All data available in the literature for the impurity hyperfine fields in Fe, Co, Ni and Gd matrices are collected and tabulated. The literature search was carried out for all references listed in Physics Abstracts on papers published till the end of December 1978. The present work is an extension of similar earlier compilations [1–6]. The data are arranged in ten columns as explained below:

Table of hyperfine fields for impurities in Fe, Co, Ni, Gd and Cr

An x‐ray diffraction study of the substitution of gallium in Tb2Fe17 to form the Tb2Fe17−xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a‐axis lattice parameter increase linearly with increasing gallium content. The c‐axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ∼150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in x. Neutron diffraction studies of Nd2Fe15Ga2 and Tb2Fe17−xGax, with x equal to 5, 6, and 8, indicate that the gallium completely avoids the 9d site, occupies the 6c ‘‘dumbell’’ site only at high values of x and strongly prefers the 18f site at high values of x. The magnetic neutron scattering indicates both that the terbium sublattice magnetization couples antiferromagnetically with the iron sublattice and that there is a change in easy magnetization direction f...

/pdf/a-magnetic-neutron-diffraction-and-mossbauer-spectral-study-1jvwzib0p9.pdf

A magnetic, neutron diffraction, and Mössbauer spectral study of Nd2Fe15Ga2 and the Tb2Fe17−xGax solid solutions

57Fe Mossbauer spectra have been obtained at room temperature and at 15 K for R2Fe17 and R2Fe17N3- delta ( delta approximately=0.4) with R identical to Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The easy direction of magnetization of the R2Fe17 compounds can be identified by analysis of the hyperfine field and quadrupole interactions. For rare-earth elements with J>3, the sixth-order crystal-field parameter B66 determines the easy magnetization direction in the basal plane. In the nitrides, the average hyperfine field at 15 K increases by approximately 13% above the value in the parent compounds, from about 31 to 35 T, and it is anisotropic, being greatest when the magnetization lies along the c-axis. There is also an increase in the isomer shift of 0.12(2) mm s-1. Spin reorientation transitions occur in the nitrides of Er and Tm; only the samarium nitride has an easy c-axis at room temperature, but Sm, Er and Tm all have easy c-axis magnetic structures at 15 K.

A 5e Mossbauer study of a new series of rare-earth iron nitrides: R2Fe17N3- delta

Publisher Summary This chapter discusses rare earth compounds. The number of stable binary intermetallic compounds in which one of the components is a rare earth element is of the order of a thousand. Combination with elements of much smaller metallic radii then encompasses a much larger number of possible atomic arrangements of sufficiently high space filling than would be the case for two components of almost equal size. A meaningful study of the physical properties of intermetallic compounds can only be made on single phase materials. Only a fraction of the compounds is in single phase condition after the melting together of the components. The chapter explains the compounds with non-magnetic elements and compounds with d-transition metals. It also explains ternary compounds or hydrides.

Chapter 4 Rare earth compounds

Anisotropy of the magnetization and of the iron hyperfine field in R2Fe17 compounds

Mossbauer measurements are performed on rhombohedral Y2F17 in the temperature range 5 to 300 K and in fields up to 20 kOe. The dipole fields and the crystalline electric field gradients are calculated for both structure types. From this a subdivision of the four crystallographically non-equivalent lattice sites into seven (eight) groups for the Th2Zn17 (Th2Ni17) compounds is concluded, by neglecting all contributions of the asymmetry parameter. An exact allocation of the resulting subspectra to these different Fe sites is only possible for the c (f)- and a fraction of the d (g)-sites. The field and the temperature dependence of the hyperfine interactions of the distinguishable Fe sites are discussed.



Im Temperaturbereich 5 bis 300 K und in Feldern bis 20 kOe werden Mosbauermessungen am rhomboedrischen Y2Fe17 durchgefuhrt. Die Dipolfelder und die kristallelektrischen Feldgradienten werden fur die beiden auftretenden Strukturtypen berechnet, wobei eine Unterteilung der vier kristallographisch nichtaquivalenten Gitterplatze in sieben (acht) Untergruppen fur die Th2Zn17 (Th2Ni17)-Verbindungen bei Vernachlassigung aller Beitrage des Asymmetrieparameters erhalten wird. Eine genaue Zuordnung dieser Subspektren zu den verschiedenen Fe-Platzen ist jedoch nur fur die c (f)- und fur einen Teil der d (g)-Platze moglich. Die Feld- und Temperaturabhangigkeit der Hyperfeinwechselwirkung fur die unterschiedlichen Fe-Platze wird diskutiert.

