The structural and magnetic properties of HoErFe17-xGax (x = 0-7) were studied by means of X-ray diffraction and magnetization measurements. Powder X-ray diffraction studies show that the compounds transform from the hexagonal Th2Ni17 structure (x ≤ 4) to rhombohedral Th2Zn17 structure (x ≥ 5) with increasing Ga concentration. The substitution of Ga for Fe leads to an increase in lattice constants a, c and unit-cell volume v. The Curie temperature is found to first increase and then decrease with increasing Ga concentration, attaining a maximum value of 535 K at about x = 4, which is 207 K higher than that of HoErFe17. Both iron sublattice anisotropy and rare-earth sublattice anisotropy are found to be modified by the introduction of the Ga atoms and have been confirmed through X-ray diffractograms of magnetically aligned samples. © 1998 Elsevier Science B.V. All rights reserved.

Upadhyayula V Varadaraju

Department Of Chemistry

K. V.S. Rama Rao

Composition effects

Crystal atomic structure

HOLMIUM ALLOYS

Lattice constants

magnetic anisotropy

Magnetic variables measurement

Magnetization

Permanent magnets

Substitution reactions

X ray crystallography

Curie temperature

Magnetic materials

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IIT Madras

Structural and magnetic properties of HoErFe17−xGax compounds

Journal of Magnetism and Magnetic Materials

The alloys ErPrFe17-xGax and ErPrFe17-xSix (x = 0-3.5) have been prepared and their structure and magnetization have been investigated. Powder X-ray diffraction patterns show that these compounds crystallize in hexagonal Th2Ni17 (2:17) structure. The lattice parameters are found to increase as the Ga concentration is increased and decrease with increase of Si concentration. The saturation magnetization (Ms) measured at 20 K is found to increase initially and then decrease as the Ga and Si concentration are increased beyond 0.1. The Curie temperatures of ErPrFe15Ga3.5 and ErPrFe15Si3.5 are 528 and 537 K which are 241 and 250 K, respectively, higher than that of the parent compound ErPrFe17 and this has been explained on the basis of band model. The X-ray diffraction patterns taken for the magnetically aligned samples suggest that the easy magnetization direction (EMD) is in the basal plane in the Si substituted samples whereas in the case of the Ga substituted samples the EMD tend to be away from the basal plane. The anisotropy fields (HA) calculated from the magnetization measurements on aligned samples show that in the case of the Ga substituted compounds there is a significant increase in HA compared to the ones that are seen in the Si substituted compounds. © 2002 Elsevier Science B.V. All rights reserved.

Journal of Alloys and Compounds

Structural and magnetic properties of ErPrFe17-xMx (M = Ga, Si; x = 0-3.5)

(formula presented) Mössbauer studies were carried out on the phases (formula presented) (formula presented) and (formula presented) (formula presented) 1, and 2) at 25 K and room temperature. The weighted average hyperfine field at room temperature is found to increase initially for low Ga content and then decreases for phases with higher Ga concentration. The hyperfine fields at Fe sites follow the sequence (formula presented) which is determined mostly by the number of Fe and R nearest neighbors. The variation of the weighted average hyperfine field with temperature is found to obey (formula presented) behavior, suggesting the presence of single-particle excitations. Insertion of carbon at interstitial sites is found to increase the individual site hyperfine fields and hence an increase in the weighted average hyperfine field. The (formula presented) and (formula presented) sites of Fe show significant increase in isomer shift compared to other Fe sites. © 2001 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

