R. Cid | European Synchrotron Radiation facility (original) (raw)

Papers by R. Cid

Research paper thumbnail of Topological Defects and Misfit Strain in Magnetic Stripe Domains of Lateral Multilayers With Perpendicular Magnetic Anisotropy

Physical Review Letters, 2012

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a perio... more Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.

Research paper thumbnail of Large negative thermal expansion of the Co subnetwork measured by EXAFS in highly disordered Nd 1− x Co x thin films with perpendicular magnetic anisotropy

Journal of Physics: Condensed Matter, 2013

We have measured a negative thermal expansion (NTE) of the Co subnetwork in amorphous Nd1-xCox (0... more We have measured a negative thermal expansion (NTE) of the Co subnetwork in amorphous Nd1-xCox (0.78 < x < 0.84) thin films of the order of 1% in volume using linearly polarized EXAFS spectroscopy at RT and 10 K. The expansion, which is anisotropic, is uncorrelated with the perpendicular magnetic anisotropy (PMA) observed in all the films, but correlated with the method used to deposit them. The atomic environments of the Nd atoms resulted in such a strong disorder that Nd-Nd and Nd-Co environments were invisible to EXAFS, and only Co-Co atomic environments were detected. The information on the Nd subnetwork was obtained through its magnetic moment measured by XMCD. These measurements demonstrate an increasing interaction of neodymium atoms with their particular local crystal field as the temperature decreased, suggesting possible structural modifications at their sites. Since the magnetic moment of the cobalt subnetwork remains essentially constant with the temperature, it is proposed that its detected NTE may be caused by the mechanical response of the amorphous network to structural transformations at the Nd sites. These results support that the PMA in RE-TM alloys is localized at the RE sites. The complete absence of EXAFS oscillations in the Nd L3 EXAFS spectra is remarkable: it means that the coherence length of the photoemitted electrons in disordered matter can be strongly reduced from that expected by atomic calculations to the point of being less than first neighbor distances, which is contrary to the common belief that first neighbors are always visible by EXAFS.

Research paper thumbnail of Microscopic origin of perpendicular magnetic anisotropy in amorphous Nd-Co homogeneous and compositionally modulated, thin films studied by XMCD

Journal of Physics: Conference Series, 2010

ABSTRACT Amorphous Nd-Co films deposited by DC-magnetron sputtering presented perpendicular magne... more ABSTRACT Amorphous Nd-Co films deposited by DC-magnetron sputtering presented perpendicular magnetic anisotropy (PMA) with energies, K(N), of the order of 10(6) erg/cc at RT. To understand the origin of their PMA, we measured the orbital and spin magnetic moments in Co and Nd by XMCD at the Co L(3,2) and Nd M(5,4) edges in two kinds of samples of similar thickness (30 nm) and composition: one compositionally modulated Nd/Co film (CM) with strong PMA (K(N) similar to 10(7) erg/cc at 10 K) and a homogenous alloy (A) with not strong enough PMA to see stripe domains for such thickness. The XMCD analysis evidenced the significant role of Nd in the PMA of these films.

Research paper thumbnail of Design, construction and tests of the ICARUS T600 detector

Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2004

We have constructed and operated the ICARUS T600 liquid argon (LAr) time projection chamber (TPC)... more We have constructed and operated the ICARUS T600 liquid argon (LAr) time projection chamber (TPC). The ICARUS T600 detector is the largest LAr TPC ever built, with a size of about 500 tons of fully imaging mass. The design and assembly of the detector relied on ...

Research paper thumbnail of Indirect detection of dark matter weakly interacting massive particles in a liquid argon time projection chamber

Journal of Cosmology and Astroparticle Physics, 2005

We assess the prospects for indirect detection of Weakly Interacting Massive Particles using a la... more We assess the prospects for indirect detection of Weakly Interacting Massive Particles using a large Liquid Argon TPC detector. Signal events will consist of energetic electron (anti)neutrinos coming from the decay of τ leptons and b quarks produced in WIMP annihilation in the core of the Sun. Background contamination from atmospheric neutrinos is expected to be low, thanks to the superb angular resolution and particle identification capabilities provided by the considered experimental set-up. We evaluate the event rates predicted for an annihilating WIMP as a function of its elastic scattering cross section with nucleons. This technique is particularly useful for WIMPs lighter than ∼ 100 GeV.

