Cr multilayer films prepared by vapor deposition and electrodeposition

Journal of Magnetism and Magnetic Materials 156 (1996) 353 354

Journalof magneUsm and

magnetic ~ H materials

ELSEVIER

Magnetic properties and magnetoresistance of Fe/Cr multilayer films prepared by vapor deposition and electrodeposition Y. Ueda a,*, S. Ikeda a, S. Hama a, A. Yamada h Dept. ~f Electrical and Electronic Engineering, Muroran Institute ~["Technology, 27-I Mizumoto-cho, Muroran 050..lapan b Tomakomai Technical College. Tomakomai 059-12. Japan

Abstract F e / C r system multilayers were prepared by electron beam deposition and electrodeposition. The effect of Cr alloying of the Fe layers, Fe alloying of the Cr layers and annealing on the magnetic properties and the magnetoresistance (MR) have been investigated. MR depends on the alloy composition in the Fe-rich ferromagnetic layer and the Cr-rich nonmagnetic layer. The MR ratio decreases remarkably with increasing content of Fe into the Cr interlayer. However, MR was not observed for the electrodeposited films.

Many studies of giant magnetoresistance (GMR) and magnetic properties on F e / C r multilayers have been carried out. The lattice constant of the Fe crystal is nearly equal to that of a Cr crystal and both crystal structures are bcc. It is useful to investigate the magnetism of the Fe film, since the crystal growth of Fe on the Cr substrate is expected not to be affected by the crystal structure of Cr. Moreover, both atoms belong to the 3d transition series, and the metals are alike in the electronic state of atoms. Therefore, it is interesting to study F e / C r multilayers and alloy layers. Since the discovery of GMR in multilayers of F e / C r systems produced by MBE [1], GMR has been successively found in various multilayers produced by other methods. However, the GMR of a system shows different values depending on the method of preparation [1,2]. The GMR depends on the roughness at the interface between magnetic and nonmagnetic layers and the substrate [3,4]. The effect of alloying impurities into Fe and Cr layers on GMR is yet unclear. We prepared F e / C r multilayer films by vapor deposition and electrodeposition. We investigated the effect of Cr alloying of the Fe layers, Fe alloying of the Cr layers and annealing on the magnetic properties and the GMR. F e / C r , F e C r / C r and F e / C r F e multilayer films were prepared by electron beam deposition in a vacuum of ( 1 - 5 ) )< 10 -7 Tort onto a glass substrate. The thickness of the Fe-rich and Cr-rich layers were 25-100 ,~ and 5-25 ,~, respectively. The total thickness of the Fe-rich layers was

* Corresponding author. Fax: ueda@ waspet.cc.muroran-it.ac.jp.

+ 81-143-47-3290;

email:

1000 A. The samples were annealed in a vacuum of 2 × 10 ~' Torr at temperatures of 300 and 500°C liu I h. Electrodeposition was performed from a chloride electrolyte containing Fe 2 + and Cr ~ " ions in a single cell, and carried out with a square wave of 1-150 m A / c n l 2 in a plating solution maintained at a pH value of 4.0. Fe and Cr concentrations in the electrodeposited films were determined by X-ray fluorescence spectroscopy and atomic absorption spectrometry. Magnetoresistance was measured at room temperature. The MR ratio was calculated as the absolute value of A p / p o = ( On -- P~)/t)(), where p, is the resistivity at a zero field, and Pn is the resistivity produced by an applied field H, The magnetic properties were measured by VSM. Fig. 1 shows the MR ratio and the magnetization of the F e / C r multilayer fihns produced by vapor deposition against the Cr interlayer thickness. The MR ratio has a maximum at a Cr thickness of 15 ek. In the Fe thickness region 25-100 ,~, the MR ratio shows a larger wdue for the thinner Fe layer. Alter annealing at 300 and 500°C liw I h, the MR ratio decreases and magnetization increases lbr all thicknesses of the Cr interlayers. The increase of the magnetization is based upon the assumption that the magnetization is easy to saturate in small magnetic fields. Fig. 2 shows the change in the MR ratit~ as a function of the Cr concentration in the ferromagnetic Fe layer for Femo_ ~Cr,/Cr fihns. The tendency of the MR ratio in the iron-rich region varies with the applied magnetic field (10-20 kOe). For fields less than 21 kOe, a maximum in the MR ratio is observed at about 5 at';/, Cr. The MR ratio o1' the samples annealed at 300°C for I h decreases. Fig. 3 shows the MR ratio as a function of Fe concen-

0304-8853/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0 3 0 4 - 8 8 5 3 ( 9 5 ) 0 0 8 9 5 - 0

354

Y. Ueda et al. / Journal of Magnetism and Magnetic Materials 156 (1996) 353-354

g ".~"-..

