Magnetic and magnetotransport properties in (La_xSm_1–x)_2/3Sr_1/3MnO₃ (x = 1/3, 1/2 and 2/3) manganites

Abstract

The magnetic and transport properties of (La x Sm 1-x ) 2/3 Sr 1/3 MnO 3 (x = 1/3, 1/2 and 2/3) manganites, prepared by the citrate-gel route, have been investigated. These compounds are found to crystallize in the orthorhombic structure. The hopping between Mn 3+ and Mn 4+ sites is controlled by the Mn -O -Mn bond angle. The magnetoresistance in 8.5 kOe fields varies from 15 to 25 percent over the temperature range 300 K to 80 K. The conduction mechanism can be understood by using the correlated small polaron model. The metal -insulator as well as magnetic transition temperatures are close to each other, which indicates the dominance of long-range ferromagnetic ordering in the present system. At low temperatures, a weak ferromagnetic to antiferromagnetic transition is indicated, which could be due to competing superexchange and double exchange interactions. The charge localization at lower temperatures could be the possible explanation for increasing magnetoresistance. The maximum magnetic moment at 5 K, for all the samples is ∼ 3.6µ B /Mn, which is close to the 3.7µ B /Mn, as obtained by considering the Mn spins only.

Magnetic Structure of La_0.54Ho_0.11Sr_0.35Mn_1-XCu_xO₃ Manganites

“…The sintered samples contain only one phase, with orthorhombic structure (Pnma space group) (see Fig. 1), in agreement with the available data [7]. The micrographs of the manganites indicated also the presence of only one phase and a significant increase of the average size of the crystallites with the increase of the Cu content in the samples (results will be published).…”

Exchange-Coupling Behavior in SrFe12O19/La0.7Sr0.3MnO3 Nanocomposites

“…xFexO3) [37] and Mn substitution at the Fe site (SrFe12-xMnxO19) has brought a reduction in the Ms values [31]. Ideally, the saturation magnetization of the composite consisting of hard and soft phases can be measured as [15,38] M = Ms,hard (1−fs) + Ms, soft × fs (1) where Ms,hard is the saturation magnetization of hard-phase SFO, Ms,soft is the saturation magnetization of soft-phase LSMO, and fs is the weight fraction of the soft phase in the composite. The measured value of 34.93 emu/g for the Ms of the composite with 40 wt % LSMO is about 38% lower than that predicted by Equation (1).…”

“…Ideally, the saturation magnetization of the composite consisting of hard and soft phases can be measured as [15,38] M = Ms,hard (1−fs) + Ms, soft × fs (1) where Ms,hard is the saturation magnetization of hard-phase SFO, Ms,soft is the saturation magnetization of soft-phase LSMO, and fs is the weight fraction of the soft phase in the composite. The measured value of 34.93 emu/g for the Ms of the composite with 40 wt % LSMO is about 38% lower than that predicted by Equation (1). Most likely, the intermixing of atoms, as discussed above, could be the factor for the observed deviation in the Ms value as compared to that of projected by Equation (1).…”

“…Following the success of the observed phenomenon of exchange-coupling in the metallic hard-soft systems, efforts have been directed to studying the exchange-coupling phenomenon in oxide-based hard-soft composite magnets. These rare-earth-free exchange-coupled oxide composite magnets are economical, show oxidation resistance, have a high operating temperature, and are technologically important [1][2][3][4][5]. Recently, many studies on exchange-coupled hard-soft composites have been reported, where ferrites are used as a magnetically soft-phase, such as SrFe 10 Al 2 O 19 /NiZnFe 2 O 4 [6], SrFe 12 O 19 /γ-Fe 2 O 3 [7], CoFe 2 O 4 /Fe 3 O 4 [8] [12], and SrFe 12 O 19 /La 0.7 Sr 0.3 MnO 3 [13].…”

Effects of A‐site ionic size variation on the magnetic and transport properties of (PrxSm1–x)2/3Sr1/3MnO3 (0 ≤ x ≤ 1)

“…The DE interaction, which favors ferromagnetic (FM) and metallic behavior, competes with the Jahn-Teller (JT) effect which favors antiferromagnetic (AFM) and insulating behavior. Recent studies have shown that DE alone cannot explain various physical properties of manganites [2] and other effects such as charge ordering, average Asite cationic radius <r A > , A-size cationic size mismatch [3,4], etc. also play important roles.…”