N.M.R. and magnetic susceptibilities of the CeAl intermetallic compounds

Volume 34A, number 5

PHYSICS LETTERS

N.M. H.

22 March 1971

AND MAGNETIC SUSCEPTIBILITIES OF THE Ce-Al INTERMETALLIC COMPOUNDS V. NICULESCU, I.POP Physics Department. University of Cluj, Romania

and N. ROSENBERG Physics Department. University of Bucarest. Academiei 14, Romania

Received 8 February 1971 The temperature dependence of the Knight shift, N. M. R. line width and magnetic susceptibilities of CeA1 4, CeA13, CeA12 have been measured. All the calculated exchange constants95f are negative and between 0.15 and 0.25 eV.

In order to provide further informations on lanthanide intermetallic compounds, the temperature dependence of the Knight shift and magnetic susceptibility were investigated. The measurements were carried out with a Jeol-type spectrometer at 15.085 Mc,in the temperature range of 140-460°K. The magnetic susceptibility was measured with a Faraday type magnetic balance in the temperature range of 77-450°K. The samples were prepared by melting the stoichiometric quantities of the elements in vacuum in a Tamman furnace, then crushed and ground, getting a powder with a particle size less than 0.07 mm. The crystallographic structure of the investigated compounds have been described earlier; CeA14 belongs to the spatial group D13 [1], CeAl3 to the group P63 [2] and CeA12 to the group C15 [3]. The main interaction in the lanthanide intermetallic compounds is the exchange polarisation of the conduction electrons owing to the localized 4f electrons of the rare earth ions, giving rise to a strong temperature dependent Knight shift [4]. 9~f Xf (1) K —K — OL~ ~ggf~j2~ ~ j(j+i)J’

/

~

42

1..

A1~Ge £AI 3Ce ~A14Ce

(S.J)1

where the symbols have the same meaning as in ref. [4]. polarized Since ininthe thecase direction of Ce,ofthe the4fmagnetic spins are field, a positive K-K 0 results. The dependence of the Knight shift on the susceptibility for all three compounds is shown in fig. 1, as expected by formula (1), thus confirming the essential contribution of the f electrons to the magnetic suscep-

5enu/g) X(~ 0

45

1,5

1

2

2,5

Fig. 1

265

Volume 34A. number 5

PHYSICS

LETTERS

Tablel Experimental values O~(OK)

22 March 1971

25~ A

Compound

K(%)

K0(%)

AI4Ce

at 300°K -iO.156

+0.08

—20

—0.169

AI3Ce Al2Ce

+0.198 +0.292

+0.075 +0.136

—25 — 5

—0.439 —0.23

AL

3Cc

~5f(eV) 20

a Al4 Ce

~ 15 tibility. The constants calculated from the temperature dependence of the Knight shift and susceptibility, are summarised in table 1. The obtained values for CeA13 are close to those reported earlier [5]. The negative sign of is an evidence of the antiferromagnetic sf exchange interaction in Ce-Al alloys, as in the other lanthanide intermetallic compounds. The temperature dependence of the line width for CeAl3 and CeA1,4 is plotted in fig. 2. Contrary to CeA12, where the shape and the line width ~H are practically temperature independent [6], CeA13 shows a slight broadening of the line width at lower temperatures, whereas CeA14 exhibits a strong distortion of the NMR line, with a sharp increase of the line width below, about 200°K. In the case of CeAl3 the low-temperature - line broadening can be due to an anisotropic Knight shift. The extremely large broadening observed for CeAI,4 below 200°Kcould be in connection with the ferromagnetic ordering occurring in this material at 9°K[7]. We would like to thank Mr. Ghizdeanu for performing some susceptibility measurements and Mrs. H. Niculescu and Mr. S. Mandache for their kind assistance concerning the N. M. R. measurements.

~

__

I

0

~

200

300 ~

500

4~

(~

Fig. 2

References [1] H. Nowotny, Z.Metallkunde, 34 (1942) 22. [2] J. H. N. van Vucht and K. H.J. Buschow, J. Less Common Metals. 10 (1966) 98. [3] H. J. Wailbaum, Z. Krlst., 103 (1941) 147. [4] V. Jaccarino, B. T. Matthlas, M. Peter, H. Suhi and J. H. Wernick, Phys. Rev. Letters 5(1960)251. [5]V.A.Van Diepen, H.W.De WlJn and K. H. J. Buschow, J. Chem. Phys., 46 (1967) 3489. [6] R. G. Barnes, W. H. Jones Jr and T. P. Graham, Phys.Rev. Letters 6 (1961) V.Jaccarlno, J. Appl. Phys.,221; 32 (1961) Suppl. 102S. [7] K. H. Mader and W. M. Swift, J. Phys. Chem. Solids 29 (1968) 1759.

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