Sample thickness dependence of giant magnetoimpedance under low fields for La0.67Sr0.33Mn0.98Co0.02O3 manganites

The La0.67Sr0.33Mn0.98Co0.02O3 plate sintered at 1250 degrees C shows a low field magnetoresistance (LFMR) effect under fields H<4.6 kOe. However, the DC magnetoresistance Delta R/R-0 is very small, only -1.84% under H=4.6 kOe. The character of helical growth was observed on grain surface of La0.67Sr0.33Mn0.98Co0.02O3 phase. The LFMR is connected with the interface of grain or grain boundary, while the giant magnetoimpedance under low fields for La0.67Sr0.33Mn0.98Co0.02O3 sintered plates strongly depends upon the plate thickness. With an increase of sample thickness, the magnetoimpedance increases and the frequency, where the maximum magnetoimpedance occurs, shifts to low frequencies. A giant magnetoimpedance of -15.6% and a large AC magnetoresistance of -30.5% could be obtained under a very small field H=600 Oe for the plate with a thickness of 3 mm. (C) 2010 Elsevier B.V. All rights reserved.