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Competing Magnetic Interactions in Co Doped La0.7Sr0.3MnO3

The crystallographic structural and magnetic properties of polycrystalline La0.7Sr0.3Mn1-xCoxO3 (x =0.4, 0.5, 0.6, 1.0) have been systematically studied in detail by neutron powder diffraction and magnetic measurements.The introduction of Co dopant to the Mn network has decreased the bandwidth (W)and the overlap between the O-2p and the Mn-3d orbitals. Also it in turn weakened the fragile double exchange coupling of Mn3+-O-Mn4+and reduced the magnetization Mas well as magnetic ordering temperature TC. The magnetic measurements indicate the presence of mixed magnetic phases in this system. When the temperature is above Tc,the jump of field dependent magnetization disappeared,which is related to the competition of FM and AFMinteractions.

The average atom magnetization extracted from M-H curve at 5K usingthe approach-to-saturation method, is ~1.70μB/Cofor La0.7Sr0.3CoO3.This value approaches to the neutron refined data 1.93(8)μB. However, asfor x=0.4, x=0.5 and x=0.6 samples, the calculated data from magnetization at 5T areallsmaller than the refined one, due to the existence of spin-glass-like phase. The weak magnetic peaks are responsible for the small magnetic moment data (0.48μBfor LSMO-Co0.5and 0.65μBfor LSMO-Co0.6). These results indicate the competing magnetic interactions in the system of La0.7Sr0.3Mn1-xCoxO3 compounds.

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