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We report here a comprehensive study of the gradual resistive switching (RS) observed in La 0.5 Ca 0.5 MnO 5 − δ epitaxial films. We find that the inverse gradual RS as well as the relaxation can be well fitted by a biexponential function or alternatively by a stretched exponential function. We also unravel that the gradual RS kinetics can be further interpreted within the Landau-Khalatnikov theory of critical slowing down. This unified theoretical modeling properly incorporates the microstructural fluctuations owing to the presence of single isolated and clustered oxygen vacancies at the metal-oxide interface. [ABSTRACT FROM AUTHOR]

We provide evidence of phase separation in La[sub 0.45]Sr[sub 0.55]MnO[sub 3-δ] using electron spin resonance, magnetic force microscopy (MFM), x-ray diffraction, and magnetic and transport measurements. The results reveal that ferromagnetic and antiferromagnetic phase coexist at low temperature and that ferromagnetic and paramagnetic phases coexist in the temperature range between the Néel and the Curie temperature. Moreover, the size and shape of ferromagnetic phase (the minority phase) in the sample were observed directly by MFM. From these results, we infer an electroneutral type phase separation, possibly resulting from a nonuniform distribution of oxygen vacancies, as opposed to charge segregation. [ABSTRACT FROM AUTHOR]

Magnetic properties of Nd[sub 0.5]Ca[sub 0.5]Mn[sub 0.98]Ga[sub 0.02]O[sub 3] were investigated systematically through magnetization and electron spin resonance (ESR) measurements. It was found that substituting 2% Mn with Ga reduces the charge ordering temperature and induces an additional peak in the magnetization-temperature curve at about 45 K. The magnetization and ESR measurements suggest that the spin-glass-like phase induced by doping Ga at Mn sites and antiferromagnetic charge-orbital-ordered phase coexist at low temperature, the paramagnetic phase and antiferromagnetic phase coexist when the temperature is between the Néel temperature and the charge-ordering temperature. [ABSTRACT FROM AUTHOR]

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.

La[sub 0.67]Sr[sub 0.33]MnO[sub 3] ultrathin films grown on vicinal SrTiO[sub 3](100) surface show an in-plane uniaxial magnetic anisotropy with easy axis along the substrate atomic steps generated by a 10° miscut off the (100) plane. Over a large angular range, the angular dependence of magnetic switching field is found to obey the 1/cos φ law, indicating that the magnetic reversal is completed by a 180° domain nucleation and sweeping along the easy axis. However, when the applied field is perpendicular to the hard axis (φ = 90°), the magnetization reversal is found to be well described by the StonerWohlfarth model, in which the magnetization coherently rotates from the easy axis to hard axis. [ABSTRACT FROM AUTHOR]

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]

Magnetic and transport properties of rare-earth manganites La[sub 0.5]Ca[sub 0.5]Mn[sub 1-x]Ge[sub x]O[sub 3] with 0≤x≤0.1 have been investigated systematically. Doping Ge at Mn sites increases the metal-insulator transition temperature (T[sub P]) from 124 to 210 K with increasing x from 0 to 0.08. The introduction of Ge severely destroys the charge-ordered state and hardly affects the ferromagnetic ordering. For low-doped samples, T[sub P] is also increased dramatically by the magnetic field, especially in the field-cooled mode. Magnetic analysis suggests the coexistence of the charge-ordered antiferromagnetic phase and the ferromagnetic phase. We propose that the proportion of the ferromagnetic phase and the charge-ordered phase can affect T[sub P] in phase-separated compounds. The phase diagram of La[sub 0.5]Ca[sub 0.5]Mn[sub 1-x]Ge[sub x]O[sub 3] with 0≤x≤0.1 is presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structure, magnetic, and transport properties of La[sub 0.5]Ca[sub 0.5]Mn[sub 1-x]M[sub x]O[sub 3] (0≤x≤0.1) with M=Ge and Sn have been investigated systematically. A significant lattice expansion is observed in the Sn-doped samples, but not in the Ge-doped ones. At the same time, a substitution of Mn by Ge has little effect on Curie temperature (T[sub C]), but increases the metal-insulator transition temperature (T[sub P]). In contrast, the T[sub C] decreases sharply for Sn doping, while the T[sub P] shows an increase for x<0.02 and a decrease for x>0.02. Compared with Ge doping, Sn doping is more effective in destroying the charge-ordered state. The difference in local lattice distortions due to the Ge and Sn doping is believed to be responsible for the present observations. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a correction to an article published in the 2003 issue of the periodical 'Applied Physics Letters,' vol. 82.