Francesco Orsini – CV
Paolo Arosio – CV
Elena Garlatti - CV
Fatemeh
Adelnia - CV
Congresses and publications
· 117 publications on national/international journals and about 100 participations at national and international congresses.
Scientific apparatuses
· Spectrometers for Nuclear Magnetic Resonance (NMR) and Quadrupolar Resonance (NQR), for Muon Spin Resonance (mSR), for Electron Paramagnetic Resonance (EPR), for MR Imaging (Magnetic Resonance Imaging)
· Adiabatic Calorimeter
· SQUID (Superconducting Quantum Interference Device) for magnetic measurements
·
· Apparatus for resisitivity measurements.
· Superconducting magnets and electromagnets
· Electronic and cryogenic apparatuses (4He flux cryostat , 3He cryostat , dilution cryostat and so on).
RESEARCH : ACTUAL ACTIVITY
a)
Magnetic Resonance
Imaging on animal models for studying : (1) the blood perfusion and cerebral
ischemia on rats; (2) the rheumatoid arthritis pathology; (3) new contrast agents (characterization by
magnetometry and relaxometry)
The
Magnetic Resonance Imaging (MRI) technique is currently exploding due to its
non-invasive character and continuosly increasing performances for clinical
applications. A crucial role is played by Molecular Imaging, a term which refers
to MRI used in conjuction with specific contrast agents able to reach specific
molecule inside the tissues and to target them during (or hopefully before) a
pathology evolution.
Our MRI activity concentrated on several research lines :
(a) project, desing and development of coils for low-field Imagers (0.2 Tesla, E-SCAN, Esaote SpA), used for pathologies of ostheo-articular system (e.g. : acute inflammation (IA), rheumatoid arthritis (AR) );
(b) optimization of sequences devoted to the study of AR and IA, in low-field systems (0.2 Tesla) and high-field systems (e.g. 7 Tesla, Pharmascan, Bruker SpA);
(c) individuation iof a MRI protocol
(e.g. T2 maps, dynamic MRI, etc.) to study the precursor effects and
the evolution of AR, IA and, in near future, tumours;
(d) analysis of the contrast agents (CA)
effects on images for specific pathologies , in the framework of “targeted-MRI”
projects (e.g. CA that tend to link to macrophages)
(e) studies about MRI protocols able to
better describe the devlopment and evolution of cerebral damages and to
distinguish different kinds of damages, with and without CA; we are trying also
to search for the better CA to study cerebral ischemia;
(f) study of the nuclear spin-spin
relaxation curves in terms of multiexponential components to access to the
microscopic mechanisms responsible for the cerebral damages.
b) NMR-NQR and susceptibility
measurements to study superconducting (SC) fluctuations and spin and charge-gap
in YBa2Cu3O7-d , YBa2Cu4O8,
YBa2Cu3O7:Ca, La2-XSrXCuO4,
MgB2, YNi2B2C, zero-dimensional SC
nano-particles
This research field regards the study of superconducting fluctuations (SF) and of the precursor diamagnetism (PD) in conventional and high-Tc superconductors (HTSC), in forms of orientend powders, bulk or nano-particles. In general terms, by following the phenomenological theory of phase transitions Ginzburg-Landau (GL) the behaviour of the fluctuations of the order parameter y(r), linked to the number of Cooper pairs, can be followed for T>Tc (Tc=transition temperature). For T>Tc the Cooper pairs are metastable and SF arise. Sf can give direct information on the mechanism of superconductivity and the role of eventual charge and spin “gap”, possibly opening for T>>Tc.
In BCS-like system, a special role is played by the recently discovered MgBs that presents a relatively high Tc~40K. For the first time we studied the magnetization curves M(H) at constant temperature T®Tc+ and experimentally was individuated a magnetic upturn field Hup , theoretically predicted, whose presence is due to the Cooper pairs breaking generated by the applied field itself.
In HTSC like i.e. YBa2Cu3O7-d , YBa2Cu3O7:Ca,
La2-XSrXCuO4 , the effect of the magnetic
field depends on the hole doping. In the case of optimally doping (maximum Tc)
the M(H) curves for T®Tc+ can be explained in the framework of
anisotropic GL theory. If the sample is “underdoped” or “overdoped”, for T>Tc
mesoscopic regions (not chemically trivially disordered) with |y(r)|¹0 are formed ; the phase q(r) is site-dependent. This
situation favours the formation of couples vortex-antivortex that induce an
upturn field in M(H) of different nature
with respect to standard
In the systems YNi2B2C
and MgB2:Al , again an upturn field is displayed by M(H) but its
origin resides in chemical disorder or distribution of Tc’s.
