Interface Crystallography of Iron-Group Metals and Alloys Electrodeposited on Copper BY J. M. O'SULLIVAN" AND D. P. OXLEY~ Received 12 June, 1972 A wide range of binary Co, Fe, Ni alloys has been prepared by electrodeposition on to cube- textured copper substrates. The alloys, after removal from the substrate were examined by trans- mission electron microscopy. All alloys were found to be of either b.c.c., f.c.c. or c.p.h. structure according to their composition. The interface crystallography of these alloys is discussed in terms of the relationships between prominent directions in the iron-group alloys, and the direction of the copper face diagonals in the cube-textured substrate. The metals and binary alloys of the iron, nickel, cobalt group are of interest because of their ferromagnetic properties,l.which have important applications in the thin foil state in magnetic recording and computer memory devices. Although these metals and alloys have been used for such applications, the crystallography at the interface between substrate and deposit foil has not been surveyed for all possible alloys of all the possible phases in this group. It is thought that a detailed knowledge of the crystallographic structure is important in interpretation of the ferromagnetic properties of such materials especially in the thin foil condition. Previously, most attention has been given tc alloys of the nickel +iron system, in which both f.c.c., b.c.c. interface crystallography with respect to copper have been investigated. In the other binary systems containing cobalt, measurements of magnetic parameters have been made but structural factors have not had such attention.The purpose of this paper is to extract the general crystallographic relations from the interface situations available in the iron, nickel, cobalt group electrodeposited on to electropolished cube-oriented copper foil. The group provides examples of f.c.c., b.c.c. and c.p.h. foils. Since lattice constants of the metals and alloys of a given phase are close, the crystallographic relations are described conveniently by means of three simple two-dimensional models of the interface structure for f.c.c., b.c.c. and c.p.h. phases. These are based on the transmission electron diffraction pattern of a typical metal or alloy in each phase. EXPERIMENTAL All metals and alloys were deposited from static aqueous salt baths at a current density of 10 mA cm-2.The foils were chemically removed from their substrates and examined by transmission electron diffraction. Analyses of foil compositions were carried out by atomic absorption spectrophotometry. * Department of Physics, University of Warwick, Coventry. t School of Physics, Leicester Polytechnic, Leicester. 194J . M. O'SULLIVAN AND D. P. OXLEY 195 RESULTS F . C . C . FOIL DEPOSITION O N COPPER F.c.c. foils of nickel, cobalt, nickel-iron,2 iron-cobalt and nickel-cobalt may be deposited on to copper so that (100) [Ol 11 alloy 11 (100) [Oll] Cu. Some evidence of (1 11) microtwinning was also apparent in all systems. Grain size was comparable to that of the substrate, -0.01 mm.Plate l(a), a diffraction FIG. 1. pattern of a (100) 94 nickel, 6 % cobalt alloy, shows extra diffraction features at A and B indicating twinning. The geometry and associated diffraction effects have been thoroughly discussed previ~usly,~ and these are not included in the model (fig. 1) of the arrangement of planes in copper and alloy in this situation. B . C . C . FOIL DEPOSITION O N COPPER The iron+cobalt and ironfnickel systems give b.c.c. alloys in the iron-rich regions. Some previous work has been carried out on iron+nickel alloys of this phase,2 but this has not been extended to the iron+cobalt system. It was found in the present work that the interface structure of both systems in the b.c.c. phase is identical and can best be stated as where the last term expresses the misfit between two sets of orthogonal (110) deposit orientations in the foil plane as in fig.2. When @ = 19" 30', the structure consists of two orthogonal ( 1 lo] deposit orientations. Grain size in these alloys was small, - 500 A in extent, with no marked growth habit. A typical diffraction pattern of a 43 % cobalt, 57 % iron alloy foil is given in plate l(b). 2-G*196 IRON-GROUP ALLOYS ELECTRODEPOSITED ON COPPER - ~ l l o y - ----- Copper FIG. 2. FIG. 3.PLATE 1 [To face page 1 96J . M. O'SULLIVAN AND D. P. OXLEY 197 C.P.H. FOIL DEPOSITION ON COPPER As representative of the c.p.h. phase, only cobalt was stripped from the substrate successfully, even then only with great difficulty, in small pieces. The interface crystallography is described by (001)[210]aCo~~{ 100)(011)Cu, so that there are six equivalent positions of the cobalt basal plane.One such position is shown in fig. 3, which is based on plate l(c). The crystallographic relations found here are in agreement with those determined by a reflection electron diffraction method for cobalt foils on copper single crystal (001) faces.' Due to difficulties in stripping cobalt from the substrate, it was not possible to measure the grain size accurately. DISCUSSION Matching in the interface planes may be discussed in a unified fashion with refer- ence to a particular dimension in the copper substrate (100) surface. Taking the lattice parameter for copper as 3.61 A, typical f.c.c. as 3.55A, b.c.c. as 2.86A and c.p.h.(ao) as 2.50A, a slightly more quantitative model may be used to support that found from the diffraction experiments reported above. From the diffraction experi- ments and approximate lattice parameters, the copper cube-face diagonal may be used to describe the interface crystallography. For f.c.c. deposition the misfit along cube- face diagonals is small, i.e., 5.02 A in the alloy against 5.12 A in copper. For b.c.c. deposits, misfit is small between the body diagonal, 4.95 A, and the copper cube-face diagonal. In the c.p.h. deposit there is closer agreement between a basal-plane diagonal and the copper cube-face diagonal. Thus, the variety of structures available in thin foil metals and alloys of the iron group may be correlated with a tendency to minimize misfit along prominent directions in substrate and electrodeposit. Hence, the main structures obtainable in thin foil form in the iron group electrodeposited on to copper foil have been described with respect to the interface crystallography between substrate and deposit.The importance of copper cube-face diagonals in this description has been noted. It was found that close correlation occurred in the length of the copper cube-face diagonal and prominent directions in the various iron group structures. The bulk of the above work was carried out in the Applied Sciences Department, Lanchester Polytechnic, Rugby. The authors are especially grateful to Dr. R. F. Y. Randall, Head of Department, for provision of laboratory facilities and encouragement during the project, and to Mr. N. F. Hall who carried out analyses of foils. H. W. Fuller and M. E. Hale, J. Appl. Phys., 1960, 31, 238. G. A. Jones, D. P. Oxley and R. S. Tebble, Phil. Mag., 1966, 14, 881. I. M. Wolf, J. Appl. Phys., 1962, 33, 1152s. J. M. O'Sullivan and D. P. Oxley, J. Elect. Micr., to be published. ' R. D.. Burbank, R. D. Heidenreich, Phil. Mag., 1960, 5, 373. ti G. A. Jones, Phys. Stat. Sol., 1967, 19, 811. J. Goddard and J. G. Wright, Brit. J. Appl. Phys., 1964, 15, 807.