Enhancement of Tc and the re-entrant spin glass transition in La0.86Ca0.14Mn1-yCryO3 (y = 0, 0.1 and 0.2)

Abstract

We report on structural, frequency dependent ac susceptibility, dc magnetization and magnetoresistance (MR) measurements on polycrystalline samples of La0.86Ca0.14Mn1-yCryO 3 (y = 0, 0.1 and 0.2) prepared by the sol-gel technique. For y = 0, a paramagnetic to ferromagnetic transition was observed at Tc = 185 K. For y = 0.1, the value of Tc = 200 K, an increase of 15 K, and for y = 0.2, Tc = 195 K, an increase of 10 K. The imaginary part of the ac susceptibility for all three samples shows a secondary transition at T f < Tc. For y = 0, there is no definite law accounting for the frequency dependence of Tf and it is attributed to a transition arising out of a canted structure. However, in the cases of y = 0.1 and 0.2, the frequency dependence indicates the presence of a re-entrant spin glass transition at Tf. Although all three samples show a semiconducting behaviour between 300 and 5 K, a negative MR was observed corresponding to Tc and Tf. The value of MR decreased for the Cr substituted samples.