rodolfo sanchez - Academia.edu (original) (raw)
Papers by rodolfo sanchez
Physica B, 2002
We present electric and magnetic properties of polycrystalline Pr 0.5- δCa 0.2+ δSr 0.3MnO 3, for... more We present electric and magnetic properties of polycrystalline Pr 0.5- δCa 0.2+ δSr 0.3MnO 3, for δ between -0.04 and 0.04, where the hole concentration is n=0.5+ δ. In this series, we study the effects of moving n away from 0.5 on both, the phase diagram and phase separated state. We found that the low temperature ferromagnetic fraction XFM continuously decreases when n increases. As a result, the samples with n<0.5 (large XFM) exhibit metallic resistivity at low T while for n>0.5 the insulating state predominates. We construct a detailed T- n phase diagram showing the asymmetries around half-doping.
Journal of Low Temperature Physics, Apr 1, 2004
Physica B Condensed Matter, 2002
We measure voltage-current curves at low temperature in La 2/3B 1/3MnO 3 samples (B=Ca,Sr). The p... more We measure voltage-current curves at low temperature in La 2/3B 1/3MnO 3 samples (B=Ca,Sr). The powder oxides were prepared by different wet-chemical routes and low calcination temperatures were used for nanoparticles formation. We studied samples prepared by three different synthesis methods: gel-combustion, urea sol-gel and liquid-mix. Although the average particle size was almost the same for all the samples (~30 nm) , we found different behaviors in the V- I curves depending on the synthesis route. The obtained data are analyzed in the electronic tunneling picture.
J Magn Magn Mater, 2001
We have performed measurements of thermoelectric power, electrical resistivity and DC magnetizati... more We have performed measurements of thermoelectric power, electrical resistivity and DC magnetization in polycrystalline samples of Pr 0.65Ca 0.35- xSr xMnO 3 with x=0, 0.02, 0.05, 0.10 and 0.20. The system presents an evolution from a charge-ordered manganite at x=0, with an insulating-like resistivity and low magnetization values, towards a ferromagnetic (FM) metallic state for x=0.20. We show that in the intermediate region a strong competition between the FM double-exchange and the localized charge-ordering occurs, inducing the phase segregation of the two competing states in a wide temperature range. We estimate the temperature ( T) evolution of the FM phase fraction of the x=0.10 sample and construct a complete T- x phase diagram.
We address the problem of the percolative phase separation in polycrystalline samples of Pr$_{0.5... more We address the problem of the percolative phase separation in polycrystalline samples of Pr$_{0.5-\delta}$Ca$_{0.2+\delta}$Sr$_{0.3}$MnO$_3$ for −0.04leqdeltaleq0.04-0.04\leq \delta \leq 0.04−0.04leqdeltaleq0.04 (hole doping nnn between 0.46 and 0.54). We perform measurements of X-ray diffraction, dc magnetization, ESR, and electrical resistivity. These samples show at TCT_CTC a paramagnetic (PM) to ferromagnetic (FM) transition, however, we found that for n>0.50n>0.50n>0.50 there is a coexistence of both of these phases below TCT_CTC. On lowering TTT below the charge-ordering (CO) temperature TCOT_{CO}TCO all the samples exhibit a coexistence between the FM metallic and CO (antiferromagnetic) phases. In the whole TTT range the FM phase fraction ($X$) decreases with increasing nnn. Furthermore, we show that only for nleq0.50n\leq 0.50nleq0.50 the metallic fraction is above the critical percolation threshold XCsimeq15.5X_C\simeq 15.5%XCsimeq15.5. As a consequence, these samples show very different magnetoresistance properties. In addition, for nleq0.50n\leq 0.50nleq0.50 we observe a percolative metal-insulator transition at TMIT_{MI}TMI, and for TMI<T<TCOT_{MI}<T<T_{CO}TMI<T<TCO the insulating-like behavior generated by the enlargement of XXX with increasing TTT is well described by the percolation law rho−1=sigmasim(X−XC)t\rho ^{-1}=\sigma \sim (X-X_C)^trho−1=sigmasim(X−XC)t, where ttt is a critical exponent. On the basis of the values obtained for this exponent we discuss different possible percolation mechanisms, and suggest that a more deep understanding of geometric and dimensionality effects is needed in phase separated manganites. We present a complete TTT vs nnn phase diagram showing the magnetic and electric properties of the studied compound around half doping.
