RESUMEN
The magnetic, magnetotransport, and magnetocaloric properties near compound phase transitions in Ni50Mn35In14Z (Z = In, Ge, Al), and Ni48Co2Mn35In15 Heusler alloys have been studied using VSM and SQUID magnetometers (at magnetic fields (H) up to 5 T), four-probe method (at H = 0.005-1.5 T), and an adiabatic magnetocalorimeter (for H changes up to deltaH = 1.8 T), respectively. The martensitic transformation (MT) is accompanied by large magnetoresistance (up to 70%), a significant change in resistivity (up to 200%), and a sign reversal of the ordinary Hall effect coefficient, all related to a strong change in the electronic spectrum at the MT. The field dependences of the Hall resistance are complex in the vicinity of the MT, indicating a change in the relative concentrations of the austenite and martensite phases at strong fields. Negative and positive changes in adiabatic temperatures of about -2 K and +2 K have been observed in the vicinity of MT and Curie temperatures, respectively, for deltaH = 1.8 T.
RESUMEN
Recently the inverse magnetocaloric effect has been observed in different compounds. However, it is very rare for any manifestation of the effect to be seen in manganites. We have found the inverse magnetocaloric effect in the case of polycrystalline La(0.125)Ca(0.875)MnO(3). Such a phenomenon is attributed to the stabilization of the antiferromagnetic state associated with inherent magnetic inhomogeneous phases for this compound.
RESUMEN
A study of the magnetocaloric effect has been performed on a polycrystalline CeRu(2)Ge(2) compound, which exhibits an antiferromagnetic ordering below T(N) = 8.3 K and enters into a ferromagnetic ground state at T(C) = 7.4 K. The origins of the magnetocaloric parameters (the isothermal entropy change: -ΔS and the adiabatic temperature change: ΔT(ad)) of the CeRu(2)Ge(2) compound below T(C) have been analyzed. A sharp decrease in -ΔS has been observed below T(C). However, the ΔT(ad) does not fall as sharply as -ΔS with decreasing temperature in the corresponding temperature region. This behavior results in an additional value of ΔT(ad) at low temperature, which originates from the exponential decrease of the magnetic contribution of specific heat associated with an increase of energy-gap in the ferromagnetic spin-wave spectrum with the application of magnetic field.
