Javier Blasco - Academia.edu (original) (raw)
Papers by Javier Blasco
International Journal of Modern Physics B, 2002
Temperature dependence of local structure of the CuO 2 plane has been studied by in plane polariz... more Temperature dependence of local structure of the CuO 2 plane has been studied by in plane polarized (E//ab) Cu K-edge extended X-ray absorption fine structure (EXAFS) experiments on an under-doped single crystal of superconducting La1.87Sr0.13CuO 4-y system with T c =32 K . The temperature dependence of the Debye–Waller factors for the Cu-O and Cu-La/Sr pairs are determined. We find that the motion of Cu and O atoms in the Cu-O bond is partially correlated at higher temperatures, going over to an uncorrelated motion at lower temperatures. The results are discussed in terms of the local lattice instabilities and stripes as reported in other systems.
Co"03 perovskites with 0.3~x~0.8 show a peak anomaly at low temperatures (=28 K) in their y"(T) c... more Co"03 perovskites with 0.3~x~0.8 show a peak anomaly at low temperatures (=28 K) in their y"(T) curve. The frequency dependence of the peak anomaly and magnetization experiments after different thermal cycles, i.e. , cooling the samples in the presence of a magnetic field or zero-field cooling, shows that the anomaly is associated with magnetic relaxation processes indicating a new spin-glass transition. X-ray diffraction, transmission electron microscopy, and analysis of the magnetic data agree with the absence of small magnetic impurities which could give smaller relaxation phenomena. A discussion of the microscopic origin of such behavior has also been given.
Physical Review B, 2000
We report that the first-order antiferromagnetic to ferromagnetic transition in the Ge-rich magne... more We report that the first-order antiferromagnetic to ferromagnetic transition in the Ge-rich magnetocaloric compound Gd 5 ͑Si 0.1 Ge 0.9 ͒ 4 is associated with a structural phase transformation from a high-temperature Gd 5 Ge 4-type Pnma to a low-temperature Gd 5 Si 4-type Pnma orthorhombic structure. This magnetostructural transition can be triggered reversibly by application of an external magnetic field, resulting in strong magnetoelastic effects above the transition. The revised magnetic and crystallographic phase diagram for the Gd 5 (Si x Ge 1Ϫx) 4 series is proposed.
Physical Review B, 2008
The crystal and local structures of La 1−x Sr x FeO 3−␦ ͑0 ഛ x ഛ 1͒ samples have been studied by ... more The crystal and local structures of La 1−x Sr x FeO 3−␦ ͑0 ഛ x ഛ 1͒ samples have been studied by x-ray diffraction and x-ray absorption spectroscopy techniques. The Fe-O bond length decreases with increasing x. Accordingly, the x-ray absorption near edge spectroscopy ͑XANES͒ spectra reveal a chemical shift of the iron K edge to higher energies. Both results agree with an Fe valence increase as La is substituted with Sr. Extended x-ray absorption fine structure spectroscopy and XANES show that the chemical state of Fe atoms in intermediate compositions can be described either by a bimodal distribution of formal Fe 3+ and Fe 4+ ions or by an Fe 3.x+ intermediate valence. The large value of the Debye-Waller factors obtained for intermediate compositions indicates that hole doping produces local disorder around the Fe ions. These factors show unusually large values below the metal-insulator ͑MI͒ transition for x =2/ 3 or 3/ 4. We show that a significant charge disproportionation of the type 2Fe 4+ → Fe 3+ +Fe 5+ cannot account for the local structure observed below the MI transition temperature of these samples. We suggest that an electronic localization arises from an order-disorder transition between dynamic and static distortions, resulting in the opening of a gap at the Fermi level.
