Abstract The EPR powder spectra of high spin Co(II) and Cr(III) diluted in partially inverse spin... more Abstract The EPR powder spectra of high spin Co(II) and Cr(III) diluted in partially inverse spinel matrix MgIn2S4 are reported. While the spectrum of Co(II) in octahedral sites is orthorhombic the Cr(III) one is axial. Evidence is given that the EPR spectra cannot be directly associated with the cation distribution of the matrix.
The critical probability for the cationic B-sublattice in spinels has been calculated by the Mont... more The critical probability for the cationic B-sublattice in spinels has been calculated by the Monte Carlo technique as a function of the connectivity of the atomic octahedral sites.
We have studied the magnetic properties of a sample obtained by high-energy mechanical milling fr... more We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of α-Fe nanocrystallites (∼23%), and magnetization dynamics effects characterize the magnetic behavior. In particular, a magnetic transition occurs at T ∼ 50 K, from a low temperature disordered collective frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. The phenomenon has been ultimately ascribed to the local modification of the interatomic distance distribution in the amorphous matrix, induced by milling.
The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed... more The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed by Joule heating at di!erent DC current densities have been investigated by magnetization, DC and AC susceptibility measurements. The increase of the heating current density has been found to promote grain growth and to enhance the strength of intergrain interactions, determining a change of magnetic behavior: from a collective freezing in random directions of moments of nanosized Co particles to an inhomogeneous and progressive blocking of moments of particles with increasing size. The e!ects of Joule heating on microstructure and magnetic properties are discussed in relation to the giant magnetoresistance properties exhibited by the system, which con"rm the development of interparticle correlations with increasing the heating current density. 0304-8853/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 9 9 ) 0 0 3 0 3 -0
A dynamical magnetic susceptibility study on La1−xSrxCoO3 samples obtained by a coprecipitation m... more A dynamical magnetic susceptibility study on La1−xSrxCoO3 samples obtained by a coprecipitation method is reported for x⩽0.30. For x<0.20 differences between zero field cooled and field cooled dc magnetic susceptibility appear at a temperature Ta below the Curie point, TC≈240 K, as well as a magnetic freezing point at a temperature Tb<Ta. Alternating current magnetic susceptibility shows two maxima at
The critical probability for the cationic B-sublattice in spinels has been calculated by the Mont... more The critical probability for the cationic B-sublattice in spinels has been calculated by the Monte Carlo technique as a function of the connectivity of the atomic octahedral sites.
The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers... more The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers has been investigated as a function of the soft layer thickness (t Fe = 2, 3.5, 5 nm) combining magnetization loops at variable angle, magnetic domain analysis by magnetic force microscopy and numerical micromagnetic simulations. The analytical model proposed in the literature can properly account for some features of the reversal mechanism, such as positive nucleation fields and the reduction of the perpendicular coercive field and remanence by increasing the soft layer thickness, but cannot satisfactorily describe the magnetization process of real systems. We showed that for a thickness of the soft layer exceeding the FePt exchange length (∼2 nm), numerical micromagnetic calculations are needed to reproduce experimental observations. Indeed, just above the coercive field, the magnetization reversal does not proceed in single step switching, as predicted by the analytical model, but according to a more complex process: evolution of nucleated magnetic domains whose magnetization is approximately along the surface normal in the hard layer and slightly out of the film plane in the soft layer, followed by rotation of Fe moments along the field direction.
We have studied the magnetic properties of a sample obtained by high-energy mechanical milling fr... more We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of α-Fe nanocrystallites (∼23%), and magnetization dynamics effects characterize the magnetic behavior. In particular, a magnetic transition occurs at T ∼ 50 K, from a low temperature disordered collective frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. The phenomenon has been ultimately ascribed to the local modification of the interatomic distance distribution in the amorphous matrix, induced by milling.
The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed... more The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed by Joule heating at di!erent DC current densities have been investigated by magnetization, DC and AC susceptibility measurements. The increase of the heating current density has been found to promote grain growth and to enhance the strength of intergrain interactions, determining a change of magnetic behavior: from a collective freezing in random directions of moments of nanosized Co particles to an inhomogeneous and progressive blocking of moments of particles with increasing size. The e!ects of Joule heating on microstructure and magnetic properties are discussed in relation to the giant magnetoresistance properties exhibited by the system, which con"rm the development of interparticle correlations with increasing the heating current density. 0304-8853/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 9 9 ) 0 0 3 0 3 -0
... 1 Y. Tokura, H. Takagi, and S. Uchida, Nature 337, 345 (1989); JT Mark-ert, EA Early, T. Bjor... more ... 1 Y. Tokura, H. Takagi, and S. Uchida, Nature 337, 345 (1989); JT Mark-ert, EA Early, T. Bjornholm, S. Ghamaty, BW Lee, JJ Nuemeier, R. D. Price, CL Seaman, and MB Maple, Physica C 158, 178 (1989). 2 TR Thurston, M. Matsuda ...
The temperature and time dependence, in di!erent magnetic "elds, of the "eld-cooled and zero-"eld... more The temperature and time dependence, in di!erent magnetic "elds, of the "eld-cooled and zero-"eld-cooled magnetisation on ball-milled nanocrystalline Fe has been studied. The results indicate the existence, below about 70 K, of a disordered frozen magnetic state which is erased by applying an external "eld H"1000 Oe, favouring the ferromagnetic order.
