  In a micro ring of a superconductor with a spin-triplet equal-spin pairing
state, a fluxoid, a combined object of magnetic flux and circulating
supercurrent, can penetrate as half-integer multiples of the flux quantum. A
candidate material to investigate such half-quantum fluxoids is
Sr$_\mathsf{2}$RuO$_\mathsf{4}$. We fabricated Sr$_\mathsf{2}$RuO$_\mathsf{4}$
micro rings using single crystals and measured their resistance behavior under
magnetic fields controlled with a three-axes vector magnet. Proper Little-Parks
oscillations in the magnetovoltage as a function of an axially applied field,
associated with fluxoid quantization are clearly observed, for the first time
using bulk single crystalline superconductors. We then performed magnetovoltage
measurements with additional in-plane magnetic fields. By carefully analyzing
both the voltages $V_+$ ($V_-$) measured at positive (negative) current, we
find that, above an in-plane threshold field of about 10 mT, the magnetovoltage
maxima convert to minima. We interpret this behavior as the peak splitting
expected for the half-quantum fluxoid states.
