Specific heat and magnetocaloric effect measurements using commercial heat-flow sensors

Abstract

We present a technique for measuring the specific heat (C) and the isothermal magnetocaloric effect (MT) in the temperature range from 30 to 300 K. The method consists of precise measurements of the heat flux between the sample and its surroundings. This design, which uses commercially available Peltier elements as heat-flow meters, is simple and robust. A high density of statistically independent data can be obtained, e.g., 30 points/K in specific heat measurements at 1 K/min heating rate, or 150 points/T in magnetocaloric experiments at 0.2 T/min sweep rate. The signal/noise ratio is in the range of 103 to 104. C can be measured with increasing or with decreasing temperature. Test runs with Cu, NdBa2Cu3O7, and UAs samples show that this method provides measurements of the specific heat in magnetic fields up to ⩾14 T with 2% accuracy, is able to characterize small anomalies at the ∼0.1% level (e.g., melting of the flux line lattice in a superconductor), can detail sharp first-order anomalies, and detect their hysteresis. The magnetocaloric effect in NdBa2Cu3O7 shows clear signatures of vortex melting, crossover to irreversibility, and the “fishtail” effect.