FePt thick films by electrodeposition
Electrodeposition of hard magnetic FePt thick films
FePt films are of interest for use as high density storage media or as micromagnets in microelectromechanical systems (MEMS) due to the excellent hard magnetic properties of the L10 phase. In contrast to physical deposition techniques, electrodeposition of FePt would be a less expensive and simple way to deposit FePt films, as no vacuum environment is needed and the material is used more efficiently. Thick films, especially for MEMS, could be produced in an economic way. However, to form the L10 phase, post annealing of the films is required. The composition of the films is controlled by the applied potential [1]. Films are amorphous or nanocrystalline after deposition. During the electrodeposition a large amount of oxygen (30 at. %) is incorporated into the films. This is presumably due to hydroxide formation in front of the cathode, resulting from a pH rise induced by the strong hydrogen evolution reaction that is catalysed by Pt.
Annealing of the films was carried out in vacuum and later on in hydrogen atmosphere. In Fig. 1 the magnetic properties after annealing are summarized. When annealing in vacuum high temperatures are needed to form the L10 phase and achieve reasonable coercivities. The magnetization values remain low at all times. In contrast, during annealing in hydrogen as a reducing atmosphere, the oxygen content is decreased to < 10 at.% which leads to a strong increase of the magnetization values. At the same time phase formation is enhanced and hard magnetic properties are obtained already from 400°C on. A very high coercivity for electrodeposited films of 1.1 T is achieved at 600°C [2].
Microstructural analysis of the H2-annealed films show some remaining iron oxides and Cu interdiffusion from the buffer (Fig. 2) [3]. Grain growth is hindered by the remaining iron oxides and at 600°C, grain sizes are still in the range of 20-30 nm. This favours the high coercivity. In addition, the Cu in the grain boundaries might decouple the grains.
It can be seen that it is possible to produce FePt films with good hard magnetic properties using electrodeposition and post annealing in H2. A further improvement can be obtained by using Fe/Pt multilayers [4].
Fig. 1: a) Coercivity and b) Remanence of electrodeposited FePt films after annealing in different atmospheres [2]
Fig. 2: STEM-HAADF image of a film annealed in hydrogen at 800°C for 10 min combined with EDX line scans identifying Fe-O and Cu [3]
Key publications
K.
Leistner, H. Schlörb, J. Thomas, L. Schultz, S. Fähler
Remanence enhancement in nanoscaled
electrodeposited FePt films
Appl. Phys. Lett. 92 (2008) 052502
Interfacial Fe (III)-hydroxide formation
during Fe-Pt alloy deposition
Electrochimica Acta 53 (2008) 6973
K. Leistner, J. Thomas, H. Schlörb, M. Weisheit, L. Schultz, S. Fähler
Highly coercive electrodeposited FePt films by postannealing in hydrogen
Appl. Phys. Lett. 85(16) (2004) 3498
Publications
2008
M. S.
Khatri, H. Schlörb, S. Fähler, L. Schultz, B. Nandan, M.
Böhme, R. Krenek, M. Stamm
Electrodeposition of Co-Pt continuous films and
nanowires within diblock copolymer template
Electrochimica
Acta (2008), in press
K. Leistner, P. Schaaf,
A.Voss, S. Fähler, H. Schlörb, L. Schultz
Interfacial Fe (III)-hydroxide formation
during Fe-Pt alloy deposition
Electrochimica Acta 53 (2008) 6973
K.
Leistner, H. Schlörb, J. Thomas, L. Schultz, S. Fähler
Remanence enhancement in nanoscaled
electrodeposited FePt films
Appl. Phys. Lett. 92 (2008) 052502
2007
M. S. Khatri, H. Schlörb, S. Fähler, L. Schultz, B. Nandan, M. Böhme, R. Krenek, M.
Stamm
Electrodeposition of Co-Pt continuous
films and nanowires
Proc. Euro-Interfinish Conference (2007) O21
K. Leistner, H. Schlörb, S. Fähler, L. Schultz
Electrodeposition of FePt films and Fe/Pt multilayers
ECS Trans. 3 (25)
(2007) 267
K. Žužek Rožman, A. Krause, S. Baunack, K. Leistner, S. Fähler, L. Schultz, H. Schlörb
Electrodeposition and hard magnetic properties of Co-Pt films in comparison to Fe-Pt films
J. Mag. Mag. Mat. 314(2) (2007) 116
2006
J. Buschbeck, S. Fähler, M. Weisheit, K. Leistner, J. McCord, B. Rellinghaus, L. Schultz
Termodynamics and kinetics during pulsed laser annealing and patterning of FePt films
J. Appl. Phys. 100 (2006) 123901
K. Leistner, S. Oswald, J.
Thomas, S. Fähler, H. Schlörb, L. Schultz
Potential dependence of composition and
structure of electrodeposited Fe-Pt films
Electrochimica Acta 52(1) (2006) 194
K. Leistner, A. Krause, S.
Fähler, H. Schlörb, L. Schultz
Electrode processes during Fe-Pt
electrodeposition studied by electrochemical quartz crystal microbalance
Electrochimica Acta 52(1) (2006) 170
K. Leistner, S. Fähler, H. Schlörb, L. Schultz
Preparation and characterization of electrodeposited Fe/Pt mulitlayers
Electrochemistry Communications 8 (2006) 916
2005
K. Leistner, J. Thomas, S. Baunack, H. Schlörb, L. Schultz, S. Fähler
Influence of oxygen and copper in electrodeposited FePt films
J. Mag. Mag. Mat. 290-291, 2 (2005) 1270
2004
K. Leistner, E. Backen, B. Schüpp, M. Weisheit, L. Schultz, H. Schlörb, S. Fähler
Phase formation, microstructure and hard magnetic properties of electrodeposited FePt films
J. Appl. Phys. 95(11) (2004) 7267
K. Leistner, J. Thomas, H. Schlörb, M. Weisheit, L. Schultz, S. Fähler
Highly coercive electrodeposited FePt films by postannealing in hydrogen
Appl. Phys. Lett. 85(16) (2004) 3498
K. Leistner, H. Schlörb, M. Weisheit, L. Schultz, S. Fähler
The influence of composition on the hard magnetic properties of electrodeposited Fe-Pt films
Proc. 18th Int. Workshop on High Performance Magnets and their Applications Vol. 2 (2004), 866