Enhanced low-field magnetoresistance of La_0.7Sr_0.3Mn_1-xNi_xO₃compounds by annealing process

Abstract

A study of Mn‐site substitution by Ni2+ and the effect of annealing time in polycrystalline bulk La0.7Sr0.3MnO3 in composition range (0 ≤ x ≤ 0.1) is presented. This study involves structural, electrical, magnetoresistance, and thermoelectric power (TEP) measurements. X‐ray diffraction was used to examine the structure for the as‐prepared and annealed samples, and it shows that there is no change in structure with annealing time. Electrical resistivity and magnetoresistance are strongly affected by annealing process, where there is a dramatic increase in resistivity with annealing time and an enhancement in magnetoresistance in different temperature ranges. Moreover, conduction mechanisms above and below transition temperature (Tms) are discussed, since, variable‐range hopping and small‐polaron hopping models are applied above Tms, in addition to some experimental relations below it. In addition, the TEP sign changes from positive to negative with doping and annealing.

Magnetic, magnetocaloric and thermoelectric properties of nickel doped manganites

“…The partial substitution of Mn-site by other transition metal is an interesting topic that leads to a change in the magnetic coupling between Mn 3+ and Mn 4+ ions [11], sometimes leads to a structural transition [12] and has the advantage of charge ordering suppression in some manganites [13]. The partial substitution of Mn by Ni ions was studied before and the system showed prominent magnetoresistive results [14,15]. So, in this work, we are trying to understand the magnetic behavior of La 0.7 Sr 0.3 Mn 1-x Ni x O 3 system.…”