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MAGNETISM OF IRON INTERFACE IN CONTACT WITH VANADIUM
T. Shinjo, N. Hosoito, K. Kawaguchi, T. Takada, Y. Endoh
To cite this version:
T. Shinjo, N. Hosoito, K. Kawaguchi, T. Takada, Y. Endoh. MAGNETISM OF IRON INTERFACE IN CONTACT WITH VANADIUM. Journal de Physique Colloques, 1984, 45 (C5), pp.C5-361-C5-365.
�10.1051/jphyscol:1984554�. �jpa-00224172�
M A G N E T I S M OF IRON I N T E R F A C E IN C O N T A C T W I T H V A N A D I U M
T . S h i n j o , N. Hosoito, K. Kawaguchi, T . Takada and Y. ~ n d o h *
I n s t i t u t e for ChernicaZ Research, Kyoto University, U j i , Kyoto-fu 611, Japan
* ~ e ~ a r t m e n t of Physics, Tohoku University, Sendai 9 8 0 , Japan
s sum& - Les propri&t&s magngtiques d'interfaces Fe-V sont 6tudi6es par combinaison de la spectroscopie MBssbauer du 5 7 ~ e et de la diffraction neutrons. L'aimantatio? des atomes de £er dans la couche superficielle est nettement reduite par rapport
2 la valeur massive.
Abstract - 5 7 ~ e MBssbauer spectroscopy and neutron diffraction were applied to investigate the magnetic properties of Fe inter- faces in contact with V. The magnetization at the outermost Fe atom layer is significantly reduced with respect to the bulk atom.
I - INTRODUCTION
We have studied the magnetic properties of Fe interfaces in con- tact with various materials such as MgF2, MgO, Sb, Cu and Pd, by means of Mdssbauer spectroscopy, and showed how the magnetization of the interface Fe atom depends on the coating materials /l-3/.
Very recently we have published a study on Fe-Sb interfaces by using not only 5 7 ~ e Mdssbauer spectroscopy but also neutron diffraction, ferromagnetic resonance and l 2 1 ~ b MBssbauer spectroscopy / 4 / .
In this paper we report some experimental results on Fe-V inter- faces. Samples were thin multilayered films prepared by UHV deposition techniques. Typical structures of the prepared samples are
illustrated in Fig. 1.
The vacuum during the (a) deposition was in the
range of 10 7 ~ a .
The details of the sample preparation are similar with those described in
the preceding paper / 4 / . Fe (38)
m y l a r Fig. 1 - Structure of samples
(a) Surface-selectively enriched sample;
b changing the thickness of the second layer ( ' X R ) , the location of the Mdssbauer microprobe, 5 7 ~ e , is varied.
(b) Multilayered film with artificial superstructure.
mylar
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984554
C5-362 JOURNAL DE PHYSIQUE
I1 - SURFACE-SELECTIVELY EFIRICHED SAMPLE: M~SSBAUER SPECTROSCOPY Using the samples as shown in Fig. l(a), we are able to observe the hyperfine field as a function of the distance from the interface boundary, in a rather thick Fe film. Thus the interface effect excluding any thickness effect is investigated. The values of "X" in the prepared samples were 0, 3.5 and 72, respectively.
Assuming ideally uniform and flat films and absence of diffusion at the interface, the MBssbauer spectra of these samples should reveal the situations at the depth ranges of 0-3.5, 3.5-7 and 7-10.52, respectively.
The MBssbauer spectra at 4.2K are shown in Pig. 2.
The spectrum for the depth range of 7-10.52 is a normal six-line pattern. This suggests that the interface effect does not extend to this depth. The spectrum for the intermediate depth range is also a six-line pattern but with sliqhtly broadened widths, suggesting the existence of reduced h perfine field components.
The spectrum for 0-3.55 is very broad. The hyperfine field has a wide distribution at the topmost
interface region.
The solid line drawn in the figure
is the best fit with a hyperfine I field distribution as in the a inserted figure. Here the isomer
shift is assumed constant and quadrupole interaction was
.,,/
Q--(
0 200 1100
? -
neglected. Although the distribu- H / k0e
tion of hyperfine field is wide
and rather continuous, we can .,. , .. .... . . identify
approximately two peaks at 240kOe in the and curve,
kr
320kOe, respectively. . ' . . . - .