(formula presented) Mössbauer spectroscopy of (formula presented) compounds

The phases RR′Fe17-xGaxCy [(RR′) = (Tm, Pr), (Nd, Sm), (Sm, Pr); x = 0-7; y = 0 and x = 0, 1, 2; y = 1] were synthesized by arc melting technique. The substitution of larger Ga atoms for smaller Fe leads to an expansion of the lattice. Substitution of Ga atoms increase the Curie temperature in the initial Ga concentration range (x ≤ 4). The increase in TC with Ga content is attributed to the increase in the Fe-Fe exchange coupling as a result of increasing interatomic distance, thereby reducing the effect of negative exchange interactions between Fe-Fe pairs. The primary effect of the interstitial carbon on the magnetic properties is related to volume expansion. The magnetization of all compounds increases with carbon and is probably due to the competition between band narrowing effect as a result of lattice dilation and chemical effect due to charge transfer mechanism. Concepts of spin fluctuation theory are invoked to understand variation of TC with carbon insertion. X-ray diffraction measurements on magnetically oriented powder samples show that the substitution of Ga for Fe in RR′Fe17 and further modification with interstitial carbon has an exceptionally important effect on their magnetocrystalline anisotropy. The EMD lies along the c-axis in the compounds NdSmFe17-xGaxC (x = 0, 1 and 2) and SmPrFe17-xGaxC (x = 1 and 2) and is probably due to the increase in the magnitude of the A20 which increases the positive contribution of rare earth sublattice to total anisotropy.

Physica B: Condensed Matter

Magnetic properties of RR′Fe17-xGaxCy [(RR′) = (Tm, Pr), (Nd, Sm), (Sm, Pr)] compounds

A detailed investigation of the structure and magnetic properties of R2Fe17-xGax (R = Tm, Er and Sm and x = 0-7) was carried out by means of powder X-ray diffraction, magnetization and AC magnetic susceptibility measurements. With increasing Ga content, a structural transformation from hexagonal Th2Ni17-type structure to rhombohedral Th2Zn17-type structure is observed in compounds Er2Fe17-xGax (x = 0-7) and Tm2Fe17-xGax (x = 0-7). The compounds Sm2Fe17-xGax (x = 0-7) crystallize in rhombohedral Th2Zn17-type structure. The Curie temperature increases in the initial Ga concentration range, reaches a maximum and then decreases at higher Ga concentration. The exchange interaction parameter JFeFe reaches a maximum and then decreases whereas the value of JRFe is almost independent of Ga concentration. X-ray diffraction measurements on magnetically aligned powder samples show a uniaxial anisotropy for compounds with at x = 2, 3 and 4 in the Sm2Fe17-xGax series whereas, it was observed for x = 7 in the Tm2Fe17-xGax compounds.

Structural, magnetic and exchange interaction studies on R2Fe17-xGax (R = Tm, Er and Sm) compounds

Powder neutron diffraction studies were carried out on (Ho1-xErx)2Fe15Ga2C y (x=0, 0.5, 1; y =0, 2) with a view to study the effect of substitution of Ga for Fe and the insertion of carbon at the interstitial sites on the structural and magnetic properties. All Ga substituted compounds (y=0) possess hexagonal Th2Ni17 type structure (space group: P63/mmc). However, the carbides adopt rhombohedral Th2Zn17 type structure (Space group: R3m). The unit cell volume increases with Ga substitution as well as with interstitial modification by carbon. An increase in the Curie temperature of about 260 K is observed for the compound HoErFe15Ga2C2 vis-a-vis HoErFe17. The increase is attributed to the preferential occupancy of Ga atoms in 18/(12j) and 18h(12k) sites and the presence of interstitial carbon. The magnetization increases with carbon addition. X-ray diffraction studies on magnetically aligned samples and neutron diffraction studies show that the easy magnetization direction lies in the basal plane at room temperature. © 1999 American Institute of Physics.

Fulltext

Journal of Applied Physics

Neutron diffraction studies on (Ho1-xErx)2Fe15Ga2C y compounds

A magnetic, neutron diffraction, and Mössbauer spectral study of Nd2Fe15Ga2and the Tb2Fe17−xGaxsolid solutions

The Plant Cell

Synechocystis sp PCC 6803 strains lacking photosystem I and phycobilisome function.

Journal of Physics: Condensed Matter

Effects of Al substitutions on the magnetic anisotropy of Sm2Fe17compounds

Reports on Progress in Physics

New developments in hard magnetic materials

Improved magnetic properties by treatment of iron-based rare earth intermetallic compounds in anmonia

Structural and magnetic properties of HoErFe17-xGax compounds

Journal	Data powered by TypesetJournal of Magnetism and Magnetic Materials
Publisher	Data powered by TypesetElsevier
ISSN	03048853
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