Specific heat of La1.2Sr1.8Mn2O7

The specific heat of a single crystal of the layered perovskite La1.2Sr1.8M n2O7 has been measured for 83 <T<290K. A high, narrow peak associated with the ferromagnetic ordering of the Mn3+-Mn4+ ions is observed to have a maxi mum at T-c =115.57 K, in agreement with magnetization, neutron scattering, and resistivity measurements. A second, hysteretic, peak at 260 K is also o bserved. An estimate is made of the substantial magnetic entropy removed by cooling the crystal from 290 K to T-c. [S0163-1829(99)1 1533-9].