J Mater Res, 1998
ABSTRACT
Physica B, 2002
We present electric and magnetic properties of polycrystalline Pr0.5−δCa0.2+δSr0.3MnO3, for δ bet... more We present electric and magnetic properties of polycrystalline Pr0.5−δCa0.2+δSr0.3MnO3, for δ between −0.04 and 0.04, where the hole concentration is n=0.5+δ. In this series, we study the effects of moving n away from 0.5 on both, the phase diagram and phase separated state. We found that the low temperature ferromagnetic fraction XFM continuously decreases when n increases. As a result, the samples with n<0.5 (large XFM) exhibit metallic resistivity at low T while for n>0.5 the insulating state predominates. We construct a detailed T–n phase diagram showing the asymmetries around half-doping.
J Appl Phys, 2003
We study the effect of the introduction of a controlled amount of oxygen vacancies on the magneti... more We study the effect of the introduction of a controlled amount of oxygen vacancies on the magnetic and transport properties of the phase separated manganite Pr0.5Ca0.2Sr0.3MnO3-δ, for δ=0 and 0.01. This compound presents a paramagnetic to ferromagnetic (FM) transition below TC˜240 K, and then to a charge-ordered (CO) and antiferromagnetic (AFM) phase at TCO˜175 K. However, below TCO an appreciable FM component (˜20%) still survives, related to a FM volume immersed within the CO/AFM matrix. At low temperatures, in the mainly CO phase, the introduction of oxygen vacancies enhances the FM ordering, with the consequent decrease of resistivity and magnetoresistance (MR). On the contrary, in the FM phase (in the range TCO<T<TC) the magnetization is reduced and the resistivity and MR increase. These results are discussed in the frame of percolative transport in metal-insulator mixtures, and frustrated double exchange interaction due to the interruption of some Mn-O-Mn chains.
Inorganic Chemistry, Dec 1, 2008
Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport usin... more Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er 3 CrS 6 octahedral sites are occupied exclusively by Cr 3+ cations, leading to one-dimensional CrS 4 5chains of edge-sharing octahedra, while in Er 2 CrS 4 , Er 3+ , and Cr 2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er 6 Cr 2 S 11 and Er 4 CrS 7 , Er 3+ and Cr 2+ ions are disordered over the octahedral sites. In Er 2 CrS 4 , Er 6 Cr 2 S 11 , and Er 4 CrS 7 , the network of octahedra generates an anionic framework constructed from M 2 S 5 slabs of varying thickness, linked by one-dimensional octahedral chains. This suggests that these three phases belong to a series in which the anionic framework may be described by the general formula [M 2n+1 S 4n+3 ] x-, with charge balancing provided by Er 3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er 4 CrS 7 , Er 6 Cr 2 S 11 , and Er 2 CrS 4 may thus be considered as the n ) 1, 2, and ∞ members of this series. While Er 4 CrS 7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er 3 CrS 6 (T C (Cr) ) 30 K; T C (Er) ) 11 K) and Er 2 CrS 4 (T N (Cr) ) 42 K, T N (Er) ) 10 K) whereas Er 6 Cr 2 S 11 exhibits ordering of the chromium sub-lattice only (T N ) 11.4 K).
