M. Lantieri | Università degli Studi di Firenze (University of Florence) (original) (raw)
Papers by M. Lantieri
Inorganic chemistry, Jan 17, 2017
Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising... more Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising strategies for the development of advanced magnetic biomaterials. However, especially in the case of iron-doped magnetic hydroxyapatites, it is not clear if the magnetic features come merely from the magnetic phases/ions used as dopants or from complex mechanisms involving interactions at the nanoscale. Here, we report an extensive chemical-physical and magnetic investigation of three hydroxyapatite nanocrystals doped with different iron species and containing small or no amounts of maghemite as a secondary phase. The association of several investigation techniques such as X-ray absorption spectroscopy, Mössbauer, magnetometry, and TEM allowed us to determine that the unusual magnetic properties of Fe(2+/3+)-doped hydroxyapatites (FeHA) occur by a synergy of two different phenomena: i.e., (i) interacting superparamagnetism due to the interplay between iron-doped apatite and iron oxide n...
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary
Journal of Magnetism and Magnetic Materials, 2008
ABSTRACT The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule [Fe(OMe)(... more ABSTRACT The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule [Fe(OMe)(dpm)2]2 are analyzed by means of Mössbauer spectroscopy in the temperature range [7.6–33] K. Spectra in the presence of a 5 T magnetic field directed along the γ rays were collected, by using a sample of pseudo-single crystal prepared by oriented grains. From the fits of the spectra, the hyperfine parameters are determined. Fits give also the value and direction of the magnetic anisotropy, referred to the electric field gradient (EFG) principal axes. The latter, together with the EFG components, were evaluated by means of ROHF ab initio calculations. Lastly, the rate of the spin transitions in function of T is discussed.
Scientific Reports, 2016
Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanio... more Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanion compounds with high theoretical capacity such as the lithium metal orthosilicates, Li 2 MSiO 4 is of great importance. In particular, mixed silicates represent an advancement with practical applications. Here we present results on a rapid solid state synthesis of mixed Li 2 (FeMnCo)SiO 4 samples in a wide compositional range. The solid solution in the P2 1 /n space group was found to be stable for high iron concentration or for a cobalt content up to about 0.3 atom per formula unit. Other compositions led to a mixture of polymorphs, namely Pmn2 1 and Pbn2 1. All the samples contained a variable amount of Fe 3+ ions that was quantified by Mössbauer spectroscopy and confirmed by the T N values of the paramagnetic to antiferromagnetic transition. Preliminary characterization by cyclic voltammetry revealed the effect of Fe 3+ on the electrochemical response. Further work is required to determine the impact of these electrode materials on lithium batteries. Promising cathode materials for lithium ions batteries have recently emerged belonging to the Li 2 MSiO 4 (M = Fe, Mn, Co) orthosilicates family 1-3. These compounds have attracted great interest due to their high safety and, especially for those based on Fe and Mn ions, also for their low cost, low toxicity and environmental friendliness 4,5. In addition, they all appear particularly interesting due to the theoretical possibility to reversibly de-intercalate two lithium equivalents from the structure, so increasing the overall electrode capacity. In fact, Li 2 MnSiO 4 could in theory deliver 333 mAhg −1 , Li 2 CoSiO 4 325 mAhg −1 , while Li 2 FeSiO 4 166 mAhg −1 for the extraction of one Li ion per formula unit 6. However, the low electronic conductivity of silicates has to be overcome in order to reach the theoretical capacity: different approaches have been tried, e.g. the doping with Cr, V, Mg, Zn, Cu and Ni 7-10 , the carbon-coating 11 or the preparation of composites with carbon nanotubes 12. Another critical feature of the orthosilicates, also reported as tetrahedral structures, is their rich polymorphism with numerous crystal structures that, having similar lattice energies, can be stabilized depending on subtle differences in the synthesis conditions 6,13-14. Usually, the monoclinic P2 1 /n and the orthorhombic Pmn2 1 or Pmnb space groups are reported for both the Li 2 MnSiO 4 and Li 2 FeSiO 4 compounds 15,16. For Li 2 CoSiO 4 , three stable polymorphs were prepared and structurally characterized: the orthorhombic β II (Pmn2 1) and β I (Pbn2 1) and the monoclinic γ 0 (P2 1 /n or P2/n) 6,17. The differences among these structures are mainly due to different arrangements of the cation tetrahedra. The polymorphism, with the associated small transition energies, is one of the factors affecting the long-term cyclability of these materials 18. To gain new insights in this field the relationships between structural and electrochemical properties have been studied by using in situ X-ray diffraction measurements during the cell cycling 19. The formation of either a disordered orthorhombic or monoclinic structure was observed during the lithium extraction, but more studies are needed to better explain the electrochemical behaviour of these compounds. Sesto Fiorentino (FI), Italy.
