  Nuclear spin-lattice relaxation times are measured on copper using magnetic
resonance force microscopy performed at temperatures down to 42 mK. The low
temperature is verified by comparison with the Korringa relation. Measuring
spin-lattice relaxation times locally at very low temperatures opens up the
possibility to measure the magnetic properties of inhomogeneous electron
systems realized in oxide interfaces, topological insulators and other strongly
correlated electron systems such as high-Tc superconductors.
