Low temperature properties of the abnormal cerium compounds

(1)

HAL Id: jpa-00218896

https://hal.archives-ouvertes.fr/jpa-00218896

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.

Low temperature properties of the abnormal cerium compounds

Angélique Benoit, J. Flouquet, M. Ribault

To cite this version:

Angélique Benoit, J. Flouquet, M. Ribault. Low temperature properties of the abnor- mal cerium compounds. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-328-C5-329.

�10.1051/jphyscol:19795112�. �jpa-00218896�

(2)

JOURNAL DE PHYSIQUE

Colloque C5, supplément au n° 5, Tome 40, Mai 1979, page C5-328

Low temperature properties of the abnormal cerium compounds

A. Benoit, J. Flouquet, M. Ribault

Universite de Pans-Sud, Lab. de Physique des Solides, Bat. 510, 91405 Orsay, France

Résumé. — Après le rappel des résultats d'orientation nucléaire obtenus sur les composés de cérium, nous dis- cutons leurs propriétés de basse température notamment le diagramme de phase champ magnétique-température critique.

Abstract. — After a short summary of the nuclear orientation results obtained on the cerium compounds, we discuss their low temperature properties mainly the phase diagram magnetic field-critical temperature.

1. Nuclear orientation results. — The nuclear of the magnetic properties of the Al

2

La

;c

Ce

1

_

x

orientation measurements (N.O.) are very sensible alloys. We will discuss some details mainly the tempe- to the local symmetry seen by the radioactive nuclei, rature and field dependence.

For the

137m

Ce nuclei and a paramagnetic cerium ion in an isotropic doublet T

7

ground state, the

axial gamma ray anisotropy, E(0), along the applied 2. Simple model. — The model takes into account field H must be positive (£(0) is defined as the diffe- three main terms. Firstly a correlation term (k

B

T

k

) rence between the number of the 255 keV gamma of one ion should lead to a Kondo singlet at low rays emitted at high and low temperatures nor- temperature (its temperature dependence is taken malized by the high temperature counting). In low from the resonance model of Schotte and Schotte [6]).

fields, the main points are that for In

³

Ce and Al

²

Ce, Secondly an exchange term (J) between the ions

£(0) < 0 whereas for Sn

3

Ce, Al

3

Ce, Pb

3

Ce, E(0) > 0. may breakdown the non-magnetic state of the ion.

The first situation is well explained by an antiferro- Thirdly, a weak crystalline anisotropy term (K

0

) magnetic-like ordered ground state; in low fields, is introduced in order to take into account that the the local moments choose to be perpendicular to the r

⁷

doublet is not completely isotropic due to the applied field, the sign of £(0) is reversed since the applied field mixing of the crystal field levels (the equatorial and axial anisotropics have opposite notations are those of reference [6]). In a molecular sign [1]. The second situation seems to describe a field approximation, the occurrence of a long range paramagnetic behaviour as shows a comparison with magnetic structure can be easily discussed as a function the results obtained on the dilute alloy of Al

²

LaCe of the three parameters (T

^k

, J, K

⁰

) ; furthermore an wellknown as a Kondo state of the cerium ions attempt can be made to derive the electronic specific (T

k

~ 400 mK). The case of Pb

3

Ce is not clear as, heat (yT) assuming on each site the Kondo behaviour in low fields, the gamma ray anisotropy is rather of the ion :

weak. Recent magnetization measurements seem to

indicate an antiferromagnetic ordering near 1 K [2]. _ 2_Jt B T*

k

Experimentally, Al

²

Ce is the most studied

^y

° 3 (k

^B

T

^k

)

²

+ (gfi

^B

H)

²

compound by other measurements. Barbara et al. [3]

have reported the occurrence of a long range magnetic which is submitted to the fictitious field produced ordering of a sinusoidal mode by neutron measure- by the other ions. The discussion will be restricted ments below the maximum of the specific heat anomaly to i) a linear chain of cerium ions, ii) a first exchange at T

M

= 3.8 K. The absence of any other specific neighbour /

t

ferromagnetic and a second neighbour J

2

heat anomaly at lower temperature [4], the persistence antiferromagnetic interactions, iii) the special case of the sinusoidal mode down TJ10 [3] and the obser- y | / |*

w h e r e a n

helicoidal structure occurs for vation by N.O. of an ordering down to 5 mK strongly 4

support the persistence of the same structure at 0 K. T

^k

= 0. We have chosen to draw the phase diagram This behaviour is completely unusual for local for constant values of the exchange and anisotropy moments in a r

⁷

doublet ground state. parameters, the variables being the temperature, the In order to understand this phenomena, we have applied field (H) and T

k

. The scale of the energy is recently derived a simple model [5] which is similar given by reference to the exchange term J

l

and by to that used by Bredl et al. [4] for the interpretation assuming an isotropic magnetic moment of 1 u

B

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19795112

(3)

LOW TEMPERATURE PROPERTIES OF THE ABNORMAL CERIUM COMPOUNDS C5-329

Finally a weak J, interaction between the third neigh- bour is added in order to visualize the interchain coupling, its effect is marked only on the magnetiza- tion behaviour.

