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147 results on '"Bartolome, F."'

3. Parimagnetism in RCo$_2$ series (R=Dy, Ho, and Tm)

Author

Bonilla, C. M., Herrero-Albillos, J., Figueroa, A. I., Castan-Guerrero, C., Bartolome, J., Calvo-Almazan, I., Schmitz, D., Weschke, E., García, L. M., and Bartolome, F.

Subjects
Condensed Matter - Materials Science
Abstract

X-ray circular magnetic dichroism (XMCD), longitudinal ($\chi_{ac}$) and transverse (TS) ac magnetic susceptibility have been measured in several members of the $R$Co$_2$ series ($R$ = Dy, Ho, and Tm) as a function of temperature and applied magnetic field. We show that parimagnetism is a general behavior along the $R$Co$_2$ ferrimagnetic series ($R$ being a heavy rare earth ion). XMCD results evidence the presence of two compensation temperatures, defining two different parimagnetic configurations, which is a fully unexpected result. The inverse $\chi_{ac}$ curve exhibits a deviation from Curie-Weiss behavior which is recovered under applied magnetic field. The large excess of polarizability above the critical temperature proves the existence of an enhanced effective moment due to the presence of short range magnetic correlations, which are also observed in TS measurements. The combination of TS and XMCD measurements allows to depict new magnetic phase diagrams for the $R$Co$_2$ series. A new scenario allowing to understand the observed phenomenology as a Griffiths phase-like behavior is proposed, where the amorphous $R$Co$_2$ represents the undiluted system case., Comment: 12 figures

Published
2013

6. Magnetic nanoparticles with bulk-like properties

Author

Batlle, Xavier, Pérez, N., Guardia, P., Iglesias, O., Labarta, A., Bartolomé, F., García, L. M., Bartolomé, J., Roca, A. G., Morales, M. P., and Serna, C. J.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The magnetic behavior of $Fe_{3-x}O_4$ nanoparticles synthesized either by high-temperature decomposition of an organic iron precursor or low-temperature co-precipitation in aqueous conditions, is compared. Transmission electron microscopy, X-ray absorption spectroscopy, X-ray magnetic circular dichroism and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulk-like magnetic and electronic properties, while nanoparticles synthesized by co-precipitation show much poorer crystallinity and particle-like phenomenology, including reduced magnetization, high closure fields and shifted hysteresis loops. The key role of the crystal quality is thus suggested since particle-like behavior for particles larger than about 5 nm is only observed when they are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or bio-distribution studies., Comment: Review article. 20 pages, 7 figures. Invited contribution to 55th MMM Conference 2010 (Atlanta), Session HG-01. To be published in J. Appl. Phys

Published
2010
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7. Magnetic ground state of CeNi$_{1-x}$Cu$_{x}$: A calorimetric investigation

Author

Marcano, N., Espeso, J. I., Sal, J. C. Gomez, Fernandez, J. Rodriguez, Herrero-Albillos, J., and Bartolome, F.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We present a detailed specific heat study of the CeNi$_{1-x}$Cu$_{x}$series in a large temperature range of 0.2 K to 300 K. The analysis of these data, considering also previous neutron scattering, magnetic characterization and $\mu$SR results, allows us to present a convenient description of the system as inhomogeneous on the nanometric scale. Two regimes are detected in the compositional range depending on the dominant RKKY or Kondo interactions. We propose that the long-range magnetic order at low temperatures is achieved by a percolative process of magnetic clusters that become static below the freezing temperature $T_{f}$. In this scenario the existence of a Quantum Critical Point at the magnetic-nonmagnetic crossover must be discarded., Comment: 13 pages, 12 figures, submitted to Phys. Rev. B

Published
2005
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21. Annexin A5 prevents amyloid-ß-induced toxicity in choroid plexus: implication for Alzheimer’s disease

Author

Bartolome F., Krzyzanowska A., de la Cueva M., Pascual C., Antequera D., Spuch C., Villarejo-Galende A., Rabano A., Fortea J., Alcolea D., Lleo A., Ferrer I., Hardy J., Abramov A.Y., and Carro E.

Subjects
Male, Proteomics, autophagy, very elderly, blood brain barrier, Apoptosis, Wistar rat, lipocortin 5, Alzheimer Disease, cognitive defect, middle aged, Animals, Humans, animal, genetics, rat, Cognitive Dysfunction, human, Annexin A5, Rats, Wistar, Cells, Cultured, Aged, Aged, 80 and over, Neurons, cell culture, calcium, choroid plexus, Amyloid beta-Peptides, Rats, female, Blood-Brain Barrier, amyloid beta protein, physiology, pathology, nerve cell, metabolism
Abstract