Abstract The EPR powder spectra of high spin Co(II) and Cr(III) diluted in partially inverse spin... more Abstract The EPR powder spectra of high spin Co(II) and Cr(III) diluted in partially inverse spinel matrix MgIn2S4 are reported. While the spectrum of Co(II) in octahedral sites is orthorhombic the Cr(III) one is axial. Evidence is given that the EPR spectra cannot be directly associated with the cation distribution of the matrix.
The critical probability for the cationic B-sublattice in spinels has been calculated by the Mont... more The critical probability for the cationic B-sublattice in spinels has been calculated by the Monte Carlo technique as a function of the connectivity of the atomic octahedral sites.
We have studied the magnetic properties of a sample obtained by high-energy mechanical milling fr... more We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of α-Fe nanocrystallites (∼23%), and magnetization dynamics effects characterize the magnetic behavior. In particular, a magnetic transition occurs at T ∼ 50 K, from a low temperature disordered collective frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. The phenomenon has been ultimately ascribed to the local modification of the interatomic distance distribution in the amorphous matrix, induced by milling.
The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed... more The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed by Joule heating at di!erent DC current densities have been investigated by magnetization, DC and AC susceptibility measurements. The increase of the heating current density has been found to promote grain growth and to enhance the strength of intergrain interactions, determining a change of magnetic behavior: from a collective freezing in random directions of moments of nanosized Co particles to an inhomogeneous and progressive blocking of moments of particles with increasing size. The e!ects of Joule heating on microstructure and magnetic properties are discussed in relation to the giant magnetoresistance properties exhibited by the system, which con"rm the development of interparticle correlations with increasing the heating current density. 0304-8853/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 9 9 ) 0 0 3 0 3 -0
A dynamical magnetic susceptibility study on La1−xSrxCoO3 samples obtained by a coprecipitation m... more A dynamical magnetic susceptibility study on La1−xSrxCoO3 samples obtained by a coprecipitation method is reported for x⩽0.30. For x<0.20 differences between zero field cooled and field cooled dc magnetic susceptibility appear at a temperature Ta below the Curie point, TC≈240 K, as well as a magnetic freezing point at a temperature Tb<Ta. Alternating current magnetic susceptibility shows two maxima at
The critical probability for the cationic B-sublattice in spinels has been calculated by the Mont... more The critical probability for the cationic B-sublattice in spinels has been calculated by the Monte Carlo technique as a function of the connectivity of the atomic octahedral sites.
The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers... more The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers has been investigated as a function of the soft layer thickness (t Fe = 2, 3.5, 5 nm) combining magnetization loops at variable angle, magnetic domain analysis by magnetic force microscopy and numerical micromagnetic simulations. The analytical model proposed in the literature can properly account for some features of the reversal mechanism, such as positive nucleation fields and the reduction of the perpendicular coercive field and remanence by increasing the soft layer thickness, but cannot satisfactorily describe the magnetization process of real systems. We showed that for a thickness of the soft layer exceeding the FePt exchange length (∼2 nm), numerical micromagnetic calculations are needed to reproduce experimental observations. Indeed, just above the coercive field, the magnetization reversal does not proceed in single step switching, as predicted by the analytical model, but according to a more complex process: evolution of nucleated magnetic domains whose magnetization is approximately along the surface normal in the hard layer and slightly out of the film plane in the soft layer, followed by rotation of Fe moments along the field direction.
We have studied the magnetic properties of a sample obtained by high-energy mechanical milling fr... more We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of α-Fe nanocrystallites (∼23%), and magnetization dynamics effects characterize the magnetic behavior. In particular, a magnetic transition occurs at T ∼ 50 K, from a low temperature disordered collective frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. The phenomenon has been ultimately ascribed to the local modification of the interatomic distance distribution in the amorphous matrix, induced by milling.
The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed... more The magnetic properties of a granular Co}Cu alloy (Co Cu ) produced by melt-spinning and annealed by Joule heating at di!erent DC current densities have been investigated by magnetization, DC and AC susceptibility measurements. The increase of the heating current density has been found to promote grain growth and to enhance the strength of intergrain interactions, determining a change of magnetic behavior: from a collective freezing in random directions of moments of nanosized Co particles to an inhomogeneous and progressive blocking of moments of particles with increasing size. The e!ects of Joule heating on microstructure and magnetic properties are discussed in relation to the giant magnetoresistance properties exhibited by the system, which con"rm the development of interparticle correlations with increasing the heating current density. 0304-8853/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 9 9 ) 0 0 3 0 3 -0
... 1 Y. Tokura, H. Takagi, and S. Uchida, Nature 337, 345 (1989); JT Mark-ert, EA Early, T. Bjor... more ... 1 Y. Tokura, H. Takagi, and S. Uchida, Nature 337, 345 (1989); JT Mark-ert, EA Early, T. Bjornholm, S. Ghamaty, BW Lee, JJ Nuemeier, R. D. Price, CL Seaman, and MB Maple, Physica C 158, 178 (1989). 2 TR Thurston, M. Matsuda ...
The temperature and time dependence, in di!erent magnetic "elds, of the "eld-cooled and zero-"eld... more The temperature and time dependence, in di!erent magnetic "elds, of the "eld-cooled and zero-"eld-cooled magnetisation on ball-milled nanocrystalline Fe has been studied. The results indicate the existence, below about 70 K, of a disordered frozen magnetic state which is erased by applying an external "eld H"1000 Oe, favouring the ferromagnetic order.
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Papers by D. Fiorani