Atomic structures and the Mossbauer effect in amorphous La(Fe_xAl_1-x)₁₃alloys consisting of icosahedral clusters

Abstract

Atomic structures of amorphous La(FexAl1-x)13 alloys (x=0.80, 0.85, 0.90 and 0.95) were studied by X-ray diffraction. The distance between the icosahedral cluster and the La atom is slightly reduced with the increase in x. This indicates a slight change in arrangements of the icosahedral clusters around the La atom without changing the basic structure of the icosahedral clusters. On the other hand, the concentration dependence of coordination numbers for Fe-Fe pairs in the amorphous state resembles that in the crystalline From the 57Fe Mossbauer spectra, it was revealed that local environment around Fe atoms in the La(Fe0.9Al0.1)13 alloy is very similar to that in the crystalline counterpart. The magnetic properties of the amorphous and crystalline alloys have been closely correlated with their characteristic atomic strictures.

Formation of Icosahedral Clusters and Spin Freezing in RE(Fe<SUB>1-<i>x</i></SUB>Al<SUB><i>x</i></SUB>)<SUB>13</SUB> Amorphous Alloys

“…2 4) The results of the least-squares variational analysis for La(Fe 1Àx Al x ) 13 amorphous alloys clearly suggest that the appearance of the icosahedral clusters. 4,5) It should be noted that the structural parameters are the average values for all Fe atoms in the icosahedral cluster.…”

“…4,5) Therefore, we need the least-squares variational method employed in the structural study for SiO 2 and BeF 2 glasses, 9) because their intensity profiles are similar to the present amorphous alloy case. Therefore, a brief description for this method is given below.…”

“…Furthermore, it is noteworthy that this distance hardly depends on the Fe concentration. 4) The magnetization curves for La(Fe 1Àx Al x ) 13 amorphous alloys are not easily saturated in high magnetic fields in the concentration range 0:05 x 0:10, and the high-field susceptibility hf increases remarkably with increasing Fe content. 6) These results suggest that these alloys exhibit spinglass behavior at low temperatures in this concentration range.…”

“…4,5) It should be noted that the structural parameters are the average values for all Fe atoms in the icosahedral cluster. In addition, the distance of the nearest-neighbor Fe-Fe pair is about 0.255 nm, coinciding with the Fe-Fe averaged distance in the corresponding crystal.…”

“…It should be noted that the number of the icosahedral clusters around La atom is very different between the crystalline and amorphous states in La(Fe 1Àx Al x ) 13 system. 4) Accordingly, in the present paper, the possibility of the formation of icosahedral clusters is examined for other RE systems. A brief report of RE(Fe 1Àx Al x ) 13 amorphous alloys has been published elsewhere.…”