Journal of Magnetism and Magnetic Materials 272–276 (2004) e353–e355
Microstructure and magnetic properties
of Co
70.5 x
Tb
29.5
Pd
x
films
C.T. Lie
a,*, P.C. Kuo
a, C.Y. Chou
a, S.C. Chen
b, T.H. Wu
a, A.C. Sun
aa
Institute of Materials Science and Engineering and Center for Nanostorage Research, National Taiwan University, Taipei 106, Taiwan
b
Department of Mechanical Engineering, De Lin Institute of Technology, Taipei 236, Taiwan
Abstract
The Co70.5 xTb29.5Pdx films (x=0B22.5 at%) were prepared at room temperature. Transmission electron
microscopy diffraction patterns revealed that all the films are amorphous. The saturation magnetization is decreased and the perpendicular coercivity is increased with increasing Pd content as xo5 at%. But the perpendicular coercivity is decreased rapidly with increasing Pd content as x>5 at%. Compensation temperature of the Co70.5 xTb29.5Pdxfilm is
decreased with increasing Pd content. Compensation composition of the film occurs at xB5 at%. r2004 Published by Elsevier B.V.
PACS: 75.50.Kj; 75.70.-i
Keywords: Co70.5 xTb29.5Pdxfilm; Compensation temperature
Amorphous films of rare earth-transition metal (RE-TM) alloys such as Co–Tbare of interest in the basic research and their application. They have been widely studied by many investigators[1,2]. Previously, we had shown that the magnetic properties of amorphous CoTb film are sensitive to the composition of the film and the process parameters[3]. In this work, we investigated the effects of Pd content on the microstructure and magnetic properties of the CoTbPd film.
The Co70.5 xTb29.5Pdx films (x=0B22.5 at%) were
prepared on glass and natural-oxidized silicon wafer substrates at room temperature by DC magnetic sputtering of the composite target which made by over-laying Tband Pd chips on the Co target. The CoTbPd magnetic film was sandwiched between the SiNx protective layers to prevent oxidization. Thicknesses of the CoTbPd magnetic layer and the SiNx protective layer were 75 and 30 nm, respectively. Structure of the film was examined by transmission electron microscopy (TEM). Composition and homogeneity of the film were determined by energy dispersive spectroscopy (EDS).
The film thickness was measured by atomic force microscope (AFM). Magnetic properties of the film were measured by using vibrating sample magnetometer (VSM) at room temperature and superconducting quantum interference device (SQUID) at temperatures between 25 and 400 K.
TEM analysis shows that the Co70.5 xTb29.5Pdxfilm is
amorphous structure as Pd content is less than 22.5 at%.
Fig. 1is a typical example;Fig. 1(a)is the TEM image of the Co63.5Tb29.5Pd7 film. No crystal grains and grain
boundaries are observed in Fig. 1(a). Fig. 1(b) is the electron diffraction pattern ofFig. 1(a). The broad halo diffraction pattern indicates that this film is an amorphous structure.
Fig. 2shows the variations of saturation magnetiza-tion Ms and perpendicular coercivity Hc with Pd content of the Co70.5 xTb29.5Pdxfilm at room
tempera-ture. The Ms value of pure Co70.5Tb29.5film (x=0 at%)
is about 130 emu/cm3. It is found that the Ms value decreases with increasing Pd content and approaches 0 at xB5 at% then increases as x>5 at%. CoTballoy is sperimagnetic. The magnetization of the Co subnetwork is antiparallel to that of the Tbsubnetwork. Co70.5Tb29.5
is RE-rich because its compensation temperature (Tcomp) is higher than room temperature [4]. The net
ARTICLE IN PRESS
*Corresponding author. Tel.: +2364-8881; fax: 886-2-2363-4562.
E-mail address:[email protected] (C.T. Lie).
