Mössbauer-Effect Determination of Crystalline Electric Field Splittings in Several Intermetallic Compounds of Thulium

Abstract

By measuring the temperature dependence of the nuclear quadrupole splitting of the Tm 169 8.4-keV Mossbauer y transition, a measure of the strength of the crystalline electric field (CEF) in several hexagonal intermetallic compounds of the type TmX 2 , where X is another transition element, has been obtained. As in thulium metal, a zero-order model of the CEF incorporating only the C2 0 parameter is found sufficient to describe the experimental results. On this basis, the over-all CEF splitting of the Z HQ ground term of the Tm 3+ ion is found to be 94 cm" 1 in TmRu 2 , 88 cm -1 in TmRe 2 , and 42 cm -1 in TmMn 2 . The nuclear and ionic shielding parameters RQ and <r 2 were also determined from the experimental measurements, in reasonable agreement with theoretical expectations. Best agreement between experimental and calculated values of the CEF parameters is obtained when the effective charge on the X ions is taken to be zero. Details of the calculation of the CEF parameter d° by the plane-wise summation method for the hexagonal Laves-phase intermetallics are also given.

A study of crystalline electric fields in some thulium aluminum compounds

“…In comparing this data with previous data it was noted that the crystal-field splitting is much larger than previously found for rareearth metallic compounds (12,13), but still smaller than those of rareearth salts (7). Some covalency effects may be present since the fitted asymmetry parameter does not agree with that calculated using the point-ion model.…”

“…The Hamiltonian which describes this interaction for the crystal field with the 4f electrons can be expressed as follows For the experimental determination, it is desirable to define the crystal-field parameters cJJ = 'Aj[<r^>4f (13) Although it is customary to introduce a factor here to account for the shielding of the outer electrons, it will not be done at this time due to the uncertainty about the significance of such a term. …”

Study of crystalline electric fields in some thulium aluminum compounds

“…As can be seen in Figure 1, the ME spectrum consists of five indivi- This asymmetric pattern has been noted in previous studies (7,12,13,17), but it was still possible to fit the pattern with two Lorentzian lines. However, the Tm 3 Al 2 spectra could not be fit this way since the observed asymmetry is much more pronounced.…”

“…However, his results suggest little shielding or even anti-· shielding for the fourth-and sixth-order terms, in agreement with the ideas of Burns. However, semi-empirical fits with the data for various rare earth materials (7,(11)(12)(13)(14)(15) indicate some agreement with the secondorder shielding term. · Unfortunately, these experiments are not conclusive in regards to higher-order terms.…”

“…These levels will now interact with the quadrupole moment of the nucleus through the term Vq mentioned above. For the experimental determination, it is desirable to define the crystal-field parameters (13) Although it is customary to introduce a factor here to account for the shielding of the outer electrons, it will not be don~ at this time due to the uncertainty about the significance of such a term. In part B the Hamiltonian for a point-charge crystal field was derived.…”