MÖSSBAUER AND MAGNETIC MEASUREMENTS IN AMORPHOUS RARE EARTH-TRANSITION METAL FILMS

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MÖSSBAUER AND MAGNETIC MEASUREMENTS IN AMORPHOUS RARE EARTH-TRANSITION

METAL FILMS

T. Katayama, Y. Nishihara, Y. Yamaguchi, S. Ogawa, T. Tsushima

To cite this version:

T. Katayama, Y. Nishihara, Y. Yamaguchi, S. Ogawa, T. Tsushima. MÖSSBAUER AND MAGNETIC

MEASUREMENTS IN AMORPHOUS RARE EARTH-TRANSITION METAL FILMS. Journal de

Physique Colloques, 1979, 40 (C2), pp.C2-135-C2-136. �10.1051/jphyscol:1979246�. �jpa-00218644�

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JOURNAL DE PHYSIQUE Colloque C2, suppl&ment au n o 3, Tome 40, mars 1979, page ^C2-135

MOSSBAUER AND MAGNET1 C MEASUREMENTS I N AMORPHOUS RARE EARTH-TRANS I T 1 ON METAL F I LMS

T. Katayama, Y. Nishihara, Y. Yamaguchi, S. Ogawa and T. Tsushima EZectrotechnical Laboratory, T m a s h i , Tokyo 188, Japan

R6sum6.- Des mesures de l'effet NGssbauer et de l'aimantation ont 6tC faites sur des couches minces amorphes de GdFe et de DyFe, qui ont st6 prdpardes par pulvGrisation cathodique avec ou sans Vb. Nous avons constatd que la dSsagr6gation prdfsrentielle des atomes isol6s Gd ou Dy donne un effet consids- rable d'anisotropie perpendiculaire et qu'elle augmente l'intensits des champs hyperfins moyens des couches minces.

Abstract.- assbauer and magnetic studies were carried out on the amorphous GdFe and DyFe films prepared under the conditions with or without negative voltage Vb. It is found that the preferential resputtering of isolated Gd or Dy atoms has the considerable effects on the perpendicular anisotropy and it increases the average hyperfine fields in the films.

1. Introduction.- The magnetic properties of amor- aligns along the direction perpendicular to the film phous rare earth-transition metal (R-T) films, being planes. But the spectra of B and D show that the net studied extensively as bubble and thennomagnetic me- magnetization lies in the film plane. And E, F, G, mory materials, strongly depend on the preparation and H show the distributions of the hyperfine fields, conditions. Particularly, perpendicular magnetic whose values spread out from about 150 to 330 kOe anisotropy (K ) , which is one of the most important and from about 0 to 230 kOe at 292 K in the GdFe and

u

properties for the above mentioned memories, is very DyFe films, respectively.

sensitive to the negative voltage (Vb) applied to the substrate during the sputtering. On this subject, we have pointed out that the induction of Ku is di- rectly related to the resputtering and the stress effect in the amorphous GdCo and GdFe films, respectively 111, and have pointed out also that, in the case of the GdCo films, an anisotropic distribution of atomic pairs produced by the preferential resputtering effect of isolated Gd atoms is thought to be main origin of Ku 121.

In this paper, we describe the measurements of Msssbauer effect and magnetic properties on the amorphous DyFe films in order to extend the field of the study of the amorphous films.

2. Experimental Procedures.- All the amorphous R-T (R = Gd, Dy; T = Co, Fe) films were prepared by R.F.

sputtering method using arc melted targets. And all the films were covered with a thin film of A1 to prevent oxidation. assbauer spectra of the ''~e were measured in a transmission geometry with the

film placed normal to the y-ray beam. Magnetic measurements were carried out by means of a vibrating sample magnetometer and a torque magnetometer.

3. Results and Discussions.- In figure 1 are shown the dssbauer spectra and distributions of the hy- perfine field (8) at Fe in the amorphous GdFe and DyFe films at 292 K

.

As seen in the figures, the spectra of A and C show that the net magnetization

- 8 -4 0 4 8 VELOCITY

INTERNAL FIELD H ( kOe )

Fig. 1 : assbauer s ectra and distributions of the hyperfine fields at 'TF~ in the amorphous GdFe and DyFe films prepared under the conditions with and without Vb. (A), ( 0 , (El, (GI; KU > 0, (B), (Dl,

(F), (H); Ku < 0. Temperature; 292 K.

In table I are summarized the assbauer parameters and Curie temperature (Tc) of the amorphous

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979246

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JOURNAL DE PHYSIQUE GdFe and DyFe films.

