Anisotropic magnetoresistance (AMR) is an important physical phenomenon that has broad application potential in many relevant fields. Thus, AMR is one of the most attractive research directions in material science t...Anisotropic magnetoresistance (AMR) is an important physical phenomenon that has broad application potential in many relevant fields. Thus, AMR is one of the most attractive research directions in material science to date. In this article, we summarize the recent advances in AMR, including traditional permalloy AMR, tunnel AMR, ballistic AMR, Coulomb blockade AMR, anomalous AMR, and antiferromagnetic AMR. The existing problems and possible challenges in developing more advanced AMR were briefly discussed, and future development trends and prospects were also speculated.展开更多
Transport properties of magnetron-sputtered CoO/Co/Pt heterostructures were investigated by physical property measurement system.Different types of magnetoresistance are observed in the heterostructures,including isot...Transport properties of magnetron-sputtered CoO/Co/Pt heterostructures were investigated by physical property measurement system.Different types of magnetoresistance are observed in the heterostructures,including isotropic anisotropic magnetoresistance(AMR),AMR with geometric size effect,and interfacial effect.A reversal in sign of perpendicular AMR is found in the film CoO(3 nm)/Co(3 nm)/Pt(3 nm)compared to the film CoO(3 nm)/Co(3 nm)/CoO(3 nm),which is associated with Pt.Moreover,perpendicular AMR is tunable in the films CoO(3 nm)/Co(3 nm)/CoO(t)/Pt(3 nm)and CoO(3 nm)/Co(3 nm)/Pt(t)/CoO(3 nm)at will,with either positive or negative value,by varying the inserting layer thickness.The electronic structure information of the samples was measured by X-ray photoelectron spectroscopy(XPS).The spin-related transport and XPS results manifest that magnetic proximity effect,surface scattering,together with oxygen migration contribute to the tunable function of Pt.展开更多
Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers....Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm)and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity(HC) of both layers. The perpendicular giant magnetoresistance(GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.展开更多
The effect of ultrathin Fe layer on perpendicular magnetic anisotropy(PMA) in magnetron-sputtered Co/Pt multilayers was investigated by magnetic measurements.Magnetization hysteresis(M-H) loops and microstructures of ...The effect of ultrathin Fe layer on perpendicular magnetic anisotropy(PMA) in magnetron-sputtered Co/Pt multilayers was investigated by magnetic measurements.Magnetization hysteresis(M-H) loops and microstructures of the samples were measured by vibrating sample magnetometer(VSM) and X-ray diffraction(XRD) and highresolution transmission electron microscopy(HRTEM),respectively.It is found that the PMA is strongly dependent on the interface where Fe layer was doped.When Fe layer was doped at Co/Pt interface where Pt was deposited on Co,the PMA decreases monotonically with Fe layer thickness(tFe) increasing.However,when Fe layer was doped at Pt/Co interface where Co was deposited on Pt,the PMA shows a peak at t_(Fe)=0.1 nm.It is considered that the PMA variation is mainly due to the tuning in the electron occupation states of 3 d orbits at Fe-doped Pt/Co interface.Furthermore,the annealing stability of PMA can also be improved when Fe layer was doped at Pt/Co interface.HRTEM results demonstrate that the magnetic anisotropy evolution is mainly caused by anneal-induced interdiffusion.展开更多
With the development of spintronics,the investigation on the behavior of oxygen in two-dimensional materials has never ceased.On account of its lively nature,oxygen is hard to exist alone in the system.However,it will...With the development of spintronics,the investigation on the behavior of oxygen in two-dimensional materials has never ceased.On account of its lively nature,oxygen is hard to exist alone in the system.However,it will interact with other atoms and produce complex orbital hybridization effect,which has influenced the performance of the material.Especially for materials in nanoscale,it is inevitable to introduce the oxygen atoms,no matter what in the process of preparation or employ.Therefore,it is necessary to carry on the research about the effect of oxygen behaviors in the two-dimensional thin films.In this paper,it will mainly introduce the effect of oxygen behaviors on the magnetic properties,electrical properties,phase transition,spin-dependent properties and thermal stability,summarize several factors which influence the oxygen behaviors,and generalize the research progress of the mechanism behind the oxygen behaviors.展开更多
