Condensed Matter Physics with Pelletron
Facility
Nuclear
techniques like perturbed angular correlation (PAC) and perturbed angular
distribution (PAD), involving hyperfine interaction between a nuclear probe and the electromagnetic fields produced
by atomic electronic states in a solid, provde a elegant and accurate tool to study various aspects
of condensed matter physics viz. electronic and magnetic properties at short
length and time scales. With the help of
energetic heavy ion beams from an accelerator like the Pelletron
facility, it is not only possible to produce a wide variety of probes but also
implant them into hosts (recoil implantation) that are other wise inaccessible
by conventional methods. Over the past years we have carried out several
experiments to study some problems like formation and stability of magnetic
moment on d/f ions embedded in different metallic hosts. Some of our important
findings are
i)
Observation of giant 4d magnetic moment on Rh atom in Pd and Pt metal.
ii)
Elucidation of moment
stabilizing influence of ferromagnetic host spin polarization. Compared to
conventional Kondo type antiferromagnetic spin
polarization that always increase spin fluctuation and hence destabilize the
magnetic moment, we have shown that ferromagnetic polarization of host
conduction electrons lead to suppressed spin fluctuation rates and hence a more
stable magnetic moment.
More recently via in beam
TDPAD measurement we have found evidence for the existence of highly stable 4d
magnetic moment on interstitial Mo atoms in Yb host.
It should be noted that at interstitial lattice sites due to enormously large
overlap of atomic orbitals, Mo atoms are not expected
to develop local magnetic moment. Another important mile stone of our studies
is the successful demonstration of Kondo behaviour of
Fe impurities in Ag nanoparticles. Compared to Fe in bulk Ag, in the nanoparticles we find a ten fold increase in the magnitude
of Kondo temperature Tk . Employing PAC technique we have also studied
static and dynamic spin correlation in some Uranium based heavy fermion systems. The results provide clear indication that
the manifestations of “heavy fermions” viz. enhancement of electronic specific
heat can arise from dynamic spin correlation between U atoms without any
enhancement of electronic mass.
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