  If a hypothetical elementary particle called an axion exists, to solve the
strong CP problem, a 57Fe nucleus in the solar core could emit a 14.4-keV
monochromatic axion through the M1 transition. If such axions are once more
transformed into photons by a 57Fe absorber, a transition edge sensor (TES)
X-ray microcalorimeter should be able to detect them efficiently. We have
designed and fabricated a dedicated 64-pixel TES array with iron absorbers for
the solar axion search. In order to decrease the effect of iron magnetization
on spectroscopic performance, the iron absorber is placed next to the TES while
maintaining a certain distance. A gold thermal transfer strap connects them. We
have accomplished the electroplating of gold straps with high thermal
conductivity. The residual resistivity ratio (RRR) was over 23, more than eight
times higher than a previous evaporated strap. In addition, we successfully
electroplated pure-iron films of more than a few micrometers in thickness for
absorbers and a fabricated 64-pixel TES calorimeter structure.
