Current-dependent positive magnetoresistance in La_(0.8)Ba_(0.2)MnO_(3)ultrathin films

We report an investigation into the magnetoresistance(MR)of La_(0.8)Ba_(0.2)MnO_(3)ultrathin films with various thicknesses.While the 13 nm-thick film shows the commonly reported negative magnetoresistive effect,the 6 nm-and 4 nm-thick films display unconventional positive magnetoresistive(PMR)behavior under certain conditions.As well as the dependence on the film's thickness,it has been found that the electrical resistivity and the PMR effect of the thinner films are very dependent on the test current.For example,the magnetoresistive ratio of the 4 nm-thick film changes from+46%to-37%when the current is increased from 10 nA to 100 nA under 15 kOe at 40 K.In addition,the two thinner films present opposite changes in electrical resistivity with respect to the test current,i.e.,the electroresistive(ER)effect,at low temperatures.We discuss the complex magnetoresistive and ER behaviors by taking account of the weak contacts at grain boundaries between ferromagnetic metallic(FMM)grains.The PMR effect can be attributed to the breaking of the weak contacts due to the giant magnetostriction of the FMM grains under a magnetic field.Considering the competing effects of the conductive filament and local Joule self-heating at grain boundaries on the transport properties,the dissimilar ER effects in the two thinner films are also understandable.These experimental findings provide an additional approach for tuning the magnetoresistive effect in manganite films.

Large positive magnetoresistance in photocarrier-doped potassium tantalites

We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive,non-saturating,and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient.When cooling down to 10 K,the magnetoresistance value of KTaO_(3)(100)reaches~433%at a magnetic field of 12 T.Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit.Light inhomogeneity may also contribute to large linear magnetoresistance.These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.

Simulation of Temperature-Dependent Resistivity for Manganite La1/3Ca2/3MnO3

The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered （CDO） state embedded with a few ferromagnetic （FM） metallic clusters to a charge-ordered （CO） state, corresponding to the transition from a high-temperature paramagnetic （PM） insulating state to a low-temperature antiferromagnetic （AF） insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.

Large unsaturated positive and negative magnetoresistance in Weyl semimetal TaP

After successfully growing single-crystal TaP, we measured its longitudinal resistivity （Pxx） and Hall resistivity （Pyx） at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance （MR） reached 3.28 ×10^5% at 2 K, 176% at 300 K. Neither value appeared saturated. We confirmed that TaP is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility ofμh=3.71 × 105 cm2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field （H） was applied in parallel to the electric field （E）, a negative MR due to a chiral anomaly was observed and reached -3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals （WSMs）. The analysis of the Shubnikov-de Haas （SdH） oscillations superimposed on the MR revealed that a nontrivial Berry＇s phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.