In recent years the synthesis of antiferromagnetic rings traced a path to the observation of inte... more In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. 57Fe Mössbauer spectroscopy is an efficient and powerful technique to contribute to this
Journal of Coordination Chemistry, 2015
Based on 1-(cyclohexylmethyl)-1H-tetrazole (C6mtz), a series of mononuclear iron(II) spin-crossov... more Based on 1-(cyclohexylmethyl)-1H-tetrazole (C6mtz), a series of mononuclear iron(II) spin-crossover complexes with the general formula [Fe(C6mtz)6]X2, where X is the non-coordinating anion (1), (2), or (3), have been synthesized and characterized. Temperature-dependent magnetic susceptibility measurements for 1, 2, and 3 show reversible one-step spin crossover (SCO) behavior between high-spin (HS, S = 2) and low-spin (LS, S = 0) states without hysteresis. The compound shows spin transition at T1/2 = 213 K at a considerably higher temperature than the other compounds, (T1/2 = 126 K) and (T1/2 = 119 K). Temperature-dependent Far-IR and Mössbauer spectra of 2 and 3 were compared with the measured magnetic susceptibility and confirm the one-step SCO behavior of the compounds. Graphical abstract
Journal of Physics: Condensed Matter, 2015
RSC Advances, 2011
Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for highe... more Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for highenergy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mö ssbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mö ssbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014
ABSTRACT
Journal of Mathematical Physics, 2004
ABSTRACT Spin motion is studied by means of the direct use of the Schrödinger equation. The solut... more ABSTRACT Spin motion is studied by means of the direct use of the Schrödinger equation. The solution is found in terms of Lommel’s polynomials. An expression of the tunneling splitting is obtained, in good agreement with the results coming from other calculations. © 2004 American Institute of Physics.
Inorganic Chemistry, 1975
... Structural and Magnetic Characterization of Di-p-hydroxo-bis [ bis ( 1 10-phenanthroline) chr... more ... Structural and Magnetic Characterization of Di-p-hydroxo-bis [ bis ( 1 10-phenanthroline) chromium(II1) ] Iodide Tetrahydrate RAYMOND P. SCARINGE, PHIRTU SINGH, RICHARD P. ECKBERG, WILLIAM E. HATFIELD, and DEREK J. HODGSON' Received August 22, 1974 ...
Canadian Journal of Physics, 2004
The one-dimensional random walk between two reflecting walls is considered from two different poi... more The one-dimensional random walk between two reflecting walls is considered from two different points of view: the first, as a particular case of jumps between neighbouring, discrete states; the second, as a system that obeys a generalized diffusion equation. By performing the suitable limits, the identity of the two results is pointed out and a physical application is presented. PACS Nos.: 02.50.Ey, 02.30.Jr
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity fs 1+B , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary measurements in evaluating the quantity fs 1+B . It is useful when the Mössbauer line-shape rapidly evolves in narrow temperature ranges: a real application for single molecule magnets spectra and an analytical example are reported, too
Journal of Magnetism and Magnetic Materials, 2008
The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule ½FeðOMeÞðdpmÞ 2 2 ... more The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule ½FeðOMeÞðdpmÞ 2 2 are analyzed by means of Mo¨ssbauer spectroscopy in the temperature range [7.6-33] K. Spectra in the presence of a 5 T magnetic field directed along the g rays were collected, by using a sample of pseudo-single crystal prepared by oriented grains. From the fits of the spectra, the hyperfine parameters are determined. Fits give also the value and direction of the magnetic anisotropy, referred to the electric field gradient (EFG) principal axes. The latter, together with the EFG components, were evaluated by means of ROHF ab initio calculations. Lastly, the rate of the spin transitions in function of T is discussed.