0304-8853/$ - see front matter r 2004 Published by Elsevier B.V. doi:10.1016/j.jmmm.2003.11.369
magnetization of the Co70.5Tb29.5alloy is parallel to the
direction of Tbmagnetization. When some Co atoms are substituted for the non-magnetic Pd atoms, the net magnetization of the Co70.5 xTb29.5Pdx alloy will be
increased. So, Ms value of the Co70.5 xTb29.5Pdx film
will increase with Pd content. However, as shown inFig. 2, Ms value of the Co70.5 xTb29.5Pdxfilm is decreased
with increasing Pd content as xo5 at%. This is due to the effect of Co–Pd interface on the magnetization of Co70.5 xTb29.5Pdx. It had been shown that the
satura-tion magnetizasatura-tion of Co/Pd multilayers exceed than that of pure Co, owing to the spin polarization of non-magnetic Pd[5]. The magnetization of TM subnetwork is increased in RE-rich CoTbPd alloy due to the polarization of the Pd atoms. This results in reducing the Ms value of Co70.5 xTb29.5Pdxfilm as Pd content is
less than 5 at%. The Co70.5 xTb29.5Pdx alloy becomes
TM-rich as x>5 at%, as shown inFig. 3.
The Hc value of pure Co70.5Tb29.5film (x=0 at%) is
about 2500 Oe as shown inFig. 2. The Hc value increases rapidly from 2500 to 8000 Oe when Pd content increases from 0 to 3.5 at%. Hc decreases rapidly as x larger than about 5 at%. The compensation temperature Tcomp of
RE-TM alloy is very sensitive to the composition of the alloy[4]. At room temperature, the Ms value is zero and Hc value is infinite at the compensation composition. In the RE-rich region, Ms decreases but Hc increases as Tcompis decreased. In the TM-rich region, Hc decreases
as Tcomp is decreased. In Fig. 2, we can see that the
Co70.5 xTb29.5Pdx alloy is transform from RE-rich to
TM-rich when x>5 at% at room temperature.
Fig. 3shows the variation of Tcompwith Pd content of
the Co70.5 xTb29.5Pdxfilm. The Co70.5Tb29.5film is
RE-rich because Tcomp of the Co70.5Tb29.5 film is about
410 K which is higher than room temperature. Tcompof
the Co70.5 xTb29.5Pdx film is decreased from 410 to
130 K as Pd content is increased from 0 to 22 at%. The compensation composition of the Co70.5 xTb29.5Pdxfilm
is about at x=5 at%, as shown inFig. 3. Tcompof the
Co70.5 xTb29.5Pdxfilm is lower than room temperature
as x>5 at%.
The effects of Pd content on the microstructure and magnetic properties of the Co70.5 xTb29.5Pdxfilms with
x=0B22.5 at% have been investigated. TEM analysis indicated that all these films are amorphous. Substitut-ing Co for the non-magnetic Pd will decrease the compensation temperature of the Co70.5 xTb29.5Pdx
film. The compensation composition of the film occurs at xB5 at%.
This work was supported by the National Science Council and Ministry of Economic Affairs of R.O.C.
ARTICLE IN PRESS
Fig. 1. (a) TEM bright-field image and (b) electron diffraction pattern of the Co63.5Tb29.5Pd7film. 0 5 10 15 20 25 0 25 50 75 100 125 150 175 Hc (Oe) Pd (at.% ) Ms (emu/cm 3 ) Ms 0 2000 4000 6000 8000 10000 12000 Hc
Fig. 2. Variations of Ms and Hc with the Pd content of the Co70.5 xTb29.5Pdxfilm. 0 5 10 15 20 25 100 150 200 250 300 350 400 450 500
T
com p(
K)
Pd ( at.% )
Fig. 3. Relationship between Tcomp and Pd content of the
Co70.5 xTb29.5Pdxfilm.
C.T. Lie et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e353–e355 e354
through Grant No. NSC 90-2216-E 002-036 and 92-EC-17-A-08-S1-0006, respectively.
References
[1] H. Katayama, et al., Appl. Phys. Lett. 81 (2002) 4994.
[2] R. Carey, et al., Thin Solid Films 259 (1995) 75. [3] P.C. Kuo, et al., J. Appl. Phys. 84 (1998) 3317. [4] P. Hansen, et al., J. Appl. Phys. 69 (1991) 3194. [5] K. Miura, et al., J. Appl. Phys. 72 (1992) 4826.
