HAL Id: jpa-00218641
https://hal.archives-ouvertes.fr/jpa-00218641
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.
SPIN TEXTURE DETERMINATION IN
AMORPHOUS Fe80B20 BY LINEARLY POLARIZED RECOIL-FREE γ -RAYS
U. Gonser, M. Ghafari, H. Wagner, H. Fischer
To cite this version:
U. Gonser, M. Ghafari, H. Wagner, H. Fischer. SPIN TEXTURE DETERMINATION IN AMOR-
PHOUS Fe80B20 BY LINEARLY POLARIZED RECOIL-FREE γ-RAYS. Journal de Physique Col-
loques, 1979, 40 (C2), pp.C2-126-C2-128. �10.1051/jphyscol:1979243�. �jpa-00218641�
JOURNAL DE PHYSIQUE Colloque C2, suppldment au n O 3, Tome 40, mars 1979, page C2-126
SPIN TEXTURE DETERMINATION
IN
AMORPHOUS Fe80B20 BYLINEARLY
POLARIZED RECOIL-FREETRAYS
U. Gonser, M. Ghafari, H.G. Wagner and H. Fischer
Fachbereich Angewmdte Physik, U n i v e r s i t d t d e s SaarZmdes, 6600 Saarbriicken, Germany
Rbsum6.- Pour le metglas FeeoBno la texture des spins a &tb analysde en mesurant les intensitds de 180 raies en utilisant une technique de rayons 'y linsairement polaris&.
Abstract.- By use of linearly polarized y-rays the preferred orientation of the spins (spin texture) in the metglass F e e ~ B n o has been analyzed evaluating the relative line intensities of 180 lines.
When a transversely magnetized 5 7 ~ o
-
a-Fe rather complicated, but a pronounced difference is source is observed in the direction perpendicular to clearly discernible.the applied field HS all six emitted lines are li- nearly polarized. The plane of polarization of the y-rays from the Am = 2 1 transitions is perpendicu- lar to the plane of polarization of the y-rays from the dm = 0 transitions. In conjunction with a magne- tic six line absorber one expects 36 lines. The con- dition of absorption depends mainly on the polariza- tion of the corresponding transitions in the source (polarizer) and absorber (analyzer). If transverse magnetic fields in the source HS and absorber HA are oriented parallel (HS 1 1 HA) or perpendicular (Hd HA) to each other, we expect for the two cases 20 and 16 lines, respectively. For discussion of the origin of the lines in the rather complex spectra the fol- lowing nomenclature was adopted : the six emission lines are designated by capital letters A, B, C, D, E, F and the six absorption lines by the Greek let- ters a , b , y , 6 , ~ , q , in ascending order of energy.
A spectrum of amorphous Fee oBno (Metglas 2605) obtained with a single-line'source /1,2/ is shown in figure 1. The broad spectral lines indicating a magnetic hyperfine distribution were fitted by cor- relating the distribution function from the Bernal /3/ model of the five most probable next-nearest neighbor coordinations (8, 9, 10, 1 1 and 12) with appropriate hyperfine fields (dashed in figure I ) /2/. The relative line intensities indicate that the spins are oriented close to the plane ofthe FeeoBzo ribbon. Using polarized y-rays we can get further information regarding any preferred spin orientation (texture) within the plane of the ribbon. For this purpose HS and the ribbon direction B of the metglass absorber were arranged first parallel (HSIJ R) and then perpendicular (HSIR), to each other, see figu- re 2. If no texture is present in the FeeoBno sample the two spectra should be identical. The spectra are
V e l o c i t y I m m l s l
Fig. 1 : Spectrum of amorphous FesoHno at room tem- perature (relative to a-Fe)
.
If, for simplicity, we treat the spectrum in figure 1 as a six-line pattern with a certain avera- ge hyperfine field, then we expect 36 lines whose positions are easily calculated by adding and sub- tracting the energies of the resonances in source andabsorber. The two stick diagrams in the center of
figure 2 represent the two extreme cases : HS1[ HA and H HA resulting in 20 or 16 lines, respectively.
d
The lengths of the bars indicate the expected rela- tive line intensities. If, for instance, the spins in the amorphous metal were aligned uniquely either along the ribbon direction R or perpendicular to it, the direction of the source 'magnetization eithter parallel or perpendicular to R, would determinewhich set of lines indicated in the stick diagrams would be observed. In other words, the resonances in the two spectra would be mutually exclusive. In compa- ring the observed spectra of figure 2 with the stick diagrams, however, it becomes evident that both the
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979243
20 line and the 16-line pattern are present in both spectra, although in different relative amounts. By inspection it is easy to see that the upper spectrum
(HS [IR) agrees better with the stick diagram for HSll HA and correspondingly that the lower spectrum
(HSLR) agrees better with the stick diagram for Hs lH*.
Fig. 2 : Spectra of amorphous FesoB20 at room tempe- rature obtained with a transversely magnetized "CO- a-Fe source. Stick diagrams and nomenclature are described in the text.
Therefore, we can conclude that hhe spins in the metglass are preferentially oriented in the ribbon direction R.
A quantitative result was obtained by computer analysis. The FeeoB~o spectrum (Fig. I ) was treated as a superposition of five subspectra (30 lines) corresponding to the five predominant atomic coordi- nations. Accordingly, the number of lines in the spectra obtained with the six-line source increased to 6x30 = 180 Cnot shown as stick digarams). Assu- ming that the five hyperfine fields all reflect the same polarization, the two spectra could be computer fitted rather well by taking into account all 180 resonances (solid lines in figure 2). From this ana- lysis a "hypothetical" spin orientation in the absor- ber of 34' to the ribbon direction R could be deter- mined. This angle can be regarded as an average value
of the preferred orientation of the spin relative to R. A more realistic representation of the spin tex- ture distribution D is shown in figure 3 . This fi- gure is the result of a calculation based on our experimental data and it represents the minimum tex- ture / 4 , 5 / in the sense that the true distribution may have additional structure beyond what is shown, but this experimental method is inherently incapable of detecting it.
Fig. 3 : Experimentally determined distribution of the spin orientations D. 8 is the angle between the spin and the normal to the ribbon plane (y-ray di- rection). @is the angle between the projection of the spins on the ribbon plane and the ribbon direction R.
Recently additional experiments with amorphous Fet,~NiboPlt+Bs.have been made. In the original state the spins were nearly randomly distributed in the plane of the ribbon. However, drastic changes in the spectral line intensities can be produced by applying a tensile stress a along the ribbon direction R as shown in figure 4 . Due to the stress the spins align themselves along R in a nearly unique magnetization direction. Consequently, the patterns corresponding to the two stick diagrams are seen separately in the spectra for HSll a, R and H
&
a, R.Acknowledgements.- This work was supported by the DFG.
C2- 128 JOURNAL DE PHYSIQUE
References
/I/ Chien, C.L., Hasegawa, R., J. Appl. Phys.
2
(1976) 2234.
/2/ Gonser, U., Ghafari, M., Wagner, H.G., J. Magn.
Mag. Mater.
5
(1978) 175./3/ Bernal, J.D., Nature
185
(1960) 68./4/ Gonser, U., Pfannes, H.D., J. Physique Colloq.35 (1974) 06-1 13.
/ 5 / Pfannes, H.D., Fischer, H., Appl. Phys.
2
(1977)325.
Fig. 4 : Spectra of a stressed ribbon of amorphous FeroNi40PlrBs at room tem eratures obtained with a transversely magnetized "Co in a-Pe source.