Physical Review B, 2011
F. Mezzadri,1,* G. Calestani,1,2 C. Pernechele,3 M. Solzi,3 G. Spina,4 L. Cianchi,5 F. Del Giallo... more F. Mezzadri,1,* G. Calestani,1,2 C. Pernechele,3 M. Solzi,3 G. Spina,4 L. Cianchi,5 F. Del Giallo,5 M. Lantieri,5 M. Buzzi,3 and E. Gilioli2 1Dipartimento di Chimica GIAF, Universit`a di Parma, Area delle Scienze 17/A, 43124 Parma, Italy 2IMEM-CNR, Area delle Scienze ...
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity fs 1+B , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary measurements in evaluating the quantity fs 1+B . It is useful when the Mössbauer line-shape rapidly evolves in narrow temperature ranges: a real application for single molecule magnets spectra and an analytical example are reported, too
Solid State Communications, 2010
In recent years the synthesis of antiferromagnetic rings traced a path to the observation of inte... more In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. 57 Fe Mössbauer spectroscopy is an efficient and powerful technique to contribute to this knowledge in antiferromagnetic wheels containing iron ions. We analyze the Cr 7 Fe II wheel: the Mössbauer line shape evolution of low temperature spectra (2.1 K) at different external fields is illustrated and the mean spin value of the iron ion is evaluated.
![Research paper thumbnail of Spin dynamics of the magnetic dimer [Fe(OMe)(dpm)2]2 studied using Mössbauer spectroscopy](https://attachments.academia-assets.com/40038446/thumbnails/1.jpg)
](Physical Review B, 2004
We present a study of the spin dynamics of the magnetic dimer ͓Fe(OMe)(dpm) 2 ͔ 2 , using Mössbau... more We present a study of the spin dynamics of the magnetic dimer ͓Fe(OMe)(dpm) 2 ͔ 2 , using Mössbauer spectroscopy. In this cluster, the two iron͑III͒ ions are antiferromagnetically coupled so that the dimer presents a Sϭ0 spin ground state. Spin multiplets with values of S ranging from 1 to 5 follow in order of increasing energy. Axial anisotropy DS z 2 is also present with D of the order of a few kelvin. Spectra were collected over a range from 6.5 K to room temperature. They consist of doublets in which any magnetic structure is lacking, but the line widths of which increase with the temperature, due to relaxation effects. We performed their fits by assuming a fast-fluctuating hyperfine field which stochastically inverts its direction along the anisotropy axis. The zero-frequency Fourier transform J z of the hyperfine-field correlation function versus the temperature was obtained from the spectrum fittings. The trend of J z suggests that the basic mechanisms of the spin dynamics consist of a tunnel effect due to magnetic-anisotropy transversal terms, as well as of spin-thermal bath interactions. By assuming this, the following parameters were estimated from the fitting of J z (T): D(1)Ϸ8.1 K, E/D(1)Ϸ8.5ϫ10 Ϫ4 , and wϭw 0 exp(Ϫ2T 0 /T) with w 0 Ϸ9.2ϫ10 8 s Ϫ1 and T 0 Ϸ732 K. Lastly, similarities in spin dynamics between the dimer and the ring shaped clusters were discussed.
