Magnetoresistance and hall effect in amorphous CoZr films

1475

Journal of Magnetism and Magnetzc Materials 31-34 (1983) 1475-1476 MAGNETORESISTANCE T. Y A M A G A T A

AND HALL EFFECT

IN AMORPHOUS

CoZr FILMS

a n d S. I T O

Mlcroelectronlcs Research Laboratories, Nippon Electric Co. Ltd, Kawasakt, Japan

Transport propemes for rf sputtered amorphous Co I ~Zr~(0 05 < x < 0.28) films have been mvesUgated It was found that anisotrop~c magnetoreststance ~s negative above x = 0 13, unhke m most 3d alloys Spontaneous Hall coefficient increased hnearly with Zr content, and was dominated by the side-jump contnbutmn 1. Introduction T r a n s p o r t properties for a m o r p h o u s alloys, including metalloid atoms have been investigated extensively Recently, m e t a l - m e t a l a m o r p h o u s alloys have been rep o r t e d to have remarkable magnettc properties for practical use. A m o r p h o u s C o Z r is one of such m e t a l - m e t a l alloys, which has low coercive forces and high saturation magnetizations [1,2]. Nevertheless, little has been published o n transport properties of CoZr a m o r p h o u s alloys In the present study, resistivity, anlsotroplc magnetoresistance a n d Hall effect in Co~_~Zrx films were investigated 2. Experimental A m o r p h o u s Co 1 xZrx films were deposited on glass substrates by rf sputtering, using a target composed of a 100 m m O pure Co disk and 3 × 3 m m 2 pure Z r pieces. The film composition was controlled by changing the n u m b e r of Z r pieces laid on the Co disk. It was e x a m i n e d by electron macroprobe analysis. Film thicknesses ranged from 1000 A to 1 # m . Amorphlclty was confirmed by the electron diffraction method. Square a n d stripe p a t t e r n film specimens were used for magnetic and electrical measurements, respectively. They were prepared simultaneously on the same substrate. Magnetization was measured using a vibrating sample m a g n e t o m e t e r M e a s u r e m e n t s of resistivity a n d anlsotroplc magnetoresistance were made by a fourp r o b e m e t h o d and a dc bridge method, respectively Hall voltage was measured by a dc method in a magnetic field up to 22 kOe. N o thickness dependence in magnetization, magnetoreslstance a n d Hall effect was observed in the prepared thickness range

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F~g 1 Saturated magnetization as a functmn of Zr content ous change was observed in 47rM~ corresponding to the phase change. Electrical reslstivtty p a n d anlsotroplc magnetoreslstance a p ( = P. - P ± ) are shown in fig. 2, where P,, and p± imply the resistivity when magnetization directions are parallel and perpendicular to the current, respectively. Resistivity p increases smoothly with Z r content, except for a discontinuous change from x = 0.024 to 0.055, whtch corresponds to a change from crystalline to amorphous. The extrapolated value m p to x = 0 was 0.49 /g2 cm, M u c h agreed approximately with that for a m o r p h o u s pure Co at room temperature [3]. Amsotropic magnetoreslstance Ap decreases monotonically as Z r content increases, a n d crosses zero a r o u n d

3. Results and discussion Saturation magnetizations 4~rM, at room temperature are shown m fig. 1 as a function of Z r content The values of 4TrM, decrease hnearly with increasing Z r concentration. The specimens above and below x = 0.05 were a m o r p h o u s a n d crystalline, respectively, according to the electron diffraction patterns. However, no obvx0304-8853/83/0000

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terms imply skew scattering and side-jump c o m p o n e n t [4]. respectively It was observed that R, was exactl3. proportional to p2 Therefore, R, in amorphous Co I Z r is dominated by the side-jump contribution In fig 4 amsotroplc magnetores~stance ratio A p / p and spontaneous Hall conductivity YH, ( = R 4~rM,/p 2 ) ,ire ~hown together with saturated magnetostn~.tion X reported by Shlmada and Kojlma [1] Berger [5] discussed the correlations between d p / p Ytl, and ~ l-le showed that YH, is proportional to ~, and that J p / p becomes maximum where 711, and k become zero These correlations have been experimentally confirmed in several alloy systems However, In the present experiment on Co I _ Z r amorphous alloys, no such correlation could be observed

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Fig 4 Anisotroplc magnetores[stance ratio Ap/o, spontaneous Hall conductiv~ty 71h and saturated magnetostriction X as a funchon of Zr content

x = 0 13 Then, Ao has a negative peak, - 3 × 10 ~ ~'2 cm at x = 0 2 No magnetoreslstance could be observed at x = 0 3 2 , even at 78 K The esumated number of Bohr electrons per Co atom was about 1 47 at x = 0 13, where At) crosses zero The negative magnetoreslstance in amorphous alloys is qmte rare, whereas AO is positive m most 3d ferromagnetic alloys at room temperature This sign reversal m A 0 might be correlated to changes in density of state at Fermi level N ( E v ) for each subband. The origin of this negative magnetoresistance is still unknown. Spontaneous Hall coefficient R~ is shown m fig 3 R, Is positive and increases linearly to 3 8 × 10 Io $2 c m / G at x = 0 28 with Zr content R~ can be expressed m the form R , - ap + bp 2, where the first and second

Transport properties have been measured on rf sputtered amorphous Co I , Z r , (0 05 < .~ < 0 28) hires The experimental results are summarized as follows Resistivity p increases monotonically with Zr content Anisotroplc magnetoresistance AO decreases monotonically ,is Zr content increases and changes its sign from positive to negative at around _x - 0 13 Spontaneous Hall coefficient R, increases linearly with Zr content Proportionality between R, and p2 unphes that R, in Co I ~Zr, is dominated by the sidej u m p contribution There were no obvious correlations between magnetostricuon X, and anisotroplc magnetoresistance ratio A O / p nor Hall conductivity YH,, which is expected from Berger's theoretical model

The authors wish to thank Dr D Shmoda, Mr K Matsumi and Dr T Furuoya for their guidance and encouragement They also thank Mrs Y Hayama, Mr T Maruyama and Mr F. G o t o for their assistance with sample preparation and measurement References [1] Y Shtmada and H Kojuna, in Digest ot the 4th Ann Conf on Mag in Japan, Osaka (1980) p 23 [2] T Yamagata and S Ito, IECE Tech Group Meeting ol Comp and Materials Japan, CPM82-7 (1982) p 49 [3] G Bergmanm Phys Lett 54A(1975) 291 [4] L Berger, Phys Rev B2(1970) 4559 [5] L Berger, Phys Rev 138 (1965) A1083