Stoichiometry and electronic properties of

Abstract

Treating off-stoichiometric (LaMn) 0.95 O 3 in hydrogen transforms its electrical and magnetic properties. The untreated material is a ferromagnetic narrow-gap semiconductor (T c = 125 K) whereas the near-stoichiometric reduced material is an antiferromagnetic insulator T N = 110 K). Although the off-stoichiometric manganite has formally the same mixed manganese valency as compounds such as (La 0.7 Ca 0.3 )MnO 3 , there is no resistivity peak at T c and no giant magnetoresistance. The difference may be due to potential fluctuations associated with cation vacancies.

Symmetry breaking in Ni-doped PrFeO3 thin films established by Raman study

“…Further increasing of the intensity of the mode at 574 cm À1 is an indication that the degree of disorder is increasing, since Fe atoms are replaced by Ni atoms. Another possible explanation would be the Jahn-Teller (J-T) modes [31]. But the present orthorhombic structure is slightly distorted from the cubic one and in this case the J-T distortion has a very small contribution.…”

Structural and Magnetic Properties of Ultrafine La0.7Ca0.3MnOz Powders Prepared by Mechanical Alloying

“…The coexistence of positive and negative exchange interactions causes frustration, resulting in a spin}glass state at low temperature (30). The electronic and magnetic structures in the as-milled La Ca MnO powder are probably similar to those in LaMnO >B ( &0.15) which also has a v + of 3.3, contains a high density of cation vacancies and exhibits magnetic properties very similar to those of the former (17,18,23). The coexistence of …”

“…[The e!ect of vacancies on the potential #uctuation is stronger than that of the divalent cations substituted for La, e.g., Ca ions in La \V Ca V MnO , because of the higher e!ective charges of the former (17,19,20).] This results in an introduction of negative SE interactions between Mn> ions, which tend to be trapped near cation vacancies (18).…”

Magnetoresistance behavior inLa0.7CaxMnO3<

“…Therefore, the random potential fluctuations due to missing La 3ϩ ions will favor the Anderson localization more strongly in the former system than in the latter system. 31 As a result of this, the MR ratio obtained for La 0.7 MnO 3 film is less than that of La 0.7 Ca 0.2 MnO 3 film. There is no such localization effect in stoichiometric La 0.7 Ca 0.3 MnO 3 films due to absence of vacancies, which is manifested with the realization of the highest MR ratio among the three systems discussed here.…”