Inorganic chemistry, Jan 17, 2017
Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising... more Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising strategies for the development of advanced magnetic biomaterials. However, especially in the case of iron-doped magnetic hydroxyapatites, it is not clear if the magnetic features come merely from the magnetic phases/ions used as dopants or from complex mechanisms involving interactions at the nanoscale. Here, we report an extensive chemical-physical and magnetic investigation of three hydroxyapatite nanocrystals doped with different iron species and containing small or no amounts of maghemite as a secondary phase. The association of several investigation techniques such as X-ray absorption spectroscopy, Mössbauer, magnetometry, and TEM allowed us to determine that the unusual magnetic properties of Fe(2+/3+)-doped hydroxyapatites (FeHA) occur by a synergy of two different phenomena: i.e., (i) interacting superparamagnetism due to the interplay between iron-doped apatite and iron oxide n...
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary
Journal of Magnetism and Magnetic Materials, 2008
ABSTRACT The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule [Fe(OMe)(... more ABSTRACT The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule [Fe(OMe)(dpm)2]2 are analyzed by means of Mössbauer spectroscopy in the temperature range [7.6–33] K. Spectra in the presence of a 5 T magnetic field directed along the γ rays were collected, by using a sample of pseudo-single crystal prepared by oriented grains. From the fits of the spectra, the hyperfine parameters are determined. Fits give also the value and direction of the magnetic anisotropy, referred to the electric field gradient (EFG) principal axes. The latter, together with the EFG components, were evaluated by means of ROHF ab initio calculations. Lastly, the rate of the spin transitions in function of T is discussed.
Scientific Reports, 2016
Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanio... more Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanion compounds with high theoretical capacity such as the lithium metal orthosilicates, Li 2 MSiO 4 is of great importance. In particular, mixed silicates represent an advancement with practical applications. Here we present results on a rapid solid state synthesis of mixed Li 2 (FeMnCo)SiO 4 samples in a wide compositional range. The solid solution in the P2 1 /n space group was found to be stable for high iron concentration or for a cobalt content up to about 0.3 atom per formula unit. Other compositions led to a mixture of polymorphs, namely Pmn2 1 and Pbn2 1. All the samples contained a variable amount of Fe 3+ ions that was quantified by Mössbauer spectroscopy and confirmed by the T N values of the paramagnetic to antiferromagnetic transition. Preliminary characterization by cyclic voltammetry revealed the effect of Fe 3+ on the electrochemical response. Further work is required to determine the impact of these electrode materials on lithium batteries. Promising cathode materials for lithium ions batteries have recently emerged belonging to the Li 2 MSiO 4 (M = Fe, Mn, Co) orthosilicates family 1-3. These compounds have attracted great interest due to their high safety and, especially for those based on Fe and Mn ions, also for their low cost, low toxicity and environmental friendliness 4,5. In addition, they all appear particularly interesting due to the theoretical possibility to reversibly de-intercalate two lithium equivalents from the structure, so increasing the overall electrode capacity. In fact, Li 2 MnSiO 4 could in theory deliver 333 mAhg −1 , Li 2 CoSiO 4 325 mAhg −1 , while Li 2 FeSiO 4 166 mAhg −1 for the extraction of one Li ion per formula unit 6. However, the low electronic conductivity of silicates has to be overcome in order to reach the theoretical capacity: different approaches have been tried, e.g. the doping with Cr, V, Mg, Zn, Cu and Ni 7-10 , the carbon-coating 11 or the preparation of composites with carbon nanotubes 12. Another critical feature of the orthosilicates, also reported as tetrahedral structures, is their rich polymorphism with numerous crystal structures that, having similar lattice energies, can be stabilized depending on subtle differences in the synthesis conditions 6,13-14. Usually, the monoclinic P2 1 /n and the orthorhombic Pmn2 1 or Pmnb space groups are reported for both the Li 2 MnSiO 4 and Li 2 FeSiO 4 compounds 15,16. For Li 2 CoSiO 4 , three stable polymorphs were prepared and structurally characterized: the orthorhombic β II (Pmn2 1) and β I (Pbn2 1) and the monoclinic γ 0 (P2 1 /n or P2/n) 6,17. The differences among these structures are mainly due to different arrangements of the cation tetrahedra. The polymorphism, with the associated small transition energies, is one of the factors affecting the long-term cyclability of these materials 18. To gain new insights in this field the relationships between structural and electrochemical properties have been studied by using in situ X-ray diffraction measurements during the cell cycling 19. The formation of either a disordered orthorhombic or monoclinic structure was observed during the lithium extraction, but more studies are needed to better explain the electrochemical behaviour of these compounds. Sesto Fiorentino (FI), Italy.
