Abstract
The effects of double substitution of Ti and Al for Fe on the structural and magnetic properties of Nd2Fe17−x−yTixAly compounds were investigated. A series of Nd2Fe17−x−yTixAly compounds (0⩽x⩽1.0;0⩽y⩽3) were prepared by arc melting techniques in high pure Ar atmosphere. Rietveld analyses of x-ray and neutron diffractions indicate that all the samples crystallize in the rhombohedral Th2Zn17-type structure. The lattice parameters a, c and the unit-cell volumes of Nd2Fe17−x−yTixAly increase linearly with increasing aluminum content for a given Ti content and increase with the increase of Ti content for a given Al content. The addition of Ti atoms has a positive effect on the increasing rates of the a axis and the unit-cell volume on the Al content, but has a negative effect on the increasing rate of the c axis. Neutron-diffraction analyses indicate that Ti atoms and Al atoms prefer to take 6c sites and 18h sites, respectively, in doubly substituted Nd2Fe17−x−yTixAly but the site occupancies change slightly compared to that in the corresponding singly substituted compounds. The effects of Ti and Al substitutions on the bond lengths in the doubly substituted compounds are quite different from that in the singly substituted compounds. The Curie temperature measurements show that a higher Ti content results in a slower increase of TC on the Al content in Nd2Fe17−x−yTixAly (y⩽3). The TC of doubly substituted Nd2Fe16.5−yTi0.5Aly are higher than that of singly substituted Nd2Fe17−yAly when Al content is low (y⩽0.8) but reversely for y>0.8. For a given Ti content, the Ms of Nd2Fe17−x−yTixAly with x=0,0.5 first both increase a little and then decrease with the increase of Al content. The Ms of Nd2Fe17−x−yTixAly decreases with the increase of Ti content for a given Al content.
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