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Rare-earth manganites were studied for their magnetic and transport properties.

Research describing the characteristics of manganites of LCMMO structure where M = germanium and tin is presented. In particular the structure and magnetic and transport properties are investigated for differences between the effects of Ge and Sn doping.

A study was conducted on the magnetic and magnetotransport behavior in La(sub 0.67)Sr(sub 0.33)(Mn(sub 0.8)Ni(sub 0.2))O3. Findings showed that the substitution of Ni for Mn in La(sub 0.67)Sr(sub 0.33)MnO3 weakens the ferromagnetic double exchange and leads the oxide to a cluster glass-like state. This indicated that the ferromagnetic superexchange between Ni and Mn is helpful for the overall ferromagnetic exchange components which leads to the presence of the cluster glass-like state.

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]

A detailed investigation of the La(sub 0.45)Sr(sub 0.55)MnO(sub 3-delta) (LSMO) through x-ray diffraction, magnetic force microscopy (MFM), and magnetic and transport measurements is given. The investigation revealed that ferromagnetic (FM) and paramagnetic (PM) phases, as well as the FM and antiferromagnetic (AFM) phases, coexist in different temperature regions in LSMO.

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]

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]