In recent years the synthesis of antiferromagnetic rings traced a path to the observation of inte... more In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. 57Fe Mössbauer spectroscopy is an efficient and powerful technique to contribute to this
Journal of Coordination Chemistry, 2015
Based on 1-(cyclohexylmethyl)-1H-tetrazole (C6mtz), a series of mononuclear iron(II) spin-crossov... more Based on 1-(cyclohexylmethyl)-1H-tetrazole (C6mtz), a series of mononuclear iron(II) spin-crossover complexes with the general formula [Fe(C6mtz)6]X2, where X is the non-coordinating anion (1), (2), or (3), have been synthesized and characterized. Temperature-dependent magnetic susceptibility measurements for 1, 2, and 3 show reversible one-step spin crossover (SCO) behavior between high-spin (HS, S = 2) and low-spin (LS, S = 0) states without hysteresis. The compound shows spin transition at T1/2 = 213 K at a considerably higher temperature than the other compounds, (T1/2 = 126 K) and (T1/2 = 119 K). Temperature-dependent Far-IR and Mössbauer spectra of 2 and 3 were compared with the measured magnetic susceptibility and confirm the one-step SCO behavior of the compounds. Graphical abstract
Journal of Physics: Condensed Matter, 2015
RSC Advances, 2011
Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for highe... more Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for highenergy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mö ssbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mö ssbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014
ABSTRACT
Journal of Mathematical Physics, 2004
ABSTRACT Spin motion is studied by means of the direct use of the Schrödinger equation. The solut... more ABSTRACT Spin motion is studied by means of the direct use of the Schrödinger equation. The solution is found in terms of Lommel’s polynomials. An expression of the tunneling splitting is obtained, in good agreement with the results coming from other calculations. © 2004 American Institute of Physics.
Inorganic Chemistry, 1975
... Structural and Magnetic Characterization of Di-p-hydroxo-bis [ bis ( 1 10-phenanthroline) chr... more ... Structural and Magnetic Characterization of Di-p-hydroxo-bis [ bis ( 1 10-phenanthroline) chromium(II1) ] Iodide Tetrahydrate RAYMOND P. SCARINGE, PHIRTU SINGH, RICHARD P. ECKBERG, WILLIAM E. HATFIELD, and DEREK J. HODGSON' Received August 22, 1974 ...
Canadian Journal of Physics, 2004
The one-dimensional random walk between two reflecting walls is considered from two different poi... more The one-dimensional random walk between two reflecting walls is considered from two different points of view: the first, as a particular case of jumps between neighbouring, discrete states; the second, as a system that obeys a generalized diffusion equation. By performing the suitable limits, the identity of the two results is pointed out and a physical application is presented. PACS Nos.: 02.50.Ey, 02.30.Jr
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity fs 1+B , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary measurements in evaluating the quantity fs 1+B . It is useful when the Mössbauer line-shape rapidly evolves in narrow temperature ranges: a real application for single molecule magnets spectra and an analytical example are reported, too
Journal of Magnetism and Magnetic Materials, 2008
The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule ½FeðOMeÞðdpmÞ 2 2 ... more The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule ½FeðOMeÞðdpmÞ 2 2 are analyzed by means of Mo¨ssbauer spectroscopy in the temperature range [7.6-33] K. Spectra in the presence of a 5 T magnetic field directed along the g rays were collected, by using a sample of pseudo-single crystal prepared by oriented grains. From the fits of the spectra, the hyperfine parameters are determined. Fits give also the value and direction of the magnetic anisotropy, referred to the electric field gradient (EFG) principal axes. The latter, together with the EFG components, were evaluated by means of ROHF ab initio calculations. Lastly, the rate of the spin transitions in function of T is discussed.
