Perpendicular magnetic anisotropy studies in
Tb-Dy-Fe-Co thin films
*
Himalay Basumatary*,†, J. Arout Chelvane*, S. V. Kamat* and Rajeev Ranjan†
Advanced Magnetics Group, Defence Metallurgical Research Laboratory, Hyderabad, India
†Department of Materials Engineering, Indian Institute of Science, Bengaluru, India
Email: jac@dmrl.drdo.in
Key words: Magnetic anisotropy, magnetization measurements, magnetic thin films
Abstract: We report the structural and magnetic properties
of amorphous Tb10Dy23Fe56Co6 thin films grown with
different thicknesses. Room temperature magnetization
studies indicate the presence of perpendicular magnetic
anisotropy. The coercivity is found to increase with
increasing film thickness due to the internal stress developed
in the film during growth the process. The field cooled and
zero field cooled thermo-magnetization display the presence
of large magnetic anisotropy.
1. INTRODUCTION
Magnetic tunnel junctions with perpendicular
magnetic anisotropy (PMA) layer have generated
considerable interest in recent years for spin based
random access memory devices. In contrast to the inplane anisotropy materials, the PMA materials are
found to operate at low switching currents, possess
high thermal stability and aid larger data-storage
capacity. PMA in magnetic thin films can be tuned by
bi-layer ratio, annealing temperature, under layer
material and under-layer material thickness etc. PMA
has been exhibited by multilayers of transition metals,
Co and Fe based alloy thin films and R-TM [R-rare
earth; TM-transition metal] based amorphous thin
films. Of these, several R-TM based thin films with
PMA have been studied for magneto-optical based
memory device applications [1]. The high Curie
temperature exhibited by these films makes them
thermally more stable for Curie point writing. Further
these films are also studied for spin torque based
random access memory applications because of their
tunable magnetic properties such as saturation
magnetization, Curie temperature and coercivity. It is
observed from literature that highly anisotropic
TbFeCo and very low anisotropic GdFeCo films are
found to exhibit strong PMA [2]. Therefore, it is of
interest to examine whether such PMA behaviour is
also exhibited by Cobalt based anisotropy
compensated systems such as TbDyFeCo. Hence, a
detailed study has been carried out by depositing
TbDyFeCo films with various thicknesses by electron
beam evaporation and characterizing them for
structural and magnetic properties.
2. EXPERIMENTAL
The films of Tb10Dy23Fe56Co6 were grown to different
thicknesses (50 – 800 nm) by electron beam
evaporation at a substrate temperature of 450o C.
Structural studies were carried out employing
glancing incidence X-ray diffraction (GIXRD). Room
temperature magnetization measurements were carried
out employing a SQUID magnetometer upto magnetic
field of 4 Tesla. Field cooled (FC) and Zero field
cooled (ZFC) measurements were carried out in the
temperature range 4 – 390 K with an applied magnetic
field of 1 Tesla.
3. RESULTS AND DISCUSSION
The GIXRD studies show that all films are
found to be amorphous in nature. In-plane and out-ofplane magnetization studies indicate that all the films
are found to exhibit PMA with large coercivity [Fig.
1a]. The anisotropy energy calculated from the inplane and out-of-plane magnetization curves indicate
large PMA is observed in films grown with 600 nm
due to large magnetic texture.
(a)
(b)
Fig. 1(a) In plane and out of plane magnetization curves
of 600 nm thick Tb10Dy23Fe56Co6 thin films. (b) FC and
ZFC thermo-magnetic curves of 600 nm thick
Tb10Dy23Fe56Co6 thin film in out of plane direction.
The large irreversibility observed in the FC and
ZFC thermo-magnetic curves indicate the presence of
large magnetic anisotropy at low temperatures [Fig.
1b]. The coercivity is also found to increase gradually
with increasing film thicknesses due to the internal
stress developed in the films during deposition.
Further, the presence of increasing stress with
increasing thickness is confirmed by the fact that the
films grown above 800 nm delaminate due to growth
stresses.
Acknowledgement: The authors thank Director,
DMRL for the support and encouragement.
REFERENCES:
[1] M. Nakayama et. al. J. Appl. Phys.103, 07A710
(2008).
[2] Manli Ding and S. Joseph Poon, J.Magn. Magn.
Mater., 339, 51 (2013).