8 research outputs found
Vortex-like state observed in ferromagnetic contacts
Point-contacts (PC) offer a simple way to create high current densities, 10^9
A/cm^2 and beyond, without substantial Joule heating. We have shown recently
(Nano Letters, 7 (2007) 927) that conductivity of nanosized PCs between a
normal and ferromagnetic metals exhibits bi-stable hysteretic states versus
both bias current and external magnetic field - the effect typical for
spin-valve structures. Here we report that apart from the bi-stable state a
third intermediate-resistance state is occasionally observed. We interpret this
state as due to a spin-vortex in the PC, nucleated either by Oersted field of
the bias current and/or by the circular geometry of PC. The observed
three-level-states in the PC conductivity testify that the interface spins are
both weakly coupled to the spins in the bulk and have depressed exchange
interaction within the surface layer.Comment: 4 pgs., 4 figs. submitted to ICM-09 (July 26-21, Karlsruhe) V2:
corrected typos, accepted for publication in J. Phys.: Conf. Serie
Spin Torques in Point Contacts to Exchange-Biased Ferromagnetic Films
Hysteretic magneto-resistance of point contacts formed between non-magnetic
tips and single ferromagnetic films exchange-pinned by antiferromagnetic films
is investigated. The analysis of the measured current driven and field driven
hysteresis agrees with the recently proposed model of the surface spin-valve,
where the spin orientation at the interface can be different from that in the
bulk of the film. The switching in magneto-resistance at low fields is observed
to depend significantly on the direction of the exchange pinning, which allows
identifying this transition as a reversal of interior spins of the pinned
ferromagnetic films. The switching at higher fields is thus due to a spin
reversal in the point contact core, at the top surface of the ferromagnet, and
does not exhibit any clear field offset when the exchange-pinning direction or
the magnetic field direction is varied. This magnitude of the switching field
of the surface spins varies substantially from contact to contact and sometimes
from sweep to sweep, which suggests that the surface coercivity can change
under very high current densities and/or due to the particular microstructure
of the point contact. In contrast, no changes in the effect of the exchange
biasing on the interior spins are observed at high currents, possibly due to
the rapid drop in the current density away from nanometer sized point contact
cores.Comment: 3 pages, 3 figs, presented on 11th Joint MMM-Intermag Conference,
Jan. 18-22, 2010, Washington, US