6 research outputs found
Finite-size effects in amorphous Fe90Zr10/Al75Zr25 multilayers
The thickness dependence of the magnetic properties of amorphous Fe90Zr10
layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25
layer thickness is kept at 40 \AA, while the thickness of the Fe90Zr10 layers
is varied between 5 and 20 \AA. The thickness of the Al75Zr25 layers is
sufficiently large to suppress any significant interlayer coupling. Both the
Curie temperature and the spontaneous magnetization decrease non-linearly with
decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed
in the multilayer with 5 {\AA} Fe90Zr10 layers. The variation of the Curie
temperature with the Fe90Zr10 layer thickness is fitted with a
finite-size scaling formula [1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-\lambda},
yielding , and a critical thickness \AA, below which the
Curie temperature is zero.Comment: 8 pages, 8 figure
Multi-Step Ordering in Kagome and Square Artificial Spin Ice
We show that in colloidal models of artificial kagome and modified square ice
systems, a variety of ordering and disordering regimes occur as a function of
biasing field, temperature, and colloid-colloid interaction strength, including
ordered monopole crystals, biased ice rule states, thermally induced ice rule
ground states, biased triple states, and disordered states. We describe the
lattice geometries and biasing field protocols that create the different states
and explain the formation of the states in terms of sublattice switching
thresholds. For a system prepared in a monopole lattice state, we show that a
sequence of different orderings occurs for increasing temperature. Our results
also explain several features observed in nanomagnetic artificial ice systems
under an applied field.Comment: 16 pages, 11 postscript figure
Thermodynamics of elementary excitations in artificial magnetic square ice
We investigate the thermodynamics of artificial square spin ice systems
assuming only dipolar interactions among the islands that compose the array.
The emphasis is given on the effects of the temperature on the elementary
excitations (magnetic monopoles and their Dirac strings). By using Monte Carlo
techniques we calculate the specific heat, the density of poles and their
average separation as functions of temperature. The specific heat and average
separation between monopoles and antimonopoles exhibit a sharp peak and a local
maximum, respectively, at the same temperature,
(here, is the strength of the dipolar interaction and is the
Boltzmann constant). As the lattice size is increased, the amplitude of these
features also increases but very slowly. Really, the specific heat and the
maximum in the average separation between oppositely charged
monopoles increase logarithmically with the system size, indicating that
completely isolated charges could be found only at the thermodynamic limit. In
general, the results obtained here suggest that, for temperatures , these systems may exhibit a phase with separated monopoles, although
the quantity should not be larger than a few lattice spacings for
viable artificial materials.Comment: 7 pages, 9 figure