Cooling and Heating by Adiabatic Magnetization in the Heusler Magnetic Shape Memory Alloys on Ni 54 Fe 19 Ga 27 single crystal K.V. Klimov and A.N. Vasiliev (Moscow State University, Russia)
The temperature dependence of resistance R of Ni 54 Fe 19 Ga 27 single crystal This viewgraph presents the results of electrical resistance measurements. At T M = 285 K the sharp drop is seen at R vs. T curve which corresponds to the transition from austenite to martensite phase.
The temperature dependence of specific heat C of Ni 54 Fe 19 Ga 27 single crystal in double logarithmic scale This graph present the results of specific heat measurements. Once again the sharp anomaly corresponds to the structural phase transition. The magnetic phase transition anomaly is too small to bee seen in double logarithm scale. ( T M = 288 K T C = 291 K)
C = T + T3/2 + T 3
= (2/3) 2 k B 2 N( F )
= 4Rn -3
Debye temperature was estimated as = 430 K
Temperature dependence of magnetic susceptibility In wide temperature range the magnetic susceptibility is shown on this viewgraph. The anomalies at both Curie temperature and structural transitions are clearly seen.
The temperature dependencies of magnetization of Ni 54 Fe 19 Ga 27 single crystal in ac-mode
Basing on these measurements we undertook direct study of magnetocaloric effect. This study relates to the formula Evidently the change of temperature is proportional to derivative of magnetization with respect to temperature and inversely proportional to specific heat.
This slide show the results of magnetocaloric measurements. Clearly the effect is relatively small of about 0,2 K. Magnetocaloric measurements For comparison the similar experiment was performed on gadolinium single crystal, the result shown at this graph. The effect is significantly large, above 1.5 К at some field.
In conclusion we have shown that the magnetocaloric effect can be observed at room temperatures in Ni 2 FeGa alloy, but close vicinity to structural transition increases specific heat and hinders the change of temperature.
Probably, the samples with separated magnetic and structural transitions will be better for this kind of application.