The unconventional long range (m=1) spin triplet proximity
effect is theorised to be created at a
Superconductor/Ferromagnet (SC/FM) interface that is
magnetically inhomogeneous and provides the conditions for
spin mixing. Many experimental and theoretical works have
identified the existence of the m=1 spin triplet state using
Josephson junctions to show how the critical current does not
diminish significantly in a thick FM layer, (thickness being
relative to the decay length of a Cooper pair in an FM). In
this thesis the challenge was to examine single SC/FM,
interfaces via point-contact Andreev Reflection spectroscopy
(PCARS), to see if it were possible to find clear signatures
of the spin mixing or spin scattering conditions that facilitates
formation of the spin triplet state.
PCARS measurements were performed on Ho single crystals
and thin films as a function of contact resistance. The results
show an anomalous decrease of the polarisation parameter
and an increase in interface scattering parameter as the
contact resistance decreases. This is interpreted in terms of
the tip experiencing a region in which some form of spin
mixing or spin scattering dominates.
Measurements of Ni0.19Pd0.81 spectra were also taken as a
function of contact resistance but the change of polarisation
and scattering parameter that was observed in the Ho samples
was not observed here. PCARS temperature measurements
were also taken for Ni0.03Pd0.97 to investigate if spin
fluctuations close to TC could provide the magnetic
inhomogeneity required for spin-mixing. However the trend in
the results proved inconclusive. This is likely due to
broadening that result in the fitting procedure, and the
extremely small polarisation in these samples.
During the course of the thesis I contributed to the
development of the spectral fitting routines and examined the
challenges associated with three and four parameter fitting,
degenerate fits and series resistance.