Enhancement of post-annealing stability in Co/ Ni multilayers with perpendicular magnetic anisotropy (PMA) was obtained by inserting Au layers into Ni/Co interfaces. After annealing at 350 ℃, the effective mag- net...Enhancement of post-annealing stability in Co/ Ni multilayers with perpendicular magnetic anisotropy (PMA) was obtained by inserting Au layers into Ni/Co interfaces. After annealing at 350 ℃, the effective mag- netic anisotropy density (Kef0 for Ta(3)/Pt(2)/[Co(0.3)/ Ni(0.6)/Au(0.3)]× 3/Co(0.3)/Pt(1)/Ta(3) (in nm) keeps at 0.48 × 105 J·m^-3. Scanning transmission electron micro- scopy-high-angle annular dark field (STEM-HAADF) analysis shows that the diffusion between Ni and Co layers is obstructed by the Au insertion layers among them, which is responsible for the post-annealing stability enhancement of the multilayers. Multilayers with Pt insertion layers were also investigated as reference samples in this work. Com- pared with Pt-layer-inserted Co/Ni multilayers, the Au insertion layers are found to bring seldom interfacial PMA to the multilayers, making it competitive in being employed to enhance the post-annealing stability of PMA Co/Ni multilayers which are used for magnetic random access memory devices (MRAM).展开更多
In this work, cobalt nanoparticles were syn- thesized by chemical reduction procedure. After the hydrophilic functionalization, Co/polypyrrole (PPy) nanocomposites were prepared by in situ polymerization of pyrrole ...In this work, cobalt nanoparticles were syn- thesized by chemical reduction procedure. After the hydrophilic functionalization, Co/polypyrrole (PPy) nanocomposites were prepared by in situ polymerization of pyrrole in aqueous dispersion of Co nanoparticles. The Co/ PPy nanocomposites show good electromagnetic properties with both magnetic loss and dielectric loss to electromag- netic wave. The electromagnetic wave absorbing band- width (reflection loss 〈-10 dB) for Co/PPy (20 wt%) is above 5.5 GHz at a thickness of 2 mm, and with a maximum reflection loss (around -20.02 dB) at 14.77 GHz. This magnetic nanoparticles/conducting polymer nanocomposites are great potential candidates for electromagnetic wave absorbent, because of their wide-absorbing frequency, strong absorption, good compatibility, low density, and controllable absorbing properties.展开更多
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...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.展开更多
The anisotropic magnetoresistance film is an important core material for developing the magnetic sensors.Here,Ta(5)/Mg O(3)/Ni Fe(10)/Mg O(3)/Ta(3)multilayers(in nanometer)were prepared by magnetron sputtering and fur...The anisotropic magnetoresistance film is an important core material for developing the magnetic sensors.Here,Ta(5)/Mg O(3)/Ni Fe(10)/Mg O(3)/Ta(3)multilayers(in nanometer)were prepared by magnetron sputtering and further applied to construct a sensor element by combining with the Wheatstone bridge.The 1/f noise of the sensor element was greatly reduced by three orders of magnitude after annealing at 400℃for 7200 s,which was mainly due to the significant microstructural changes during the annealing.However,when the sensor element was applied to detect the magnetic signal of a magnetic code disk with 512 N-S magnetic poles,the output voltage signal of the sensor displayed a large fluctuation of±0.05 V.In order to reduce the voltage fluctuation,a magnetic sensor chip by using a parallelly arranged multipath Wheatstone bridges and auto-gain compensation structure was designed,and magnetic sensor elements and the high-performance computing drive module were prepared.The output voltage fluctuation of the magnetic sensor was reduced by about 90%and approached to±0.005 V.These findings provide an important basis for the practical application of Ni Fe-based magnetic sensing film materials.展开更多