Research paper thumbnail of Measurement of the � decay spectrum with the ICARUS liquid Argon TPC

The European Physical Journal C - Particles and Fields, 2004

Examples are given which prove the ICARUS detector quality through relevant physics measurements.... more Examples are given which prove the ICARUS detector quality through relevant physics measurements. We study the µ decay energy spectrum from a sample of stopping µ events acquired during the test run of the ICARUS T600 detector. This detector allows the spatial reconstruction of the events with fine granularity, hence, the precise measurement of the range and dE/dx of the µ with high sampling rate. This information is used to compute the calibration factors needed for the full calorimetric reconstruction of the events. The Michel ρ parameter is then measured by comparison of the experimental and Monte Carlo simulated µ decay spectra, obtaining ρ = 0.72 ± 0.06 (stat.) ± 0.08 (syst.). The energy resolution for electrons below ∼ 50 MeV is finally extracted from the simulated sample, obtaining (E e meas − E e MC )/E e M C = 11%/ E [MeV] ⊕ 2%.

Research paper thumbnail of Temperature dependence of the anisotropy of amorphous NdCo5 thin films

Journal of Magnetism and Magnetic Materials, 2007

The magnetic anisotropy energy of the Co sublattice of amorphous NdCo 5 thin films deposited by m... more The magnetic anisotropy energy of the Co sublattice of amorphous NdCo 5 thin films deposited by magnetron sputtering has been measured in 30 nm thick films from 220 K up to 420 K using the magneto-optical transverse Kerr effect (TMOKE). They had a strong perpendicular magnetic anisotropy, with an anisotropy energy of 2 Â 10 6 erg/cm 3 at room temperature. The increase in the perpendicular anisotropy energy when the temperature decreased was smaller than expected if it was mainly caused by the Nd ions. An irreversible decrease in the anisotropy energy was observed when the films were annealed to only 420 K. Such a change was accompanied by an increase in the magnetic moment of Co, indicating that the origin of the perpendicular anisotropy in these films has to be associated with an asymmetry in the local atomic environment of Co and Nd induced during the deposition process. r

Research paper thumbnail of Topological Defects and Misfit Strain in Magnetic Stripe Domains of Lateral Multilayers With Perpendicular Magnetic Anisotropy

Physical Review Letters, 2012

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a perio... more Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.

Research paper thumbnail of Large negative thermal expansion of the Co subnetwork measured by EXAFS in highly disordered Nd 1− x Co x thin films with perpendicular magnetic anisotropy

Journal of Physics: Condensed Matter, 2013

We have measured a negative thermal expansion (NTE) of the Co subnetwork in amorphous Nd1-xCox (0... more We have measured a negative thermal expansion (NTE) of the Co subnetwork in amorphous Nd1-xCox (0.78 < x < 0.84) thin films of the order of 1% in volume using linearly polarized EXAFS spectroscopy at RT and 10 K. The expansion, which is anisotropic, is uncorrelated with the perpendicular magnetic anisotropy (PMA) observed in all the films, but correlated with the method used to deposit them. The atomic environments of the Nd atoms resulted in such a strong disorder that Nd-Nd and Nd-Co environments were invisible to EXAFS, and only Co-Co atomic environments were detected. The information on the Nd subnetwork was obtained through its magnetic moment measured by XMCD. These measurements demonstrate an increasing interaction of neodymium atoms with their particular local crystal field as the temperature decreased, suggesting possible structural modifications at their sites. Since the magnetic moment of the cobalt subnetwork remains essentially constant with the temperature, it is proposed that its detected NTE may be caused by the mechanical response of the amorphous network to structural transformations at the Nd sites. These results support that the PMA in RE-TM alloys is localized at the RE sites. The complete absence of EXAFS oscillations in the Nd L3 EXAFS spectra is remarkable: it means that the coherence length of the photoemitted electrons in disordered matter can be strongly reduced from that expected by atomic calculations to the point of being less than first neighbor distances, which is contrary to the common belief that first neighbors are always visible by EXAFS.