Table I : %ssbauer parameters of amorphous GdFe and DyFe films at 292 K. AE,., is the isomer shift relative to metallic iron, H the hyperfine field at the maximum proba&ility in P(H) curve and

R

the average hyperfine field.

Here, the point to which special attention should be paid is that the average hyperfine fields

(R)

in the films with KU < 0 are about 20 % 25 kOe higher than those with KU > 0. Tc of the films with K,, > 0 are higher than those of the films with KU < 0. (The va- riations of 2' can be explained with the concentration changes of Fe). The difference of (@) ^cannot be explained only with Fe concentration changes nor with the changes of Tc. Namely, the anomalous in- crease of @ could be attributed to a local ihnomo- geneity of Fe concentration in the films 121. And the X-ray diffraction patterns also suggest the existence of the local inhomogeneity of the Fe concen-.

tration in the DyFe films prepared under the conditions with Vb (K < 0).

U

By the way, in the case of the DyFe films, Mgss- bauer and magnetic measurements suggest that the Fe moment are also distributed over all directions within a narrow cone as reported by J.P. Rebouillat et al. 131. Namely, the Gssbauer spectra measured at 77 K suggest the existence of the perpendicular components of Fe moments to y-ray direction. And the DyFe films represent a large high-field susceptibi- lity and a large field dependence of polar Kerr ro- tation (Qk) at wavelength of 5000

A

^which^Ok^is

thought to be caused principally by the Fe atoms.

In figure 2 is shown K as a function of Vb

U

for amorphous DyFe films. The V dependences of KU b in the GdCo and GdFe films are also shown for compa- rison. The Vb dependence in the DyFe films showing the reverse tendency to the GdCo films is just simi-

1 1 1 1 I I

I I I I I I

ALLOY

:

ANISOTROPY

:

^L1EISS.^(mmls): ^H^(kOe) ^z(k0e) ^G(k0e) ^Tc(K)

I 1 I P I 1 I

I I I I I I

I 1 1 1 1 I

:KU>O(Vb=OV,72%Fe)

:

0.010f0.003

:

^246f3 ^227f5 ^I^I ⁵¹⁰

GdFe

:

I ¹ ¹I ^I1

;

²⁴ ^I^I

:K <O(Vb=-100V,79%Fe)

:

0.011f0.003

:

²⁶⁵⁺³ ^251f3 ^I ⁴⁹²

I U 7 I I % I

lar to the GdFe films. Namely, the resputtering ef-

+

fect of the isolated Gd or Dy atoms produces negative KU in the GdFe /1/ and DyFe films. It should be noticed that KU in the DyFe films changes again from negative to positive in the V region between -80

b

and -130 V. In this region, the anisotropic pair distribution decreases, because the resputtering of

:

K >O(Vb=OV, 74ZFe) _U

:

^I^I 118f4

:

¹⁰⁶⁺⁴ ÎÎ ÎÎ ³⁴⁰

DyFe

: ----

^II ^I1

:

²³ ¹^I

:K <O(Vb =-70V,79%Fe)

:

^t^I ¹⁴¹⁺⁴

:

^129f4 Î ÎÎ

r u I I I I I

330

Dy atoms other than the isolated Dy atoms takes pla- ce. Since Dy atoms are sputtered more easily than Gd atoms 141, this phenomenon is observable in DyFe.

Therefore, the Vb dependence of XU in the DyFe can be explained with the microscopic changes in atomic arrangements caused by the resputtering effect of the isolated Dy atoms.

Target

(1) 74at01eCo-Gd alloy (11) 72at.I. Fe-Gd alloy '>

'.

8

Fig. 2 : K as a function of Vb for the amorphous GdCo, ~ d ~ e y and DyFe films

.

Ar Press : & x 10-z forr

x

lo5

Vrf. : 650V

-

^d ^{: 35mm}

References

/ 1 / Katayama, T., Hirano, M., Koisumi, Y., Kawanishi, K. and Tsumshima, T., IEEE Trans. Magnetics MAG-13 (1977) 1603.

/2/ Nishihara, Y., Katayama, T., Yamaguchi, Y., Ogawa, S., and Tsushima, T., Jap. J. Appl. Phys.

17 (1978) 1083.

-

131 Rebouillat, J.P., Lienard, A., Coey, J.M.D., Aprese-Boggiano, R., and Chappert, J.; Physica 86-88B (1977) 773.

141 Carter, G. and Colligon, J.S., "Ion Bombardment of solid" (Heineman Educational Books, London)

1968, p. 323.