| Summary: | 碩士 === 中原大學 === 物理研究所 === 101 === Abstract
Various size of HoMn2O5 nanorods were fabricated by combining hydrothermal and annealing method with 240、300、500、700、900、1100 °C annealing temperatures. X-ray diffraction experiments reveal that all the samples are crystallized in orthorhombic with space group Pbam phase. The extreme value of lattice parameters is observed at the sample with annealing temperature of 700 °C. Six samples with annealing temperatures of 240、300、500、700、900、1100 °C are idendified by TEM and SAED scheme, which can be labeled in the form of long axis × short axis as 23(6) nm×44(14) nm、24(7) nm×49(19) nm、33(14) nm×66(25) nm、31(9) nm×69(24) nm、54(13) nm×95(27) nm、114(52) nm×409(109) nm, respectively。All the long axis of nanorods are parallel to c axis of the crystal. The <LC> symbol is employed to label the long axis of nanorods and in place of sample name.
An antiferromagnetic (AFM) peak was observed in <LC>=409 nm sample in the ac magnetic susceptibility experiment. No similar peak was found in another sample. These observations implied the occurrence of size effect between <LC>=69 and 409 nm. The AFM peak of <LC>=409 nm is decreased with increasing applied magnetic field, and shifted to lower temperature. The 1 T magnetic field is not able to eliminate the AFM peak. Hystersis loop were not found in all samples at 2 K. The maxima fitted saturated magnetic moment were found in <LC>=69 nm sample, which is consisted with the observation of the maxima value of lattice parameters.
Raman spectroscopy revealed a Raman peak at 697 cm-1 is correlated with Mn1-O2/O3 plane of <LC>=409 nm as temperature varied. The Mn1-O2 bond length is also associated with Raman peak at 686 cm-1. No similar behavior of these two Raman peak were found in <LC>=69 nm sample. This indicates that the more
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distortion inside the smaller size of nanorods, the less adjust and response of crystal vibration. And this phenomena, also weakness the magnetic ordering at lower temperature.
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