Research paper thumbnail of Microscopic origin of perpendicular magnetic anisotropy in amorphous Nd-Co homogeneous and compositionally modulated, thin films studied by XMCD

Journal of Physics: Conference Series, 2010

ABSTRACT Amorphous Nd-Co films deposited by DC-magnetron sputtering presented perpendicular magne... more ABSTRACT Amorphous Nd-Co films deposited by DC-magnetron sputtering presented perpendicular magnetic anisotropy (PMA) with energies, K(N), of the order of 10(6) erg/cc at RT. To understand the origin of their PMA, we measured the orbital and spin magnetic moments in Co and Nd by XMCD at the Co L(3,2) and Nd M(5,4) edges in two kinds of samples of similar thickness (30 nm) and composition: one compositionally modulated Nd/Co film (CM) with strong PMA (K(N) similar to 10(7) erg/cc at 10 K) and a homogenous alloy (A) with not strong enough PMA to see stripe domains for such thickness. The XMCD analysis evidenced the significant role of Nd in the PMA of these films.

Research paper thumbnail of Design, construction and tests of the ICARUS T600 detector

Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2004

We have constructed and operated the ICARUS T600 liquid argon (LAr) time projection chamber (TPC)... more We have constructed and operated the ICARUS T600 liquid argon (LAr) time projection chamber (TPC). The ICARUS T600 detector is the largest LAr TPC ever built, with a size of about 500 tons of fully imaging mass. The design and assembly of the detector relied on ...

Research paper thumbnail of Indirect detection of dark matter weakly interacting massive particles in a liquid argon time projection chamber

Journal of Cosmology and Astroparticle Physics, 2005

We assess the prospects for indirect detection of Weakly Interacting Massive Particles using a la... more We assess the prospects for indirect detection of Weakly Interacting Massive Particles using a large Liquid Argon TPC detector. Signal events will consist of energetic electron (anti)neutrinos coming from the decay of τ leptons and b quarks produced in WIMP annihilation in the core of the Sun. Background contamination from atmospheric neutrinos is expected to be low, thanks to the superb angular resolution and particle identification capabilities provided by the considered experimental set-up. We evaluate the event rates predicted for an annihilating WIMP as a function of its elastic scattering cross section with nucleons. This technique is particularly useful for WIMPs lighter than ∼ 100 GeV.

Research paper thumbnail of Measurement of the � decay spectrum with the ICARUS liquid Argon TPC

The European Physical Journal C - Particles and Fields, 2004

Examples are given which prove the ICARUS detector quality through relevant physics measurements.... more Examples are given which prove the ICARUS detector quality through relevant physics measurements. We study the µ decay energy spectrum from a sample of stopping µ events acquired during the test run of the ICARUS T600 detector. This detector allows the spatial reconstruction of the events with fine granularity, hence, the precise measurement of the range and dE/dx of the µ with high sampling rate. This information is used to compute the calibration factors needed for the full calorimetric reconstruction of the events. The Michel ρ parameter is then measured by comparison of the experimental and Monte Carlo simulated µ decay spectra, obtaining ρ = 0.72 ± 0.06 (stat.) ± 0.08 (syst.). The energy resolution for electrons below ∼ 50 MeV is finally extracted from the simulated sample, obtaining (E e meas − E e MC )/E e M C = 11%/ E [MeV] ⊕ 2%.

Research paper thumbnail of Temperature dependence of the anisotropy of amorphous NdCo5 thin films

Journal of Magnetism and Magnetic Materials, 2007

The magnetic anisotropy energy of the Co sublattice of amorphous NdCo 5 thin films deposited by m... more The magnetic anisotropy energy of the Co sublattice of amorphous NdCo 5 thin films deposited by magnetron sputtering has been measured in 30 nm thick films from 220 K up to 420 K using the magneto-optical transverse Kerr effect (TMOKE). They had a strong perpendicular magnetic anisotropy, with an anisotropy energy of 2 Â 10 6 erg/cm 3 at room temperature. The increase in the perpendicular anisotropy energy when the temperature decreased was smaller than expected if it was mainly caused by the Nd ions. An irreversible decrease in the anisotropy energy was observed when the films were annealed to only 420 K. Such a change was accompanied by an increase in the magnetic moment of Co, indicating that the origin of the perpendicular anisotropy in these films has to be associated with an asymmetry in the local atomic environment of Co and Nd induced during the deposition process. r