Cobalt thin films were deposited on silicon substrates by magnetron sputtering two commercial cobalt targets with different pass-through fluxes(PTFs).The influences of PTF on the magnetic properties of sputtered thin ...Cobalt thin films were deposited on silicon substrates by magnetron sputtering two commercial cobalt targets with different pass-through fluxes(PTFs).The influences of PTF on the magnetic properties of sputtered thin films were investigated.The results indicate that under the same sputtering conditions,cobalt thin film deposited by Co target with high PTF(84.21%) has lower remanence ratio(0.65),while cobalt thin film prepared by Co target with low PTF(69.13%) has higher remanence ratio(0.87).Through introducing an external magnetic field parallel to the film surface during sputtering processes,both the remanence ratios of cobalt thin films prepared by the two targets can be enhanced to approach 1.High-resolution transmission electron microscopy(HRTEM) images show that in the absence of the external magnetic field during sputtering,cobalt thin film deposited by the target with high PTF is randomly oriented in crystallographic orientations,which is due to that Co atoms have no enough time to migrate and diffuse on substrate and the atomic stacking is disordered.It is worth mentioning that crystallographic orientations of cobalt thin film deposited by target with low PTF are relatively consistent,resulting in relatively higher remanence ratio.In addition,HRTEM analysis indicates that the external magnetic field during sputtering drives the Co grains to arrange in a regular order with(002) orientation,leading to the improvement in remanence ratios.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51071023 and 51101047)the Natural Science Foundation of Hainan Province (No. 512114)+1 种基金the Ph.D. Programs Foundation of Ministry of Education (No. 20120006130002)Program for Changjiang Scholars and Innovative Research Team in University
文摘Anisotropic magnetoresistance (AMR) is an important physical phenomenon that has broad application potential in many relevant fields. Thus, AMR is one of the most attractive research directions in material science to date. In this article, we summarize the recent advances in AMR, including traditional permalloy AMR, tunnel AMR, ballistic AMR, Coulomb blockade AMR, anomalous AMR, and antiferromagnetic AMR. The existing problems and possible challenges in developing more advanced AMR were briefly discussed, and future development trends and prospects were also speculated.
基金financially supported by the National Key Science Research Projects of China(No.2015CB921502)the National Natural Science Foundation of China(Nos.51331002,51371025,51471028,11504019)the Postdoctoral Science Foundation of China(No.2016M590043)。
文摘Transport properties of magnetron-sputtered CoO/Co/Pt heterostructures were investigated by physical property measurement system.Different types of magnetoresistance are observed in the heterostructures,including isotropic anisotropic magnetoresistance(AMR),AMR with geometric size effect,and interfacial effect.A reversal in sign of perpendicular AMR is found in the film CoO(3 nm)/Co(3 nm)/Pt(3 nm)compared to the film CoO(3 nm)/Co(3 nm)/CoO(3 nm),which is associated with Pt.Moreover,perpendicular AMR is tunable in the films CoO(3 nm)/Co(3 nm)/CoO(t)/Pt(3 nm)and CoO(3 nm)/Co(3 nm)/Pt(t)/CoO(3 nm)at will,with either positive or negative value,by varying the inserting layer thickness.The electronic structure information of the samples was measured by X-ray photoelectron spectroscopy(XPS).The spin-related transport and XPS results manifest that magnetic proximity effect,surface scattering,together with oxygen migration contribute to the tunable function of Pt.
基金financially supported by the National Natural Science Foundation of China (Nos. 11174020, 51331002, and 51371027)the Fundamental Research Funds for the Central Universities FRF-SD-12-011A
文摘Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm)and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity(HC) of both layers. The perpendicular giant magnetoresistance(GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.
