Abstract
Nanosized La0.9Ca0.1MnO3 perovskite-type crystalline complex oxides have been prepared at the low calcination temperature of 300 °C. The preparation procedure was carried out by the two-step process of amorphous formation and calcination. The amorphous phase was obtained by the reaction of metal ions with tetrabutylammonium hydroxide at 245 °C, and then calcined at 300 °C (sample A) or 400 °C (sample B) to prepare the nanocrystalline materials. The magnetic measurement shows that spin-glass behavior exists at 45 K and the blocking temperature increases with an increase of calcination temperature. The result of the spin-glass temperature of 45 K demonstrates that the particle size of the two samples A and B is below 50 nm. The increase of blocking temperature from A to B indicates that the particle size of A is less than that of B. The measurement of the normalized resistivity versus temperature for samples A and B shows that they have the change of the normalized resistive value at 230 K.
Highlights
Perovskite-type Ln1ϪxAxMnO3 ͑A representing divalent cations such as Ca, Sr, or Bacompounds have been of interest for many years due to their special magnetotransport properties.[1,2,3,4] As Ln3ϩ metal ions were partially replaced by divalent ions A2ϩ, a mixed Mn3ϩ/Mn4ϩ valence was observed
After the dried amorphous material was heated at 300 °CFig. 1͑a, sample Aand 400 °CFig. 1͑b, sample Bin the air, respectively, the perovskite-type LCMO was obtained
The results of magnetic analysis show that a freezing temperature (TF) due to spin-glass behavior is observed at 45 K, which demonstrates that the particle size of samples A and B is below 50 nm and the blocking temperature (TB) shifts from 150 to 160 K with the increase of calcination temperature from 300 to 400 °C
Summary
Perovskite-type Ln1ϪxAxMnO3 ͑A representing divalent cations such as Ca, Sr, or Bacompounds have been of interest for many years due to their special magnetotransport properties.[1,2,3,4] As Ln3ϩ metal ions were partially replaced by divalent ions A2ϩ, a mixed Mn3ϩ/Mn4ϩ valence was observed. The temperature dependence of magnetoresistance is improved and the onset of the freezing behavior of surface spin-glass takes place at 45 K when the nanoparticle size is below 50 nm.[8] As these nanoparticles are prepared above 500 °C,9 they connect strongly with each other and the capping ligand on the surface of nanoparticles. In order to study the effect of the capping ligand on the resistivity of La0.9Ca0.1MnO3 ͑LCMOnanoparticles and further demonstrate the feature of surface spinglass, we used another preparation method at 300 °C to obtain LCMO nanoparticles. We report the preparation of LCMO nanoparticles at lower temperature and the freezing temperature of spin-glass behavior at 45 K. Magnetization measurement demonstrated that the onset of freezing temperature of spin-glass behavior is at 45 K
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