2940 zyxwvutsrqponml IEEE zyxwvutsr TRANSACTIONSON zyxwvu MAGNETICS. VOL. 28, NO. 5. SEPTEMBER 1992 In-Plane Magnetic Anisotropies in Polycrystalline Ni Films Induced by Xe Bombardment during Growth M. Farle, H. Saffari, W. A. Lewis, E. Kay and S. B. Hagstrom Department of Materials Science and Engineering, Stanford University, Stanford, California 94305-2205 zyxwv Abstract zyxwvutsrqpo - 250 to 1500 A thin Ni films were ion beam sput- tered onto a fused quartz substrate with simultaneous bombardment by Xe ions of 100 eV. Hysteresis loops were recorded ex situ by the longitudinal magneto-optic Kerr effect. A maximum in-plane uniaxial anisotropy field of 12 kA/m (151 Oe) w1u found in 750 A thick films that were deposited with a flux ratio of Xe ions to Ni atoms of 0.12. The easy axis of magnetization was found to lie perpendicular to the plane of incidence of the secondary ions. Films showing the strong uniaxial in-plane anisotropy were almost completely (111) textured normal to the film plane. A maximum lattice expansion of 0.5 .! normal to the film plane was observed for these films. 1. INTRODUCTION The control of magnetic anisotropy and coercivity is a very important aspect in the production of practical magnetic recording media. It is a well-known experimental fact that uniaxial in-plane magnetic anisotropies can be induced in several Werent ways, for example, by deposition at an oblique incidence angle [l] or in an applied magnetic field. The zyxwvutsrq easy axis of the anisotropy can be found either perpendicular or parallel to the plane of incidence of the arriving atoms. As an extension of our earlier work [2] we demonstrate here in the case of Ni that secondary ion bombardment during film growth induces an uniaxial anisotropy, whose orientation and magnitude is controlled by the secondary ion beam parameters. It has been found, that depending on the ion zyxwvu beam parameters, different degrees of texturing and considerable lattice contraction or dilation zyxwvutsrq can be induced in such films [3]. While the micro structural analysis of such films has been performed extensively, there are only a few systematic studies on the influence of these structural modifications, that is, grain structure and preferred orientation of crystal- lites (texture), on the magnetic properties. In the case of Ni it was found [2] that secondary ion bombardment with 500 eV Ar+ ions during film growth at an angle of 45' from the film nod induces a very weak uniaxial in-plane anisotropy (< 1.6 kA/m) in thin (400 A) films that is absent for unbombarded films. The easy axis of the in-plane anisotropy the Stiflung Volkswagenwedc and by the IBM Almaden Research Center Manuscript received February 17,1992. This work was supported in part by was dependent on the flux ratio of secondary ions to deposited Ni atoms. A careful structural analysis of these films excluded a preferred tilt of the (111) grains along a direction of the incidence plane of the secondary ions. The origin of the weak observed anisotropy was found to be of magneto elastic origin. In a related work [l] on 8000 A Ni films which were obliquely deposited at an angle of 45' from the substrate normal, the easy axis was found to lie parallel to the incidence plane with a maximum anisotropy field Hk = 12 W m . There, it was also concluded that an induced anisotropic stress in the crystallites is the origin of the observed anisotropy. The purpose of our present work is to increase the magnitude of the in-plane magnetic anisotropy induced by secondary ion bombardment during deposition to a compa- rable level with the results in [l] and to begin a systematic study on the relationship between modification of the micro structure and the observed magnetic anisotropy. To increase the momentum transfer of the secondary ion beam to the growing film we chose Xe as the sputter gas. II. EXPERIMENTAL Details of the dual ion beam system used in our study have been described elsewhere [4]. The base pressure of the vacuum system is 10-6 Pa. The partial pressure of Xe during deposition is 10-2 Pa without any detectable impurities. A Ni target is sputtered at rates of 0.1 to 2 us by a primary monoenergetic (1000 ev) Xe+ beam. Xe ions were chosen because they have a very low reflection coefficient at the Ni target, thereby minimizing bombardment of the substrate by high energy back scattered neutrals. A secondary Xe ion beam was incident on the growing film at an angle of 45' from the film normal. The ion energy was varied between 50 to 200 eV. Above 200 eV considerable resputtering of the growing film was observed and below 50 eV the ion beam parameters became unstable. The Xe+ ion flux was determined by placing a Faraday cup at the position of the sample and measuring the ion current. Care was taken to minimize erroneous readings due to secondary electrons. The relative flux ratio R of secondary Xe+ to Ni atoms was varied between R = Xe/Ni = 0.1 and 0.5. Films 250 to 1500 A were deposited on an amorphous fused quartz substrate held at a temperature of app. 330 K. The substrate was sputter cleaned for 5 minutes before deposition. __ 0018-9464~2$03.00 0 1992 IEEE