Physical Review B, 2004
ABSTRACT We substitute Mg for Mn in the LaMnO3 compound. LaMn1-xMgxO3 single phases can be formed... more ABSTRACT We substitute Mg for Mn in the LaMnO3 compound. LaMn1-xMgxO3 single phases can be formed up to x=0.5 . Structural and electronic properties were studied by means of x-ray diffraction and x-ray absorption spectroscopy. A double perovskite is observed for x=>0.4 whereas no long Mn/Mg ordering is detected for x0.3 undergo a spin-glass transition at low temperatures. The frequency dependence of the freezing temperature follows a Vogel-Fulcher law and it is similar to canonical spin-glasses. The high temperature ac susceptibility of all samples obeys the Curie-Weiss law but the effective paramagnetic moments do not agree with a spin-only contribution for x
Physical Review B, 2004
The origin of the x-ray resonant scattering of (002) and (006) forbidden reflections in the spine... more The origin of the x-ray resonant scattering of (002) and (006) forbidden reflections in the spinel ferrites has been investigated. Resonant features were previously observed in Fe3O4 at the pre-edge and main-edge energies of the FeK -absorption edge. They were ascribed to dipole-quadrupole and dipole transitions at the tetrahedral and pseudo-octahedral Fe ions, respectively. To corroborate this origin and to
Physica Scripta, 2005
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Journal of Synchrotron Radiation, 2001
The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray a... more The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray absorption spectroscopy at the Mn K-edge. Higher resolution than in conventional measurements has been achieved by measuring the Mn Kβ fluorescence line. We have found a unique resonance at the edge in the XANES spectra of intermediate composition RE1−xCaxMnO3 samples. The features of these XANES spectra do not depend on small changes in the local structure around the Mn atom. However, the spectra of the intermediate composition samples can not be reproduced by a linear combination of REMnO3 and CaMnO3 spectra. Accordingly, the electronic state of Mn atoms in these compounds can not be considered as a mixture of Mn3+ and Mn4+ pure states.
Journal of Physics: Condensed Matter, 2011
We report on experimental oxygen K-edge x-ray absorption near-edge structure (XANES) spectra of t... more We report on experimental oxygen K-edge x-ray absorption near-edge structure (XANES) spectra of the LaFe 1-x Ga x O 3 and LaMn 1-x Ga x O 3 series. The transition-metal substitution by the 3d full shell Ga atom is mainly reflected in a systematic decrease of the pre-edge structures in the XANES spectra of the two series. This result shows that the associated states originate from the hybridization of oxygen 2p and unoccupied Fe (or Mn) 3d states. We have analyzed the experimental results in terms of detailed calculations based on multiple-scattering theory. In order to relate the pre-edge features to the corresponding atomic arrangements and electronic characters, we performed simulations with variable cluster size and composition around the absorber oxygen in the LaFeO 3 and LaMnO 3 crystal structures. We find that the low-energy prepeak is correctly reproduced if just the absorbing oxygen and the two nearest neighbours Fe (or Mn) ions are considered in the cluster. Conversely, higher energy pre-peaks only arise when the full oxygen-coordination geometry around the two metal sites is taken into account. The coupled electronic and structural origin of the pre-peaks successfully explains the difference observed in the pre-edge structures between the XANES spectra of LaFeO 3 and LaMnO 3 .
Journal of Physics: Conference Series, 2011
The value of TC and the magnetic behavior of La2MnCoO6 depend on preparation conditions, in parti... more The value of TC and the magnetic behavior of La2MnCoO6 depend on preparation conditions, in particular on the cooling rate after the last calcinations process. The valence state and the degree of order of cobalt and manganese ions vary according. We expose here two samples of La2MnCoO6 sintered by solid state reaction with different cooling rates. The Rietveld refinement of neutron powder diffraction (NPD) data showed that our samples crystallize in a monoclinic structure with symmetry P21/n up room temperature and ferromagnetic transition around 230K. Sample with lower cooling rate presents a saturation magnetization of 5.58muB/f.u. besides the value of 4.41muB/f.u. for that with higher cooling rate.
Journal of Physics: Conference Series, 2009
The emergence of superlattice periodicities at metal to insulator transitions in hole doped perov... more The emergence of superlattice periodicities at metal to insulator transitions in hole doped perovskite oxides responds to a rearrangement of the local atomic structure, and electron and spin density distribution. Originally, the ionic model based on a checkerboard-type atomic distribution served to describe the low temperature charge and orbital ordered (COO) phases arising in half-doped manganites. In the last years, the exploitation of resonant x-ray scattering (RXS) capabilities has shown the need to revisit these concepts and improve the picture. Yet, we have realised that COO is a more common phenomenon than expected that can be observed in a wide range of doping levels. Here we compare the experimental data recently collected by RXS on La 0.4 Sr 1.6 MnO 4 (x=0.60) and La(Pr) 1/3 Sr 2/3 FeO 3 (x=0.67). The first shows a COO phase similar to that found in the x=0.5 sample but angular peak positions vs. T denotes the incommensurability of superlattice reflections. Meanwhile, the analysis of the commensurate CO phase in the studied ferrite underlines the role of the structural changes also involving La(Sr) and O atoms.
