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Structure, magnetic, and transport properties of the compounds La[sub 2/3]Ca[sub 1/3]Mn[sub 1-x]Ti[sub x]O[sub 3](0≤x≤0.3) have been investigated. The substitution of a Ti[sup 4+] ion for a Mn[sup 4+] ion suppresses the ferromagnetism and metallic conduction significantly. In the case of low doping (x≤0.04), Curie temperature T[sub C] decreases linearly with the substitution at a rate of about 31 K for 1% Ti. The magnetic spontaneous state has become a cluster glass state for the sample where x=0.06. Corresponding to the decrease of T[sub C], the metal–insulator transition temperature and the peak of magnetoresistance (MR) shift to low temperature, while the resistivity and the maximum of MR increase with increasing Ti concentration. The magnetic dilution should be responsible for the experimental results. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetization, resistance, and current–voltage (I–V) measurements have been performed in La[sub 0.5]Sr[sub 0.5]MnO[sub 3] compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (T[sub C]) and has a substantial drop in the thermomagnetic curve below 158 K (T[sub DP]). After undergoing a metal–to–semiconductor transition at 140 K (T[sub MS]), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below T[sub DP]. Instead of showing a feature near T[sub MS], the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I–V curve. Although La[sub 0.5]Sr[sub 0.5]MnO[sub 3] has a relatively high T[sub C], the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher T[sub C] seems to be a prerequisite. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the magnetic and magnetotransport behavior in an insulating nickel doped perovskite lanthanum-strontium (manganese nickel) oxide. Experimental details; Results and discussion.

A large low-field magnetoresistance (MR) slightly above the metal-insulator transition temperature (234 K) was observed in single-crystalline Pr[sub 0.7]Pb[sub 0.3]MnO[sub 3]. Combining the temperature dependence of magnetization, resistance, and electron spin resonance spectra, it was suggested that phase separation occurs above the Curie temperature; ferromagnetic metallic clusters imbedding in the insulating paramagnetic matrix, and spin-polarized electron tunneling between isolated ferromagnetic clusters should be responsible for the large low-field MR observed. Undoubtedly, this observation opens a window to explore large low-field MR at high temperature, which is very important for the practical application of colossal MR effect. [ABSTRACT FROM AUTHOR]