Effect of the crystal structure defectiveness on magnetic state of sodium-doped lanthanum manganites

• Main Authors: Tovstolytkin, A.I., Pogorily, A.N., Kotov, V.V., Belous, A.G., V’yunov, O.I.
• Format: Article
• Language: English
• Published: НТК «Інститут монокристалів» НАН України 2004
• Series: Functional Materials
• Online Access: http://dspace.nbuv.gov.ua/handle/123456789/139549

Structural, electric, magnetoresistive, and resonance properties of La₁-xNaxMnO₃₊y samples synthesized by solid phase reactions have been studied. It is shown that the valence state of manganese remains essentially unchanged as x increases from 0.08 to 0.16: the positive charge reduction in lanthanum sublattice caused by the increase in sodium content occurs due to formation of vacancies either in cation sublattices or in both cation and anion ones. In addition to magnetically ordered phases, all the samples have been found to contain the magnetically disordered low-conductive phase even at low temperatures (77 K), and its amount is greater in the samples with the lower x values. The Curie temperature (T&) for La₁-xNaxMnO₃₊y system rises monotonically as x changes from 0.08 to 0.16. A correlation is revealed between the characters of concentration induced changes in T& and number of vacancies in manganese sublattice. It is shown that, as x changes, the change character of the unit cell parameters (the diminution in both the cell volume and rhombo-hedral distortion angle) is also directed towards an enhancement of the ferromagnetic double exchange interaction and the TC elevation. The magnetoresistance (MR) measured at room temperature in 15 kOe field exhibits a maximum (20 %) in the samples with x = 0.12. For the samples of this composition, MR(+) dependence is close to the linear one, which stresses a good utilization prospect of such materials in the magnetic field measurement devices.