Phase diagram (T, Tk for H

=

0).

At 0 K, two different magnetic structures may

1

occur, their period is defined by the J parameters.

For Tk > Tk2 a non-magnetic ground state is found,

for Tkl Tk < Tk2 a sinusoldal structure, for Tk < Tkl a helicoidal structure. The temperature boundary is reported on the figure 1 with the following para- meters J,

=

- 1, J ,

=

0.4, KO

=

0.07. The figure 2 shows the low temperature dependence of the sus- ceptibility X of y and of the reduced amplitude of the magnetization M/pB which is carried by each site

assuming a period of eight ions. The Kondo sus-

Fig. 2. - y, X , M / p B dependence as a function of T, at H = 0,

ceptibility law of one isolated ion drawn on the figure

^T^<T,. The single ion value q,, X, is drawn by comparison. The,

is equal to

: zero moment carried by one site in the S domain is not represented.

2 1

x o = ; n T .

B k

Hh

M

//H

Comparatively to the single ion law, the main

points are

:

i) the strong increase of X near Tk2 and its decrease for Tk

+

0

;

ii) the maximum of

y

at Oe5 Tk2.; iii) the ratio of

y / ~

near from 1 in the sinusoldal reglme which goes to zero for T,

+

0 and is always lower than the single ion behaviour even in the non- magnetic regime (y0/x,

¹^:

3.3).

H T A

k6 TK

k

T

B

K1 1 k T

B K2 Fig. 3. - Phase diagram (H, T, at T = 0).

the dependence of the critical temperature does not

0.78 TK

follow that of the figure 1 but that a maxima occur

for a given value of Tk.

The authors would like to thank Dr J. X. BoucherIe, Dr B. Coqblin, Dr G . Chouteau, Dr J. Peyrard,

k g T~

Dr J. Odin and Dr R. Tournier for stimulating dis-

k T 1

B K1 k T

B K 2

cussions.

Fig. 1.

-

Phase diagram (T, T, at H = 0), H, S and N.M. are used for helicoidal, sinusoidal and non-magnetic states.

Phase diagram (H, Tk, for T

=

0).

At 0 K, the magnetic field leads to a metamagnetic- like transition as is reported on the figure 3

;

for low values of Tk intermediate configurations may occur.

PRESSURE

EFFECTS. -

Finally pressure effects can be predicted assuming a relation between Tk and J . The situation is similar from that discussed by Larsen

et

al. [7] for the transition from spin glass to Kondo behaviour in dilute alloys. For example, taking into account the relation (T,, J), it can be predicted that

References

[l] BENOIT, A., FLOUQUET, J. and RIBAULT, M., J. Physique Lett.

39 (1978) 63.

[2] SERINI, J. G., Private Communication.

[3] BARBARA, B., BOUCHERLE, J. X., BUEVOZ, J. L., ROSSIGNOL, M. F. and SCHWEIZER, J., Solid State Commun. 24 (1977) 481 and to be published.

[4] BREDL, C. D., S T E G L ~ H , F., SCHOTTE, K., Z. Phys. B 29 (1978) 327.

[5] BENOIT, A., FLOUQUET, J., RIBAULT, M., FLOUQUET, F., CHOU- TEAU, G . and TOURNIER, R., J . Physique h t t . 39 (1978) 94.

[6] SCHOTTE, K. D. and SCHOTTE, Z. R., Phys. Lett. 55A (1975) 38.

[7] LARSEN, Z. R., SCHILLING, J. S., FORD,^. J. and MYDOSH, J. A., Physica 86-88B (1977) 846.

Low temperature properties of the abnormal cerium compounds

HAL Id: jpa-00218896

https://hal.archives-ouvertes.fr/jpa-00218896

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.

Low temperature properties of the abnormal cerium compounds

Angélique Benoit, J. Flouquet, M. Ribault

To cite this version:

Angélique Benoit, J. Flouquet, M. Ribault. Low temperature properties of the abnor- mal cerium compounds. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-328-C5-329.

