SUPERTRANSFERRED MAGNETIC FIELDS ACTING ON Sn119 IN TIN SUBSTITUTED IRON GARNET SYSTEMS

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SUPERTRANSFERRED MAGNETIC FIELDS ACTING ON Sn119 IN TIN SUBSTITUTED IRON

GARNET SYSTEMS

E. Bauminger, I. Nowik, S. Ofer

To cite this version:

E. Bauminger, I. Nowik, S. Ofer. SUPERTRANSFERRED MAGNETIC FIELDS ACTING ON Sn119 IN TIN SUBSTITUTED IRON GARNET SYSTEMS. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-913-C1-914. �10.1051/jphyscol:19711324�. �jpa-00214357�

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EFFET MOSSBAUER DANS LES COMPOSES DE TERRES RARES ET DANS LES COMPOSES D'A CTINIDES

SUPERTRANSFERRED MAGNETIC FIELDS ACTING ON Snl

^{l 9}

IN TIN SUBSTITUTED IRON GARNET SYSTEMS

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E. R. BAUMINGER, I. NOWIK and S. OFER Department of Physics, The Hebrew University, Jerusalem, Israel

Rksumk. - Nous avons Ctudie le noyau de Sn119 dans les grenats de formule generale {CaZYs-z ) [SnZFez-Zl (Fed0 I 2

a I'aide de mesures Mossbauer a 4,2 OK. Le spectre obtenu pour 1'echantillon x = 0,l indique qu'un champ magnetique bien dCfini agit sur lenoyau de l'etain. A des taux de substitution plus eleves (x > 0,5), on obtient des spectres plus complexes qui suggerent la presence de champs varies.

Les spectres expirimentaux ont Cte reconstruits a partir d'un modele publie ricemment qui tient compte de I'incli- naison et du renversement des spins du fer dus a la substitution diamagnktique.

Abstract. - Mossbauer studies of Sn119 in { CaZY3-= ) [SnzFez-z] (Fes)O12 at 4.2 OK were performed. The spectrum obtained with the x = 0.1 sample indicates that a very well defined magnetic field is acting on the tin nuclei. As the amount of substitution increases, the spectra show a distribution of magnetic hyperfine fields acting on the Sn nuclei.

The observed spectra have been reproduced using a recently published model, which takes into account canting and flipping of iron spins due to diamagnetic substitution.

Mossbauer studies of the 23.8 keV transition of Sn119 in { CaxY3-, ) [SnxFe2-,] (Fe,)O,, at 77 and 295 OK were carried out by Belov and Lyubutin [I].

In the present work similar measurements for various values of x between 0.1 and 1.5 were performed at 4.2 OK, where all samples used were in magnetic satu- ration. The spectra obtained are shown in figure 1.

I I I I

-2 -1 0 1 2

V E L O C I T Y (cm/s)

FIG. 1. - Experimental Mossbauer spectra of the 23.8 keV transition in Sn119 in { CazY ^3-z} [SnzFe2-~] (Fe3)Olz.

(*) Supported in part by the Stiftung Volkswagenwerk.

The x = 0.1 sample exhibits a very well resolved spectrum. This spectrum corresponds to a magnetic hyperfine field of 209.5

k

0.5 kOe, acting on the tin nuclei. The spectra of the samples in which x > 0.5 are complicated and do not correspond to one defined hyperfine field. This result seems strange since from recent Mossbauer studies of Sn119 in

it is known that more than 95

%

of the magnetic field acting on the Sn119 nuclei is produced by the tetrahedral iron neighbors, which are not substituted in the compounds investigated in the present work [2]. It is possible to explain the spectra shown in figure 1 by the recently published model [3, 41, according to which the substitution of tin in the octa- hedral site causes ⁽⁽canting D [4] of tetrahedral iron spins if three out of the four nearest neighbors of a tetrahedral iron ion are substituted by a non magnetic ion - and flipping of the tetrahedral iron spin if all four nearest neighbors are substituted. This canting and flipping creates many inequivalent tin nuclei according to the distribution of the spin directions of their first nearest iron neighbors. For x

<

0.1 each iron out of the six first nearest neighbors contributes equally and independently a field of h, ⁼33 kOe [2]

(more than 90

%

of the field is produced by the tetrahedral first nearest iron neighbors). If the number of canted and flipped spins among the first nearest' iron neighbors of a tin nucleus is K and L respectively, then the hyperfine field acting on that nucleus will be given by

The angle u is the average canting angle defined in reference [3] and the canted spins contribute to H(K, L) only through their longitudinal compo- nents [4]. h, is the residual contribution of iron ions not belonging t o the first neighboring shell. The rela-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711324

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C 1

-

⁹¹⁴ E. R. BAUMINGER, I. N O W K A N D S. OFER

tive probability of such a hyperfine field is given by

where PI and Po are the probabilities of a tetrahedral iron spin to be canted or flipped respectively [3].

In the present case, taking into account the fact that each relevant Fe ion has at least one diamagnetic nearest neighbor (the Sn ion responsible for the observed Mossbauer absorption) the probabilities are given by Po = ( ~ 1 2 ) ~ and PI = 3 ( ~ / 2 ) ~ (1 - x/2).

Formulas (1) and (2) were used to calculate theoretical Mossbauer spectra for various values of x taking

the average canting angle a as a free parameter. It was found that a = 530 gives quite good agreement with the experimental observations (Fig. 1 and Fig. 2).

We have also calculated the average magnetic hyperfine field on the Sn nuclei assuming that a = 530.

This field is given by

The experimental value of Hav,(x) was determined by measuring the distance between the centroids of the positive and negative velocity parts of the spectra.

I n figure 3, the experimental and theoretical results

V E L O C I T Y , cm/s

FIG. 2. -Theoretical Mossbauer spectra of the 23.8 keV transition in Snl19 in { CazY ^3-z ) [SnzFe2-zl (Fe3)012, assuming

an average canting angle of 53O.

FIG. 3. --The average magnetic hyperfine ficld acting on Sn119 in { CazY3-, } [SnzI:e2-z] (Fe3)012. The solid curve is predicted by the theory outlined in the text assuming a = 53O.

for Ha,, are shown. It is seen that the agreement is very good. It is not surprising that a simple model predicts better average observables (like Hav,(x), M,(x) [3] and T,(x) [3]) than the most detailed struc- ture of a Mossbauer spectrum. The above simple model has also been used to explain the Eut51 spectra in the equivalent system ( Eu, ) [Sc,Fe,-,] (Fe3)OI2

[5]. For this system also a canting angle a of

-

⁵⁰⁰

gives good agreement between the experimental and theoretical results.

References

[I] BELOV (K. P.) and L Y U B U ~ N (I. S.), Soviet Physics [3] NOWIK (I.), J. Appl. Phys., 1969, 40, 5184.

JETP, 1966, 22, 518. [4] LEBENBAUM (D.) and NOWIK (I.), Phys. Letters, 1970, [2] NOWIK (I.), BAUMINGER (E. R.), HESS (J.), MUSTA- 31A, 373.

CHI (A.) and OFER (S.), to be published'in Physics [5] BAUMINGER (E. R.), NOWIK (I.) and OFER (S.), Phys.

Letters, 1970. Letters, 1969, 29 A, 328.