Hyperfine Interactions
Sanchez, Rodolfo Noertershaeuser, Wilfried Dax, Andreas Ewald, Guido Goette, Stefan Kirchner, Rei... more Sanchez, Rodolfo Noertershaeuser, Wilfried Dax, Andreas Ewald, Guido Goette, Stefan Kirchner, Reinhard Kluge, H. -Juergen Kuehl, Thomas Wojtaszek, Agnieszka Bushaw, Bruce A. Drake, Gordon W. F. Yan, Zong-Chao Zimmermann, Claus Albers, Daniel Behr, John Bricault, Pierre Dilling, Jens Dombsky, Marik Lassen, Jens Levy, C. D. Phil Pearson, Matthew R. Prime, Erika J. Ryjkov, Vladimir
Phys Rev B, 2004
The relationship between structural and magnetic properties in stoichiometric pyrrhotite Fe7S8 ha... more The relationship between structural and magnetic properties in stoichiometric pyrrhotite Fe7S8 has been investigated using variable-temperature neutron-diffraction data. Below its magnetic ordering temperature, TN=598(5)K , Fe7S8 exhibits a monoclinic 4C structure, related to that of NiAs, in which fully occupied cation layers alternate with cation-deficient layers. The magnetic structure consists of ferromagnetically aligned layers, with antiferromagnetic coupling of adjacent layers.
Physical Review Letters, 2015
J Magn Magn Mater, 2002
We present magnetic and transport properties of nanocrystalline La 2/3Sr l/3MnO 3 powders prepare... more We present magnetic and transport properties of nanocrystalline La 2/3Sr l/3MnO 3 powders prepared following a novel gel-combustion method using citric acid as the fuel. Magnetization ( M) and magnetoresistance (MR) loops as a function of the applied magnetic field show that the coercive magnetic field Hc is significantly different to the field Hc* for which the resistance is maximum. A power-law dependence of the MR with magnetization, MR∝M n, with n⩾2.5 has been observed at low fields between 5 and 200 K. The results are discussed in terms of spin-polarized tunneling models with a distribution of particle size in our sample.
Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2013
ABSTRACT An optical technique to study the longitudinal distribution of ions in a bunched ion bea... more ABSTRACT An optical technique to study the longitudinal distribution of ions in a bunched ion beam circulating in a storage ring is presented. It is based on the arrival-time analysis of photons emitted after collisional excitation of residual gas molecules. The beam-induced fluorescence was investigated in the ultraviolet regime with a channeltron and in the visible region using a photomultiplier tube. Both were applied to investigate the longitudinal shape of bunched and electron-cooled 209Bi80+ ion beams at about 400 MeV/u in the experimental storage ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Bunch lengths were determined with an uncertainty of about 0.5 m using the UV-sensitive channeltron and with slightly lower accuracy from the photomultiplier data due to the slower transitions in the red region of the spectrum. The Gaussian shape of the longitudinal distribution of ions inside the bunch was confirmed. With the information of the transverse beam size that can be measured simultaneously by a newly installed ionization profile monitor (IPM) at the ESR, an accurate determination of the ion density in the bunched beam will be allowed.
Physical review letters, Jan 19, 2014
We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ i... more We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the 7Li+3S1 →3P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10(-9) using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β2=1 to within ±2.3×10(-9) at this velocity. The result, which is singled out by a high boost velocity β, is also interpreted within Lorentz invariance violating test theories.
Physical Review Letters, 2012
The nuclear charge radius of 12 Be was precisely determined using the technique of collinear lase... more The nuclear charge radius of 12 Be was precisely determined using the technique of collinear laser spectroscopy on the 2s 1/2 → 2p 1/2, 3/2 transition in the Be + ion. The mean square charge radius increases from 10 Be to 12 Be by δ r 2 c 10,12 = 0.69(5) fm 2 compared to δ r 2 c 10,11 = 0.49(5) fm 2 for the one-neutron halo isotope 11 Be. Calculations in the fermionic molecular dynamics approach show a strong sensitivity of the charge radius to the structure of 12 Be. The experimental charge radius is consistent with a breakdown of the N = 8 shell closure.