Finally , to verify the GL
analytical solution in zero-dimension (diameter of SC particles d<x , x=coherence length) , preliminary
experiments on Pb nanoparticles of different dimensions were performed. From
M(H) and c(T) behaviour the theoretical
predictions seem verified while the crossover toward the critical zone T~Tc+
will be studied. This study is possible in nano-particles because the extension
of the critical zone is sizeable, differently from other SC systems.
c)
NMR, mSR, XMCD and susceptibility measurements on mesoscopic magnetic
molecules, powders, films and single crystals, with properties similar to
ferritin and on low-dimensional magnetic
clusters.
I have studied fundamental properties as spin
dynamics, quantum tunneling of the magnetization (QTM) , topological spin
structure, level crossing problem and basic magnetic interactions. The
investigated systems are constituted by molecules containing a “core” of
metallic ions (till 30) and magnetically isolated one each other by organic
screens. This allows to study the properties of the single molecule (single
molecule magnets, SMM, or molecular nanomagnets, MNM) with bulk quantitiy of
sample.
The most famous examples are high-spin molecules
like Mn12 and Fe8, theoretically useful for magneti storage due to their
bistability in the ground state. In thse
systems, an axial anisotropy (easy-axis z) due to the crystal field, determines
a preferential direction of the magnetization M. The spin topology is complex
and variable from one compound to the other; the excahbnge interactions are
antiferromagnetic (AF), the dominant one being >100K . At low T, Mn12 and
Fe8 are superparamagnetic with total ground state spin S=10 and an energy
barrier (for M reorientation) ~ 60K and 27K, respectively. The energy levels
has a double well with degenerate ±MS levels. By applying an external magnetic
field, level crossings are induced for different Ms. For T<10K
QTM is present. This process is thermally activated for T>1K (Mn12) and
T>0.4K (Fe8) while is pure for the lowest T.
The low-dimensional nano-molecules (MNM) have
spin topology of different kinds. We will give as example the magnetic rings.
In these compounds the exchange interactions in the ground state (GS) are AF
(total GS spin S=0). The spectrum of levels is discrete and follows
approximately the Lande’s rule, the lowest energy gap being of the order of
some tenths of K. Even here level crossings can be induced. For low
temperatures , some anisotropic parts of the Hamiltonian (anisotropic exchange,
Dzyaloshinki-Moriya interaction, etc.) determines the main physical properties.
By NMR-NQR , susceptibility and mSR measurements, we studied the spin dynamics of all
the above systems in the different temperature regions. Novel information on
microscopic parameters (like energy levels broadening, spin-phonon interaction,
QTM paths, local spin arrangement, level
crossing properties, etc.) were obtained.
d)
Magnetic measurements on
molecular 1-D magnetic chains containing rare earth ions (Gd,Eu) or metals (Co)
alternated to radicals (Et,iPr,Ph,Me ; PhOMe) for the study of peculiar phase
transitions and/or slow-relaxation of magnetization (nano-wires)
In the rare-earth chains, the molecular magnetic 1D
system is formed by Gd(3+) s=7/2 spins
alternating to radicals R s=1/2. The intrachain interactions are AF and the
system is frustrated by the presence of competing nearest-neighbour (Gd-R) and
next-nearest-neighbour (Gd-Gd and R-R) interactions. The interchain interaction
is negligible (Jinter
~ 10-4 Jintra). As a final result one has a XY
system that at low T presents an effective spin Seff arrange in a
helicoidal scheme. In these systems the Villain’s conjecture was verified, thus
demonstrating that at high T the system is paramagnetic, at intermdiate T has a
transition to a chiral phase and at low T a transition to a 3D ordered
helicoidal system.
Particularly, by the use of mSR measurements coupled to specific heat, one has observed the absence of an anomaly in the 2-spin correlation function in Gd-iPr compound at T~2K, where a transition to a chiral phase was suggested.
In the transition metal based chains, the system is constituted by Co(II) (S=1/2 for
T<80K) ions alternated to radicals (s=1/2); the chains are not interacting (Jinter ~ 10-4
Jintra). The g-factor of the Co(II) ion is ~7.4 while the one of
radical is ~2; in this way a ferrimagneti chain is obtained with just one
effective intrachain AF exchange interaction (Jintra~200K). The
peculiarity of these systems is that at low The magnetization M relaxes slowly
(nanowires) and they can be suggested as bistable units for memory storage. The
relaxation time of M follow an Arrhenius law t=t0 exp(D/T),
with a barrier ~150K.
