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

Profile analysis of powder neutron diffraction data: Its scope, limitations, and applications in solid state chemistry

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

Combining different experimental techniques, investigations in hexagonal $P{6}_{3}/mmc$ Er${}_{2}$Fe${}_{17}$ show remarkable magnetovolume anomalies below the Curie temperature, ${T}_{C}$. The spontaneous magnetostriction reaches $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ at 5 K and falls to zero well above ${T}_{C}$, owing to short-range magnetic correlations. Moreover, Er${}_{2}$Fe${}_{17}$ exhibits direct and inverse magnetocaloric effects (MCE) with moderate isothermal magnetic entropy $\ensuremath{\Delta}{S}_{M}$, and adiabatic temperature $\ensuremath{\Delta}{T}_{\mathrm{ad}}$ changes [$\ensuremath{\Delta}{S}_{M}\ensuremath{\sim}\ensuremath{-}4.7$ J(kgK)${}^{\ensuremath{-}1}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}\ensuremath{\sim}2.5$ K near the ${T}_{C}$, and $\ensuremath{\Delta}{S}_{M}\ensuremath{\sim}1.3$ J(kgK)${}^{\ensuremath{-}1}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}\ensuremath{\sim}\ensuremath{-}0.6$ K at 40 K for $\ensuremath{\Delta}H=80$ kOe, respectively, determined from magnetization measurements]. The existence of an inverse MCE seems to be related to a crystalline electric field-level crossover in the Er sublattice and the ferrimagnetic arrangement between the magnetic moments of the Er and Fe sublattice. The main trends found experimentally for the temperature dependence of $\ensuremath{\Delta}{S}_{M}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}$ as well as for the atomic magnetic moments are qualitatively well described considering a mean-field Hamiltonian that incorporates both crystalline electric field and exchange interactions. $\ensuremath{\Delta}{S}_{M}(T)$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}(T)$ curves are essentially zero at $\ensuremath{\sim}$150 K, the temperature where the transition from direct to inverse MCE occurs. A possible interplay between the MCE and the magnetovolume anomalies is also discussed.

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Magnetovolume and magnetocaloric effects in Er2Fe17

Mossbauer effect spectra are obtained in the temperature range 3.7 to 750 K for various compounds of the series Tm2Fe17−xBx (B = Co, Ni) and for Er2Fe15Ni2. A slight preference for Fe was observed for substitutions involving the dumbbell shaped f-site atoms in these compounds. In all Tm2Fe17−xBx compounds investigated (0 ≦ x ≦ 7) a change in anisotropy from an easy c-axis (T TM) is observed. The values of TM are found to increase with x. For an easy c-axis magnetization the hyperfine fields at the f-site Fe atoms are observed to decrease with x, whereas the average hyperfine field due to the other Fe sites is found to increase.



Mosbauerspektren von einigen Tm2Fe17−xBx (B = Co, Ni)-Verbindungen und Er2Fe15Ni2 werden im Temperaturbereich von 3,7 bis 750 K aufgenommen. Es wird ein geringer Vorzug fur Substitution von Eisen auf den hantelformigen f-Platzen in der Elementarzelle festgestellt. Samtliche untersuchten Verbindungen Tm2Fe17−xBx (0 ≦ x ≦ 7) zeigen eine Anderung der Anisotropie von der Vorzugsrichtung parallel zur c-Achse (T TM). Die Werte fur TM zeigen eine Zunahme mit x. Fur Falle mit magnetischer Vorzugsrichtung parallel zur c-Achse, stellt sich eine Abnahme der Hyperfeinfelder der Fe-Atome an den f-Platzen mit zunehmendem x heraus, wahrend die Hyperfeinfelder der ubrigen FePlatze eine Zunahme aufweisen.

J. B. A. A. Elemans

Papers

The Magnetic Structure of Tm2Fe17