Physical Review B, 2011
F. Mezzadri,1,* G. Calestani,1,2 C. Pernechele,3 M. Solzi,3 G. Spina,4 L. Cianchi,5 F. Del Giallo... more F. Mezzadri,1,* G. Calestani,1,2 C. Pernechele,3 M. Solzi,3 G. Spina,4 L. Cianchi,5 F. Del Giallo,5 M. Lantieri,5 M. Buzzi,3 and E. Gilioli2 1Dipartimento di Chimica GIAF, Universit`a di Parma, Area delle Scienze 17/A, 43124 Parma, Italy 2IMEM-CNR, Area delle Scienze ...
Journal of Physics: Conference Series, 2010
The interpretation of Mössbauer spectra often requires the use of the Transmission Integral funct... more The interpretation of Mössbauer spectra often requires the use of the Transmission Integral function (TI). It contains the quantity fs 1+B , where fs is the source Mössbauer factor and B depends on the background radiation rate and on the inhomogeneity of the target: both of them usually obtained by ancillary measurements and tests. We present a simple method, that avoids ancillary measurements in evaluating the quantity fs 1+B . It is useful when the Mössbauer line-shape rapidly evolves in narrow temperature ranges: a real application for single molecule magnets spectra and an analytical example are reported, too
Solid State Communications, 2010
In recent years the synthesis of antiferromagnetic rings traced a path to the observation of inte... more In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. 57 Fe Mössbauer spectroscopy is an efficient and powerful technique to contribute to this knowledge in antiferromagnetic wheels containing iron ions. We analyze the Cr 7 Fe II wheel: the Mössbauer line shape evolution of low temperature spectra (2.1 K) at different external fields is illustrated and the mean spin value of the iron ion is evaluated.
Physical Review B, 2004
We present a study of the spin dynamics of the magnetic dimer ͓Fe(OMe)(dpm) 2 ͔ 2 , using Mössbau... more We present a study of the spin dynamics of the magnetic dimer ͓Fe(OMe)(dpm) 2 ͔ 2 , using Mössbauer spectroscopy. In this cluster, the two iron͑III͒ ions are antiferromagnetically coupled so that the dimer presents a Sϭ0 spin ground state. Spin multiplets with values of S ranging from 1 to 5 follow in order of increasing energy. Axial anisotropy DS z 2 is also present with D of the order of a few kelvin. Spectra were collected over a range from 6.5 K to room temperature. They consist of doublets in which any magnetic structure is lacking, but the line widths of which increase with the temperature, due to relaxation effects. We performed their fits by assuming a fast-fluctuating hyperfine field which stochastically inverts its direction along the anisotropy axis. The zero-frequency Fourier transform J z of the hyperfine-field correlation function versus the temperature was obtained from the spectrum fittings. The trend of J z suggests that the basic mechanisms of the spin dynamics consist of a tunnel effect due to magnetic-anisotropy transversal terms, as well as of spin-thermal bath interactions. By assuming this, the following parameters were estimated from the fitting of J z (T): D(1)Ϸ8.1 K, E/D(1)Ϸ8.5ϫ10 Ϫ4 , and wϭw 0 exp(Ϫ2T 0 /T) with w 0 Ϸ9.2ϫ10 8 s Ϫ1 and T 0 Ϸ732 K. Lastly, similarities in spin dynamics between the dimer and the ring shaped clusters were discussed.