Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System

A novel
synthesis method, “arc-melting-self-flux”, has been
developed and a series of five Tsai-type 1/1 approximant crystals
in the Tb-Au-Si system have been synthesized. The synthesis method,
by employing a temperature program which oscillates near the melting
and nucleation points of the approximants, has provided high-quality
and large single crystals in comparison to those obtained from the
standard arc-melting-annealing and self-flux methods. The atomic structures
of the approximants have been determined from single-crystal X-ray
diffraction data and described using concentric atomic clusters with
icosahedral symmetry. The compounds are nearly isostructural with
subtle variations; two types of atomic clusters which mainly vary
at their cluster centers are observed. One type contains a Tb site
at the center, and the other contains a disordered tetrahedron decorated
with Au/Si mixed sites. Both cluster types can be found coexisting
in the approximants. The compounds have different average weighted
ratios of central Tb to disordered tetrahedron in the bulk material.
Furthermore, a strategy for chemically tuning magnetic behavior is
presented. Magnetic property measurements on the approximants revealed
that the magnetic transition temperature (Tc) decreases as the occupancy of the central Tb site increases. Tc decreased from 11.5 K for 0% occupancy of
the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline
anisotropy is observed for the approximants with higher central Tb
occupancy in comparison to their low central Tb occupancy counterparts.
Hence, the previously reported “ferrimagnetic-like”
magnetic structure model remains valid.