Physica B, 2002
We present electric and magnetic properties of polycrystalline Pr 0.5- δCa 0.2+ δSr 0.3MnO 3, for... more We present electric and magnetic properties of polycrystalline Pr 0.5- δCa 0.2+ δSr 0.3MnO 3, for δ between -0.04 and 0.04, where the hole concentration is n=0.5+ δ. In this series, we study the effects of moving n away from 0.5 on both, the phase diagram and phase separated state. We found that the low temperature ferromagnetic fraction XFM continuously decreases when n increases. As a result, the samples with n<0.5 (large XFM) exhibit metallic resistivity at low T while for n>0.5 the insulating state predominates. We construct a detailed T- n phase diagram showing the asymmetries around half-doping.
Journal of Low Temperature Physics, Apr 1, 2004
Physica B Condensed Matter, 2002
We measure voltage-current curves at low temperature in La 2/3B 1/3MnO 3 samples (B=Ca,Sr). The p... more We measure voltage-current curves at low temperature in La 2/3B 1/3MnO 3 samples (B=Ca,Sr). The powder oxides were prepared by different wet-chemical routes and low calcination temperatures were used for nanoparticles formation. We studied samples prepared by three different synthesis methods: gel-combustion, urea sol-gel and liquid-mix. Although the average particle size was almost the same for all the samples (~30 nm) , we found different behaviors in the V- I curves depending on the synthesis route. The obtained data are analyzed in the electronic tunneling picture.
J Magn Magn Mater, 2001
We have performed measurements of thermoelectric power, electrical resistivity and DC magnetizati... more We have performed measurements of thermoelectric power, electrical resistivity and DC magnetization in polycrystalline samples of Pr 0.65Ca 0.35- xSr xMnO 3 with x=0, 0.02, 0.05, 0.10 and 0.20. The system presents an evolution from a charge-ordered manganite at x=0, with an insulating-like resistivity and low magnetization values, towards a ferromagnetic (FM) metallic state for x=0.20. We show that in the intermediate region a strong competition between the FM double-exchange and the localized charge-ordering occurs, inducing the phase segregation of the two competing states in a wide temperature range. We estimate the temperature ( T) evolution of the FM phase fraction of the x=0.10 sample and construct a complete T- x phase diagram.
We address the problem of the percolative phase separation in polycrystalline samples of Pr$_{0.5... more We address the problem of the percolative phase separation in polycrystalline samples of Pr$_{0.5-\delta}$Ca$_{0.2+\delta}$Sr$_{0.3}$MnO$_3$ for −0.04leqdeltaleq0.04-0.04\leq \delta \leq 0.04−0.04leqdeltaleq0.04 (hole doping nnn between 0.46 and 0.54). We perform measurements of X-ray diffraction, dc magnetization, ESR, and electrical resistivity. These samples show at TCT_CTC a paramagnetic (PM) to ferromagnetic (FM) transition, however, we found that for n>0.50n>0.50n>0.50 there is a coexistence of both of these phases below TCT_CTC. On lowering TTT below the charge-ordering (CO) temperature TCOT_{CO}TCO all the samples exhibit a coexistence between the FM metallic and CO (antiferromagnetic) phases. In the whole TTT range the FM phase fraction ($X$) decreases with increasing nnn. Furthermore, we show that only for nleq0.50n\leq 0.50nleq0.50 the metallic fraction is above the critical percolation threshold XCsimeq15.5X_C\simeq 15.5%XCsimeq15.5. As a consequence, these samples show very different magnetoresistance properties. In addition, for nleq0.50n\leq 0.50nleq0.50 we observe a percolative metal-insulator transition at TMIT_{MI}TMI, and for TMI<T<TCOT_{MI}<T<T_{CO}TMI<T<TCO the insulating-like behavior generated by the enlargement of XXX with increasing TTT is well described by the percolation law rho−1=sigmasim(X−XC)t\rho ^{-1}=\sigma \sim (X-X_C)^trho−1=sigmasim(X−XC)t, where ttt is a critical exponent. On the basis of the values obtained for this exponent we discuss different possible percolation mechanisms, and suggest that a more deep understanding of geometric and dimensionality effects is needed in phase separated manganites. We present a complete TTT vs nnn phase diagram showing the magnetic and electric properties of the studied compound around half doping.
