We have studied the dependence of magnetic properties on the carrier concentration of IV–VI diluted magnetic semiconductor Ge1−xMnxTe prepared by ionized-cluster beam technique. With increasing carrier concentration, the magnetic properties drastically change; saturation magnetization increases and coercive field decreases in hysteresis loop, and the Curie temperature increases. These results obviously show carrier-enhanced ferromagnetic order. The similar effect is also observed in magnetoresistance behavior.
We analyzed the sensor response from aptamer-modified carbon nanotube thin film transistors that adsorb immunoglobulin E (IgE) with an inhomogeneous charge distribution. The net charge of the target molecules within the Debye length reflects the polarity of the electrical sensor signal. The complicated sensor response, which depends on the Debye length, can be interpreted by two kinds of adsorption states considering the influence of steric hindrance by previously adsorbed IgE molecules. These results explain the anomalous behavior of the sensor response in previous reports and pave the way to control the dynamic range.
The dependence of magnetic properties on the carrier concentration for Ge1−xMnxTe films prepared by ionized-cluster beam technique has been studied to clarify the mechanism of carrier-induced ferromagnetism. The experimental results suggest that the cluster of spins aligned by short-range ferromagnetic interaction tends to be formed for samples with the lower carrier concentration than the critical value for the occurrence of homogeneous ferromagnetic order. With increasing carrier concentration, the long-range ferromagnetic interaction grows. The magnetotransport properties of Ge1−xMnxTe films are found closely related to its magnetic properties, indicating carrier-enhanced ferromagnetic effects.
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