Magneto-calorimetric studies of reversible magnetisation

Abstract Working on well-annealed single-grain samples of YBa 2 Cu 3 O 7− δ containing 30 mol% of Y 2 BaCuO 5 grown by the seeded melt-growth process, we have obtained values of the field dependence of the free energy, Δ F ( H a , T ), and the reversible magnetisation, M rev ( T )=−(∂Δ F /∂ H a ) T , through measurements of the electronic specific heat coefficient γ ( H a , T ) in a series of fixed applied magnetic fields H a . The ability to deduce reliable values of M rev (0) in the irreversible region of a superconductor is an exciting development as hitherto this quantity could only be poorly estimated from magnetic hysteresis data.