  Proper characterisation of investigated samples is vital when studying
superconductivity as impurities and doping inhomogeneities can affect the
physical properties of the measured system. We present a method where a
polarised neutron imaging setup utilises the precession of spin-polarised
neutrons in the presence of a trapped field in the superconducting sample to
spatially map out the critical temperature for the phase transition between
superconducting and non-superconducting states. We demonstrate this method on a
superconducting crystal of the prototypical high-temperature superconductor
(La,Sr)$_2$CuO$_4$. The results, which are backed up by complementary magnetic
susceptibility measurements, show that the method is able to resolve minor
variations in the transition temperature across the length of the LSCO crystal,
caused by inhomogeneities in strontium doping.