�10.1051/jphyscol:19795112�. �jpa-00218896�

Colloque C5, supplément au n° 5, Tome 40, Mai 1979, page C5-328

Low temperature properties of the abnormal cerium compounds

A. Benoit, J. Flouquet, M. Ribault

Résumé. — Après le rappel des résultats d'orientation nucléaire obtenus sur les composés de cérium, nous dis- cutons leurs propriétés de basse température notamment le diagramme de phase champ magnétique-température critique.

1. Nuclear orientation results. — The nuclear of the magnetic properties of the Al

La

Ce

_

orientation measurements (N.O.) are very sensible alloys. We will discuss some details mainly the tempe- to the local symmetry seen by the radioactive nuclei, rature and field dependence.

For the

Ce nuclei and a paramagnetic cerium ion in an isotropic doublet T

ground state, the

axial gamma ray anisotropy, E(0), along the applied 2. Simple model. — The model takes into account field H must be positive (£(0) is defined as the diffe- three main terms. Firstly a correlation term (k

T

) rence between the number of the 255 keV gamma of one ion should lead to a Kondo singlet at low rays emitted at high and low temperatures nor- temperature (its temperature dependence is taken malized by the high temperature counting). In low from the resonance model of Schotte and Schotte [6]).

fields, the main points are that for In

Ce and Al

Ce, Secondly an exchange term (J) between the ions

£(0) < 0 whereas for Sn

Ce, Al

Ce, Pb

Ce, E(0) > 0. may breakdown the non-magnetic state of the ion.

The first situation is well explained by an antiferro- Thirdly, a weak crystalline anisotropy term (K

) magnetic-like ordered ground state; in low fields, is introduced in order to take into account that the the local moments choose to be perpendicular to the r

LaCe of the three parameters (T

, J, K

) ; furthermore an wellknown as a Kondo state of the cerium ions attempt can be made to derive the electronic specific (T

~ 400 mK). The case of Pb

Ce is not clear as, heat (yT) assuming on each site the Kondo behaviour in low fields, the gamma ray anisotropy is rather of the ion :

weak. Recent magnetization measurements seem to

indicate an antiferromagnetic ordering near 1 K [2]. _ 2_Jt *B T

Experimentally, Al

Ce is the most studied

° 3 (k

T

)

+ (gfi

H)

compound by other measurements. Barbara et al. [3]

= 3.8 K. The absence of any other specific neighbour /

ferromagnetic and a second neighbour J

heat anomaly at lower temperature [4], the persistence antiferromagnetic interactions, iii) the special case of the sinusoidal mode down TJ10 [3] and the obser- y * | / |

helicoidal structure occurs for vation by N.O. of an ordering down to 5 mK strongly 4

support the persistence of the same structure at 0 K. T

= 0. We have chosen to draw the phase diagram This behaviour is completely unusual for local for constant values of the exchange and anisotropy moments in a r

doublet ground state. parameters, the variables being the temperature, the In order to understand this phenomena, we have applied field (H) and T

. The scale of the energy is recently derived a simple model [5] which is similar given by reference to the exchange term J

and by to that used by Bredl et al. [4] for the interpretation assuming an isotropic magnetic moment of 1 u

.

Finally a weak J, interaction between the third neigh- bour is added in order to visualize the interchain coupling, its effect is marked only on the magnetiza- tion behaviour.

Phase diagram (T, Tk for H

0).

At 0 K, two different magnetic structures may

occur, their period is defined by the J parameters.

For Tk > Tk2 a non-magnetic ground state is found,

for Tkl Tk < Tk2 a sinusoldal structure, for Tk < Tkl a helicoidal structure. The temperature boundary is reported on the figure 1 with the following para- meters J,

- 1, J ,

0.4, KO

0.07. The figure 2 shows the low temperature dependence of the sus- ceptibility X of y and of the reduced amplitude of the magnetization M/pB which is carried by each site

assuming a period of eight ions. The Kondo sus-

ceptibility law of one isolated ion drawn on the figure

is equal to

2 1

Hh

M

Comparatively to the single ion law, the main

points are

i) the strong increase of X near Tk2 and its decrease for Tk

0

indicate an antiferromagnetic ordering near 1 K [2]. _ 2_Jt B T*

heat anomaly at lower temperature [4], the persistence antiferromagnetic interactions, iii) the special case of the sinusoidal mode down TJ10 [3] and the obser- y | / |*