HoMn2O5奈米尺寸效應與結構、磁性交互作用研究

Interplay between structure and magnetism and effect of size of HoMn2O5 nanorods

游聲翔(SHENG-SIANG YOU)

指導教授 ： 楊仲準

中原大學/理學院/物理研究所/碩士(2013年)

https://doi.org/10.6840/cycu201300720

摘要

摘要
利用水熱法配合240、300、500、700、900、1100 °C的熱退火方法可以得到不同尺寸之HoMn2O5 奈米棒。X光繞射實驗顯示所有樣品均為斜方晶系之Pbam純相。而700 °C之樣品具有晶格常數的極值。高解析度TEM影像與選區電子繞射得到六種樣品的短軸×長軸可標示為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。且發現其長軸皆平行晶軸c軸。在本論文中以來代表樣品之長軸，並用來標示不同奈米棒樣品。
磁化率實驗僅在=409 nm之樣品，發現一42 K的反鐵磁化率峰。而其他樣品均無。這顯示了尺寸效應發生在=69與409 nm之間。而=409 nm之磁化率峰，隨著外加磁場增加，而逐漸的減弱且往低溫移動。1 T的磁場尚不足以消去此一反鐵磁化率峰。2 K的磁滯曲線顯示所有樣品均無磁滯現象。=69 nm之樣品具有最大的擬合飽和磁矩，這與具有晶格常數極值的觀測相符。
拉曼光譜實驗顯示=409 nm樣品其697 cm-1處之拉曼峰與Mn1-O2/O3所構成的平面上Mn-O之鍵長平均值有關；而686 cm-1處之拉曼峰與Mn1-O2的變化趨勢有直接的對應。但同樣之兩拉曼峰在=66 nm之樣品上則沒有發現對應關係。這顯示較小的奈米棒，雖然內部鍵長、鍵角有較大的扭曲，但是可微調的空間較小，因此反應在晶格常數上的變化較大。但卻減弱了聲子的微調位移機制，並抑制了低溫下磁有序的發生。

關鍵字

多鐵材料

並列摘要

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 symbol is employed to label the long axis of nanorods and in place of sample name.
An antiferromagnetic (AFM) peak was observed in =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 =69 and 409 nm. The AFM peak of =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 =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 =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 =69 nm sample. This indicates that the more
III
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.

並列關鍵字

HoMn2O5

參考文獻

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