Estimation of the charge carrier localization length from Gaussian fluctuations in the magnetothermopower of La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}
Abstract
The magnetothermoelectric power (TEP) ΔS(T,H) of perovskitetype manganese oxide La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3} is found to exhibit a sharp peak at some temperature T^{*}=170 K. By approximating the true shape of the measured magnetoTEP in the vicinity of T^{*} by a linear triangle of the form ΔS(T,H)~=S_{p}(H)+/B^{+/}(H)(T^{*}T), we observe that B^{}(H)~=2B^{+}(H). We adopt the electron localization scenario and introduce a GinzburgLandau (GL)type theory which incorporates the two concurrent phase transitions, viz., the paramagneticferromagnetic transition at the Curie point T_{C} and the ``metalinsulator'' (MI) transition at T_{MI}. The latter is characterized by the divergence of the fielddependent charge carrier localization length ξ(T,H) at some characteristic field H_{0}. Calculating the average and fluctuation contributions to the total magnetization and the transport entropy related magnetoTEP ΔS(T,H) within the GL theory, we obtain a simple relationship between T^{*} and the above two critical temperatures (T_{C} and T_{MI}). The observed slope ratio B^{}(H)/B^{+}(H) is found to be governed by the competition between the electronspin exchange JS and the induced magnetic energy M_{s}H_{0}. The comparison of our data with the model predictions produce T_{C}=195 K, JS=40 meV, M_{0}=0.4M_{s}, and ξ_{0}=5 Å for the estimates of the Curie temperature, the exchange coupling constant, the critical magnetization, and the localization length, respectively. The magnetoTEP data obtained by other authors are discussed and found to be consistent with the model predictions as well.
 Publication:

Physical Review B
 Pub Date:
 November 1999
 DOI:
 10.1103/PhysRevB.60.12322
 arXiv:
 arXiv:condmat/9812219
 Bibcode:
 1999PhRvB..6012322S
 Keywords:

 72.15.Jf;
 71.30.+h;
 75.70.Pa;
 Thermoelectric and thermomagnetic effects;
 Metalinsulator transitions and other electronic transitions;
 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 6 pages (REVTEX), 2 PS figures (epsf.sty)