K.. University of California at San Diego; Estados Unido

Interlayer Exchange Coupling Mediated by Valence Band Electrons

The interlayer exchange coupling mediated by valence band electrons in all-semiconductor IV-VI magnetic/nonmagnetic superlattices is studied theoretically. A 3D tight-binding model, accounting for the band and magnetic structure of the constituent superlattice components is used to calculate the spin-dependent part of the total electronic energy. The antiferromagnetic coupling between ferromagnetic layers in EuS/PbS superlattices is obtained, in agreement with the experimental evidences. The results obtained for the coupling between antiferromagnetic layers in EuTe/PbTe superlattices are also presented.Comment: 8 pages, 6 figures, to be submitted to Phys.Rev.

Jorge A. Swieca's contributions to quantum field theory in the 60s and 70s and their relevance in present research

After revisiting some high points of particle physics and QFT of the two decades from 1960 to 1980, I comment on the work by Jorge Andre Swieca. I explain how it fits into the quantum field theory during these two decades and draw attention to its relevance to the ongoing particle physics research. A particular aim of this article is to direct thr readers mindfulness to the relevance of what at the time of Swieca was called "the Schwinger Higgs screening mechanism". which, together with recent ideas which generalize the concept of gauge theories, has all the ingredients to revolutionize the issue of gauge theories and the standard model.Comment: 49 pages, expansion and actualization of text, improvement of formulations and addition of many references to be published in EPJH - Historical Perspectives on Contemporary Physic

Solitons in a Grassmannian sigma-model Coupled to Chern-Simons Term

We propose an exactly solvable Grassmannian sigma-model coupled to the Chern-Simons theory. In the presence of a novel topological term our model admits exact self-dual vortex solutions which are identical to those of pure Grassmannian model, but the topological charge has a physical meaning as a magnetic flux since the gauge field is no longer auxiliary. We also extend the theory to a noncommutative plane and analyze the BPS solutions.Comment: 10+1 pages, No figure, LaTeX; Reference added, Minor changes, to appear in Phys. Rev.

A critical look at 50 years particle theory from the perspective of the crossing property

The crossing property is perhaps the most subtle aspect of the particle-field relation. Although it is not difficult to state its content in terms of certain analytic properties relating different matrixelements of the S-matrix or formfactors, its relation to the localization- and positive energy spectral principles requires a level of insight into the inner workings of QFT which goes beyond anything which can be found in typical textbooks on QFT. This paper presents a recent account based on new ideas derived from "modular localization" including a mathematic appendix on this subject. Its main novel achievement is the proof of the crossing property of formfactors from a two-algebra generalization of the KMS condition. The main content of this article is the presentation of the derailments of particle theory during more than 4 decades: the S-matrix bootstrap, the dual model and its string theoretic extension. Rather than being related to crossing, string theory is the (only known) realization of a dynamic infinite component one-particle wave function space and its associated infinite component field. Here "dynamic" means that, unlike a mere collection of infinitely many irreducible unitary Poincar\'e group representation or free fields, the formalism contains also operators which communicate between the different irreducible Poincar\'e represenations (the levels of the "infinite tower") and set the mass/spin spectrum. Wheras in pre-string times there were unsuccessful attempts to achieve this in analogy to the O(4,2) hydrogen spectrum by the use of higher noncompact groups, the superstring in d=9+1, which uses instead (bosonic/fermionic) oscillators obtained from multicomponent chiral currents is the only known unitary positive energy solution of the dynamical infinite component pointlike localized field project.Comment: 66 pages, addition of new results, addition of references, will appear in this form in Foundations of Physic

Global surveillance of cancer survival 1995-2009: analysis of individual data for 25,676,887 patients from 279 population-based registries in 67 countries (CONCORD-2)

BACKGROUND: Worldwide data for cancer survival are scarce. We aimed to initiate worldwide surveillance of cancer survival by central analysis of population-based registry data, as a metric of the effectiveness of health systems, and to inform global policy on cancer control. METHODS: Individual tumour records were submitted by 279 population-based cancer registries in 67 countries for 25·7 million adults (age 15-99 years) and 75,000 children (age 0-14 years) diagnosed with cancer during 1995-2009 and followed up to Dec 31, 2009, or later. We looked at cancers of the stomach, colon, rectum, liver, lung, breast (women), cervix, ovary, and prostate in adults, and adult and childhood leukaemia. Standardised quality control procedures were applied; errors were corrected by the registry concerned. We estimated 5-year net survival, adjusted for background mortality in every country or region by age (single year), sex, and calendar year, and by race or ethnic origin in some countries. Estimates were age-standardised with the International Cancer Survival Standard weights. FINDINGS: 5-year survival from colon, rectal, and breast cancers has increased steadily in most developed countries. For patients diagnosed during 2005-09, survival for colon and rectal cancer reached 60% or more in 22 countries around the world; for breast cancer, 5-year survival rose to 85% or higher in 17 countries worldwide. Liver and lung cancer remain lethal in all nations: for both cancers, 5-year survival is below 20% everywhere in Europe, in the range 15-19% in North America, and as low as 7-9% in Mongolia and Thailand. Striking rises in 5-year survival from prostate cancer have occurred in many countries: survival rose by 10-20% between 1995-99 and 2005-09 in 22 countries in South America, Asia, and Europe, but survival still varies widely around the world, from less than 60% in Bulgaria and Thailand to 95% or more in Brazil, Puerto Rico, and the USA. For cervical cancer, national estimates of 5-year survival range from less than 50% to more than 70%; regional variations are much wider, and improvements between 1995-99 and 2005-09 have generally been slight. For women diagnosed with ovarian cancer in 2005-09, 5-year survival was 40% or higher only in Ecuador, the USA, and 17 countries in Asia and Europe. 5-year survival for stomach cancer in 2005-09 was high (54-58%) in Japan and South Korea, compared with less than 40% in other countries. By contrast, 5-year survival from adult leukaemia in Japan and South Korea (18-23%) is lower than in most other countries. 5-year survival from childhood acute lymphoblastic leukaemia is less than 60% in several countries, but as high as 90% in Canada and four European countries, which suggests major deficiencies in the management of a largely curable disease. INTERPRETATION: International comparison of survival trends reveals very wide differences that are likely to be attributable to differences in access to early diagnosis and optimum treatment. Continuous worldwide surveillance of cancer survival should become an indispensable source of information for cancer patients and researchers and a stimulus for politicians to improve health policy and health-care systems