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Submitted on 1 Jan 1988
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MAGNETIC PROPERTIES OF COMPOSITIONALLY
MODULATED FILMS
L. Smardz, J. Baszynski
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, SuppMment au no. 12, Tome 49, decembre 1988
MAGNETIC PROPERTIES OF COMPOSITIONALLY MODULATED FILMS
L. Smardz and J. Baszynski
Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17/19, 60-179 Poznan, Poland Abstract. - The compositionally modulated Cu/Ni, Cu/Co and Cu/Fe films have been prepared where both the wave- length of modulation and average composition vary. The magnetic properties were measured in the temperature range 4.2-850 K.
Compositionally modulated films (CMF) have at- tracted much attention in the last few years because these films have the possibility of exhibiting novel phe- nomena such as the following [l]: 2D behaviour, cou- pling, interface and superlattice effects. We report here the structural and magnetic properties of the Cu/Ni, Cu/Co and Cu/Fe CMF.
The CMF composed of alternating regions of m
atomic planes of Cu and n atomic planes of Ni (Co, Fe) were prepared by sputter deposition using a technique described earlier [2-41. The films prepared had total thicknesses between 0.8 and 1.2 pm, wavelengths of modulation between 2 and 15 nm, and average compo- sitions which varied from 5 to 70 at. % of ferromagnetic component. A buffer layer of Cu was first deposited
onto the mica substrate t o establish a strong texture.
The structure of the CMF was examined .by X-
ray diffraction. Typical 0
-
28 X-ray diffractograms showed the satellite reflections and the central Bragg peaks (CBP), which were located between position of Cu(111) and Ni(ll1) (Fig. la), Cu(ll1) and Co(ll1) (Fig. lb), and Cu(ll1) and Fe(ll0) (Fig. lc) peaks. The X-ray results can be explained in terms of a struc- ture which consists of alternating sublayers of fcc- Cu(ll1) and fcc-Ni(lll), fcc-Cu(ll1) and fcc-Co(lll), and fcc-Cu(ll1) and bcc-Fe(ll0) planes, respectively. An important question is to obtain with good accur- acy the composition profile of the CMF in the growth direction. A complete Cu-Ni solid solution can be ob- tained over a wide temperature range at all compo- sitions. In the previous papers [5, 61 concerned with Cu/Ni CMF, which were prepared by electron beam evaporation, a sinusoidal profile of composition was taken. For our Cu/Ni CMF, which were prepared by sputtering, we examined both, the sinusoidal [7] and trapezoidal profile. Co and Cu have reduced solubility under equilibrium conditions, and therefore, for this system rather sharp interfaces are expected. Since Cu and Fe practically do not form solid solutions below 550 K, chemically sharp Cu-Fe interfaces are to be ex- pected. On the other hand, during the growth process may occur some diffuseness of the interfaces.A total magnetic moment of the CMF was measured at 4.2 K by a SQUID magnetometer and a vibrating
Fig. 1. - The 8 - 28 X-ray diffrxtograms (Cu-Ka) of the Cu/Ni (a), Cu/Co (b) and Cu/Fe (c) CMF. The satellites are labelled: 1-first-, 2-second-order.
/ Nig
sample magnetometer, and in the temperature range 77-850 K by a magnetic balance. The average magneti- zation (M) of the Ni sublayers was calculated dividing the total magnetic moment by the volume of Ni in fer- romagnetic part of the Cu/Ni CMF for the sinusoidal and trapezoidal profile of composition with interface thicknesses t = 3, 4 and 6 atomic planes'. For the si- nusoidal profile the average magnetization (solid lines in Fig. 2) is lower than the bulk value and decreases rapidly for Ni sublayer thickness less than 8 atomic planes. At RT the value of ( M ) for the trapezoidal profile (broken lines in Fig. 2a) seem to low for great n compared to the bulk magnetization and is practi-
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C8 - 1764 JOURNAL DE PHYSIQUE
Fig. 2. - The average magnetization of Ni sublayers as a function of number of Ni atomic planes for sinusoidal (solid line) and trapezoidal (broken lines) profile of composition a t RT (a) and 4.2 K (b). For the trapezoidal profile of composition the interface thickness t = 3, 4 and 6 atomic planes.
cally independent of the Ni sublayer thickness for t = 6 atomic planes. At 4.2 K trapezoidal profile gives the value of (M) (broken lines in Fig. 2b) similar to that for the sinusoidal profile. The dependence of the aver- age magnetization on the interface thickness at 4.2 K for trapezoidal profile is very weak. The magnetization of the Co and Fe sublayers was determined assuming a rectangular profile of composition. For Co and Fe sub- layer thickness greater than 2.1 nm low-temperature magnetization was equal t o the bulk value. This re- sult confirms earlier assumed shape of the composition profile of the Cu/Co and Cu/Fe CMF.
Figure 3 shows the temperature dependence of the magnetization for the Cu/Fe CMF. The heating rate during the measurements was about 5 K/min. Above 450 K starts the interdiffusion process of the Cu and Fe sublayers [8], and therefore further comparison to the bulk value have not sense due t o the change of the composition profile.
Fig. 3. - Temperature dependence of the magnetization for the Cu/Fe CMF.
Acknowledgments
This work was supported by the Institute of Physics of the Polish Academy of Sciences, Project CPBP.01.04.
[I] Schuller, I. K., Lecture Notes of the Summer School: Physics, Fabrication and -4pplication of Multilayered Structures (Ile de Bendor, France) 1987.
[2] Smardz, L., Baszynski, J. and Dubowik, J., Acta Phys. Pol. A 72 (1987) 287.
[3] Smardz, L., Baszynski, J., Kuznetsov, V. D. and Kuznetsov, I. E., Acta Magn. Suppl. 87 (1987) 353.
[4] Smardz, L., Baszynski, J. and Bazhan, A. N.,
Acta Magn. Suppl. 87 (1987) 351.
[5] Georgy, E. M., McWhan, D. B., Dillon, J. F., Jr., Walker, L. R. and Waszczak, J. V., Phys.
Rev.
B 25 (1982) 6739.
[6] Flevaris, N. K., Ketterson, J . B. and Hilliard, J. E., J. Appl. Phys. 53 (1982) 8046.
[7] Smardz, L. and Baszynski, J., t o be published. [8] Smardz, L., Baszynski, J. and Szymanski, B., to
