Magnetic Properties and Structural Transformation in Copper-304 Stainless Steel Multilayer Materials
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Mat. Res. Soc. Symp. Proc. Vol. 382 ©1995 Materials Research Society
EXPERIMENTAL Cu-304SS multilayers have been synthesized using two magnetron sputtering sources and a rotating substrate table. The substrates were three and four inch silicon wafers [(111) and (100)] and their temperatures rose above ambient but never increased above 250 'C for the highest sputtering power. To achieve the desired multilayer period, the target power and the substrate rotation speed were varied. The individual, equal layer thicknesses were varied from 5.0 to 500 A with the total multilayer thicknesses equal to 10-25 ptm. The total time for deposition of the multilayers was 3-6 hours. Table 1 shows the list of samples synthesized and studied. Table 1. Cu-304SS multilayer films studied Sample I.D.
Cu
304SS
Period
No. Bilayers
Film thickness
289-016 289-020 289-011 289-021 289-013 289-019 289-012 289-014 289-015 291-032
4.9 7.3 9.8 13.5 24.7 49.6 98.9 247 494 0
4.9 7.4 9.8 13.4 24.7 49.6 98.9 247 494 50
9.8 14.7 19.6 26.9 49.4 99.2 197.8 494 988 -
10162 9058 9653 6499 5000 2170 1002 400 200 1000
9.99 13.2 19 17.48 19.83 21.52 19.83 19.8 19.8 5
t(A) t(A) (m ). . . . . . . . . . . . ................................................... (.... .............. ..(... . ...................... .d(A) .... (......................................................................
X-ray diffraction scans were performed using a Philips XRG 3100. Magnetic moments as a function of field and annealing temperature (T = 20 - 1000 'C) were measured with a Lake Shore 4500 Vibrating Sample Magnetometer with the magnetic field in the range 0 - ±10 kOe. OBSERVATIONS Structural studies of Cu-304SS multilayers have been reported elsewhere [7]. Fig. 1 shows the x-ray diffraction results of selected multilayers of Cu-304SS and a foil of 304SS. Two thickness regimes are observed in the XRD data. In multilayers with periods d (d=2t) less than 20 A, 304SS grows as FCC where (111) planes are normal to growth direction. Multilayers with periods d larger than 20 A contain both FCC and BCC 304SS in each layer. The ratio of BCC to FCC increases as the period is increased. The presence of an FCC phase in all samples is generated by the epitaxial growth of the 304SS on copper. However the BCC structure growth takes place away from the interface, particularly in large period samples. Completely BCC structure is observed only in the 304SS foil with no copper. We have measured magnetic moment as a function of field at room temperature to correlate the magnetic response with the structural studies. A paramagnetic response characterized by lack of hysterics loop and a linear dependence of magnetic moment on the field in the range 0 - ±10 kOe is observed for the two thinnest samples with periods 9.8 A and 14.7 A containing only FCC 304SS. The 19.6 A period multilayer shows a weak ferromagnetism indicating the presence of a minute amount of BCC phase which has not been revealed in the
192
FCC d -19.6 A
d = 75 A
d =5,oA
d= 1CCOA
304,S only
L
(50 A/l yer)
40
O
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