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Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

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Samoilenko Z., Okunev V., Pushenko E., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szymczak R.

Acta Physica Polonica A

2004

vol. 105

issue 1-2

93-98

We have investigated thin films of lanthanum manganites epitaxially grown by pulsed laser deposition on single-crystalline substrates. X-ray diffraction studies show that the characteristic feature of the investigated films is a superposition of fractions with long range atomic order in the basic single-crystalline matrix, and mesoscopic order in the clusterized structure encompassing the Mn-O layers. A detailed analysis of diffusive scattering shows that the size of metallic clusters and their volume concentration in the dielectric matrix varies. In the case of a small size and concentration, the metallic clusters in low temperature behave as quantum dots and their presence leads to a tunneling mechanism of conductivity with characteristic R(T)= const. In the case of large cluster size, the discrete energy levels become smeared. It appears also that the optical, transport, and magnetic properties of the investigated films depend critically on the distribution of Mn^{2+}, Mn^{3+}, and Mn^{4+} ions in the clusters.

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

100%

Okunev V., Samoilenko Z., D'yachenko T., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szewczyk A., Szymczak R.

Acta Physica Polonica A

2004

vol. 105

issue 1-2

121-126

We have investigated the structure, and electric, optical, and magnetic properties of LaSr(Ca)MnO films containing atomic clusters of various types coherently built into the basic crystallographic matrix. Below the transition to the metallic state, the electrical conductivity of the films is determined by tunneling of charge carriers between metallic clusters. We have found that for each sample there exists a threshold value of magnetic ordering, above which the magnetic subsystem starts to affect actively the film conductivity. The observed increase of conductivity with decreasing temperature is caused by the fact that in the process of magnetic ordering of the samples the cluster size and concentration of metallic phase increase. Experimental results are in agreement with theoretical calculations.

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2 Acta Physica Polonica A

2 2004

2 Abal'oshev A.

2 Baran M.

2 Gierłowski P.

2 Lewandowski S.

2 Okunev V.

2 Samoilenko Z.

2 Szymczak R.

1 D'yachenko T.

1 Pushenko E.

1 Szewczyk A.

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Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films