Structural and magnetic properties of FeN gradient thin films

Journal of Magnetism and Magnetic

Materials 140444 (1995) 719-720

ELSEVIER

struc1,Ul%i.1andmagneticpropertiesof FeE,.Y. hang ay*, DC Sun b, H, Liu ‘, H.L. Bai a, X.X. Zhang a a Department of App!ied Physics, Tianjin Unioersiry, Tianjin 3UOO72,Chim Department of Materials Science and Engineering, Tsinghw Unicersiry Beving lm,

Abstract Fe-N gradient thin films are fabricated by a facing targets sputtering (FTS) system. Rutherford bat spectrometry shows that the concentration of Fe atoms or N atoms varies gradually from the substrate to the surface of film. The Fe-N gradient films contain crystal phases of <-Fe,N, e-Fe,N (2
Iron nitrides have a variety of phases with different crystal structures and magnetic properties owing to different nitrogen contents. They are ‘Y”-Fe,,N2 (bet) [l], y’Fe,N (fee), c-Fe,N (2
pressure of about 2.0 X 10-j Pa, argon gas was introduced. Keeping the sputtering gas pressure PAr at 3.0 x 10-l Pa, then introducing nitrogen gas, whik i~e~~~ the pressure from 0.1 X lo- ’ Pa to an ultimate vdw (such as 3.0 X 10-l Pa) evenly in 20 min, one can that has more Fe atoms gathered near the substrate Fe atoms at the surface of the film. The a 400 W. The substrate temperature was about w)“C film thickness ranged from 450 to about 500 nm.

H, and saturation magnetization &fs of the films are examined with a vibrating sample magnetometer (VSM) at room temperature. Fig. 1 shows the Rutherford backscattering spe the Fe-N films and the concentration of the Fe atoms. incident a-ions are of 2.1 MeV and the back scatterin angle is 170“. The abscissa origin in Fig. I(b) represents the surface of the gradient film. The Fe concentrat decreases from the substrate to the surface tbro~~~t whole thickness of the film, ranging from 9.5 to about at% in the gradient Fe-N films. X-ray photoele troscopy (XPS) is also employed and the profile well in accordance with the RBS result. From Fig. 1, o~lc can see that the film possesses a composition gradient. The X-ray diffraction pattern for the gradient Fe-N films prepared under different ultimate nitrogen pressure PN, demonstrates four phases (y’-Fe,N, I;-FeZN, c-Fe,N

* Corresponding author. Fax: + 86-22-3358329. 03&&8853/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSRI 0304-8853(94)01568-6

et al. /Jwtpral uf Magnetism and Magnelic Materials 140-M

(1995) 719-720

I 11 7’

0123456 Ulthute Nimga Resume( x15’ Pa)

Fig. 3. Dependences of coercivity t-i, and saturation magnetization M, on ultimate nitrogen pressure PF,:.

nering spectra and (b) profile of Fe atoms of

Fig. 3 shows the dependenceof coercivity II, and saturationmagnetizaiio,lA4$on ultimateBN7for the gradient films. The samplecontainingFe,6N2 in curvea of Fig. 1 is 1252 emu/cc, not larger than thatof bulk Fe because of the existenceof the Fe,N (2
I++ X-ray ~~~~0~

L+T-+-l

40 50 60 70 80 90 24 paMm of the films deposited at various res PN2; (a) PNz= 1.5~ IO-’ Pa, (b) (cl PN2 = 4.6 x lo- ’ Pa.

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