S. Groudeva-Zotova a , H. Karl b , A. Savan a , J. Feydt a , B. Wehner a, T. Walther a , N. Zotov a* , B. Stritzker b , A. Ludwig a,c a - Combinatorial Materials Science group, CAESAR, D-53175 Bonn, Germany; b - Institut of Physics, University of Augsburg, D-86135 Augsburg, Germany; c – Institute of Materials, Faculty of Mechanical Engineering, Ruhr-University, 44780 Bochum, Germany M o t i v a t i o n M o t i v a t i o n Ion implantation in thin metal films: This method can be used to (i) tailor the magnetic properties of the films by introducing defects and changing the stress state [1], and (ii) change the film phase composition by alloying in the as-implanted state or after additional annealing [2]; System: (FeCo - Sm) thin film precursors for exchange spring magnet (ESM) materials [3]; Combinatorial approach: For screening a wide range of Sm- and Xe- implantation doses and for characterization of the resulting materials libraries in order to obtain an overview about the system. Comparison between Sm- and Xe-implantation of Fe 50 Co 50 thin films: In order to differentiate between alloy formation and effects related to defects. [1] R.Gupta, G.A.Müller, P..Schaaf, K. Zhang, K.P.Lieb, Nucl. Instr. Meth., 216 (2004) 313. [2] M. Nastasi, J.W. Mayer, J.K. Hirvonen, Ion-solid interactions: fundamentals and applications, Cambridge Univ. Press 1996, Cambridge. [3] Z.H. Cheng, J.-X. Zhang, H. Kronmüller, Phys. Rev. B, 68 (2003) 144417. E x p e r i m e n t E x p e r i m e n t A series of Fe 50 Co 50 films (80 -100 nm thick) was deposited on thermally oxidized 4” Si(100) wafers by magnetron sputtering (p Ar = 6 x 10 -1 Pa, 200 W RF). The ion implantation was performed in a combinatorial fashion using movable shutters. The dose was varied in steps from 4x10 15 to 1.57x10 17 ions/cm 2 for single-ion implantation of Xe at 180 keV and Sm at 190 keV. After measuring the film thickness with a stylus profilometer, and resistivity with an automated four-point probe, the wafers were cut into pieces (6.5 x 6.5 mm 2 ) for further characterization of materials libraries along the dose gradient direction. SIMS depth profiles were used to identify the distribution of elements through the film thickness. Energy dispersive X-ray (EDX) analysis in a scanning electron microscope (SEM) was used to determine the overall composition of the films. The change of the structure of the FeCo films before and after implantation was measured by XRD and, for selected samples, by cross-sectional TEM. Magnetic properties were measured with a vibrating sample magnetometer (VSM). Short-time annealing experiments were performed in vacuum for 30 s at 800 o C. Preliminar stress evaluation was made on the basis of curvature measurements of the square samples. R e s u l t s R e s u l t s Composition, morphology and structure (EDX/ SIMS/ TEM/ XRD) The overall Sm content of the films varies with the implantation dose from 0 to about 12 at.%. SIMS depth profiling shows peak-like distribution of the implanted element as expected by TRIM simulations. The implantation dose is limited by re-sputtering effects which occurred significantly at doses D Sm > 1x10 17 ions/cm 2 and D Xe > 6x10 16 ions/cm 2 . TEM cross-sectional analysis shows small changes of the as-deposited column morphology at low doses and a significant change at the highest Sm doses. According to the XRD data, the as-deposited and the as- implanted FeCo films are (110) textured. For ion implantation doses below 6x10 16 ions/cm 2 the (110)FeCo peak shifts are most pronounced for Sm-implantation, showing presence of lattice strains perpendicular to the film plane corresponding to enlargement of the lattice parameter in this direction. Preliminary measurements of the residual mechanical stress in the films reveal tensile stress for the samples implanted with medium Sm dose and compressive stress for the samples implanted with high dose Sm or Xe. Short-time annealing experiments lead to full relaxation in both systems for D < 6x10 16 ions/cm 2 . Electrical resistivity The electrical resistivity of the films increases by a factor of 5 after ion implantation with the highest doses. Sm-ion implantation results in slightly higher resistivity probably due to: (i) defects introduced by the ion bombardment, and (ii) possible formation of new Sm-Fe(Co) phases in the highest Sm-content samples. Short--time annealing