In Alzheimer’s disease (AD) amyloid-ß (Aß) deposits may cause impairments in choroid plexus, a specialised brain structure which forms the blood–cerebrospinal fluid (CSF) barrier. We previously carried out a mass proteomic-based study in choroid plexus from AD patients and we found several differentially regulated proteins compared with healthy subjects. One of these proteins, annexin A5, was previously demonstrated implicated in blocking Aß-induced cytotoxicity in neuronal cell cultures. Here, we investigated the effects of annexin A5 on Aß toxicity in choroid plexus. We used choroid plexus tissue samples and CSF from mild cognitive impairment (MCI) and AD patients to analyse Aß accumulation, cell death and annexin A5 levels compared with control subjects. Choroid plexus cell cultures from rats were used to analyse annexin A5 effects on Aß-induced cytotoxicity. AD choroid plexus exhibited progressive reduction of annexin A5 levels along with progressive increased Aß accumulation and cell death as disease stage was higher. On the other hand, annexin A5 levels in CSF from patients were found progressively increased as the disease stage increased in severity. In choroid plexus primary cultures, Aß administration reduced endogenous annexin A5 levels in a time-course dependent manner and simultaneously increased annexin A5 levels in extracellular medium. Annexin A5 addition to choroid plexus cell cultures restored the Aß-induced impairments on autophagy flux and apoptosis in a calcium-dependent manner. We propose that annexin A5 would exert a protective role in choroid plexus and this protection is lost as Aß accumulates with the disease progression. Then, brain protection against further toxic insults would be jeopardised. © 2020, The Author(s).

Published
2020

32. Determination of the ground state of an Au-supported FePc film based on the interpretation of Fe K- and L-edge x-ray magnetic circular dichroism measurements

Author

Natoli, C.R., Kruger, P., Bartolome, J., and Bartolome, F.

Abstract

We determine the magnetic ground state of the FePc molecule on Au-supported thin films based on the observed values of orbital anisotropy and spectroscopic x-ray magnetic circular dichroism (XMCD) measurements at the Fe K and L edges. Starting from ab initio molecular orbital multiplet calculations for the isolated molecule, we diagonalize the spin-orbit interaction in the subspace spanned by the three lowest spin triplet states of (3)A(2g) and E-3(g) symmetry in the presence of a saturating magnetic field at a polar angle theta with respect to the normal to the plane of the film, plus an external perturbation representing the effect of the molecules in the stack on the FePc molecule under consideration. We find that the orbital moment of the ground state strongly depends on the magnetic field direction in agreement with the sum rule analysis of the L-23-edge XMCD data. We calculate integrals over the XMCD spectra at the Fe K and L-23 edges as used in the sum rules and explicitly show that they agree with the expectation values of the orbital moment and effective spin moment of the ground state. On the basis of this analysis, we can rule out alternative candidates proposed in the literature.

Published
2018

43. X-ray magnetic circular dichroism at the rare earth L(sub 2,3) edges in R(sub 2)Fe(sub 14)B intermetallics

Author

Soriano, J. Miguel-, Chaboy, J., Garcia, L.M., and Bartolome, F.

Subjects
Rare earth metals -- Research, Circular dichroism -- Research, Physics
Abstract

A systematic x-ray magnetic circular dichroism (XMCD) study performed at the rare-earth(R) L(sub 2,3) edges on the R(sub 2)Fe(sub 14)B series is presented. Both XMCD sum rules and Campbell's model are revised in the atomic level.

Published
2000

47. Magnetic x-ray investigation at the L(sub2,3) edges of Nd in Nd(sub2)Fe(sub14)

Author

Bartolome, F., Tonnerre, J.M., Seve, L., Raoux, D., Lorenzo, J.E., Chaboy, J., Garcia, L.M., Bartolome, J., Krisch, M., Rogalev, A., Serimaa, R., Kao, C.c., Cibin, G., and Marcelli, A.

Subjects
Circular dichroism -- Usage, X-rays -- Scattering, Physics
Abstract

A study of x-ray magnetic circular dichroism, resonant inelastic x-ray scattering and x-ray resonant magnetic scattering at the L(sub2,3) edges of Nd on Nd(sub2)Fe(sub14)B has been undertaken. A dipolar or quadrupolar origin can be assigned to different features observed in the experimental spectra, and the thermal dependence of the Nd moment orientation under the spin reorientation transition can be studied.

Published
1998

48. Soft x-ray resonant magnetic reflectivity study of thin films and multilayers

Author

Tonnerre, J.M., Seve, L., Barbara-Dechelette, A., Bartolome, F., Raoux, D., Chakarian, V., Kao, C.C., Fischer, H., Andrieu, s., and Fruchart, O.

Subjects
X-rays -- Scattering, Magnetic resonance -- Usage, Thin films -- Magnetic properties, Physics
Abstract

The use of x-ray resonant magnetic scattering (XRMS) has been developed, particularly in the soft x-ray range, to measure resonant magnetic reflectivity on thin films and multilayers in a transverse geometry. All experimental characteristics of the angular and energy reflectivity curves have been reproduced, along with the asymmetry ratio. This was applied to FexMn(sub1-x) alloy films.

Published
1998

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