J Mater Res, 1998
ABSTRACT
Physica B, 2002
We present electric and magnetic properties of polycrystalline Pr0.5−δCa0.2+δSr0.3MnO3, for δ bet... more We present electric and magnetic properties of polycrystalline Pr0.5−δCa0.2+δSr0.3MnO3, for δ between −0.04 and 0.04, where the hole concentration is n=0.5+δ. In this series, we study the effects of moving n away from 0.5 on both, the phase diagram and phase separated state. We found that the low temperature ferromagnetic fraction XFM continuously decreases when n increases. As a result, the samples with n<0.5 (large XFM) exhibit metallic resistivity at low T while for n>0.5 the insulating state predominates. We construct a detailed T–n phase diagram showing the asymmetries around half-doping.
J Appl Phys, 2003
We study the effect of the introduction of a controlled amount of oxygen vacancies on the magneti... more We study the effect of the introduction of a controlled amount of oxygen vacancies on the magnetic and transport properties of the phase separated manganite Pr0.5Ca0.2Sr0.3MnO3-δ, for δ=0 and 0.01. This compound presents a paramagnetic to ferromagnetic (FM) transition below TC˜240 K, and then to a charge-ordered (CO) and antiferromagnetic (AFM) phase at TCO˜175 K. However, below TCO an appreciable FM component (˜20%) still survives, related to a FM volume immersed within the CO/AFM matrix. At low temperatures, in the mainly CO phase, the introduction of oxygen vacancies enhances the FM ordering, with the consequent decrease of resistivity and magnetoresistance (MR). On the contrary, in the FM phase (in the range TCO<T<TC) the magnetization is reduced and the resistivity and MR increase. These results are discussed in the frame of percolative transport in metal-insulator mixtures, and frustrated double exchange interaction due to the interruption of some Mn-O-Mn chains.
Inorganic Chemistry, Dec 1, 2008
Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport usin... more Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er 3 CrS 6 octahedral sites are occupied exclusively by Cr 3+ cations, leading to one-dimensional CrS 4 5chains of edge-sharing octahedra, while in Er 2 CrS 4 , Er 3+ , and Cr 2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er 6 Cr 2 S 11 and Er 4 CrS 7 , Er 3+ and Cr 2+ ions are disordered over the octahedral sites. In Er 2 CrS 4 , Er 6 Cr 2 S 11 , and Er 4 CrS 7 , the network of octahedra generates an anionic framework constructed from M 2 S 5 slabs of varying thickness, linked by one-dimensional octahedral chains. This suggests that these three phases belong to a series in which the anionic framework may be described by the general formula [M 2n+1 S 4n+3 ] x-, with charge balancing provided by Er 3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er 4 CrS 7 , Er 6 Cr 2 S 11 , and Er 2 CrS 4 may thus be considered as the n ) 1, 2, and ∞ members of this series. While Er 4 CrS 7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er 3 CrS 6 (T C (Cr) ) 30 K; T C (Er) ) 11 K) and Er 2 CrS 4 (T N (Cr) ) 42 K, T N (Er) ) 10 K) whereas Er 6 Cr 2 S 11 exhibits ordering of the chromium sub-lattice only (T N ) 11.4 K).