Journal of Magnetism and Magnetic Materials, 1996
The heat capacity Of the perovskite NdA10 3 has been measured in the range 0.2 K < T < 6 K. It sh... more The heat capacity Of the perovskite NdA10 3 has been measured in the range 0.2 K < T < 6 K. It shows a sharp peak that indicates antiferromagnetic ordering of the Nd at 0.93(1) K. The total value of the entropy is in agreement with the expected result for an effective spin s = 1/2.
Journal of Magnetism and Magnetic Materials, 2005
Previous work in (Ba 0.8 Sr 0.2) 2Àx La x FeMoO 6 and Ba 1+x Sr 1À3x La 2x FeMoO 6 have stated el... more Previous work in (Ba 0.8 Sr 0.2) 2Àx La x FeMoO 6 and Ba 1+x Sr 1À3x La 2x FeMoO 6 have stated electron doping as the most important parameter in terms of T c enhancement. Here we report complementary structural, magnetic and transport properties, say a series where there is no doping and only structural parameters are changed: (Ba 0.8 Sr 0.2) 2Àx La 2x/3 # x/3 FeMoO 6. We propose a complete phase diagram where structural and bandfilling impact on the Curie temperature is clearly evidenced.
Journal of Magnetism and Magnetic Materials, 1999
Mn K-edge X-ray absorption spectroscopy was used to determine the electronic and geometrical loca... more Mn K-edge X-ray absorption spectroscopy was used to determine the electronic and geometrical local structure at the Mn site in LaMnO3 + δ (δ = 0, 0.07, and 0.15) series. The XANES spectra of LaMnO3 + δ samples show a mixed valence oxidation state for the Mn atom similar to that found in La1 − xCaxMnO3 series. EXAFS spectra show a distorted Jahn—Teller octahedra for LaMnO3 which is drastically reduced as δ increases. Otherwise, an anomalous structural disorder, reported for the paramagnetic phase in magnetoresistive compounds, is also present at low temperatures in this series.
International Journal of Modern Physics B, 2002
Temperature dependence of local structure of the CuO 2 plane has been studied by in plane polariz... more Temperature dependence of local structure of the CuO 2 plane has been studied by in plane polarized (E//ab) Cu K-edge extended X-ray absorption fine structure (EXAFS) experiments on an under-doped single crystal of superconducting La1.87Sr0.13CuO 4-y system with T c =32 K . The temperature dependence of the Debye–Waller factors for the Cu-O and Cu-La/Sr pairs are determined. We find that the motion of Cu and O atoms in the Cu-O bond is partially correlated at higher temperatures, going over to an uncorrelated motion at lower temperatures. The results are discussed in terms of the local lattice instabilities and stripes as reported in other systems.
Co"03 perovskites with 0.3~x~0.8 show a peak anomaly at low temperatures (=28 K) in their y"(T) c... more Co"03 perovskites with 0.3~x~0.8 show a peak anomaly at low temperatures (=28 K) in their y"(T) curve. The frequency dependence of the peak anomaly and magnetization experiments after different thermal cycles, i.e. , cooling the samples in the presence of a magnetic field or zero-field cooling, shows that the anomaly is associated with magnetic relaxation processes indicating a new spin-glass transition. X-ray diffraction, transmission electron microscopy, and analysis of the magnetic data agree with the absence of small magnetic impurities which could give smaller relaxation phenomena. A discussion of the microscopic origin of such behavior has also been given.
Physical Review B, 2000
We report that the first-order antiferromagnetic to ferromagnetic transition in the Ge-rich magne... more We report that the first-order antiferromagnetic to ferromagnetic transition in the Ge-rich magnetocaloric compound Gd 5 ͑Si 0.1 Ge 0.9 ͒ 4 is associated with a structural phase transformation from a high-temperature Gd 5 Ge 4-type Pnma to a low-temperature Gd 5 Si 4-type Pnma orthorhombic structure. This magnetostructural transition can be triggered reversibly by application of an external magnetic field, resulting in strong magnetoelastic effects above the transition. The revised magnetic and crystallographic phase diagram for the Gd 5 (Si x Ge 1Ϫx) 4 series is proposed.
