The effect of Cu-doping on the magnetic and transport properties of La0.7Sr0.3MnO3

Abstract

The effects of Cu-doping on the structural, magnetic, and transport properties of La 0.7 Sr 0.3 Mn 1−x Cu x O 3 (0 ≤ x ≤ 0.20) have been studied using neutron diffraction, magnetization and magnetoresistance(MR) measurements. All samples show the rhombohedral structure with the R3c space-group from 10K to room temperature(RT). Neutron diffraction data suggest that some of the Cu ions have a Cu 3+ state in these compounds. The substitution of Mn by Cu affects the Mn-O bond length and Mn-O-Mn bond angle resulting from the minimization of the distortion of the MnO 6 octahedron. Resistivity measurements show that a metal to insulator transition occurs for the x ≥ 0.15 samples. The x = 0.15 sample shows the highest MR(≈80%), which might result from the co-existence of Cu 3+ /Cu 2+ and the dilution effect of Cu-doping on the double exchange interaction.

Phase Transitions in La0.73Ca0.27Mn1-xCuxO3 (0 < X < 0.19)

“…Similar results were also obtained by Kumar et al (2011). With regard to the effects of increasing the Cu concentrations in the magnetic properties, our neutron scattering (Kim et al, 2005;Gunanto et al, 2012a;Gunanto, et al, 2013) and SQUID measurements revealed that all samples were orthorhombic both at room and low temperatures, whereas the magnetic structure at room temperature was paramagnetic and ferromagnetic at low temperatures (Figure 4). The particle morphology of SEM photograph is shown in Figure 5.…”

“…In contrast, at higher Cu-doping, the smaller Cu 3+ ions are dominant, therefore reducing the internal chemical pressure, effectively increasing the resistance. Also, the Cu-doping can reduce the Mn 3+ (3d 4 , -) -Mn 4+ (3d 3 , -) ratio, therefore reducing the double exchange interaction, and hopping electrons and sites (Kim et al, 2005).…”

“…Some studies attribute such changes to the modification of the Mn 3+ -O-Mn 4+ interaction, and the more complicated interactions between the center Mn ions and the dopant Cu ions (Kumar et al, 2011) that are in a mixed state between Cu 2+ and Cu 3+ , with Cu 2+ being more dominant (Kim et al, 2008;Kim et al, 2005). Another study, however, suggests that for lower values of Cu-doping (x = 0-0.2), the Cu ions are in a Cu 2+ state with a rhombohedral crystal structure, whereas for Cu-doping of 0.3-0.5, orthorhombic Cu 3+ ions are formed (El-Hagary et al, 2008).…”

“…More recently, it has been shown that chemical doping, in this case with Cu, at the Mn site significantly alters the material's resistivity, lattice parameters, crystal structure, and various transition temperatures (Kumar et al, 2011;Kim et al, 2008;El-Hagary et al, 2008;Craus & Lozovan, 2006;Kim et al, 2005). Some studies attribute such changes to the modification of the Mn 3+ -O-Mn 4+ interaction, and the more complicated interactions between the center Mn ions and the dopant Cu ions (Kumar et al, 2011) that are in a mixed state between Cu 2+ and Cu 3+ , with Cu 2+ being more dominant (Kim et al, 2008;Kim et al, 2005).…”

Relative Cooling Power of La0.7Ca0.3Mn1–xCuxO3 (0.0 ≤ x ≤ 0.03)

“…T C decreased as the Cu-doped concentration increased, which was also found in other reports (Phan et al, 2005a;El-Hagary et al, 2009). The T C reduction was presumably due to the weakening of the DE interaction, which is probably because of the replacement Mn ions by the Cu ions that built an antiferomagnetic SE Kim et al, 2005).…”