Abstracts Book - IMRC 2018

• SF1-O009
HYSTERESIS FREE SWITCHING BETWEEN COLLINEAR AND
VORTEX STATES IN CLOSELY PACKED Fe-Pd NANOCAP ARRAYS
Anantharaman Malie Madom Ramaswamy Iyer 1 , Aravind Puthirath Balan 1 , Michael Heigl 2 ,
Mario Fix 2 , Senoy Thomas 1 , Manfred Albrecht 2
1 Cochin University of Science and Technology, Cochin, Kerala, Physics, India. 2 Universität
Augsburg, Experimentalphysik IV Institut für Physik, Germany.
Magnetic vortices are of great interest as they are potential candidates for
improving the fundamental understanding of magnetism. They also present
very promising applications, for example, in information and communication
technology. The characteristics of magnetization reversal via vortex state have
been extensively investigated both experimentally and theoretically in twodimensional
structures like cylindrical nanodots and spherically curved surfaces,
that is, caps [1-5]. Magnetic vortices were also exchange coupled to an
antiferromagnet for improving their field stability [6,7]. For soft magnetic
microdisks, in an applied magnetic field, the magnetization reversal a uniform
state to a vortex state or vice versa involves an energy barrier giving rise to
distinct nucleation and annihilation field resulting in hysteretic side lobes in the
M-H loop. If the energy barrier is small and the thermal energy is sufficient, a
magnetic bistability occurs between single domain and vortex state. This will
result in a hysteresis-free switching the single domain state to a vortex state and
vice-versa at elevated temperatures [8]. Here, we present our recent results on
the tuning of the energy barrier associated with the switching between collinear
and vortex state or vice versa. A bottom-up self-assembly method was adopted
to realise magnetic vortices in which thin films of composition Ta(5 nm)/FexPd1-
x(20 nm)/Ta(5nm) [x=0.13, 0.15, 0.17 and 0.20] were DC magnetron sputter
deposited onto dense arrays of self-assembled silica particles of 480 nm
diameter. Depositing soft magnetic FexPd1-x thin films onto a spherically curved
surface will result in the formation of magnetic cap structures, where the
equilibrium magnetic configuration will be vortex-like. Magnetisation
measurements using a SQUID-VSM showed that the critical temperature (Te) for
hysteresis-free transition can be tuned by varying the composition of the films.
Bistability above the room temperature is observed for iron concentration,
x=0.20. The evolution of vortex behaviour with respect to thickness was also
studied and salient results will be presented.