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 87Rb atoms in the Mott insulator regime. The two spin states used were the F=|1,-1〉≡|↑〉 and F=|2,-2〉≡|↓〉 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.