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Charge-Ordering and Magnetoelastic Coupling Effects on the Magnetocaloric Properties of Manganites

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Reis M., Gomes A., Araújo J., Tavares P., Amaral J., Oliveira I., Amaral V.

Acta Physica Polonica A

2004

vol. 105

issue 1-2

163-171

A study of the magnetocaloric properties of La_{1-x-y}Y_yCa_xMnO_3, La_{1-x}Cd_xMnO_3, and Pr_{1-x}Ca_xMnO_3 manganites with ferromagnetic and charge-ordered states is presented. The ferromagnetic lanthanum manganites show a negative entropy change peakΔ S under the application of a magnetic field at the Curie temperature. However, the magnetoelastic coupling effects lead to a first-order paramagnetic-ferromagn etic transition and an increasedΔ S compared to simple ferromagnets. This effect is analyzed in the framework of the Landau theory of phase transitions which shows a comparable influence of the magnetoelastic couplings and the ordinary magnetic ordering effect. The Pr_{1-x}Ca_xMnO _3 system shows a rich electric and magnetic phase diagram, with a ferromagnetic insulator phase for 0.15

Analysis of Atmospheric Aerosols Using the Lisbon Nuclear Microprobe

100%

Rita E., Alves L., Reis M., Rodrigues F., Fialho P., Soares J.

Acta Physica Polonica A

2001

vol. 100

issue 5

781-788

The nuclear microprobe installed at Instituto Tecnológico e Nuclear, in Lisbon, was used in the analysis of aerosols collected at the Azores islands. Samples from two different aerosol groups were analysed. One referred to aerosols that were carried from North America and the other one contained aerosols that were carried from the Sahara desert and crossed over Europe. Coarse and fine fractions were analysed for each aerosol group and two-dimensional elemental maps were constructed, which allowed the identification of several individual particles. For particles of interest, elemental spatial correlations and dimensions were determined and point analysis was also carried out (depth information was achieved by fitting Rutherford backscattering spectra). Some of these particles are quite interesting. For instance, in the fine fraction of the aerosols that were carried from North America, particles were found with Cu and Cl in the atomic proportion 1:2 and with dimensions 15×15×15μm^3, and in the corresponding coarse fraction a particle with K and S was identified, with dimensions 28×35×30μm^3. Some differences were found between the aerosols groups. One example of these are Ti particles (fine fraction) and Rb (coarse fraction) that were identified in one group (Sahara desert and Europe), but not in the other

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2 Acta Physica Polonica A

1 2004

1 2001

2 Reis M.

1 Alves L.

1 Amaral J.

1 Amaral V.

1 Araújo J.

1 Fialho P.

1 Gomes A.

1 Oliveira I.

1 Rita E.

1 Rodrigues F.

1 Soares J.

1 Tavares P.

Search results

Charge-Ordering and Magnetoelastic Coupling Effects on the Magnetocaloric Properties of Manganites

Analysis of Atmospheric Aerosols Using the Lisbon Nuclear Microprobe