329 research outputs found
Unsupervised Visual Representation Learning via Mutual Information Regularized Assignment
This paper proposes Mutual Information Regularized Assignment (MIRA), a
pseudo-labeling algorithm for unsupervised representation learning inspired by
information maximization. We formulate online pseudo-labeling as an
optimization problem to find pseudo-labels that maximize the mutual information
between the label and data while being close to a given model probability. We
derive a fixed-point iteration method and prove its convergence to the optimal
solution. In contrast to baselines, MIRA combined with pseudo-label prediction
enables a simple yet effective clustering-based representation learning without
incorporating extra training techniques or artificial constraints such as
sampling strategy, equipartition constraints, etc. With relatively small
training epochs, representation learned by MIRA achieves state-of-the-art
performance on various downstream tasks, including the linear/k-NN evaluation
and transfer learning. Especially, with only 400 epochs, our method applied to
ImageNet dataset with ResNet-50 architecture achieves 75.6% linear evaluation
accuracy.Comment: NeurIPS 202
Electric field control of nonvolatile four-state magnetization at room temperature
We find the realization of large converse magnetoelectric (ME) effects at
room temperature in a multiferroic hexaferrite
BaSrCoFeO single crystal, in which rapid
change of electric polarization in low magnetic fields (about 5 mT) is coined
to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then
reaches up to 0.62 /f.u. in an electric field of 1.14 MV/m. We find
further that four ME states induced by different ME poling exhibit unique,
nonvolatile magnetization versus electric field curves, which can be
approximately described by an effective free energy with a distinct set of ME
coefficients
Electric polarization enhancement in multiferroic CoCr2O4 crystals with Cr-site mixing
Single crystals of multiferroic cobalt chromite Co (Cr2-x Cox) O4 have been grown via several methods to have different Co3+ doping levels (x=0.0, 0.14, and 0.18). Under magnetic fields, all the crystals display electric polarization reversal below their spiral spin ordering temperatures. We find that both saturated electric polarization and magnetization under magnetic fields increase significantly with the increase in x. This result can be qualitatively explained by a broken balance between at least two electric polarization contributions existing in CoCr2 O4 and is expected to be useful in tailoring electric polarization in similar kinds of multiferroics. © 2009 American Institute of Physics.open222
Realization of giant magnetoelectricity in helimagnets
We show that low field magnetoelectric (ME) properties of helimagnets
Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by Al-substitution
level. As x increases, the critical magnetic field for switching electric
polarization is systematically reduced from ~1 T down to ~1 mT, and the ME
susceptibility is greatly enhanced to reach a giant value of 2.0 x 10^4 ps/m at
an optimum x = 0.08. We find that control of nontrivial orbital moment in the
octahedral Fe sites through the Al-substitution is crucial for fine tuning of
magnetic anisotropy and obtaining the conspicuously improved ME
characteristics
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