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Submitted on 1 Jan 1988
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STRUCTURAL AND MAGNETIC PROPERTIES IN
MnBiAlSi AND MnBiSbSi FILMS
Y. Wang, J. Shen, Q. Tang
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppl6ment a u no 12, Tome 49, dBcembre 1988
STRUCTURAL AND MAGNETIC PROPERTIES IN MnBiAlSi AND MnBiSbSi FILMS
Y. J. Wang, J. X. Shen and Q. Tang
Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Abstract.
-
The thermal structural stability and the crystallite size in MnBi could be much improved after it is doped by Al, Si or Sb, Si. However, the large Kerr rotation angle Bk in MnBi is maintained in the new constitution, especialy in MnBiAlSi films. Therefore, it is a promising material for the magneto-optical recording.Introduction
In recent years, many efforts have been devoted to develop new media for magnetic optical disc applica- tions, but it seems that materials with good qualities such as large read-out signal, thermal stability a d low noise are difficult t o find.
In the present paper, results on a new kind of magneto-optical medium, MnBi-base films, will be pre- sented.
Experimental
By vacuum evaporation (I), MnBiAlSi, MnBiSbSi films were prepared. The base pressure of vacuum sys- tem is about 3 x Torr. In order to obtain ho- mogeneous MnBi-base alloy films, a heat treatment in vacuum is required.
The magnetic properties, saturation magnetization
M,, perpendicular anisotropy constant K,, coercive
force Hc and Kerr rotation angle Ok were determined
by vibrating sample magnetometer, Torque measure- ment and magneto-optical spectra at 633 nm respecti- vely.
Results
The X-ray diffraction of MnBiAlSi film with an ap- propriate constitution shows that it has a perfect hexa- g o d structure with NiAs type, that is, the c axis is perpendicular to the basal plane (see Fig. 1).
Figure 2 gives the Auger electron spectroscopy pro- file for this film. It is clear that a considerable amounts of Al, Si and 0 enter in the MnBi hexagonal structure. According t o the X-ray diffraction, they are not found in ordered phases.
e k , R (reflectivity),
K,,
Ma and H, for the opti-mal MnBiAlSi composition were determined to be Ok=
1.2 deg., R = 40 %, ~,=2.2x10' erg/cc, Hc=1800 Oe and M,=250 emu/cc. The signal to be picked up in magneto-optical disc is proportional t o O k f i . It is no- ticed that this value in the MnBiAlSi film could be increased by a factor of 3 as compared with the amor- phous R E T M films.
z e (d.,l.)
Fig. 1. - X-ray diffraction for MnBiAlSi film.
SPUTTER T I M E ( r n i n . )
Fig. 2. - AES profile for MnBiAlSi film.
.
""8 0
As a magneto-optical recordidng medium, the ther- mal stability and the crystallite size in MnBi-base sys- tem are of much concern. Figure 3 gives the quenching experiments for 6k,
Ms
and Hc. It could be seen that the thermal structural stability for MnBiAlSi film is-
A E S P R O F I L EC8 - 1726 JOURNAL DE PHYSIQUE
-
MnBiAISI---
MnBiI '
Ms*0° BEPORE QUENCH
I
Fig. 3.
-
Bk, Ms and Hc as the function of the quenching T Fig. 5.-
X-ray diffraction for Mn0.s (Bi0.26Sbo.7S)0.6 film for both MnBi and MnBiAlSi film. All measurements were (because Si atoms exist as the interstitial ones, hence Simade at room T. content is not inclusive in this chemical formula).
much better than that for MnBi. A transition electron microscope picture for determination of the crystallite size d in MnBiAlSi film is shown in figure 4. The ave- rage crystallite size d could be estimated to be less than 400
k
from this picture.As compared with MnBiAISi film, 6k in MnBiSbSi film is smaller (6k=0.5 deg., R = 20 %) although its thermal structural stability is similar t o MnBiAlSi film.
In the X-ray diffraction at the optimal composition M n 0 . a ( B i ~ . ~ ~ S b o . 7 ~ ) ~ . ~ , we have found a set of X-ray peaks (see Fig. 5), 26 = 27.35, 48.8 and 62.5 deg.
These peaks do not exist in the NiAs type, it may be a CdI2 type hexagonal structure with c = 6.5
A
[2].Discussion
Analysing the hexagonal structure with NiAs type, we were able to find six interstitial sites in the unit crystal cell. Therefore, Mn atoms can jump into the interstitial sites when MnBi is annealed above
T,
point and then quenched. As a result, M,, Bk in MnBi de- crease due t o the formation of a quenched high tem- perature phase 131.In the MnBiAlSi film, a lot of foreign atoms fills up the interstitial sites, so that the phase transition could be affected. We speculate that the foreign atoms enter the grain boundaries as well, therefore, the crystallite size decreases.
Acknowledgment
This work is supported by the Joint Optical Disc Laboratory and the Magnetism Laboratory of the Chi- nese Academy of Sciences.
[I] Chen, D., J. Appl. Phys. 42 (1971) 3625. Fig. 4.
-
TEM observation for MnBiAlSi film deposited ona Cu-grid slice after annealing at an appropriate temper* [2] Wang, Y. J., Shen, J. X., Tang, Q., to be publi- ture, its electron diffraction image as shown in this figure shed in J. Magn. Magn. Muter.
