Magnetocaloric effect ob- served by differential thermal analysis

YAMILA ROTSTEIN; PABLO BERGAMASCO; ANA GABRIELA LEYVA; CECILIA ALBORNOZ; MARIANO QUINTERO; JOAQUIN SACANELL

Conferencia; At the Frontiers in Condensed Matter V - FCM 2010; 2010

Departamento de Física de la Materia Condensada, Gerencia de Investigación y Aplicaciones, CAC, CNEA

The magnetocaloric effect (MCE) is the isothermalchange of magnetic entropy and the adiabatic temper-ature change induced in a magnetic material when anexternal magnetic field is applied.In this work, we study this effect using the differen-tial thermal analysis technique (DTA), which consistsin measuring simultaneously the temperatures of thesample of interest and a reference one while an exter-nal magnetic field ramp is applied. We calculate thetemperature difference (¢T) from these values.By using this method, we study the MCE inLa0.305Pr0.32Ca0.375MnO3 , which presents phase sep-aration effects at low temperatures (< 200 K).We obtain ¢T vs H and ¢T vs t curves, and an-alyze how the MCE varies by changing the externalpressure and the rate of the magnetic field ramp. Ourresults show that the effect is amplified by workingat lower pressures (< 10−4 Torr) and at high veloc-ity. However, at high vacuum a temperature gradientappears and makes it difficult to set the temperatureproperly. Also, self-heating of the sensor becomes rel-evant at this condition. Therefore, we decide to workat pressures of the order of 1 Torr. We also mea-sured MCE at different temperatures, finding an in-verse MCE, characterized by a ¢T <0 on increasingmagnetic field, in the region between 140 K and 180K.