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Submitted on 1 Jan 1971
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THE MAGNETIC PROPERTIES OF Pd3-RARE EARTH PHASES
W. Gardner, J. Penfold, I. Harris
To cite this version:
W. Gardner, J. Penfold, I. Harris. THE MAGNETIC PROPERTIES OF Pd3-RARE EARTH PHASES. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-1139-C1-1140.
�10.1051/jphyscol:19711407�. �jpa-00214448�
JOURNAL DE PHYSIQUE Colloque C I, suppMment a u no 2-3, Tome 32, Fkorier-Mars 1971, page C 1 - 1139
THE MAGNETIC PROPERTIES OF Pd3-RARE EARTH PHASES
W. E. G A R D N E R and J. PENFOLD, 1. R. HARRIS, A. E. R . E., Harwell, Berks., England
and Department of Physical Metallurgy and Science of Materials, University of Birmingham, Edgbaston, Birmingham, England.
RbumB. - Des mesures de I'aimantation de toutes les phases Pd3 - terre rare, ont Cte faites entre 300 OC et 1,3O K La valeur du moment magnktique de l'atome de terre rare est voisine de celie de l'ion libre a la temperature ambiante mais des effets lies au champ cristallin deviennent importants a basse tem+rature. Les interactions d'echange sont faibles et seules deux phases presentent des signes d'ordre magnetique a savoir PdsGd, T N .= 7,5 OK et PdjTb, TN =: 2,O OK.
Les niveaux d'energie des multiplets d'ordre superieur de Pd3Eu et de Pd3Sm ont ete determines.
Abstratc. - Magnetization measurements have been made from 300° to 1.3 OK on all of the Pd3 - rare earth phases.
The magnetic moment of the rare earth atom is close to the free ion value at room temperature but crystal field effects become important at low temperatures. Exchange interactions are small and only two of the phases show signs of magnetic ordering, namely Pd3Gd, TN - 7.5 O K and Pd3Tb, T s = 2.0 OK. The energy levels of the higher multiplets of Pd3Eu and Pd3Sm have been deduced.
Pd3-rare earth phases probably form congruently and readily take up an ordered f. c. c. structure (L1 ,-type). The observed lattice spacing progressively decreases from 4.130 0 kX for Pd3Pr to 4.027 7 kX for Pd3Lu. Lattice parameter measurements [ I ] suggest that all of the rare earth solutes are present in the trivalent form and this has been confirmed for Pd3Eu by Mossbauer measurements [2, 31. This paper reports the magnetization measurements, which have been made on all of the phases from 300° to 1.3 OK.
Pd3Y, Pd3La, and Pd3Lu are all diamagnetic at room temperature but become paramagnetic below 50 OK presumably due to the presence of rare earth impurities. The magnetic susceptibility of the rare earth phases can be represented by the sum of a Curie- Weiss term and a diamagnetic temperature-indepen- dent term ( x
-
- 0.15 x emu.g-' taken from the behaviour of Pd,La and Pd,Lu). With the excep- tion of Eu and Sm, the moment of the rare earth atom, obtained from the Curie-Weiss behaviour between 300 and 100 OK, agrees within experimental error with the free ion value and the Curie-Weiss 0 is small ( 5 5 OK). The susceptibility shows a maximum at 7.5 _+ 0.5 OK in Pd,Gd and at 2.0 + 0.5 OK in Pd3Tb, which suggests that these phases are antiferromagnetic below these temmratures. A simple molecular field analysis for ~ d , ~ d indicates that ^the most probable type of ordering is type 111 (i. e. ferromagnetic planes) for the magnetic atoms on their s. c. lattice.In interpreting the results for Pd3Nd and Pd3Pr at low temperatures, crystal field effects become impor- tant. Frequently 141 Pr compounds show a temperature independent susceptibility behaviour at low tempera- tures due to the crystal field producing a ground state singlet (T,). However the susceptibility of Pd3Pr is temperature dependent down to 1.3 OK indicating a
not only has the crystal field to be considered but also the effects of the higher multiplets are important. In addition it is necessary to include exchange which we have treated in the molecular field approximation using only the spin-dependent contribution. In figure 1 the experimental results are compared with
FIG. I . - Jnverse gram susceptibility of Pd,Sm as a function of
temperature. 0. . . . experimental values, - . . . . calculation.
calculation. The calculated curve drawn corresponds to the multiplet separations [5] given in Table I, a crystal field splitting of 100 OK between T, and T, in the ground state multiplet, and exchange equivalent to a Curie-Weiss 8 of - 2 OK. The experimental results at low temperatures agree better with T, lower than r,
which again agrees with the prediction of the point charge model for a fourth degree term (a sixth degree term has no effect on the lowest multiplet).
magnetic ground state. In the case of a cubic field with
12-fold co-ordination the point charge model predicts TABLE I that if the fourth degree term predominates the ground Energy levels of 6H state will be the magnetic state r, but if the sixth
degree term is large enough the non-magnetic state T, J 512 712 912 1112 1312 1512 will be lowest. Our results indicate that r, is lowest. - - -- - - - -
The behaviour of Pd3Sm is more complicated since E (OK) 0 1 580 3 310 5 180 7 200 9 500
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711407
C 1- 1140 W. E. GARDNER AND J. PENFOLD, I. R. HARRIS Finally the behaviour of Pd3Eu depends entirely on
the energies of the higher order multiplets. A crystal field has no effect on the first and second multiplets but a fourth degree field would split the third multiplet 7F2 into T3 + T,. The experimental results have been
compared with various published schemes [4] of energy levels but only show good agreement after the inclusion of a spin-dependent exchange term. However it is possible to obtain good agreement with experiment by simply varying the energies of the 7F, and 7F2 mul- tiplets since the low temperature results depend on the energy of 7F1 and the values near room temperature on 7F,. The agreement between calculation and experi- ment for two energy level schemes (i) and (ii) is shown in figure 2. These values are very similar to those observed in other europium compounds [4] and with theory [6], as can be seen in Table 11. The increase of susceptibility observed experimentally below 50 OK is due either to the presence of EU: and/or to other rare earth impurities in the sample. It corresponds to an impurity level N 0.1 % of the number of europium atoms.
Energy levels of 7 F in OK
T L ° K )
E 0 477 1330 - - - - (9
FIG. 2. - Gram susceptibility of PdsEu as a function of tem- 477 250 - - - -
perature 0 . . . . experimental values, - . . . . energy (ii)
levels (i), - . . . . . energy levels (ii) of Table 2. E 0 460 1 350 2 950 4 100 5 740 7 340 [6]
References
[I] HARRIS (I, R.) and RAYNOR (G. V.), J. Less Common [3] LONGWORTH (G.) and HARRIS (I. R.), to be published.
Metals, 1965, 9, 263. [4] JUNOD (P.), MENTH (A.) and VOGT (O.), Phys. kondens.
[2] WICKMAN (H. H.), WERNICK (J. H.), SHERWOOD (R. C.), Materie, 1969, 8, 323.
WAGNER (C. F.), J. Phys. Chem. Solids, 1968, [5] GOBRECHT (H.), Ann. Physik, 1937, 28, 673.
29, 181. 161 JUDD (B. R.), Proc. Phys. Soc., 1956, A 69, 157.
