NUCLEAR RELAXATION OF Ag109m IN IRON DETECTED BY NUCLEAR ORIENTATION

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NUCLEAR RELAXATION OF Ag109m IN IRON DETECTED BY NUCLEAR ORIENTATION

N. Stone, R. Fox, F. Hartmann-Boutron, D. Spanjaard

To cite this version:

N. Stone, R. Fox, F. Hartmann-Boutron, D. Spanjaard. NUCLEAR RELAXATION OF Ag109m IN IRON DETECTED BY NUCLEAR ORIENTATION. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-897-C1-898. �10.1051/jphyscol:19711318�. �jpa-00214350�

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RESONANCE ET RELAXA TION DANS LES METAUX ET ALLIAGES

NUCLEAR RELAXATION OF AglOgm

IN IRON DETECTED BY NUCLEAR ORIENTATION

N. J. STONE and R. A. FOX Clarendon Laboratory, Oxford, England F. HARTMANN-BOUTRON and D. SPANJAARD

Laboratoire de Physique des Solides, Orsay, France

RCsurne. - L'etude de I'orientation nucleaire de Ag1ogm dans Fe a T

-

^0,015^OK^{a conduit}^Aune dependance anor- male du champ hyperfin apparent en fonction de la temperature. Cet effet est interprkte par un rkalignement partiel des noyaux pendant le temps de vie de 40 secondes de l'etat intermkdiaire. Puisque dans les conditions de I'expkrience h!, 3 kT, les theories de la relaxation nucleaire d'impuretb dissoutes dans les metaux ont ete Ctendues i la region oh I'approxlmatlon des hautes temp6ratures n'est pas valable. A I'aide des resultats on a pu obtenir les valeurs du champ hyperfin reel et de T I T pour Ag dans Fe.

Abstract. - A nuclear orientation study of Aglogm in Fe at T

-

^0.015^OKhas led to an unusual temperature dependence of the apparent hyperfine field. This effect has been interpreted as a partial realignment of the nucleus during the lifetime of the 40 second intermediate nuclear state. Since in the conditions of the experiment hvn 3 kT, theories for the nuclear relaxation of dilute impurities in metals have been extended to the region where the high temperature approximation is not valid. The experimental results have been analysed to give values of T I T and the real hiperfine field for Ag In Fe.

There has been recent interest in nuclear spinlattice relaxation in ferromagnetic metals at very low temperatures (0.01 OK). Two methods of experimentally investigating this phenomenon have been suggested and applied to several cases (1) (2). However both these methods suffer from the disadvantage that the initial state of the system before relaxation is unknown, so that a further parameter is introduced into any theoretical fit to the results.

A system in which this disadvantage is absent occurs for the metastable 88 keV (712 +) state of lo9Agm which is populated by electronic capture from lo9Cd (512 +). Knowledge of the hiperfine' splitting for lo9Cd in Fe, together with the lattice temperature, enables the nuclear level populations of l o g Cd to be calculated and hence also the initial populations in the 40s lifetime 88 keV state of '09Ag.

The hyperfine interaction in l o 9 ~ g differs in sign from that of lo9cd, so that these initial populations happen to be very far from thermal equilibrium. Since the lifetime of the 88 keV state is comparable to typical nuclear relaxation times at the temperatures of interest, the partial relaxation of the populations in the intermediate state will thus severely affect the measured anisotropy. Neglecting it would lead to a temperature depend hyperfine field.

In order to take this kind of relaxation effect into account, previous studies has used a spin temperature model, [4] but this model is unlikely to be valid in the case reported here, because of the very high dilution of the lo9Agm nuclei*. We shall therefore use the theory of ref. [3] which assumes independent relaxations of the different nuclei through their interaction with the conduction electrons

( I ) The most effective interaction for establishing a spin

temperature at low concentrations would be the Suhl-Naka- mura interaction, but its effect are certainly negligible below

1 ppm while the concentration of A g l o g m nuclei is

-

^10-10.

In these conditions one can show that the evolution of the populations of the intermediate nuclear state is given by

1

- TI = c coth

(*)

_{2 k ~ T}_qq,^1m^{~ ( q ,}^O,^an) ⁽⁵⁾

in which C Imx(q, q', w,) is the imaginary part (am,) of the transverse electronic susceptibilityat the impu- 94'

rity site. This susceptibility being practically temperature independent, l / T l has the form

- - -- _coth- ^hwn TI 2 AkB 2 kB T

which, at high temperatures, reduces to the Korringa law : T I T = cte.

Having solved the equations of evolution of the populations one gets the ray anisotropy :

w ₌

j

03 ^{dl e-'jr}

0 C ^Bk(t)^FkP~(COS 6 ) (7)

t even

in which the BLs are related to the populations in the conventional way :

and ^tis the lifetime of the intermediate state.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711318

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C 1 - 898 N. J. STONE AND R. A. FOX, F. HARTMANN-BOUTRON AND D. SPANJAARD

In order to interpret the experimental data, the and, after correcting for the hyperfine anomaly, the equations of evolution of the populations (2) have results of this experiment would lead to

been solved numerically using a computer. A first H, = 441 + ^{5 kOe}

two parameters fit for 1/T, ( A and on in Eq. (6))

had yielded A ^N0.5 and Hn for '09Agm, in very good agreement with the first determination.

(hyperfine field) = 440 +40 kOe. Using this last value of H,,, a one parameter fit has been done (Fig. 1) leading to an excellent agreement Since then, resonant destruction of nuclear orien- with experimental data taking A = 0.48 ⁺0.03 set.

tation of "OAgm in the same matrix has been observed ;

in eq. (6). Figure exhibits the values of resulting

THEORETICAL CURVES :

H for A ~ L41 k@ ~ ~ ~ ~ =

-

^T,^;48.5 tanh (0099) s T

70 -

60- Applted held = 5 kOe

s o - S t a t t s t ~ c a l + error LO -

30-

from fitting the data at each lattice temperature, plotted against the lattice temperature. The data

10 20 W 40 50 60 70

9y ^? ^K show good agreement with the theoretical tanh (tio,/2 k, 2') temperature dependence. The deviation

FIG. 1 . from the linear Korringa law is appreciable.

References

111 REID (P. G . E.). SOTI ITM.) and STONE (N. J.). Phvsics of tv~onra~hical errors : an erratum has been

. - - ^- ^, .

titters, 1967, 25 A; 450. publiihea, solid State ~ o m m . , 1970, 8 , 2 0 [2] BREWER (W. D.), SHIRLEY (D. A.) and TEMPLETON (J. E.), [4] SHIRLEY (D. A.), HyperJine Structure and Nuclear

Physics letters, 1968, 27 A, 81. Radiations, North Holland, 1968, 843.

[3] SPANJAARD (D.) and HARTMANN-BO~TRON (F.), Solid [5] KORRINGA (J.), Physica 1950, 16, 601.

State Comm., 1970. 8, 233. This paper has a lot