D.F. Chen

Cooperative effects of a combined substitution on the magnetic properties of Nd2−xYxFe17−ySiy intermetallic compounds (0⩽x⩽1.5,0⩽y⩽3.0)

The effects of a combined substitution of Nd by Y and Fe by Si in Nd2−xYxFe17−ySiy compounds (0⩽x⩽1.5,0⩽y⩽3.0) on structural and magnetic properties have been investigated by means of x-ray diffraction, neutron diffraction, and magnetic measurements. The investigated samples crystallize in Th2Zn17-type structure with only small amounts of alpha-Fe. The unit cell volume decreases with increasing Y content or Si content. Neutron diffraction analysis indicates that substitution of Y for Nd induces a decrease of Si occupancy in 18h sites and increases in 9d sites and 18f sites. With the substitution of Y for Nd, the average site bond lengths in 6c, 9d, 18f, and 18h sites all decrease, but the distances of all Fe-Fe pairs do not change negatively. The TC of Nd2−xYxFe17−ySiy increases significantly with increasing Si substitution (y⩽3.0), but it changes slightly with increasing Y substitution. Similar to the case of Si substitution, the Ms also first increases and then decreases with increasing Y substitution. ...

Effects of double substitution on the magnetic properties of Nd2Fe17−x−yTixAly: A combined investigation of x-ray diffraction, neutron diffraction, and magnetic measurement

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 c...

Effects of the substitution of Al for Fe on phase transition, crystal structures, and magnetic properties of Nd3(Fe,Ti)29-type intermetallics

Effects of the substitution of nontransition metal Al on phase transition, crystal structures, and magnetic properties of Nd3(Fe,Ti)29-type intermetallics have been systematically investigated by means of x-ray diffractions, time-of-flight powder neutron diffraction, and magnetic measurements. Rietveld analyses of x-ray diffraction patterns indicate that Nd3Fe27.5−xTi1.5Alx compounds mainly crystallize in Nd3(Fe,Ti)29-type structure (A2∕m space group) when x⩽1.5, but the main phase was replaced by Th2Zn17-type structure (R3¯m space group) when x>1.5. The lattice parameters a, b, c, and unit cell volume V of 3:29 phase in Nd3Fe27.5−xTi1.5Alx increase linearly with the substitution of Al. The site distributions of Ti and Al atoms were determined by refining the powder neutron diffraction data and it was found that Ti atoms prefer to occupy 4i1, 4i2, and 4g sites with the largest number of Fe neighbors while Al atoms prefer to take 4i4 and 8j4 sites with the largest number of rare earth neighbors. The Curie ...

Structure analysis of Nd3−xYxFe23−yCo6Moy (x=0.36–3.0;y=1.1,0.9) compounds

A series of compounds Nd3−xYxFe23−yCo6Moy (x=0.36–3.0) has been synthesized and studied by x-ray powder diffraction and neutron diffraction. Rietveld analyses of the diffraction data indicate that all the compounds crystallize in A2∕m. The lattice parameters a, b, and c and unit-cell volume V decreased monotonically with the increase of Y content. Neutron-diffraction results show that Mo atoms occupy three sites, two 4i sites and one 4g site, while Co atoms are found to occupy all the Fe sites not shared with the Mo atoms. However, the most preferential sites for Co are Fe1(2c), Fe8(8j), and Fe11(4e). It is also observed that those sites preferred by Mo have the long average bond length, while sites preferred by Co have short average bond lengths.