ESR of some RE-ions in CePd3

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ESR of some RE-ions in CePd3

T. Gambke, B. Elschner

To cite this version:

T. Gambke, B. Elschner. ESR of some RE-ions in CePd3. Journal de Physique Colloques, 1979, 40

(C5), pp.C5-331-C5-333. �10.1051/jphyscol:19795114�. �jpa-00218898�

JOURNAL DE PHYSIQUE

Colloque C5, supplément au n° 5, Tome 40, Mai 1979, page C5-331

ESR of some RE-ions in CePd

3

T. Gambke and B. Elschner

Institut fur Festkorperphysik, Technische Hochschule Darmstadt, F.R.G.

Résumé. — Nous donnons quelques résultats de la ESR de Gd3 + , E r3 + et Y b3 + dans le composé CePd3 à basse température. Les résultats sont discutés en considérant que CePd3 est un composé avec fluctuations de valence.

Abstract. — Some results of the ESR of Gd

^{3 +}

, Er

³⁺

and Yb

^{3 +}

in the intermetallic host CePd

³

at temperatures of 1.5-4.2 K in X-band and 3.5-120 K in Q-band are reported. For the Gd

3 +

resonance in a CePd

3

single crystal CEF-splitting appropriate to a cubic local environment is observed. The strong non-linear but exponential increase of linewidth of Yb

3+

in CePd

3

is explained by an additional contribution to the relaxation of the 4f momentum due to a resonant phonon relaxation process. The results are discussed with respect to the fact that CePd

³

is an intermetallic compound, which shows interconfiguration fluctuations (ICF).

The ESR of an impurity with a well-defined magne-

tic moment, for example G d

3 +

, is involved by Inter i • 1

Configuration Fluctuations in a characteristic way [1].

AH

f

n

-i

As ICF-host we have chosen CePd

³

, whose lattice . S

^c

i-x Gd

^x

Pd

³

constant, specific heat and susceptibility all show / anomalies of the type expected in an ICF-system. / It is quite clear that no bottleneck effect is to be 2 0 0 -

4 T

" /

expected in the ESR of a Gd-moment in an ICF-

A

• # y host, since the strong spin-orbit coupling in the ICF- c^Jt a ions prevents the host of having a well-defined spin / A

resonance [2]. p At first sight one might expect the fluctuations to /

couple to the Gd-moment, increasing the linewidth 150- fi

beyond that in a comparable normal metal host.

Tm r ^.^Gd,, Pd3

The various ESR spectra of Gd

^{3 +}

, Er

^{3 +}

and Yb

^{3 +}

o J" A

in CePd

3

, which exhibit some interesting ESR details, a J ,

for example the hyperfine-structure of both Yb T /*

isotopes 171 and 173, which we could resolve in an T or'

intermetallic compound for the first time, will be J>

published [7]. r T ±

We confine ourselves on the following three points : oP

0 / Ce, xGdx Pd3

1. The increase of ESR-hnewidth with temperature

^Q

o /

of the Gd-resonance in CePd

³

, ScPd

³

and YPd

³

. °

^{0 o o}

o^°o

⁰

°

^{0 0}

2. The increase of linewidth of the Yb-resonance 50 - -

#

•

in CePd

3

and , i '

3. The report on the first measurements of the • • • •* *"~~~~—sinale crystal ESR of the Gd-resonance in a CePd

3

single crystal. ••*•"***

An important quantity to be measured in the ESR

is the increase of linewidth with temperature caused I 1 1 by relaxation of the 4f-momentum via the conduction 50 100 - T [ K ] electrons, the so-called Korringa rate. The ESR-

linewidth of the Gd-resonance in CePd

³

and the for Fig.

I . — E S R

linewidth of polycrystaMne samples of Gd

^x

Ce!_

^x

Pd

³

,

c o m p a r i s o n also measured intermetallics S c P d3 a n d GdJ.Sc1_.tPd3 and Gd^Yj^Pdj as a function of temperature, at

YPd

³

are shown in figure 1. It is clearly to be seen frequency 35.0 GHz, x = 5 000ppm. For comparison you see

that the d o n e nf linewidth of CePH is three times thelinewidthdataforaCePd3-singlecrystal,dotedwith500ppmGd.

that tne Slope Ot imewiatn OI C e P a3 IS three times M e a s u r e m e n t s m t h i s c a s e w a s performed for magnetic direction

smaller as for the compared ScPd

3

and YPd

3

and

cre

ating an angle of approximately 30° with respect to the [001]

a b o u t five times smaller as in L a P d3 [3]. direction in the (110) plane of rotation.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19795114

C5-332 T. GAMBKE AND B. ELSCHNER

Hirst [l] has calculated the effect of ICF on the relaxation of a 4f-momentum. In view of the simpli- fication~ of this model, especially its inclusion of only a single ICF-ion and only S-like conduction electrons, these calculations cannot be applied quanti- tatively to our measurements. Nevertheless, we believe that they provide a qualitatively correct explanation of the observed tendency for ICF to reduce the relaxation rate of 4f-impurities in the experimental temperature range.