基金financially supported by the National Natural Science Foundation of China (Nos.51371027 and 51331002)the National Key Scientific Research Projects of China (No.2015CB921502)the Ph.D.Programs Foundation of Ministry of Education (No.20120006130002)。
文摘The effect of ultrathin Fe layer on perpendicular magnetic anisotropy(PMA) in magnetron-sputtered Co/Pt multilayers was investigated by magnetic measurements.Magnetization hysteresis(M-H) loops and microstructures of the samples were measured by vibrating sample magnetometer(VSM) and X-ray diffraction(XRD) and highresolution transmission electron microscopy(HRTEM),respectively.It is found that the PMA is strongly dependent on the interface where Fe layer was doped.When Fe layer was doped at Co/Pt interface where Pt was deposited on Co,the PMA decreases monotonically with Fe layer thickness(tFe) increasing.However,when Fe layer was doped at Pt/Co interface where Co was deposited on Pt,the PMA shows a peak at t_(Fe)=0.1 nm.It is considered that the PMA variation is mainly due to the tuning in the electron occupation states of 3 d orbits at Fe-doped Pt/Co interface.Furthermore,the annealing stability of PMA can also be improved when Fe layer was doped at Pt/Co interface.HRTEM results demonstrate that the magnetic anisotropy evolution is mainly caused by anneal-induced interdiffusion.
基金financially supported by the National Key Scientific Research Projects of China(No.2015CB921502)the National Natural Science Foundation of China(Nos.51331002,51371027 and 51571017)
文摘With the development of spintronics,the investigation on the behavior of oxygen in two-dimensional materials has never ceased.On account of its lively nature,oxygen is hard to exist alone in the system.However,it will interact with other atoms and produce complex orbital hybridization effect,which has influenced the performance of the material.Especially for materials in nanoscale,it is inevitable to introduce the oxygen atoms,no matter what in the process of preparation or employ.Therefore,it is necessary to carry on the research about the effect of oxygen behaviors in the two-dimensional thin films.In this paper,it will mainly introduce the effect of oxygen behaviors on the magnetic properties,electrical properties,phase transition,spin-dependent properties and thermal stability,summarize several factors which influence the oxygen behaviors,and generalize the research progress of the mechanism behind the oxygen behaviors.
基金financially supported by the National Natural Science Foundation of China(Nos.51101012, 51271211,51331002,51371025,51371027,51471028 and 51571017)the National Key Scientific Research Projects of China(No. 2015CB921502)+1 种基金the Beijing Nova Program(No.Z141103001814039)the Fundamental Research Funds for the Central Universities(No. FRF-TP-14-002C1)
文摘Enhancement of post-annealing stability in Co/ Ni multilayers with perpendicular magnetic anisotropy (PMA) was obtained by inserting Au layers into Ni/Co interfaces. After annealing at 350 ℃, the effective mag- netic anisotropy density (Kef0 for Ta(3)/Pt(2)/[Co(0.3)/ Ni(0.6)/Au(0.3)]× 3/Co(0.3)/Pt(1)/Ta(3) (in nm) keeps at 0.48 × 105 J·m^-3. Scanning transmission electron micro- scopy-high-angle annular dark field (STEM-HAADF) analysis shows that the diffusion between Ni and Co layers is obstructed by the Au insertion layers among them, which is responsible for the post-annealing stability enhancement of the multilayers. Multilayers with Pt insertion layers were also investigated as reference samples in this work. Com- pared with Pt-layer-inserted Co/Ni multilayers, the Au insertion layers are found to bring seldom interfacial PMA to the multilayers, making it competitive in being employed to enhance the post-annealing stability of PMA Co/Ni multilayers which are used for magnetic random access memory devices (MRAM).
