双钙态矿Sr_2Fe_(1-x)Mn_xMoO_6体系的磁性和磁输运性质的研究(英文)

我们用X射线光电子能谱、以及相关的电性和磁性测量研究了Sr2Fe1-xMnxMoO6(0相似文献   

La0.67Ba0.33MnO3薄膜的激光辐照效应研究

利用脉冲激光沉积技术在LaAlO₃（00l）单晶衬底上制备了La_067Ba_033MnO₃薄膜,研究了CO₂激光辐照对La_067Ba_033MnO₃薄膜的微结构和磁电性能的影响.结果表明,经激光辐照后,La_067Ba_033MnO₃薄膜的结晶性增强,薄膜应变减小;薄膜表面形貌由“岛状”结构变为“平原"结构,且粗糙度大大降低;同时,薄膜的饱和磁化强度、铁磁居里温度、金属—绝缘态转变温度和磁电阻增大,而矫顽场和电阻率减小.根据对传统退火效应的分析和理论计算,认为激光辐照导致的表面微结构的变化以及薄膜的氧含量和均匀性的提高对La_067Ba_033MnO₃薄膜的磁电性能的改善与优化密切相关. 关键词： 庞磁电阻 激光辐照 脉冲激光溅射沉积     

Experimental determination technique for magnetic anisotropy of individual nanowires

We present an experimental technique to determine the magnetic anisotropy of ferromagnetic nanowires. In the technique, the magnetization state is monitored by measuring the anisotropic magnetoresistance with rotating the external magnetic field. The measured magnetoresistance curves exhibit basically the same curves typically appeared in the torque magnetometric measurements, which are then readily analyzed based on the Stoner–Wohlfarth theory with a single fitting parameter – the magnetic anisotropy. By applying the present technique to Permalloy nanowires, it is shown that the shape anisotropy in real nanowires is significantly influenced by the edge roughness.     

Co掺杂的ZnO稀磁半导体块体的退火热处理研究

采用固相反应法制备了Zn_0.95Co_0.05O块体样品,并对其进行了不同方式的退火处理.实验表明在锌气氛中500℃退火的样品表现出铁磁性,而在真空中退火的样品却没有磁性,进一步,在锌气氛中1100℃退火的样品虽然表现出铁磁性,但其铁磁性来源于样品在锌气氛中1100℃退火过程中产生了1%左右的Co金属团簇杂质相.另外,在低温时所有样品都表现出较大的正磁电阻,认为正磁电阻效应是由于s-d电子交换相互作用引起的自旋劈裂造成的,而高场时出现的负磁电阻效应则可能归因于磁场 关键词： Co掺杂ZnO X射线衍射 铁磁性 磁电阻     

La0.7-xDyxSr0.3MnO3中的相分离和输运行为

通过测量样品的M-T曲线、 M-H曲线、 ESR曲线、ρ-T曲线和MR-T曲线, 研究了Dy掺杂(0.0≤x≤0.30)对La0.7Sr0.3MnO3磁电性质的影响. 实验结果表明 在TC处所有样品都经历了顺磁到铁磁的转变; 当T＜TC时, 掺杂样品进入自旋团簇玻璃态, 低温时显示出反铁磁性; x=0.20时, 样品在TC以上温区发生相分离; Dy掺杂引起的磁结构变化将导致CMR效应.     

Improvement on Electrical Properties and Magnetoresistance Induced by Pd or Ag Addition in La0.67(Ca0.65Ba0.35)0.33MnO3 Manganites

Electrical properties and magnetoresistance have been studied in two series of xAg-La_0.67(Ca_0.65Ba_0.35)_0.33MnO₃ and xPd-La_0.67(Ca_0.65Ba_0.35)_0.33MnO₃ (abbreviated by xAg-LCBMO and xPd-LCBMO) composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance (RTMR). Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.     

Multiferroic tunnel junctions

Magnetic tunnel junctions with ferroelectric barriers, often referred to as multiferroic tunnel junctions, have been proposed recently to display new functionalities and new device concepts. One of the notable predictions is that the combination of two charge polarizing states and the parallel and antiparallel magnetic states could make it a four resistance state device. We have recently studied the ferroelectric tunneling using a scanning probe technique and multiferroic tunnel junctions using ferromagnetic La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ as the electrodes and ferroelectric (Ba, Sr)TiO₃ as the barrier in trilayer planner junctions. We show that very thin (Ba, Sr)TiO₃ films can sustain ferroelectricity up till room temperature. The multiferroic tunnel junctions show four resistance states as predicted and can operate at room temperatures.     

Ultralow detection limit of giant magnetoresistance biosensor using Fe_3O_4–graphene composite nanoparticle label

A special Fe_3O_4nanoparticles–graphene(Fe_3O_4–GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance(GMR) sensors with a Wheatstone bridge. The Fe_3O_4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization M_S of approximately 48 emu/g, coercivity H_C of 200 Oe, and remanence M_r of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe_3O_4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe_3O_4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference |?V| between detecting and reference sensors undergoes the relationship of |?V| = 240.5 lgx + 515.2 with an ultralow detection limit of 10 ng/mL(very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.     

Remarkable room‐temperature magnetoresistance in silicon strip devices

In this paper, we report remarkable room‐temperature magnetoresistance (MR) in silicon strip devices. Saturating and non‐saturating MRs can be realized based on the measuring configurations with one top contact and ten top contacts, respectively. Using the one‐top‐contact measurement, a saturating MR ratio of ～400% is obtained at an applied voltage of only 1.0 V when the magnetic field is larger than 0.8 T. While the non‐saturating MR is achieved in the ten‐top‐contact measurement and the MR ratio is only ～155% for the 1.0 V applied voltage even under the magnetic field of 1.2 T. The differences for MR ratio values and change trends in these two measuring configurations are attributed to the enhanced Hall electric field with the increase of the top contact number.     

Recent observations of negative longitudinal magnetoresistance in semimetal

The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials.A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations,and therefore perform exotic features analogous to those in high-energy physics,such as the violation of the chiral charge conservation known as the chiral anomaly.One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw(ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel.Very recently,numerous experiments reported negative longitudinal magnetoresistance(NLMR) in topological materials,but the details of the measurement results are various.Here the materials and the corresponding experiment results are briefly reviewed.Besides the plausible explanation of the ABJ anomaly,some other origins of the NLMR are also discussed.