5,631 research outputs found
Large adiabatic temperature and magnetic entropy changes in EuTiO3
We have investigated the magnetocaloric effect in single and polycrystalline
samples of quantum paraelectric EuTiO3 by magnetization and heat capacity
measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to
Eu2+ magnetic moments below TN = 5.6 K. This compound shows a giant
magnetocaloric effect around its Neel temperature. The isothermal magnetic
entropy change is 49 Jkg-1K-1, the adiabatic temperature change is 21 K and the
refrigeration capacity is 500 JKg-1 for a field change of 7 T at TN. The single
crystal and polycrystalline samples show similar values of the magnetic entropy
change and adiabatic temperature changes. The large magnetocaloric effect is
due to suppression of the spin entropy associated with localized 4f moment of
Eu2+ ions. The giant magnetocaloric effect together with negligible hysteresis,
suggest that EuTiO3 could be a potential material for magnetic refrigeration
below 20 K.Comment: 12 pages, 4 figure
Specific heat and magnetocaloric effect in Pr1-xAgxMnO3 manganites
The magnetocaloric effect in alternating magnetic fields has been
investigated in Pr1-xAgxMnO3 manganites with x=0.05-0.25. The stepwise reversal
of the sign of the magnetocaloric effect has been revealed in a weakly doped
sample (x=0.05) at low temperatures (~80 K). This reversal is attributed to the
coexistence of the ferromagnetic and canted antiferromagnetic phases with
different critical temperatures.Comment: 4 pages, 4 figure
Magnetocaloric effect in manganites: metamagnetic transitions for magnetic refrigeration
We present a study of the magnetocaloric effect in La5/8-yPryCa3/8MnO3
(y=0.3) and Pr0.5Ca0.09Sr0.41MnO3 manganites. The low temperature state of both
ystems is the result of a competition between the antiferromagnetic and
ferromagnetic phases. The samples display magnetocaloric effect evidenced in an
adiabatic temperature change during a metamagnetic transition from an
antiferromagnetic to a ferromagnetic phase . As additional features,
La5/8-yPryCa3/8MnO3 exhibits phase separation characterized by the coexistence
of antiferromagnetic and ferromagnetic phases and Pr0.5Ca0.09Sr0.41MnO3
displays inverse magnetocaloric effect in which temperature decreases while
applying an external magnetic field. In both cases, a significant part of the
magnetocaloric effect appears from non-reversible processes. As the traditional
thermodynamic description of the effect usually deals with reversible
transitions, we developed an alternative way to calculate the adiabatic
temperature change in terms of the change of the relative ferromagnetic
fraction induced by magnetic field. To evaluate our model, we performed direct
measurement of the sample's adiabatic temperature change by means of a
differential thermal analysis. An excellent agreement has been obtained between
experimental and calculated data. These results show that metamagnetic
transition in manganites play an important role in the study of magnetic
refrigeration.Comment: Acepted to be published in Applied Physics Letter
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