Physical Review B, 2008
The crystal and local structures of La 1−x Sr x FeO 3−␦ ͑0 ഛ x ഛ 1͒ samples have been studied by ... more The crystal and local structures of La 1−x Sr x FeO 3−␦ ͑0 ഛ x ഛ 1͒ samples have been studied by x-ray diffraction and x-ray absorption spectroscopy techniques. The Fe-O bond length decreases with increasing x. Accordingly, the x-ray absorption near edge spectroscopy ͑XANES͒ spectra reveal a chemical shift of the iron K edge to higher energies. Both results agree with an Fe valence increase as La is substituted with Sr. Extended x-ray absorption fine structure spectroscopy and XANES show that the chemical state of Fe atoms in intermediate compositions can be described either by a bimodal distribution of formal Fe 3+ and Fe 4+ ions or by an Fe 3.x+ intermediate valence. The large value of the Debye-Waller factors obtained for intermediate compositions indicates that hole doping produces local disorder around the Fe ions. These factors show unusually large values below the metal-insulator ͑MI͒ transition for x =2/ 3 or 3/ 4. We show that a significant charge disproportionation of the type 2Fe 4+ → Fe 3+ +Fe 5+ cannot account for the local structure observed below the MI transition temperature of these samples. We suggest that an electronic localization arises from an order-disorder transition between dynamic and static distortions, resulting in the opening of a gap at the Fermi level.
Physical Review B, 2004
ABSTRACT We substitute Mg for Mn in the LaMnO3 compound. LaMn1-xMgxO3 single phases can be formed... more ABSTRACT We substitute Mg for Mn in the LaMnO3 compound. LaMn1-xMgxO3 single phases can be formed up to x=0.5 . Structural and electronic properties were studied by means of x-ray diffraction and x-ray absorption spectroscopy. A double perovskite is observed for x=>0.4 whereas no long Mn/Mg ordering is detected for x0.3 undergo a spin-glass transition at low temperatures. The frequency dependence of the freezing temperature follows a Vogel-Fulcher law and it is similar to canonical spin-glasses. The high temperature ac susceptibility of all samples obeys the Curie-Weiss law but the effective paramagnetic moments do not agree with a spin-only contribution for x
Physical Review B, 2004
The origin of the x-ray resonant scattering of (002) and (006) forbidden reflections in the spine... more The origin of the x-ray resonant scattering of (002) and (006) forbidden reflections in the spinel ferrites has been investigated. Resonant features were previously observed in Fe3O4 at the pre-edge and main-edge energies of the FeK -absorption edge. They were ascribed to dipole-quadrupole and dipole transitions at the tetrahedral and pseudo-octahedral Fe ions, respectively. To corroborate this origin and to
Physica Scripta, 2005
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Journal of Synchrotron Radiation, 2001
The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray a... more The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray absorption spectroscopy at the Mn K-edge. Higher resolution than in conventional measurements has been achieved by measuring the Mn Kβ fluorescence line. We have found a unique resonance at the edge in the XANES spectra of intermediate composition RE1−xCaxMnO3 samples. The features of these XANES spectra do not depend on small changes in the local structure around the Mn atom. However, the spectra of the intermediate composition samples can not be reproduced by a linear combination of REMnO3 and CaMnO3 spectra. Accordingly, the electronic state of Mn atoms in these compounds can not be considered as a mixture of Mn3+ and Mn4+ pure states.
Journal of Physics: Condensed Matter, 2011
We report on experimental oxygen K-edge x-ray absorption near-edge structure (XANES) spectra of t... more We report on experimental oxygen K-edge x-ray absorption near-edge structure (XANES) spectra of the LaFe 1-x Ga x O 3 and LaMn 1-x Ga x O 3 series. The transition-metal substitution by the 3d full shell Ga atom is mainly reflected in a systematic decrease of the pre-edge structures in the XANES spectra of the two series. This result shows that the associated states originate from the hybridization of oxygen 2p and unoccupied Fe (or Mn) 3d states. We have analyzed the experimental results in terms of detailed calculations based on multiple-scattering theory. In order to relate the pre-edge features to the corresponding atomic arrangements and electronic characters, we performed simulations with variable cluster size and composition around the absorber oxygen in the LaFeO 3 and LaMnO 3 crystal structures. We find that the low-energy prepeak is correctly reproduced if just the absorbing oxygen and the two nearest neighbours Fe (or Mn) ions are considered in the cluster. Conversely, higher energy pre-peaks only arise when the full oxygen-coordination geometry around the two metal sites is taken into account. The coupled electronic and structural origin of the pre-peaks successfully explains the difference observed in the pre-edge structures between the XANES spectra of LaFeO 3 and LaMnO 3 .