基金financially supported by the National Natural Science Foundation of China(Nos.51101013 and 51371055)the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-12-038A and FRF-TP-14-012A2)
文摘In this work, cobalt nanoparticles were syn- thesized by chemical reduction procedure. After the hydrophilic functionalization, Co/polypyrrole (PPy) nanocomposites were prepared by in situ polymerization of pyrrole in aqueous dispersion of Co nanoparticles. The Co/ PPy nanocomposites show good electromagnetic properties with both magnetic loss and dielectric loss to electromag- netic wave. The electromagnetic wave absorbing band- width (reflection loss 〈-10 dB) for Co/PPy (20 wt%) is above 5.5 GHz at a thickness of 2 mm, and with a maximum reflection loss (around -20.02 dB) at 14.77 GHz. This magnetic nanoparticles/conducting polymer nanocomposites are great potential candidates for electromagnetic wave absorbent, because of their wide-absorbing frequency, strong absorption, good compatibility, low density, and controllable absorbing properties.
基金financially supported by the National Natural Science Foundation of China (Nos. 51371105, 51071023, and 51101047)
文摘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.
基金financially supported by the National Key Research and Development Program of China(Nos.2019YFB2005800 and 2019YFB1309902)the National Science Foundation of China(Nos.51871017 and 51871018)+3 种基金Beijing Natural Science Foundation(No.2192031)the Science and Technology Innovation Team Program of Foshan(No.FSOAA-KJ919-44020087)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-011B1)the Foundation of Beijing Key Laboratory of Metallic Materials and Processing for Modern Transportation。
文摘The anisotropic magnetoresistance film is an important core material for developing the magnetic sensors.Here,Ta(5)/Mg O(3)/Ni Fe(10)/Mg O(3)/Ta(3)multilayers(in nanometer)were prepared by magnetron sputtering and further applied to construct a sensor element by combining with the Wheatstone bridge.The 1/f noise of the sensor element was greatly reduced by three orders of magnitude after annealing at 400℃for 7200 s,which was mainly due to the significant microstructural changes during the annealing.However,when the sensor element was applied to detect the magnetic signal of a magnetic code disk with 512 N-S magnetic poles,the output voltage signal of the sensor displayed a large fluctuation of±0.05 V.In order to reduce the voltage fluctuation,a magnetic sensor chip by using a parallelly arranged multipath Wheatstone bridges and auto-gain compensation structure was designed,and magnetic sensor elements and the high-performance computing drive module were prepared.The output voltage fluctuation of the magnetic sensor was reduced by about 90%and approached to±0.005 V.These findings provide an important basis for the practical application of Ni Fe-based magnetic sensing film materials.
基金financially supported by the National Key R&D Program of China(No.2017YFB0305502)the National Natural Science Foundation of China(Nos.51571017,51671023,and 51871018)+2 种基金the Beijing Natural Science Foundation(No.2192031)the Key Science and Technology Projects of Beijing Education Committee(No.KZ201810011013)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-011B1)。
文摘Cobalt thin films were deposited on silicon substrates by magnetron sputtering two commercial cobalt targets with different pass-through fluxes(PTFs).The influences of PTF on the magnetic properties of sputtered thin films were investigated.The results indicate that under the same sputtering conditions,cobalt thin film deposited by Co target with high PTF(84.21%) has lower remanence ratio(0.65),while cobalt thin film prepared by Co target with low PTF(69.13%) has higher remanence ratio(0.87).Through introducing an external magnetic field parallel to the film surface during sputtering processes,both the remanence ratios of cobalt thin films prepared by the two targets can be enhanced to approach 1.High-resolution transmission electron microscopy(HRTEM) images show that in the absence of the external magnetic field during sputtering,cobalt thin film deposited by the target with high PTF is randomly oriented in crystallographic orientations,which is due to that Co atoms have no enough time to migrate and diffuse on substrate and the atomic stacking is disordered.It is worth mentioning that crystallographic orientations of cobalt thin film deposited by target with low PTF are relatively consistent,resulting in relatively higher remanence ratio.In addition,HRTEM analysis indicates that the external magnetic field during sputtering drives the Co grains to arrange in a regular order with(002) orientation,leading to the improvement in remanence ratios.