Hyperfine Interactions
Sanchez, Rodolfo Noertershaeuser, Wilfried Dax, Andreas Ewald, Guido Goette, Stefan Kirchner, Rei... more Sanchez, Rodolfo Noertershaeuser, Wilfried Dax, Andreas Ewald, Guido Goette, Stefan Kirchner, Reinhard Kluge, H. -Juergen Kuehl, Thomas Wojtaszek, Agnieszka Bushaw, Bruce A. Drake, Gordon W. F. Yan, Zong-Chao Zimmermann, Claus Albers, Daniel Behr, John Bricault, Pierre Dilling, Jens Dombsky, Marik Lassen, Jens Levy, C. D. Phil Pearson, Matthew R. Prime, Erika J. Ryjkov, Vladimir
Phys Rev B, 2004
The relationship between structural and magnetic properties in stoichiometric pyrrhotite Fe7S8 ha... more The relationship between structural and magnetic properties in stoichiometric pyrrhotite Fe7S8 has been investigated using variable-temperature neutron-diffraction data. Below its magnetic ordering temperature, TN=598(5)K , Fe7S8 exhibits a monoclinic 4C structure, related to that of NiAs, in which fully occupied cation layers alternate with cation-deficient layers. The magnetic structure consists of ferromagnetically aligned layers, with antiferromagnetic coupling of adjacent layers.
Physical Review Letters, 2015
J Magn Magn Mater, 2002
We present magnetic and transport properties of nanocrystalline La 2/3Sr l/3MnO 3 powders prepare... more We present magnetic and transport properties of nanocrystalline La 2/3Sr l/3MnO 3 powders prepared following a novel gel-combustion method using citric acid as the fuel. Magnetization ( M) and magnetoresistance (MR) loops as a function of the applied magnetic field show that the coercive magnetic field Hc is significantly different to the field Hc* for which the resistance is maximum. A power-law dependence of the MR with magnetization, MR∝M n, with n⩾2.5 has been observed at low fields between 5 and 200 K. The results are discussed in terms of spin-polarized tunneling models with a distribution of particle size in our sample.
Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2013
ABSTRACT An optical technique to study the longitudinal distribution of ions in a bunched ion bea... more ABSTRACT An optical technique to study the longitudinal distribution of ions in a bunched ion beam circulating in a storage ring is presented. It is based on the arrival-time analysis of photons emitted after collisional excitation of residual gas molecules. The beam-induced fluorescence was investigated in the ultraviolet regime with a channeltron and in the visible region using a photomultiplier tube. Both were applied to investigate the longitudinal shape of bunched and electron-cooled 209Bi80+ ion beams at about 400 MeV/u in the experimental storage ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Bunch lengths were determined with an uncertainty of about 0.5 m using the UV-sensitive channeltron and with slightly lower accuracy from the photomultiplier data due to the slower transitions in the red region of the spectrum. The Gaussian shape of the longitudinal distribution of ions inside the bunch was confirmed. With the information of the transverse beam size that can be measured simultaneously by a newly installed ionization profile monitor (IPM) at the ESR, an accurate determination of the ion density in the bunched beam will be allowed.
Physical review letters, Jan 19, 2014
We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ i... more We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the 7Li+3S1 →3P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10(-9) using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β2=1 to within ±2.3×10(-9) at this velocity. The result, which is singled out by a high boost velocity β, is also interpreted within Lorentz invariance violating test theories.
Physical Review Letters, 2012
The nuclear charge radius of 12 Be was precisely determined using the technique of collinear lase... more The nuclear charge radius of 12 Be was precisely determined using the technique of collinear laser spectroscopy on the 2s 1/2 → 2p 1/2, 3/2 transition in the Be + ion. The mean square charge radius increases from 10 Be to 12 Be by δ r 2 c 10,12 = 0.69(5) fm 2 compared to δ r 2 c 10,11 = 0.49(5) fm 2 for the one-neutron halo isotope 11 Be. Calculations in the fermionic molecular dynamics approach show a strong sensitivity of the charge radius to the structure of 12 Be. The experimental charge radius is consistent with a breakdown of the N = 8 shell closure.