E.P.R. and susceptibility measurements in XAl2 (X = Sc, Y, La, Yb, Lu) compounds containing Gd, Er, Dy and Nd impurities

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E.P.R. and susceptibility measurements in XAl2 (X = Sc, Y, La, Yb, Lu) compounds containing Gd, Er, Dy

and Nd impurities

R. Levin, A. Grayevsky, D. Shaltiel, V. Zevin

To cite this version:

R. Levin, A. Grayevsky, D. Shaltiel, V. Zevin. E.P.R. and susceptibility measurements in XAl2 (X

= Sc, Y, La, Yb, Lu) compounds containing Gd, Er, Dy and Nd impurities. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-48-C5-50. �10.1051/jphyscol:1979519�. �jpa-00218936�

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JOURNAL DE PHYSIQUE Colloque C5, supplkment au no 5, Tome 40, Mai 1979, page C5-48

E.P.R. and susceptibility measurements in XAl, (X = Sc, Y, La, Yb, Lu) compounds containing Gd, Er, Dy and Nd impurities*

R. Levin, A. Grayevsky, D. Shaltiel and V. Zevin

Racah Institute of Physics, The Hebrew University of Jerusalem, Israel

RBsumB. - Nous avons BtudiC 1'6tat fondamental des impuretks Er, Dy et Nd dans les cristaux cubiques XAI (X = Sc, Y, La, Yb, Lu) et leur interaction d'tchange avec les Blectrons de conduction en utilisant la RPE et des mesures d'aimantation. Nous avons mesurB la RPE de Gd dans YbAI, et BtudiC I'effet bottleneck dans ce systhme.

Abstract. - The ground state of Er, Dy and Nd in cubic XAI, (X = Sc, Y, La, Yb, Lu) and their exchange interaction with the conduction electrons were investigatedusingE.P.R. and magnetization measurements. E.P.R. of Gd in YbAI, was measured and the bottleneck effect in this system was investigated.

1 . Introduction. - The crystal electric field (C.E.F.) in cubic symmetry lifts the (2 J

+

1) fold degeneracy of the rare earth impurities Hund's rule ground state.

The level's order and the overall splitting are deter- mined by two C.E.F. parameters, A,, A , or x and W [I]. E.P.R. and magnetization measurements of the rare earth in metals give information about the C.E.F. and about the exchange interaction between the impurities and the conduction electrons (C.E.).

In this paper we report E.P.R. of Er, Dy and Nd ions in cubic Laves phase compounds XAl, (X = Sc, Y, La, Yb, Lu) and magnetization measurements of Er and Dy in LaAl, and Dy in YAI,. These compounds form isostructural, isoelectronic alloys. APW calcula- tions [2] show that the band structure of YAI,, LaAl, and LuAl, are very similar. Nevertheless, there are some differences in the measured electronic properties of these compounds (see [2] and ref.

therein). Therefore, it is very interesting to obtain additional experimental information about the local electronic properties in the XAI, compounds. From our results we deduced the C.E.F. parameters and the R.E.-C.E. exchange parameters. E.S.R. measurements on Er in LuA1, and Er, Dy in ScAl, were reported previously [3].

E.P.R. measurements of Gd in YbAl, and in Th : YbAI, are also reported indicating the existence of bottleneck effect.

2. Experimental results and analysis. - E.P.R. was performed in the temperature range of I .5 K to 20 K, in powder samples. The results are summarized in table I. The exchange parameters J, and J,, [41 were calculated from the g shift and the line broadening respectively [4]. The ground states were extracted from the g value. We were not able to observe the

(*) This research was supported by a grant from the US.-Israel Binational Science Foundation (B.S.F.), Jerusalem, Israel.

E.P.R. of Er and Dy in YAl, and LaAl, even in single crystals nor that of Nd in powdered LaA1,.

Magnetization measurements were performed on single crystals of Er : LaAl,, Dy : YAl, and Dy :, LaAI,, at 4.2 K, as a function of the angle between the crystal axis and the external magnetic field. The C.E.F. parameters were extracted by fitting our results to the theoretical magnetization calculated using spin Hamiltonian of the R.E. ions containing C.E.F. [I] and the Ziman energy. The C.E.F. parameters and the energy of the first excited state ( A ) are given in table 11. The fit between the theoretical magnetization and our experimental results in Dy : YAl, is shown in figure 1. The impurity concentration was about 5 000 ppm in all our samples.

Our E.P.R. results on Gd in YbAl, show dependence of the g value and the line broadening on Gd concentration, indicating the existence of bottleneck effect.

Addition of Th ions opens the bottleneck. The unbottlenecked g shift and line broadening are

Angle

Fig. 1. - The magnetic moment of 5.000 ppm of Dy3+ in YAI, as a function of the magnetic field angle with respect to (100) direction in [I 101 plain.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979519

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E.P.R. AND SUSCEPTIBILITY MEASUREMENTS I N XAl,

Table 1. - fur~erimental parameters e.utracted from E.P.R. in XAl, compounds.

.4 d AHldT (G/K) Nd

.$

^(e.V.)^(*)

(e.V.)(*) Ground state

B d AHId T (G/K)

Dy - J g (e.V.) (*)

' J A H (e.V.) (*)

Ground state .4 d AHIdT (G/K)

Er , I g (e,V.) (*)

J A H (e.V.) (*)

Ground state

LaAl, YbAl,

- -

2.63

+

^0.03

72 f 10 0.2 f 0.2 1.3

+

^0.2

l-6

7.670

+

^0.030

8.0 f 0.2 0.44 & 0.10

0.4 f 0.1

rg)

^{(* *)}

r7

6.880 _+ 0.030 1.5 f 1.0 0.52

k

0.20

0.3 f 0.2

r i3)

(**)

r7

LuAl,

-

2.4

+

^0.2

(*) The difference between J , and J,, may be due to the k dependence (Davidov, D., Maki, K., Orbach, R., Rettoni, C.

and Chock, E. P., SolidSrate Commun. 12 (1973) 621.

