8 research outputs found
Vortex core size in interacting cylindrical nanodot arrays
The effect of dipolar interactions among cylindrical nanodots, with a
vortex-core magnetic configuration, is analyzed by means of analytical
calculations. The cylinders are placed in a N x N square array in two
configurations - core oriented parallel to each other and with antiparallel
alignment between nearest neighbors. Results comprise the variation in the core
radius with the number of interacting dots, the distance between them and dot
height. The dipolar interdot coupling leads to a decrease (increase) of the
core radius for parallel (antiparallel) arrays
Fabrication and thermal stability of arrays of Fe nanodots
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We have fabricated arrays of 60-nm-size magnetic Fe nanodots over a 1-cm2 -size area using nanoporous alumina membranes as shadow masks. The size and size distribution of the nanodots correlate very well with that of the membrane pores. By placing an antiferromagnetic FeF2 layer underneath the Fe nanodots, an exchange anisotropy can be introduced into the Fe/FeF2 system. We have observed an increase in the magnetic hysteresis loop squareness in biased nanodots, suggesting that exchange bias may be used as a tunable source of anisotropy to stabilize the magnetization in such nanodots
Effect of surface interactions on the hysteresis of capillary condensation in nanopores
Gas adsorption and liquid desorption of a number of organic vapors in anodized nanoporous alumina, with controlled geometry (cylindrical pore diameters from 10 to 60 nm), are studied using optical interferometry. The narrow-diameter distribution of disconnected pores allows checking the validity of the (long-predicted but not experimentally verified) Kelvin equation without any adjustable parameters, modeling or other assumptions. Evaporation occurs at liquid-vapor equilibrium according to this equation, whereas condensation occurs from metastable states of the vapor phase by nucleation, enhanced by surface defects inside the nanopores. This produces hysteresis, in qualitative agreement with theoretical models and simulations that use Van der Waals interactions between the fluid and the pore surface. The reproducibility of the hysteresis depends on the strength of these interactions, which play an important role in the dynamics of capillary condensation
Origin of temperature dependence in tunneling magnetoresistance
We present detailed measurements of the differential resistance
(\upd V/\upd I) of state-of-the-art
\chem{FM/AlO}x/\chem{FM} magnetic tunnel junctions (MTJ) as
a function of applied bias and temperature. Temperature effects
are particularly significant in physical quantities involving
narrow features such as those at low-voltage bias. We show that
the temperature evolution of the tunneling characteristics and,
in particular, the pronounced rounding of the \upd V/\upd I
curves with increasing temperature can be well explained by
thermal smearing of the tunneling electron energy distribution
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Fabrication and thermal stability of arrays of Fe nanodots
We have fabricated arrays of 60-nm-size magnetic Fe nanodots over a 1-cm2-size area using nanoporous alumina membranes as shadow masks. The size and size distribution of the nanodots correlate very well with that of the membrane pores. By placing an antiferromagnetic FeF2 layer underneath the Fe nanodots, an exchange anisotropy can be introduced into the Fe/FeF2 system. We have observed an increase in the magnetic hysteresis loop squareness in biased nanodots, suggesting that exchange bias may be used as a tunable source of anisotropy to stabilize the magnetization in such nanodots
Fabrication and thermal stability of arrays of Fe nanodots
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We have fabricated arrays of 60-nm-size magnetic Fe nanodots over a 1-cm2 -size area using nanoporous alumina membranes as shadow masks. The size and size distribution of the nanodots correlate very well with that of the membrane pores. By placing an antiferromagnetic FeF2 layer underneath the Fe nanodots, an exchange anisotropy can be introduced into the Fe/FeF2 system. We have observed an increase in the magnetic hysteresis loop squareness in biased nanodots, suggesting that exchange bias may be used as a tunable source of anisotropy to stabilize the magnetization in such nanodots
Lateral length scales in exchange bias
When a ferromagnet is in proximity with an antiferromagnet, lateral length
scales such as the respective magnetic domain sizes drastically affect the
exchange bias. Bilayers of FeF2 and either Ni, Co or Fe are studied using SQUID
and spatially resolved MOKE. When the antiferromagnetic domains are larger than
or comparable to the ferromagnetic domains, a local, non-averaging exchange
bias is observed. This gives rise to unusual and tunable magnetic hysteresis
curves.Comment: 14 pages, 2 in-line figures. Submitted to PR