If the Fe layer with the 0 - 3 ,5W .... . . :' -'
thickness of 3.52 is uniform,
this thickness corresponds roughly ':/,..s:.<~ ,..:L. .. .;
, +'.';. .y .-.. .AV.
to two atomic layers. It is then , . . . . . ,.,:>, ,.*..,:::", .-: i?.,: . .. . ,S-.. . , ,: . ,
. . . . , . . . reasonable to attribute two hyper- . . . i : , "
.. . . .
fine fields to two interface atom , . . . . .
layers; 240kOe represents the 3 . 5 - 78 ,
hyperfine field at the top inter-
face atom layer and 320kOe, the ~VLRU,
value at the second layer. I , . . . h \ . \ .. A, .. A-?,, . . ,-.h4 f-hGriY4 Assuming magnetization propor- : . . .. .. . .. .. .
tional to the hyperfine field, . . . 3
the reduction at the top interface
layer would be 30% in the average. 7 - 10.58 : However the second interface layer
has nearly the bulk value (340kOe), 1 1 I I ~ I I I I ~ I I I I ~ I I I I ~
thus having a magnetization -5 0 5
comparable to the standard value. VELOCITY / Mn S-'
The perturbation of magnetization
due to an interface effect would be Fig. 2 - MBssbauer absorption negligible already at the second spectra at 4 . 2 K for the depth
layer. ranges of 0-3.5, 3.5-7 and 7-
Measurements were also made at 10 - 521 respectively -
300K: Significant temperature Solid line drawn with the dependence was not observed. spectrum for 0-3.52 is a
calculated curve with a distrib- ution of hyperfine field as in the inserted fiaure.
By alternate deposition of Fe and V, multilayered films with artificial super- structure, as shown in Fig. l(b), were
prepared. The thicknesses of individual . . layers were controlled by automatic
shutters connected with a programmable thickness monitor. Various combinations were examined by changing the single layer thicknesses of Fe and V in the range
. . . between 2 and 602 ("P" and "Q" in Fig-lb). ... :-..
4.2K . . . ., .
The artificial superstructure established in the multilayered film was
....
confirmed from X-ray diffraction. ... ... ....-. :.:,
The shortest wavelength of the composi- : - ; - . :./... . ./.. . :-..':: ;' ....: ... . -. .
. . . tional modulation observed by X-ray
( a ) y. .:. . . . . . - measurement was 128, e.g. Fe (42) -~(82).
The Bragg reflection due to the artificial 300K period was observed in a small angle
region and satellite peaks also were .. .
:.
...
. . -..
observed near the foudamental Brag4 peak (110) of the bcc structure. . . . . . . . . . . . . . . . . . . . . .
X-ray diffraction patterns suggest that, . . . _ ... . . . _.._
as a whole, the multilayered films keep , ,
, , l , , , , , , , , , , , ,
a bcc structure and the (110) planes are - 5 0 5 preferentially oriented in the film plane.
The direction of the artificial period- Velocity / mm s-' icity is therefore [1101.
The wavelength of the artificial period- Fig.3. MBssbauer absorp- icity estimated from the angles of X-ray tion spectra at 4 . 2 K and diffraction peaks coincided with the 300X for the multi- value programmed during the sample layered films ;
deposition within an error of a few (a) Fe (158) -V (302) percent. Therefore it is certified that (b) Fe (82) -V (242) the each layer thickness was satisfac-
torily controlled. Details of cryst- allographic studies on Fe-V multilayers will be presented elsewhere.
Examples of MBssbauer spectra for the multilayered films are shown in Fig. 3. If the Fe layer thickness is larger than 202, the spectra reveal no difference from the standard Fe spectrum.
As shown in the figure, a fraction with a reduced hyperfine field becomes visible in the spectra for Fe (152) -V (308) film.
The Fe (82) -V (242) film shows remarkably broader spectra.
One should notice that the spectrum at 4.2K for the Fe thickness of 82 is very similar to that of the surface-selectively enriched sample
(Fig. 2a). The thickness, 82, roughly corresponds to 4 atom layers.
Therefore we can regard this film as consisting of two interface atom layers and two bulk atom layers.
Down to 4 atom layer thickness, the magnetism of Fe layer sandwiched in between V layers is interpreted by assuming that only the topmost layer has a reduced magnetization due to an interface effect, whereas the other atom layers have magnetization similar to the bulk (as shown in Fig. 5 b ) .
