HAL Id: jpa-00219015
https://hal.archives-ouvertes.fr/jpa-00219015
Submitted on 1 Jan 1979
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Onset of magnetic order in solid solutions of rare-earths in praseodymium
B. Sarkissian, B. Coles
To cite this version:
B. Sarkissian, B. Coles. Onset of magnetic order in solid solutions of rare-earths in praseodymium.
Journal de Physique Colloques, 1979, 40 (C5), pp.C5-264-C5-265. �10.1051/jphyscol:1979598�. �jpa- 00219015�
JOURNAL DE PHYSIQUE Colloque C5, supplkment au no 5, Tome 40, Mai 1979, page C5-264
Onset of magnetic order in solid solutions of rare-earths in praseodymium
B. V. B. Sarkissian and B. R. Coles
Physics Department, Imperial College, London SW7, U K
RBsumB. - Nous avons mesure la rksistivite electronique et la susceptibilite magnetique en champs alternatif et continu des alliages dhcp de B - T m et de B-Ce, en vue de dkterminer leur ordre magnetique. Dans les alliages de Tm, nous n'avons observe ni ordre longue distance, ni blocage en verre de spin. Dans les alliages de Ce, a fortes concentrations, nous avons trouve des effets d'ordre magnttique semblables A ceux du B-Ce ; alors que dans les alliages dilub, il s'agit d'effet de type Kondo.
Abstract. - Electrical resistivity and low field a.c. and d.c. susceptibility measurements have been used to study the magnetic ordering in double hexagonal close-packed alloys of B - T m and h - C e . In the Tm alloys, no long- range order or spin-glass freezing is observed. In Ce alloys, magnetic ordering effects like those of p-Ce are found at higher concentrations ; in the dilute alloys, Kondo-like effects are seen.
1. Introduction. - There is now a body of experi- mental evidence to suggest that the magnetic cha- racter of solid solutions of other rare earth metals in double hexagonal close packed Pr is very different for heavy rare-earth solutes. In all cases the coupling is mediated by the conduction electrons through the RKKY interaction (a spin-spin interaction) the net moment of the heavy depends on gJ(L
+
S), whilethat of the light depends on gJ(L - S). In B - N d [l]
and Pr-Sm [2] a fairly rapid onset of long-range orderis observed, rather as in the effectively heavy although non-magnetic Y quite small amounts of the heavy solutes Gd, Tb and Dy produce long range ordering after only a limited spin glass regime. In Pr-Gd and Pr-Tb, however, the magnetic order appears [l, 2]to possess spin glass character over a wide composition range, presumably because the character of the conduction electron spin-net local moment coupling differs on host and solute sites.
We have now extended this work to include two other rare-earth solute elements with rather special characteristics : Ce, where incipient 4f-conduction electron mixing may yield virtual bound state cha- racter and an effective local spin-conduction electron spin of negative sign, and Tm, where the solute, although heavy, has (like Pr) a singlet ground state rather well separated from excited states.
The standard methods of alloy preparation, electri- cal resistivity and low field (A.C. and D.C.) suscepti- bility measurements were employed as described in earlier papers [l, 21. The arc-melted samples were not annealed to avoid increasing the content of gaseous impurities.
2. Resistivity of Pr-Ce. - Resistivity data for Pr-Ce are shown in figure 1. As observed in Y-Ce 131,
Fig. 1 . - Electrical resistivity versus temperature for E - C e alloys.
a Kondo-like resistance minimum supports the sug- gestion of mixing effects and an incipient Kondo condensation. Kondo moments are well known to be stabilized as the concentration of solute increases by interaction effects, and this stabilization seems to be more rapid (no minimum being found for more than 20
%
Ce) for Pr as host than for Y. We attribute this to a contribution to the interactions made by induced Pr moments. With larger Ce contents a well marked decrease in resistivity at low temperatures develops, paralleling that found in Au-Fe and Cu-Mn alloys as spin glass freezing takesover fromond do
effects.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979598
ONSET OF MAGNETIC ORDER I N SOLID SOLUTIONS O F RARE-EARTHS IN Pr C5-265
More than 40
%
of Ce is required, however, before we find the emergence of character like that observed in P-(dhcp) Ce and presumably due to long range order [4]. This delay, as compared with Pr-Nd, in the onset of long range order must be due, aTin Y-Ce to the Kondo character of the Ce moments.3. Susceptibility of Pr-Ce. - The evolution of long-range magnetic order with increasing Ce content is also apparent in the A.C. susceptibility results, which are shown in figure 2, together with the data for pure Pr [2], where the effects of the singlet ground
Fig. 2. - a.c. susceptibilities versus temperature for &-Ce alloys performed at 450 Hz.
state can be seen. The Kondo character of the more dilute alloys is clear and good moment (approximately Curie Law) behaviour is only reached at about 20
%
Ce. At higher concentrations, interactions between such moments become apparent, but only above 40%
is anything resembling straightforward antiferromagnetism found, the behaviour at inter- mediate compositions closely resembling that of the spin-glass alloys of Pr with 2.5 and 5%
Gd [2]. Some reservations must be made, however. about too simplistic a deduction of spin glass character for the 30%
Ce alloy from the susceptibility maximum, since no irreversibility in low field magnetization measurements is found at lower temperatures ; nor are the results shown in figure 2 for the 27.3%
alloy modified by cooling in a field of 180 oersteds.4. Pr-Tm behaviour. - Susceptibility data for
~ r - ~ ~ a l l o ~ s up to the limit of the dhcp phase show - no signs of either spin glass freezing or long range magnetic order, in accord with resistivity results.
Thus here, both host and solute having fairly well isolated singlet ground states, larger solute concen- trations than can be achieved in the dhcp structure are necessary for exchange to be able to produce any low temperature magnetically frozen state. For Tb as solute, however, both the smaller singlet isolation and the larger spin make such freezing possible [l].
5. Conclusion. - The present work provides new information on the character of solid solutions of other rare-earths in Pr. In conjunction with previous work, some patterns of behaviour are emerging which depend on the light or heavy, Kramers or non- Kramers character of the solute. It is now clear that the ability of Ce to show some degree of Kondo character provides a further complication.
References
[l] SARKISSIAN, B. V. B., Physica B and C 86-88 (1977) 864.
[2] SARKISSIAN, B. V. B., Solid State Commun. 27 (1978) 57.
[3] HILL, H. H., MINER, W. N. and ELLIOTT, R. O., Phys. Lett.
28A (1969) 588.
[4] BURGARDT, P., GSCHNEIDNER Jr., K. A., KOSKENMAKI, D. C., FINNEMORE, D. K., MOORMAN, J. O., LEGVOLD. S., STASSIS, C. and VYROSTEK, T. A., Phys. Rev. B 14 (1976) 2995.
