Supervisors info:
Κεχράκος Δημήτριος Αναπλ. Καθηγητής (Επιβλέπων), Σιμσερίδης Κωσταντίνος Επίκ. Καθηγητής, Τριμπέρης Γεώργιος Καθηγητής
Summary:
We study the magnetic properties of exchange biased cylindrical nanowires
composed of a ferromagnetic core and an antiferromagnetic shell, using
atomistic modeling and the Metropolis Monte Carlo simulation algorithm.
Emphasis is given to the impact of exchange biasing on the domain wall
propagation mechanism during magnetization reversal. To this end, we compare
the properties of FM core – AF shell nanowires to bare FM nanowires of the same
size. The magnetic structure is described within a classical Heisenberg
Hamiltonian on a simple cubic lattice containing uniaxial anisotropy terms and
dipolar interactions. Our main results demonstrate that core-shell FM-AF
nanowires exhibit an initial increase of the coercivity (Hc) at small lengths
followed by a saturation value (Hc0), which increases with increasing dipolar
coupling strength (g). Similarly, the bias field (Heb) decreases at small
lengths and reaches a saturation value (Hb0) at large lengths. However, when
the FM core of the NW is hard (g<0.1KFM) the saturation value Hb0 increases
with dipolar strength, while the opposite trend is observed when the FM core is
soft (g~KFM). Magnetization reversal proceeds by nucleation of a pair of
domain walls (DW) at the opposite ends of the wire, that propagate towards the
centre of the wire with constant and opposite velocities and eventually they
merge. However, the coupling to the AF shell, obstructs the DW nucleation,
pushing the coherent rotation limit of a nanowire to higher values of the
dipolar strength. Finally, an increase in the bias field (Heb) is observed due
to interface roughness.
Keywords:
Magnetic Nanowires, Coercive Field, Exchange- Bias Field, Domain wall propagation, Interface roughness
