Spin gradient thermometry for ultracold atoms in optical lattices. In Ref.  a new thermometry method suitable for measuring temperatures of ultracold atoms in the Mott insulator regime was demonstrated. The method was applied to a two-component mixture of atoms in the Mott insulator regime. The two spin states used were the and hyperfine states. Since these two states have different magnetic moment, a magnetic field gradient induces a domain wall whose width is proportional to the temperature of the sample.