Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV2O6

We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin chain compound CoV2O6. Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to 6.Tn. Above Tn = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest neighbour exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and Tn to a state with a 1/3 magnetisation plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the AFM state has incommensurate long range order and inelastic time of flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above Tn, we find two broad bands between 3.5 and 5 meV and thermally activated low energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform FM Ising spin chain. Below Tn, we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below Tn, but above 5 K, is identified which may correspond to a crossover between 2D and 3D magnetic ordering.Comment: Expanded version, includes results from arXiv:0804.2966 and neutron powder diffraction. To appear in PR

Natural course of septo-optic dysplasia: Retrospective analysis of 20 cases

Introducción. La displasia septoóptica (DSO) es la combinación variable de signos de disgenesia de línea media cerebral, hipoplasia de nervios ópticos y disfunción hipotálamo-hipofisaria, asociándose, a veces, con un espectro variado de malformaciones de la corteza cerebral. Objetivo. Describir la evolución natural y los hallazgos de neuroimagen en una serie de 20 pacientes diagnosticados. Pacientes y métodos. Se revisan de forma retrospectiva las características epidemiológicas, clínicas y neurroradiológicas de 20 pacientes consecutivos diagnosticados de DSO entre enero de 1985 y enero de 2010. Se analizaron los datos de tomografía computarizada, resonancia magnética craneal, electroencefalograma, potenciales evocados visuales, valoración oftalmológica, cariotipo y estudio endocrinológico. En siete pacientes, se realizó estudio del gen Homeobox HESX1. Resultados. El 60% de los casos presentaba antecedentes patológicos en el primer trimestre de gestación, con las ecografías fetales normales. Clínicamente, destacaban manifestaciones visuales (85%), alteraciones endocrinas (50%), retraso mental (60%) y crisis epilépticas (55%). Un 55% se asociaba a anomalías de migración neuronal. En un 45%, la DSO era el único hallazgo de neuroimagen. Se realizó cariotipo a todos, siendo normal. El gen HESX1 fue positivo en dos de los siete casos estudiados (ambos con DSO aislada). Ninguno con mutación en el gen HESX1 presentaba consanguinidad familiar. No se realizó estudio genético a los padres. Conclusiones. La DSO debe clasificarse como un síndrome malformativo heterogéneo, que asocia múltiples anomalías cerebrales, oculares, endocrinas y sistémicas. Las formas más graves se asocian con anomalías de la migración neuronal y de la organización cortical (AU)Introduction. Septo-optic dysplasia (SOD) is the variable combination of signs of dysgenesis of the midline of the brain, hypoplasia of the optic nerves and hypothalamus-pituitary dysfunction, which is sometimes associated with a varied spectrum of malformations of the cerebral cortex. Aims. To describe the natural history and neuroimaging findings in a series of 20 diagnosed patients. Patients and methods. We review the epidemiological, clinical and neuroimaging characteristics of 20 consecutive patients diagnosed with SOD between January 1985 and January 2010. Data obtained from computerised tomography, magnetic resonance imaging of the head, electroencephalogram, visual evoked potentials, ophthalmological evaluation, karyotyping and endocrinological studies were analysed. In seven patients, a study of the gene Homeobox HESX1 was conducted. Results. Pathological antecedents in the first three months of gestation were presented by 60% of the cases, with normal results in the foetal ultrasound scans. Clinically, the most striking features were visual manifestations (85%), endocrine disorders (50%), mental retardation (60%) and epileptic seizures (55%). Fifty-five per cent were associated to abnormal neuronal migration. In 45%, SOD was the only finding in the neuroimaging scans. Karyotyping was performed in all cases, the results being normal. Gene HESX1 was positive in two of the seven cases studied (both with isolated SOD). None of those with mutation in gene HESX1 presented familial consanguinity. No gene study was conducted with the parents. Conclusions. SOD must be classified as a heterogeneous malformation syndrome, which is associated to multiple brain, ocular, endocrine and systemic anomalies. The most severe forms are associated with abnormal neuronal migration and cortical organisation (AU

