A. M. van Diepen

Magnetic Susceptibilities of Rare‐Earth–Indium Compounds: RIn3

The magnetic properties and the lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported. The magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe. With the exception of compounds with R=La, Sm, Y, and Yb Curie–Weiss behavior is observed in the high‐temperature region. At low temperatures the magnetic behavior for compounds in which R=Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er is ascribed to antiferromagnetic ordering. In the case of PrIn3 magnetic ordering is prevented by crystalline fields. The splitting of the J = 4 state of Pr3+ by cubic crystalline fields has been calculated for various combinations of fourth‐ and sixth‐order potentials. Possible energy diagrams are presented.

Effect of hydrogen absorption on the magnetic properties of YFe2 and GdFe2

Abstract The change in the magnetic properties of the compounds YFe 2 and GdFe 2 upon hydrogen absorption has been studied by means of magnetic measurements and by Mossbauer effect measurements. In both compounds H 2 absorption leads to a drastic reduction in Curie temperature and to an increase in saturation magnetization. The Mossbauer spectra of the hydrides show appreciable line broadening. The hydride of YFe 2 gives rise to an increase in hyperfine splitting in the magnetically ordered region. The isomer shift in YFe 2 as well as in GdFe 2 changes on hydride formation. X-ray diffraction showed that the cubic Laves phase structure is retained, but that the lattice constants increase considerably when hydrogen is absorbed in GdFe 2 and YFe 2 .

Crystal-field anisotropy of Sm3+ in SmCo5

It is shown that the major contribution to the high uniaxial anisotropy of the compound SmCo5 arises from the action of crystalline and exchange fields on the Sm3+ ion.

Mössbauer effect in LaFe12O19

Abstract Mossbauer spectra of 57 Fe in LaFe 12 O 19 show that the substitution of La 3+ for Ba 2+ or Sr 2+ in X Fe 12 O 19 is associated with a valency change of Fe 3+ to Fe 2+ at the 2 a or 4 f 2 site. Temperature dependences of the hyperfine fields at the various sublattices are given.

Electron exchange between Fe2+ and Fe3+ ions on octahedral sites in spinels studied by means of paramagnetic Mössbauer spectra and susceptibility measurements

Abstract Mossbauer spectra were obtained of the paramagnetic spinels Zn 2+ | Zn 2+ (1−x) 2 Ti 4+ (1+x) 2 Fe 3+ (1− x) Fe 2+ x | O 4 and susceptibilities were measured. The strong difference between the paramagnetic Fe 2+ and Fe 3+ spectrum, due to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe 3+ and the Fe 2+ spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe 3+ and Fe 2+ concentration (x = 1 2 ) while it disappears towards the end members (Fe 3+ only or Fe 2+ only) as well as with decreasing temperature (between 78 and 200 K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of ∼10 8 sec −1 for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie-Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J 11 = −1.4 K, J 22 = −3.3 K and J 12 = + 1.6 K for the Fe 3+ Fe 3+ , Fe 2+ Fe 2+ and Fe 3+ Fe 2+ interactions are derived. The experimental results are discussed in terms of a hopping model with an activation energy q ∼- 0.12eV and a non-equivalence of the octahedral sites expressed by a varying potential energy difference U 0 between neighbouring sites. The continuous absorption at 300 K for x = 1 2 is attributed to about 17% of the iron on sites with U 0 running from 0 to ≅−0.06 eV. The ferromagnetic Fe 3+ , Fe 2+ interaction ( J 12 ) is attributed to electron transfer from localized Fe 2+ ions to Fe 3+ neighbours via a transfer integral b of the order of 0.05 eV. The magnitudes of J 12 and b are tentatively explained.

Hydrogen absorption in CeFe2 and ThFe3

Abstract The effect of hydrogen absorption on the magnetic properties of CeFe 2 and ThFe 3 was studied by magnetization measurements and by the 57 Fe Mossbauer effect. In both cases an increase in the transition metal moment is observed. In CeFe 2 the long range periodicity of the crystal lattice is lost whereas in ThFe 3 a structural change occurs. Surprisingly, the magnetic anomaly observed in ThFe 3 around 250 K is still present in the hydride.

Valencies of manganese and iron ions in cubic ferrites as observed in paramagnetic Mössbauer spectra

Abstract The ground state of the ionic system Mn2++Fe3+Mn3++Fe2+ on octahedral sites in a spinel lattice is investigated on paramagnetic materials with specially chosen compositions. The valencies are established by means of the very different Mossbauer spectra of divalent and trivalent iron. Divalent iron is found to be unstable in the presence of trivalent manganese contrary to Simsas widely accepted model. A sample of ZnFe1·75Ti0·25O4 shows at room temperature an Fe3+, Fe2+ spectrum, in which divalent and trivalent iron are indistinguishable, and at 78°K the superposition of a similar spectrum and a ferrous spectrum.

Magnetization and Mossbauer spectra of non-crystalline Y3Fe5O12

Abstract Non-crystalline Y 3 Fe 5 O 12 is studied by X-ray, electron microscope, magnetic susceptibility, and Mossbauer effect techniques. The material appears to consist of X-ray amorphous platelets of several microns, which are agglomerations of particles of about 200 A. Mossbauer spectra at room temperature show Fe in tetrahedral surrounding, while at liquid helium temperature hyperfine splitting for both octahedral and tetrahedral sites is observed. Magnetization measurements show that individual particles order magnetically at ∼850 K, much higher than well-crystallized YIG (560 K). These differences are consistent with a high degree of crystallographic disorder and a small particle size. Crystallographic ordering and particle growth are induced by annealing. At 680°C crystalline YIG is formed.

Temperature dependence of the hyperfine field in amorphous Fe2O3

Abstract Mossbauer spectroscopy was used to follow the hyperfine field at 57 Fe nuclei in amorphous Fe 2 O 3 . The value of H hf at T = 0, 470 kG, indicates J = 5 2 for the Fe ions, while the reduced hyperfine field versus reduced temperature closely follows a J = 1 2 Brillouin function. This result is at variance with theoretical predictions for a spin glass and is also different from amorphous metals with a high content of magnetic ions as reported in the literature. Paramagnetic Mossbauer spectra of amorphous mixed oxides of Fe 2 O 3 with ZnO and CoO show that the 57 Fe nuclei in all amorphous ferric oxides studied so far are coordinated in a manner similar to the d site in β F 2 O 3 , and distinctly different from the coordination in their crystalline form.

Magnetic Properties and Nuclear Magnetic Resonance of Cubic RCu5 Intermetallic Compounds

The magnetic properties of the cubic RCu5 compounds TbCu5, DyCu5, HoCu5, ErCu5, and TmCu5 are reported for temperatures between 2.1° and 300°K. In the paramagnetic region the susceptibility follows a Curie‐Weiss law. The type of ordering at low temperatures changes with increasing atomic number from antiferromagnetic (R = Tb) to ferromagnetic (R = Ho, Er, Tm), while DyCu5 is metamagnetic. The Knight shifts of the 63Cu NMR in these compounds have been measured between 100° and 300°K. The results are discussed in terms of the Ruderman‐Kittel‐Kasuya‐Yosida theory.