Hyperfine interactions in Y2Fe17

Mossbauer measurements are performed on RE2(Fe1−xCox)17, RE = Y, Gd, Dy compounds. The spectra are analyzed using 7 (8) subspectra for samples with Th2Zn17(Th2Ni17) structure. The differences between Fe sites, caused by the Co substitution, are neglected. A maximum value of the hyperfine field is obtained at x ≈ 0.3. This agrees with the concentration dependence of the mean 3d moment and will be discussed by means of the model of two common, partially filled 3d subbands and a model involving a portion of negative exchange. From the concentration dependence of the isomer shift charge transfers to the Fe atoms may be excluded. This is supported by the results obtained for the quadrupole splittings for 0 < x < 0.5. For 0.5 ≦ x ≦ 0.9 a rotation of the easy axis into the c-direction is obtained from the ratio of he quadrupole splitting, which agrees very well with the theoretically predicted ratio of (−1) :2.



Mosbauermessungen werden an den Verbindungen RE2(Fe1−xCox)17, RE = Y, Gd, Dy durchgefuhrt. Die Spektren werden mit 7 (8) Subspektren fur die Proben mit Th2Zn17 (Th2Ni17)-Struktur analysiert. Die durch die Co-Substitution gegebenen Unterschiede fur die Fe-Platze werden vernachlassigt. Bei x = 0,3 liegt ein Maximum fur das Hyperfeinfeld vor. Dies ist in Ubereinstimmung mit der Konzentrationsabhangigkeit des mittleren 3d-Momentes und wird an Hand des Modells zweier nicht vollstandig aufgefullter Subbander bzw. einer teilweise auftretenden negativen Austauschwechselwirkung diskutiert. Ladungstransfers zum Fe sind aus dem Konzentrationsverlauf der Isomerieverschiebung weitgehendst auszuschliesen. Dafur sprechen auch die Werte der Quadrupolaufspaltung fur 0 < x < 0,5. Im Bereich 0,5 ≦ x ≦ 0,9 wird eine Drehung der leichten Richtung in die c-Achse aus dem Verhaltnis der Quadrupolaufspaltungen ermittelt. Dieses stimmt mit dem theoretisch geforderten Wert von (−1) :2 sehr gut uberein.

Hyperfine interactions in RE2(Fe, Co)17 RE = Y, Gd, Dy

Mosbauermessungen an der Mischkristallreihe Y(FexCo1–x)2 wurden im Temperaturbereich 5 bis 300 K durchgefuhrt. Die Richtung des elektrischen Feldgradienten und der Wert fur den Asymmetrieparameter wurden mit Hilfe eines Punktladungsmodelles berechnet. Im Konzentrationsbereich 0,5 ≧ x ≧ 0,2 konnen die Spektren mittels einer Binomialverteilung und [100] als Richtung der leichten Magnetisierung analysiert werden. Ubereinstimmend mit den summenmagnetischen Messungen ist eine mit steigendem x zunehmende magnetische Hyperfeinwechselwirkung fur die einzelnen Fe-Umgebungen zu beobachten. Fur Spektren mit reiner Quadrupolwechselwirkung ist eine Analyse mit zwei Subspektren und einem mittleren Intensitatsverhltnis von 0,88:0,12 moglich. Bei tiefen Temperaturen andert sich die Spektrencharakteristik gravierend; die Analyse ist nur unter Annahme von Spektren mit reiner Quadrupol- und solchen mit zusatzlicher Hyperfeinwechselwirkung moglich. Diese Annahmen werden durch unterschiedliche Spektren bei Abkuhlung mit und ohne auseres Magnetfeld, jedoch Messung im gleichen Feld, unterstutzt. Die Resultate weisen auf eine durch die Anordnung der nachsten Fe-Nachbarn wesentlich bestimmte magnetische Wechselwirkung hin.



Mossbauer measurements were carried out on the mixed crystal series Y(FexCo1–x)2 in the temperature range 5 to 300 K. The direction of the electric field gradient and the values of the asymmetry parameter were calculated with the help of a point charge model. For 0·5 ≧ x ≧ 0·2 an analysis of the spectra can be performed by means of a binomial distribution and [100] as the direction of the easy magnetization. In agreement with the bulk magnetic measurements an increasing magnetic hyperfine interaction with increasing x can be observed for different Fe-positioning. For spectra with pure quadrupol interaction it is possible to make an analysis with two subspectra and a medium intensity ratio of 0·88:0.12. At low temperatures the characteristics of the spectra change strongly; it is only possible to make an analysis by the assumption of spectra with pure quadrupol interaction and those with additional hyperfine interaction. These assumptions are supported by different spectra obtained on cooling with or without an applied magnetic field but measuring in the same field. The results point to a magnetic interaction substantially influenced by the positioning of the neighbouring Fe atoms.

R. Haferl

Papers

Hyperfine interactions in Y2Fe17

Hyperfine interactions in RE2(Fe, Co)17 RE = Y, Gd, Dy

Mößbaueruntersuchungen an Y(FexCo1–x)2 im Bereich kleiner Fe‐Konzentrationen