Ce基合金系統，因為常顯示Kondo行為以及RKKY等獨特的磁性行為，一直是磁特性研究的重要系統。在之前的研究中，一些Ce合金系統(例如CeAl2、CePt2等)，當尺寸縮小時為奈米尺度時，發現Ce3+會轉變為Ce4+的現象，同時觀察到磁相變點消失與Kondo效應增強的行為。本實驗中選取與先前研究不同結構的三元合金CeAuAl3，其為體心四方晶系BaNiSn3結構的CeAuAl3，以觀察在尺寸縮小為奈米尺度時上述行為是否仍然會發生。塊材CeAuAl3在c軸磁矩呈現簡單螺旋排列，在ab平面磁矩則為鐵磁排列，為一反鐵磁重費米金屬化合物(TN = 1.32 K)，在此研究以脈衝雷射濺鍍法成功將CeAuAl3製成奈米微粒。由XRD及TEM可確認該合金微粒為單相、平均粒徑約為3 nm。由磁化率的量測計算樣品之居里常數，可發現奈米微粒的居里常數明顯較塊材小。由低溫比熱觀察到在當塊材製作成奈米樣品時有下列結果：(1)電子比熱係數(γ)與晶格比熱係數(β)明顯增大。(2)由磁熵的計算，奈米微粒的磁熵約為塊材之15%，與居里常數的變化相符，這顯示應為部分Ce3+轉為Ce4+致使磁性離子濃度降低所致。 (3)沒有明顯的Kondo效應增強現象。Ce3+轉為Ce4+的結果可推測為Ce價數在奈米尺度的變化是一普遍存在的現象。 For CeAl2 , CePt2 and Ce3Pt4 nanoparticles, two phenomenon were reported : (1) the most Ce3+ transit to Ce4+ ;(2) the suppression of magnetic order is accompanied by an enhancement of the single ion Kondo interactions . These behaviors may be a universal behavior for Ce-based nanoparticles. The CeAuAl3 with body centered tetragonal BaNiSn3–type structure was choose to verify the hypotheses. Bulk CeAuAl3 is an antiferromagnetic compound with TN = 1.32 K. CeAuAl3 is of a simple spiral type with the ordered Ce moments aligned ferromagnetically within the basal planes of tetragonal CeAuAl3. The CeAuAl3 nanoparticles were successfully fabricated by Pulse laser deposition (PLD). The samples are single phase confirmed by x-ray diffraction (XRD). The transmission electron microscopy (TEM) analysis show that their particle sizes were estimated to about 3 nm. Base on the magnetic susceptibility measurement, the curie constant of nanoparticles is much smaller than that of bulk. The specific-heat measurement reveals more behaviors : (1). larger specific coefficient γ and β, which were obeyed in CeAl2, Ce3Pt4 nanoparticles, (2). the magnetic entropy of nanoparticles is about 15% of that of bulk, similar to the changing in magnetic susceptibility measurement. That should be attributed to an occurrence of valence transition from portion of Ce3+ to Ce4+, (3). no observable enhancement of Kondo effect. The transition of Ce3+ to Ce4+ is surmised to be normal phenomenon in the Ce compounds nanoparticles.