Glass Transition in the Polaron Dynamics of CMR Manganites

Neutron scattering measurements on a bilayer manganite near optimal doping show that the short-range polarons correlations are completely dynamic at high T, but then freeze upon cooling to a temperature T* 310 K. This glass transition suggests that the paramagnetic/insulating state arises from an inherent orbital frustration that inhibits the formation of a long range orbital- and charge-ordered state. Upon further cooling into the ferromagnetic-metallic state (Tc=114 K), where the polarons melt, the diffuse scattering quickly develops into a propagating, transverse optic phonon.Comment: 4 pages, 4 figures. Physical Review Letters (in Press

Charge Ordering and Phase Competition in the Layered Perovskite Lasr2mn2o7

Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing temperature they become static and form a charge ordered (CO) phase below TCO=210 K. In the static regime, superlattice reflections are observed through neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l). Crystallographic analysis of the CO state demonstrates that the degree of charge and orbital ordering in this manganite is weaker than the charge ordering in three dimensional perovskite manganites. A TN=170K a type-A antiferromagnetism (AF) develops and competes with the charge ordering, that eventually melts below T*=100K. High resolution diffraction measurements suggest that that CO- and AF-states do not coincide within the same region in the material but rather co-exist as separate phases. The transition to type-A antiferromagnetism at lower temperatures is characterized by the competition between these two phases.Comment: 9 pages, 6 figure

Lattice anisotropy in uranium ternary compounds: UTX

Several U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure type a common pattern emerges. The direction of the U-U bonds with participation of the 5f states is distinctly the "soft" crystallographic direction, exhibiting also the highest coefficient of linear thermal expansion. The finding leads to an apparent paradox: the closer the U atoms are together in a particular direction the better they can be additionally compressed together by applied hydrostatic pressure. (C) 2012 Elsevier B. V. All rights reserved

Cs2NaAl1-xCrxF6: A family of compounds presenting magnetocaloric effect

FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPIn this paper we explore the magnetocaloric effect (MCE) of chromium-doped elpasolite Cs2NaAl1-x,CrxF6 (x = 0.01 and 0.62) single crystals. Magnetization and heat capacity data show the magnetocaloric potentials to be comparable to those of garnets, perovskites, and other fluorides, producing magnetic entropy changes of 0.5 J/kg K (x = 0.01) and 11 J/kg K (x = 0.62), and corresponding adiabatic temperature changes of 4 and 8 K, respectively. These values are for a magnetic field change of 50 kOe at a temperature around 3 K. A clear Schottky anomaly below 10 K, which becomes more apparent when an external magnetic field is applied, was observed and related to the splitting of the Cr3+ energy levels. These results hint at a new family of materials with potential wide use in cryorefrigeration.90616FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPFUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPSem informaçãoSem informaçãoSem informaçãoSem informaçãoSem informaçãoWe thank Pedro von Ranke (UERJ, Brazil) and Walter Kalceff (UTS, Australia) for fruitful discussions. J.C.G.T.’s participation in this work was financed by the Science without Borders Program. Access to CICECO/Chemistry Department (Aveiro, Portugal), GPMR-UNICAMP (Campinas, Brazil), LMBT- UFF (Niter´oi, Brazil), LBT-UFRJ (Rio de Janeiro, Brazil), BERII facilities, and LaMMB MagLab (Berlin, Germany) are gratefully acknowledged by all authors. Financial support was provided by Proppi/UFF, FAPERJ, FAPESP, CAPES, CNPq, and FINEP

A novel treatment-responsive encephalitis with frequent opsoclonus and teratoma

Among 249 patients with teratoma-associated encephalitis, 211 had N-methyl-D-aspartate receptor antibodies and 38 were negative for these antibodies. Whereas antibody-positive patients rarely developed prominent brainstem-cerebellar symptoms, 22 (58%) antibody-negative patients developed a brainstem-cerebellar syndrome, which in 45% occurred with opsoclonus. The median age of these patients was 28.5 years (range = 12-41), 91% were women, and 74% had full recovery after therapy and tumor resection. These findings uncover a novel phenotype of paraneoplastic opsoclonus that until recently was likely considered idiopathic or postinfectious. The triad of young age (teenager to young adult), systemic teratoma, and high response to treatment characterize this novel brainstem-cerebellar syndrome753435441United States Department of Health & Human Services National Institutes of Health (NIH) - USA; United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Cancer Institute (NCI); Fundacio la Marato de TV3; Instituto de Salud Carlos III; KWF Kankerbestrijding; McKnight Neuroscience of Brain Disorders award; Instituto de Salud Carlos III; ICRE