Films thinner than 6 2 of Fe layers show non-magnetic fraction even at 4.2K and the magnetic behaviors are remarkably different.
A full report on the magnetic properties of Fe-V multilayers is in preparation.
C5-364 JOURNAL DE PHYSIQUE
I V - MULTILAYERED FILM WITH ARTIFICIAL SUPERSTRUCTURE:
NEUTRON DIFFRACTION
Interface magnetism is studied from observing the superlattice
reflection of polarized neutron. 0.
The principles were described alread!
in a previous paper / 5 / .
With small angle scattering measure- ments applying an external field, d the flipping ratio, R, was measured. 2 This is the intensity ratio of the neutron diffraction with the -
polarization parallel to and against ,
the bulk magnetization. CI Figure 4 shows the modified flipping -
ratio, R-1/R+1, for the first order reflection at 300K in the three samples having different Fe layer thicknesses.
In order to interpret this result, three models were considered, as shown in Fig. 5 and the calculatec values were compared with the
experimental ones. In the first model (A), no interface anomaly was assumed at all. Therefore the thick- ness of magnetic layer is exactly the same as the Fe layer thickness and the each Fe atom layer has the same magnetization as the bulk value.
In the second model (B), only the top interface atom layer has a reduced magnetization but other atoq layers have the bulk magnetization.
The third model (C) assumes one interface atom layer entirely losine the magnetization.
The modified flipping ratio £0:
the first order reflection is easil:
calculated on the basis of the modes mentioned above. Note that the
flipping ratio is entirely dependen.
on the atomic maqnetization density distribution perpendicular to the film plane. Furthermore the absolute value of the magnetization can be determined since the coherent scat- tering amplitude of vanadium is negligible. Though the analysis of the neutron diffraction data is still in the process, it is apparent that the experimental values fall on the second model suggesting that the magnetization reduces by about 30%
at the interface atom layer.
This value is estimated from the
Fig.4 - Modified flipping ratios of the first order neutron Bragg reflection at 300K in the following three samples,
(a) ~ e ( 2 0 2 ) - ~ ( 6 0 8 ) (b] Fe (252) -V (508) (C) Fe (602) -V (308) .
Fig.5 - Schematic drawing of the three models for the spatial distribution of mag- netization in a sinsle Fe layer,
(A) no interface anomaly (B)partial reduction at the
magnetization of the top interface atom layer (C)disappearance of magnet-
ization at the top inter- face atom layer.
hyperfine field measurements.
Using two independent experimental techniaues, i.e.Me)ssbauer spectroscopy and neutron diffraction, a consistent description is obtained for the magnetization of Fe interface in contact with V.
The magnetization is significantly reduced (c.a. -30%) only at the top interface atom layer, whereas the other atom layers have nearly the bulk magnetization. In other words, from the viewpoint of magnet- ism, an interface effect is remarkable only at the topmost atom layer.
Hamada et al. have carried out a self-consistent band structure calculation for Fe films with several atom layer thicknesses sand- wiched in between V layers /6/. The result that the top interface Fe atom layer has a siqnificantly reduced magnetization is in qualitative agreement with the present result. The magnetization at the second atom layer was suggested to be slightly enhanced. However, the present experimental results do not support this prediction.
More details of the experimental results on Fe-V multilayered films including NMR and FMR data will be published elsewhere.
The authors would like to thank Dr. J. M. Friedt for discussion.
REFERENCES
1. J. Lauer, W. Keune and T. Shinjo, Physica 86-88B (1977) 1407.
2. S. Hine, T. Shinjo and T. Takada, J. Phys. Soc. Jpn. 41 (1979) 767 3. N. Hosoito, T. Shinjo and T. Takada, J. Phys. Soc. Jpn. 50 (1981)
1903.
4. T. Shinjo, N. Hosoito, K. Kawaguchi, T. Takada, Y. Endoh, Y. Ajiro and J. M. Friedt, J. Phys. Soc. Jpn. 52 (1983) 3155.
5. Y. Endoh, N. Hosoito and T. Shinjo, ~.h!a~n. & Magn. Mater. 35
(1983) 93.
6. N. Hamada, K. Terakura and A. Yanase, J. Magn. & Magn. Mater. 2
(1983) 7, and private communication.