The Yb-resonance in CePd, exhibits a strong non linear but exponential rise with temperature, as to be seen in figure 2. The linear increase at tempe- ratures smaller about 8 K is smaller than 1 Oe K-'.

The sharp rise in the linewidth

versus temperature

is presumably connected with the existence of higher T, and T, excited crystal field-levels of Yb3+. Two mechanisms could produce such a rise

:

transitions to the excited level 1. driven by exchange with the conduction electrons or, 2. by the host phonons, the well known Orbach process. The first mechanism has been analyzed by L. Hirst and been observed in several metallic systems, the second is common in insulators.

The first mechanism is described by A H = A H , + b T + c

A

exp (')

^-

¹

with the energy A in respect to the ground state by the conduction electrons. It is possible to calculate the ratio blc, which is more than two orders of magni- tude smaller as the observed value.

So we conclude that the resonant phonon relaxation process is an additional contribution to the relaxation process, as Dodds, Sanny and Orbach pointed out in their publication of the Nd3+-resonance in LaRh, [4]. As far as we know this effect of the Yb- resonance has not been observed in a metallic system, yet.

The phonon-process is approximately described in [4] by

Our linewidth data can accurately be described by this formula with A

=

38 K and

as the solid line in figure 2 shows. The prefactor c*

is difficult to calculate theoretically but the experimen-

Ce Pd, -single crystal

where AH,, is the so-called residual linewidth, which is substracted in figure 2, b the Korringa rate and the last term is due to the transitions to the excited level

Fig. 2. - ESR linewidth of Yb,Ce,-,Pd, as a function of tempe- rature, at frequency 35.0 GHz, X = 0.75 - 1.5 %. For further explanation see text.

Fig. 3.

-

ESR spectra of 500 ppm Gd m a CePd, single crystal at various temperatures at frequency 35.0 GHz. Spectra were measured for the magnetic field along the [l 1 l] direction.

ESR OF SOME RE-IONS IN CePd, ^C5-333

tal value deduced from the fit is comparable to those observed with Yb3+ in insulators. The value of

A = 38

K is confirmed by Mossbauer experiments of Nowik and co-workers, who derived a T,-doublet ground state with T, and F , at 42 K and 56 K from their investigations yb170 in the cubic YbPd,. The expected influence of ICF on the Yb-resonance could not be seen because the direct relaxation due to the Orbach process 'overlaps the linear slope of linewidth.

Let us finally comment our measurements of a CePd,-single crystal doted with 500 ppm Gd (figure 3).

The spectrum at 3.5 K nicely shows the expected features, described by the Plefka-Barnes theory [6].

At higher temperatures, the spectrum shows the typical exchange narrowing. At 75 K there remains a single line with a Iorentzian line-shape. At this temperature there was a slight change in the slope of line-width of the polycrystalline sample. At this and higher temperatures the presumed crystal field effects are not to be seen. As Urban and co-workers demonstrated in their paper on the Gd-resonance in LaSb-single crystals, the appearance of the

+

^{112 ct}

-

112 transition in the intermediate tempe-

rature range is to be explained by introducing spin exchange interaction between Gd ions [6]. The measurements on this subject are not finished yet

;

the ESR measurements of the influence of a further 4f-moment, for example Er3+ on the Gd-resonance have the same intention. We hope to be able to esti- mate the 4f exchange field by these measurements.

In conclusion, we can say that our experiments of the 4f-resonances in CePd, and the compared ScPd, and YPd, exhibit a number of quite interesting ESR results. The very narrow Yb-resonance line and its therefore well resolved hyperfine splitting as well as the - in comparison to other ESR measurements

-

quite normal g-shifts point out that the 4f-resonances.

seem to be not affected by the 4f-electrons of the Ce-ion directly. The fluctuations seem to influence only the relaxation rate via the conduction electrons of the Gd-ion and therefore the temperature depen- dence of the linewidth.

We are greatful to D. ADums for leaving us the CePd, single crystal. This is a project of the Sonder- forschungsbereich Festkorperspektroskopie Darm- stadt Frankfurt, supported by the Deutsche Fors- chungsgemeinschaft.

References

[l] GAMBKE, T., ELSCHNER, B. and HIRST, L. L., Phys. Rev. Left. [5] NOWIK, I., DUNLAP, B. D. and KALVIUS, G. M., Phys. Rev. B

40 (1978) 1290. 6 (1972) 1048.

[2] HIRST, L. L., in Valence Instabilities and Related Narrow- [6] URBAN, P,, DAVIDOV, D., ELSCHNER, B., PLEFKA, T. and SPER- Band Phenomena edited by R. D. Parks (Plenum, New LICH, G., Phys. Rev. B 12 (1975) 72.

York) 1977 pp. 3, 113, 259. [7] GAMBKE, T., to be published.

[3] KARRA, K., Phys. Rev. B 15 (1977) 2538.

[4] DODDS, S. A., SANNY, J. and ORBACH, R., Phys. Rev. B 18 (1978) 1016.