7,855 research outputs found
Magnetic Frustration and Iron-Vacancy Ordering in Iron-Chalcogenide
We show that the magnetic and vacancy orders in the 122
iron-chalcogenides can be naturally derived from the
model with being the ferromagnetic (FM) nearest neighbor
exchange coupling and being the antiferromagnetic (AFM) next and
third nearest neighbor ones respectively, previously proposed to describe the
magnetism in the 11(FeTe/Se) systems. In the 11 systems, the magnetic exchange
couplings are extremely frustrated in the ordered bi-collinear
antiferromagnetic state so that the magnetic transition temperature is low. In
the 122 systems, the formation of iron vacancy order reduces the magnetic
frustration and significantly increases the magnetic transition temperature and
the ordered magnetic moment. The pattern of the 245 iron-vacancy order
() observed in experiments is correlated to the
maximum reduction of magnetic frustration. The nature of the iron-vacancy
ordering may hence be electronically driven. We explore other possible vacancy
patterns and magnetic orders associated with them. We also calculate the spin
wave excitations and their novel features to test our model.Comment: Figures are modified and more discussion is adde
Simple Recurrent Units for Highly Parallelizable Recurrence
Common recurrent neural architectures scale poorly due to the intrinsic
difficulty in parallelizing their state computations. In this work, we propose
the Simple Recurrent Unit (SRU), a light recurrent unit that balances model
capacity and scalability. SRU is designed to provide expressive recurrence,
enable highly parallelized implementation, and comes with careful
initialization to facilitate training of deep models. We demonstrate the
effectiveness of SRU on multiple NLP tasks. SRU achieves 5--9x speed-up over
cuDNN-optimized LSTM on classification and question answering datasets, and
delivers stronger results than LSTM and convolutional models. We also obtain an
average of 0.7 BLEU improvement over the Transformer model on translation by
incorporating SRU into the architecture.Comment: EMNL
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