With NMR and mSR measurements we determined the existence of a second kind of
relaxation mechanism, not detected by macroscopic techniques.
e)
mSR and susceptibility measurements
on high-Tc superconductors, Nd1.85Ce0.15CuO4+d
For many years, the magnetic phase diagram of high-Tc superconductors
(HTSC) was debated as a fundamental step toward the comprehension of the superconducting
micrioscpic mechanism and the understanding of the role of the elementary
magnetic excitations. In the system La2-xSrxCuO4+d, studied by means of NMR-NQR, mSR and susceptibility, for very low
doping (x<0.02) the system at low T (T<20K) has a transition to a
spin-glass (SG) phase; for intermediate doping (0.02<x<0.08) cluster-SG
phase is formed while for x>0.08 the transition to the supeconducting phase
is verified , with a maximum Tc~35K. In the region
0.08<x<0.12, a possible coexistence of magnetism and superconductivity
(classically forbidden) was inferred and partly demonstrated.
The described phase diagram was shown to be “universal” for all hole-doped HTSC and we confirmed it also in electron-doped HTSC like Nd2-xCexCuO4+d by means of mSR and susceptibility measurements. This superconductor has a maximum Tc~25K and can vary its phase with proper oxygen doping at fixed content of Ce (x=0.15). The result is a third line in the phase diagram, in correspondence of Ce doping =0.15, that confirms the existence of a SG phase for oxygen content d>0.06.
f)
Characterization of magnetic nanoparticles for MRI and other
functionalities
Recently
the scientific community paid a lot of attention to the synthesis of
multifunctional magnetic nanoparticles with the aim of obtaining compounds with
different applications in the field of bio-physics. Among these applications
the possibilities to obtain new contrast agents for Magnetic Resonance Imaging
(MRI) and to reveal (with magnetic techniques) the success of the local
application of a “pathology specific drug” via the use of a delivering molecule
(drug delivery), were evidenced. The success of these applications could help
in prevention and care of diseases. The research activity is focused on the
characterization of newly synthesized magnetic nanoparticles/nanomagnets to be
used possibly as MRI contrast agents, by means of Nuclear Magnetic Resonance
(NMR) and Atomic/Magnetic Force Microscopy (AFM/MFM), but also useful for
magnetic hyperthermia. Possible functionalization with fluorophores are also
investigated. By AFM/MFM, the morphological and (surface) magnetic structure of
new compounds are studied. By NMR the relaxivity curves of new nanosize
magnetic materials are investigated, after preliminary magnetic susceptibility
and magnetization measurements. The structural and morphological properties of
novel systems are put in connection with their physico-chemical properties.
· Institute of Pharmacological
Sciences - Universita’ di Milano – Prof. M.Asdente, Prof.E.Tremoli,
Dr.U.Guerrini and Dr.G.Sironi
·
Dipartimento
di Chimica, Universita’ di Torino-Italy, prof. S. Aime
·
Bracco SpA,
Milano (Italy)
·
Esaote SpA,
Genova (Italy)
·
Dipartimento
di Chimica, Universita' di Firenze-Italy, prof. D.Gatteschi
·
Dipartimento
di Chimica Fisica, Universita’ di Pavia-Italy, prof. Flor
·
Dipartimento
di Fisica di Firenze-Italy, prof.A.Rettori
·
Dipartimento
di Fisica di Genova-Italy, prof.U.Valbusa
·
CNRS-LCMI,
Grenoble (France), prof.C.Berthier and Dr.M.Horvatic
·
IEQ – CNR
(Quantum Electronics Institute), Firenze-Italy, dr.M.G.Pini and dr.U.Balucani
· Chemistry department, Universita’ di Modena-Italy, prof.A.Fabretti and Dr. A. Cornia
·
Dept.of Physics, Ames Lab,
·
Dept. of Physics,
·
Dept. Of Chemistry,
·
(OLD: Dept. Of Physics,
· (OLD: Superior Physics Department (Engineering faculty), Universita’ di Firenze-Italy, prof.Spina)
· (OLD : IROE – CNR (Institute for Electromagnetic Waves), Firenze-Italy, dr.Cianchi)
·
Dipartimento
di Fisica, Universita’ di Modena-Italy , prof. M. Affronte
·
Dipartimento
di Fisica, Universita’ di Torino-Italy, prof. C. Guiot
·
Dipartimento
di Fisica, Universita’ di Parma-Italy, Dr. L. Romano’
·
INFM-Roma
Unit, Italy, prof. A. Varlamov
· Dept. of Phys.,
· CNRS, High-Field Magnetic
Laboratory,
· Laboratoire Louis Neel-CNRS, Grenoble
(France), prof. B. Barbara
· Dept. Chemistry,
· Dept. Chemistry,