(**) Extracted from magnetization measurements.

(***) Obtained by E.P.R. measurements by Baberschke, K., Bachor, B., Luft, H. and Pellisson, J., this conference (J. Phvsique Colloq.

40 (1979) C - 51).

Table 11. - C.E.F. parameters extracted from magne- tization measurements.

Ground

state x ^(K) ^A^(K)

- - - -

Er : LaAl,

ri3)

< ^-0.2 - 0.65

+

^{0.15 19}

+

⁷

Dy : YAI,

r 3

^0.5

+

^0.1 ^{- 2 5 1} 7 5 + 2 5 Dy : LaAI,

rB3)

0.45

+

^0.10 ^-^0.2 ^0.1 ¹⁹

+

⁵

0.091 f 0.005 and 26 f 1 G/K, respectively, Jg and J,, are 0.60

+

0.06 eV and 0.70 f 0.05 eV, respectively and the relaxation rates of the C.E. to the lattice are [5] : 6:L=(50f 20) x 10"s-',

asSLlac,,

⁼⁽³⁰^f¹⁵⁾^x ^10'^S- ^ppm-

and

ddsL/dC,, = (7 f 4) x los S - I ppm-

' .

The relaxation rates were calculated by fitting our experimental results to the bottleneck equations [6].

3. Discussion. - Our magnetization results on Er : LaAI,, Dy : LaAl, and Dy : YAl, indicate that

rg)

is the ground state, suggesting that the sign of A , is positive and that of A,, negative. This result

eliminates the possibility that T7 is the ground state as suggested by Devine et al. [7]. The rg'ground state is in agreement with specific heat [8] and neutron scattering [9] results obtained on Er impurities in LaAl, and YA1, and with some measurements performed on R.E.Al, [lo], but the A , sign is in disagreement with ref. [ll]. The E.P.R. results on Er and Dy in XAl, (X = Sc, Yb, Lu) show that T 7 is the ground state suggesting a positive sign for

[I]'

Naive point charge model (P.C.M.) indicates nega- tive sign for both A , and A , in these compounds [12].

The sign reversal of A , in YAl, and LaAl, and that of A , in ScAl,, YbAl, and LuAl,, compared to P.C.M. can be understood on the basis of correspond- ing screening effects by C.E. [13, 141. The sign reversal of A, for Er and Dy in LuAl, compared to LaAl, and YAl, seems to be more interesting because of the similarity of these compounds [2]. The reason for this sign reversal is not yet fully understood.

From the E.P.R. results of the Nd impurities, which show that T, is the ground state, it is not possible to obtain information on the sign of the C.E.F. parameters. Additional measurements will be performed to obtain more information on the C.E.F.

parameters in this system.

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R. LEVIN, A. GRAYEVSKY, D. SHALTIEL AND V. ZEVIN

References

[l] LEA, K. R., LEASK, M. J. M. and WOLF, W. P., J. Phys. Chem.

Solids 23 (1962) 1381.

[2] SWITENDICK, A. C., Proc. of 10th R.E. Res. Conf. (1973) 235.

[3] RETTORI, C., DAVIDOV, D., NG, G. and CHOCK, E. P., Phys.

Rev. B 12 (1975) 1298.

DEVINE, R. A. B., POIRIER, M. and CYR, T., J. Phys. F 5 (1975) 1407.

[4] DAVIDOV, D., ORBACH, R., RETTORI, C., SHALTIEL, D., TAO, L. J. and RICKS, B., Phys. Lett. 35A (1971) 339.

[5] For definition of the relaxation rates see

CHOCK, E. P., DEVINE, R. A. B., DODDS, S. A., ORBACH, R.

and TIPPIE, L., J. Phys. F 7 Metal Phys. (1977) 1097.

[6] RETTORI, C., KIM, H. M., CHOCK, E. P. and DAVIDOV, D., Phys. Rev. B 10 (1974) 1826.

[7] DEVINE, R. A. B., ZINGG, W., MORET, J. M. and SHALTIEL, D., Solid Sfate Commun. 12 (1973) 515.

[8] SERENI, J. G., Crystal Field Effects in Metals and Alloys, Furrer, A., Ed. (Plenum Press, N.Y.) 1977.

[9] HEER, H., FURRER, A,, WALKER, E., TREYVAUD, A., PUR-

WINS, H.-G. and KJEMS, J., J. Phys. C 7 (1974) 1207.

[lo] PURWINS, H.-G., WALKER, E., BARBARA, B., ROSSIGNOL, M. F.

and FURRER, A., J. Phys. C 9 (1976) 1025.

[Ill HAPPEL, H., BLANCKENHAGEN, P. V., KNORR, K. and MURANI, A., Crystal Field Effects in Metals and Alloys, Furrer, A., Ed. (Plenum Press, N.Y.) 1977 ;

BABERSCKE, K., BACHOR, B. and LUFT, H., In the abstracts of this Conference.

[I21 INOUE, T., SANKAR, S. G., CRAIG, R. S., WALLACE, W. E.

and GSCHNEIDER, K. A. Jr, J. Phys. Chem. Solids 38 (1977) 487.

[I31 DAVIDOV, D. and RETTORI, C., Arch. SC. GenPve 27 (1974) 191.

[14] DIXON, J. M. and DUPREE, R., J. Phys. F 1 (1971) 539 ; F 3 (1973) 118.