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.

Room temperature ferromagnetism of Si-doped ZnO thin films prepared by sol-gel method

Pure ZnO and Si-doped ZnO thin films were deposited on quartz substrate by using sol-gel spin coating process. X-ray diffraction analysis shows that all the thin films have hexagonal wurtzite structure and preferred c-axis orientation. Si-doped ZnO films show room temperature ferromagnetism （RTFM） and reach the maximum saturation magnetization value of 1.54 kA.m at 3 % Si concentration. RTFM of Si-doped ZnO decreases with the increasing annealing temperature because of the formation of SiO2. Photoluminescence measurements suggest that the RTFM in Si-doped ZnO can be attributed to the defect complex related to zinc vacancies Vzn and oxygen interstitials O1.

Martensitic transformation and magnetic properties in Mn_(49-x)Cu_(x)Ni_(41)Sn_(10)(x=0-2)

The crystal structure,phase transition,metamagnetic behavior and magnetic entropy change(ΔS_(M))of the Mn_(49-x)Cu_(x)Ni_(41)Sn_(10)(x=0-2)alloys were systematically studied.The results of experiment about crystal structure confirm that Mr_(49-x)Cu_(x)Ni_(41)Sn_(10)alloys have a highly ordered cubic L2_(1)Heusler structure.With Cu element improving,all samples have a martensitic transformation and inverse martensitic transformation by analyzing the result of magnetic measurement.The saturation magnetization of samples decreases gradually,the martensitic transformation temperature(T_(M))of as-annealed samples increases to a high-temperature area,and the Curie temperature(T_(C))of samples moves to a low-temperature area with the content of Cu element increasing from x=0 to x=2.The positive values of magnetic entropy change(ΔS_(M))of all alloys were investigated near the martensitic transformation.When the applied magnetic field is 3 T,a worthwhile value ofΔS_(M)can reach up to 32.0 J·kg^(-1)·K^(-1)in Mn_(47)Cu_(2)Ni_(41)Sn_(10)alloy.

Recent progress in Heusler-type magnetic shape memory alloys

Magnetic shape memory alloys(MSMAs), both in condensed matter physics and in material science, are one of the most extensive research subjects. They show prompt response to the external magnetic field and give rise to large strain and have fine reversibility. The well-known example is Heusler-type MSMAs, which possess excellent multifunctional properties and have potential applications in energy transducer, actuator, sensor, microelectromechanical system, and magnetic refrigerator. In this paper, it is shown the recent progress in magnetostructural transformation, magnetic properties, shape deformation, magnetocaloric effect as well as magnetic field-induced shape memory effect in Ni–Mn–Ga, Ni Mn Z(Z = In, Sn, Sb),and Ni Co Mn Z(Z = In, Sn, Sb, Al) Heusler-type MSMAs.The remaining issues and possible challenges are briefly discussed.