Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance(MR)effect in a low static magnetic field environment at room temperature.However,how to obtain a large room-temperature negative MR effect in them remains to be studied.In this paper,by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side,we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment,but not in a static low magnetic field environment.Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory,we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field.This theoretical analytical model is further confirmed by regulating the geometry size of the device.Our work sheds light on the development of novel magnetic sensing,magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

Magnetoresistance retraction behaviour of Ag/p-Ge:Ga/Ag device under pulsed high magnetic field

In non-magnetic semiconductor materials,unsaturated magnetoresistance(MR)effect has attracted lots of attention due to its physical interests and potential applications in electronic devices.Under the ex-tremely high magnetic field,the stability and reliability of MR effects based on the non-ohmic transport has been rarely researched.In this paper,the transport properties of non-magnetic Ag/p-Ge:Ga/Ag devices under 45 T pulsed high magnetic field at 300 K are investigated.It is found that in ohmic conduction re-gion(I<5 mA)where the single dominant carrier is hole,the MR values increase with increasing the applied magnetic field,presenting a conventional unsaturated behavior.In the two non-ohmic regions(5 mA≤I≤100 mA)where the transport is dominated by bipolar(electrons and holes),a MR retraction has been obviously observed under pulsed high magnetic field.Combining the Hall measurement results and calculation of Hall effect with bipolar-driven transport model,the mechanism of the MR retraction is analysed,in which the MR retraction may be related to the strong regulation of electron-to-hole den-sity ratio by pulsed high magnetic field.This work provides a reference for evaluating the stability and reliability of the properties of non-magnetic semiconductor based MR devices under the interference of strong magnetic pulses.

Nitrogen-rich three-dimensional porous carbon mosaicked Na_(4)Ge_(9)O_(20)as anode material for high-performance lithium-ion batteries

Germanium-based material has attracted numerous attentions and been regarded as a promising anode material for lithium-ion batteries due to its high theoretical capacity.However,drastic pulverization and rapid capacity fading caused by large volume variation during cycling limit its practical application.In this work,three-dimensional N-doped carbon framework-wrapped Na_(4)Ge_(9)O_(20)nanoparticles(3D Na_(4)Ge_(9)O_(20)@N-C)have been synthesized via freeze-drying approach with NaCl as both template and sodium source for ion-exchanging.The employment of NaCl has two special roles:on the one hand,the NaCl crystals act as template and facilitate the formation of 3D porous structure,while on the other hand,the NaCl crystals serving as sodium source and support the ion exchange between NaCl and GeO_(2)promote the formation of Na_(4)Ge_(9)O_(20).Benefiting from the unique method,the prepared 3D Na_(4)Ge_(9)O_(20)@N-C not only suppresses the volume change by using carbon as buffer layers but also demonstrates an improved electronic conductivity and a shortened ionic diffusion.When utilized as an anode material for LIBs,the 3D Na_(4)Ge_(9)O_(20)@N-C composites deliver high reversible capacity(896.2 mAh·g^(-1)at0.1 A·g^(-1)after 100 cycles),good cycling stability(520.8 mAh·g^(-1)at 2.0 A·g^(-1)after 400 cycles)and excellent rate performance(636.0 mAh·g^(-1)at 2.0 A·g^(-1)).This work provides a strategy to improve the electrochemical performance of germanium-based anode materials for lithium-ion batteries.