Journal of Physics: Conference Series, 2011
The value of TC and the magnetic behavior of La2MnCoO6 depend on preparation conditions, in parti... more The value of TC and the magnetic behavior of La2MnCoO6 depend on preparation conditions, in particular on the cooling rate after the last calcinations process. The valence state and the degree of order of cobalt and manganese ions vary according. We expose here two samples of La2MnCoO6 sintered by solid state reaction with different cooling rates. The Rietveld refinement of neutron powder diffraction (NPD) data showed that our samples crystallize in a monoclinic structure with symmetry P21/n up room temperature and ferromagnetic transition around 230K. Sample with lower cooling rate presents a saturation magnetization of 5.58muB/f.u. besides the value of 4.41muB/f.u. for that with higher cooling rate.
Journal of Physics: Conference Series, 2009
The emergence of superlattice periodicities at metal to insulator transitions in hole doped perov... more The emergence of superlattice periodicities at metal to insulator transitions in hole doped perovskite oxides responds to a rearrangement of the local atomic structure, and electron and spin density distribution. Originally, the ionic model based on a checkerboard-type atomic distribution served to describe the low temperature charge and orbital ordered (COO) phases arising in half-doped manganites. In the last years, the exploitation of resonant x-ray scattering (RXS) capabilities has shown the need to revisit these concepts and improve the picture. Yet, we have realised that COO is a more common phenomenon than expected that can be observed in a wide range of doping levels. Here we compare the experimental data recently collected by RXS on La 0.4 Sr 1.6 MnO 4 (x=0.60) and La(Pr) 1/3 Sr 2/3 FeO 3 (x=0.67). The first shows a COO phase similar to that found in the x=0.5 sample but angular peak positions vs. T denotes the incommensurability of superlattice reflections. Meanwhile, the analysis of the commensurate CO phase in the studied ferrite underlines the role of the structural changes also involving La(Sr) and O atoms.
Journal of Magnetism and Magnetic Materials, 1996
The heat capacity Of the perovskite NdA10 3 has been measured in the range 0.2 K < T < 6 K. It sh... more The heat capacity Of the perovskite NdA10 3 has been measured in the range 0.2 K < T < 6 K. It shows a sharp peak that indicates antiferromagnetic ordering of the Nd at 0.93(1) K. The total value of the entropy is in agreement with the expected result for an effective spin s = 1/2.
Journal of Magnetism and Magnetic Materials, 2005
Previous work in (Ba 0.8 Sr 0.2) 2Àx La x FeMoO 6 and Ba 1+x Sr 1À3x La 2x FeMoO 6 have stated el... more Previous work in (Ba 0.8 Sr 0.2) 2Àx La x FeMoO 6 and Ba 1+x Sr 1À3x La 2x FeMoO 6 have stated electron doping as the most important parameter in terms of T c enhancement. Here we report complementary structural, magnetic and transport properties, say a series where there is no doping and only structural parameters are changed: (Ba 0.8 Sr 0.2) 2Àx La 2x/3 # x/3 FeMoO 6. We propose a complete phase diagram where structural and bandfilling impact on the Curie temperature is clearly evidenced.
Journal of Magnetism and Magnetic Materials, 1999
Mn K-edge X-ray absorption spectroscopy was used to determine the electronic and geometrical loca... more Mn K-edge X-ray absorption spectroscopy was used to determine the electronic and geometrical local structure at the Mn site in LaMnO3 + δ (δ = 0, 0.07, and 0.15) series. The XANES spectra of LaMnO3 + δ samples show a mixed valence oxidation state for the Mn atom similar to that found in La1 − xCaxMnO3 series. EXAFS spectra show a distorted Jahn—Teller octahedra for LaMnO3 which is drastically reduced as δ increases. Otherwise, an anomalous structural disorder, reported for the paramagnetic phase in magnetoresistive compounds, is also present at low temperatures in this series.