decreases ρ to the resistivity of as-deposited films. Magnetic properties - No in-plane magnetic anisotropy (MA) was found in the samples implanted with Xe, while the Sm-implanted films show a significant MA at medium Sm doses and two-step hysteresis curves at the highest D Sm used. This could be attributed to a possible second intermetallic phase. Short- time annealing destroys the magnetic anisotropy. - The specific saturation magnetization determined after thickness correction of the raw data agrees well with the data published for FeCo thin films and remains almost constant for both series up to relatively high implantation doses. An abrupt decrease was found only for Xe implantation, mainly due to the high degree of re-sputtering. - The comparison of the dose influence on the film magnetic characteristics reveals quite different changes of the coercivity H c and the anisotropy field H k for the Xe- and Sm- implanted series. A clear splitting in the H c - dose dependencies is seen at D > 9x10 15 ions/cm 2 , while the H k – dose dependencies show an almost negligible anisotropy for the Xe- and a very strong one for the Sm-implantation over the whole investigated range. After annealing the films show values close to the “as-deposited” H c and H k . Structural and magnetic characteristics of FeCo thin films modified by combinatorial ion implantation Combinatorial ion implantation Depth profile analyses Structural analysis Magnetic characteristics: Film resistivity 0 1 2 3 4 R , Ω FeCo+Sm 0 1 2 3 4 R , Ω FeCo+Xe 4e15 ions/cm2 1.57e17 ions/cm2 1.57e17ions/cm2 Film: Si(4“) / Si Ox (400 nm) / Fe 50 Co 50 Implantation: Sm(190 keV) ; Xe(180 keV) 44 45 46 I, a.u. 1,57e 17 at/cm 2 4e 15 at/cm 2 2θ, o FeCo+Xe (110)Fe 50 Co 50 as-deposited 44 45 46 1,57x10 17 at/cm 2 4x10 15 at/cm 2 (110)Fe 50 Co 50 FeCo+Sm I, a.u. 2θ, o as-deposited Film characteristics – f(Dose) 1E16 1E17 20 40 60 80 as-deposited +Xe +Sm ρ, µΩ.cm Dose Sm(Xe), ions/cm 2 ELECTRICAL RESISTIVITY Correlations between the film strains and the film properties 1 10 0 200 400 600 as-deposited MAGNETIC ANISOTROPY H k , Oe Sm, at.% 1 10 0 20 40 60 80 as-deposited RESISTIVITY ρ, µΩ.cm Sm, at.% * 5.51 x10 16 3.26 x10 16 **1.57 x10 17 *1.49 x10 16 Sm I Sm , a.u. Sputtered depth, a.u. * ** 190 keV Sm implantation with different doses 180 keV Xe implantation with different doses 1E16 1E17 0.0 0.5 +Sm +Xe h impl / h as-dep Dose Sm(Xe), ions/cm 2 1.0 1E16 1E17 0 4 8 12 * * +Sm Sm(Xe), at. % EDX: OVERALL CONTENT OF THE IMPLANTED ELEMENT +Xe ** -1000 -500 0 500 1000 -2 -1 0 1 2 -1000 -500 0 500 1000 -2 -1 0 1 2 -1000 -500 0 500 1000 -2 -1 0 1 2 0 o , 90 o , 45 o 5,14E16 ions/cm 2 4πM / V, kG 0 o , 90 o , 45 o 1,43E16 ions/cm 2 4πM / V, kG H, Oe 4E15 ions/cm 2 4πM / V, kG 0 o , 90 o , 45 o -1000 -500 0 500 1000 -2 -1 0 1 2 -1000 -500 0 500 1000 -2 -1 0 1 2 -1000 -500 0 500 1000 -2 -1 0 1 2 4πM / V, kG 4πM / V, kG 4E15ions/cm 2 4πM / V, kG 0 o , 90 o , 45 o 5,14E16 ions/cm 2 0 o , 90 o , 45 o H, Oe 1,43E16 ions/cm 2 0 o , 90 o , 45 o 1E16 1E17 0 10000 20000 30000 MAGNETIZATION 4πM s / V, G Dose Sm(Xe), ions/cm 2 +Xe +Sm 1E16 1E17 0 100 200 300 400 500 as-deposited H c , Oe Dose Sm(Xe), ions/cm 2 +Xe COERCIVITY +Sm 1E16 1E17 0 200 400 600 800 MAGNETIC ANISOTROPY +Xe +Sm H k , Oe Dose Sm(Xe), ions/cm 2 4e15 ions/cm2 3.26x10 16 5.51x10 16 *1.49x10 16 Xe I Xe , a.u. Sputtered depth, a.u. C o n c l u s i o n s C o n c l u s i o n s  Dose limits due to re-sputtering effects - different for Xe and Sm.  Magnetic anisotropy formation in Sm-implanted FeCo films - correlation with the lattice strains and residual film stresses.  Relaxation effects after short-time annealing and vanishing of the magnetic anisotropy.  High overall Sm content despite the dose limiting - 12 at.% > 10.5 at.% (necessary for Co(Fe)-Sm alloy formation, according to the equilibrium phase disgrams).  Two-steps hysteresis curves - first indication for the possible formation of multi-phase samples. 30s/800 o C 100 nm substrate substrate substrate 30s/800 o C 0 20 40 60 80 100 0.5 as-deposited +Xe +Sm h impl / h as-dep X, mm 1.0 1E16 1E17 44.6 44.8 45.0 45.2 XRD: (110)FeCo PEAK POSITION 2θ, o (110)FeCo +Xe +Sm 0 20 40 60 80 100 0.00E+000 4.00E+016 8.00E+016 1.20E+017 1.60E+017 Dose Sm(Xe), ions/cm 2 X, mm Gradient direction 1 10 44.6 44.8 45.0 45.2 (110)Fe 50 Co 50 XRD: (110)FeCo PEAK POSITION 2θ, o Sm, at.% 30s/800 o C