Annealing 300"C lh

200

MagnetizationNN,~............... .an/(H=2.5kOe) Fe25A

0 FegoCho/Cr

E -2

150 ._me" 100

As-prepared

FeQoCrl0/C7 ~_l~s-preparec

~-4 LL

o

6

MR r a t i o

~-6

f { ~

(H=15kOe) / . - L "X~ 4 Annealing300"C1h/ ,"" , "'-,, /N~ e25A

.k/,."

._o

2

soo~c, ~" ~"~"

.~,

50

.9~"

! /

Q.

<1 -4

TUJ

Fe/Cr~sFe5

~

g

-

/"'......,.

l

°

(b)

-,~ -15 ' -1'o -5'

0'

5'

1'o 15 '

i

-2

t

i

-1

i

i

1

2

Magnetic field (kOe) Fig. 4. Magnetic field dependence of (a) Ap/po and of (b) the corresponding magnetization for two multilayer systems. 0

5

i

10 15 20 Cr layer thickness (A)

25 100

Fig. 1. MR ratio and magnetization of Fe/Cr multilayer films produced by vapor deposition against Cr interlayer thickness.

E

._¢ g

8t

Feloo-xCrx 25A/Cr 15A

I/ ~.=----..,..~\ o~"6 In/ / ~ " ~

/

g

Appliedfield: H --~o-21 kOe

"\

-/. . . . . . . *- . . . .

\

-:-

50

8 ~3

i

5

i

10

25

i

15

i

20

Cr concentration in FeCr alloy layer x (at%)

/

Fe 25A/CrlOo-x Fex 15A

/

Appliedfield H= 15kOe

0~6'

2

150

tration in the nonmagnetic Cr layer for the films of F e / C r l o o _ , F e x. The MR ratio decreases remarkably with increasing content of Fe into the Cr interlayer. Fig. 4 shows the magnetic field dependence of (a) A P/Po and of (b) the corresponding magnetization for the Fe9oCrlo/Cr and Fe/Cr95Fe 5 multilayers. On annealing at 300°C the MR ratio has a tendency to decrease while magnetization shows a ferromagnetic hysteresis curve. Fig. 5 shows a comparison of the electrodeposited films as a function of the current density. Compositionally modulated F e - C r multilayer film could be produced by controlling the current densities. However, MR was not observed for the electrodeposited film. It seems to be due to the film structure and the Fe content in the Cr interlayer. References

I

O0

50

Fig. 5. Comparison of the electrodeposited films as a function of the current density.

Fig. 2. Change in MR ratio as a function of Cr concentration in the ferromagnetic Fe layer for Femo_xCL / C r films.

81

,!

Current density (mA/cm2)

\0 °o

"-~*

lo

Annealing ""-. \ 300°(3lh Q" \

~4

/f

.~plp.mIFe

I

I

5

10

Fe concentration in CrFe alloy layer x (at"/,,)

Fig. 3. MR ratio as a function of Fe concentration in the nonmagnetic Cr layer for Fe/Crloo_,Fe x films.

[1] M.N. Baibich, J.M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich and J. Chazelas, Phys. Rev. Lett. 61 (1988) 2472. [2] S.S.P. Parkin, N. More and K.P. Roche, Phys. Rev. Lett. 64 (1990) 2304. [3] F. Petroff, A. Barthelemy, A. Hamzic, A. Fert, P. Etienne, S. Lequien and G. Creuzet, J. Magn. Magn. Mater. 93 (1991) 95. [4] S. Araki and T. Shinjo, Jpn. J. Appl. Phys. 29 (1990) L621.