Jianwang Cai

Colossal magnetoresistance of spin-glass perovskite La0.67Ca0.33Mn0.9Fe0.1O3

The magnetic and magnetotransport properties of the perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound. A metal-to-insulator transition and colossal magnetoresistance have been observed near its spin freezing temperature; besides, the insulator behavior has been found to reappear at lower temperature. The formation of ferromagnetic and antiferromagnetic clusters and the competition between them with the introduction of Fe3+ ions, which do not participate in the double-exchange process, have been suggested to explain the experimental results.

A Centrosymmetric Hexagonal Magnet with Superstable Biskyrmion Magnetic Nanodomains in a Wide Temperature Range of 100–340 K

Superstable biskyrmion magnetic nanodomains are experimentally observed for the first time in a hexagonal MnNiGa, a common and easily produced centrosymmetric material. The biskyrmion states in MnNiGa thin plates, as determined by the combination of in situ Lorentz transmission electron microscopy images, magnetoresistivity, and topological Hall effect measurements, are surprisingly stable over a broad temperature range of 100-340 K.

Room-temperature simultaneously enhanced magnetization and electric polarization in BiFeO3 ceramic synthesized by magnetic annealing

Multiferroic BiFeO3 ceramics were synthesized by high temperature magnetic annealing using nanosized precursor powders prepared through microwave combustion. Simultaneously enhanced magnetization and electric polarization were observed at room temperature in the sample annealed under an external magnetic field of 10 T. These enhanced properties might be originated from a spin structure severely modulated or the low temperature magnetic phase driven up to room temperature and above by the large external annealing magnetic fields. These results demonstrate that the strong magnetic annealing method is an alternative way to synthesize high performance BiFeO3 materials.

Magnetoresistance of La0.5Sr0.5MnO3 nanoparticle compact

Magnetization, resistance, and current-voltage (I-V) measurements have been performed in La0.5Sr0.5MnO3 compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (T-C) and has a substantial drop in the thermomagnetic curve below 158 K (T-DP). After undergoing a metal-to-semiconductor transition at 140 K (T-MS), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below T-DP. Instead of showing a feature near T-MS, the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I-V curve. Although La0.5Sr0.5MnO3 has a relatively high T-C, the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher T-C seems to be a prerequisite

Angular Dependence of Exchange Bias and Magnetization Reversal Controlled by Electric‐Field‐Induced Competing Anisotropies

The combination of exchange-biased systems and ferroelectric materials offers a simple and effective way to investigate the angular dependence of exchange bias using one sample with electric-field-induced competing anisotropies. A reversible electric-field-controlled magnetization reversal at zero magnetic field is also realized through optimizing the anisotropy configuration, holding promising applications for ultralow power magnetoelectric devices.

Renormalization of tensor-network states

We have discussed the tensor-network representation of classical statistical or interacting quantum lattice models, and given a comprehensive introduction to the numerical methods we recently proposed for studying the tensor-network states/models in two dimensions. A second renormalization scheme is introduced to take into account the environment contribution in the calculation of the partition function of classical tensornetwork models or the expectation values of quantum tensor-network states. It improves significantly the accuracy of the coarse-grained tensor renormalization-group method. In the study of the quantum tensornetwork states, we point out that the renormalization effect of the environment can be efficiently and accurately described by the bond vector. This, combined with the imaginary-time evolution of the wave function, provides an accurate projection method to determine the tensor-network wave function. It reduces significantly the truncation error and enables a tensor-network state with a large bond dimension, which is difficult to be accessed by other methods, to be accurately determined.

Colossal magnetoresistance in cluster glass-like insulator La0.67Sr0.33(Mn0.8Ni0.2)O3

Substitution of Ni for Mn in La0.67Sr0.33MnO3 (LSMO) lowers the Curie temperature TC from 365 K for LSMO to 194 K for La0.67Sr0.33(Mn0.8Ni0.2)O3, which exhibits a cluster glass-like state. The oxide is insulating under both zero field and 60 kOe, but application of the magnetic field induces colossal magnetoresistance (CMR) especially at low temperature. Far below TC, the compound’s field dependence of resistivity has a very similar shape with that of metallic perovskite manganite at relatively high temperature when the spin fluctuation grows stronger. The results indicate that the ferromagnetic superexchange between Ni and Mn, is helpful for the overall ferromagnetic exchange components just overcoming the generic antiferromagnetic exchange components, which leads to the presence of the cluster glass-like state. The reduction of the magnetic disorder and the suppression of the spin fluctuation in Mn–O layer by the external magnetic field are suggested to explain the CMR effect in this insulating compoundSubstitution of Ni for Mn in La0.67Sr0.33MnO3 (LSMO) lowers the Curie temperature TC from 365 K for LSMO to 194 K for La0.67Sr0.33(Mn0.8Ni0.2)O3, which exhibits a cluster glass-like state. The oxide is insulating under both zero field and 60 kOe, but application of the magnetic field induces colossal magnetoresistance (CMR) especially at low temperature. Far below TC, the compound’s field dependence of resistivity has a very similar shape with that of metallic perovskite manganite at relatively high temperature when the spin fluctuation grows stronger. The results indicate that the ferromagnetic superexchange between Ni and Mn, is helpful for the overall ferromagnetic exchange components just overcoming the generic antiferromagnetic exchange components, which leads to the presence of the cluster glass-like state. The reduction of the magnetic disorder and the suppression of the spin fluctuation in Mn–O layer by the external magnetic field are suggested to explain the CMR effect in this insulating compound

Magnetic tuning of the photovoltaic effect in silicon-based Schottky junctions.

A magnetic tuning of the photovoltaic effect is demonstrated for the Schottky junction formed by a ferromagnetic (FM) layer and silicon. Obvious anisotropic magnetic photovoltaic effects (AMV) are gained not only in the FM layer but also in the Si substrate though the latter is non-magnetic. Key factors determining the AMV of Si are identified.

Exchange interaction, spin cluster and transport behaviour in perovskites La0.67Sr0.33(Mn1-xNix)O3 (x ≤ 0.2)

A systematic investigation of the magnetic and transport properties of perovskites La0.67 Sr0.33 (Mn1-x Nix )O3 (x ≤ 0.2) is reported. The replacement of the Mn ion by a Ni ion results in a reduction of ferromagnetism and metallic conduction. For the sample with x = 0.1, in addition to a metal-insulator (M-I) transition at 240 K, there is a weak insulating behaviour at low temperatures. As the magnetization drop below the Curie temperature (TC ) in the thermomagnetic curve appears for the dosage of x = 0.15, the insulating behaviour at low temperatures becomes pronounced. For the sample with x = 0.2, a cluster glass-like state with no M-I transition near TC 194 K is shown. The ferromagnetic superexchange interaction between the Mn3+(4+) ion and the Ni2+ ion is found to account for the formation of the cluster glass-like state rather than a spin glass state. All samples have a colossal magnetoresistance (CMR). In particular, with the suppression of the ferromagnetism, the MR effect shifts towards low temperatures and becomes considerably enhanced. Besides the depletion of hopping electrons and the destroyed metallic paths due to the foreign Ni ion terminating the double exchange interaction in the Mn-O network, the randomly frozen spin cluster at low temperatures has been revealed as another crucial factor for localizing charge carriers.

Comparison of the magnetic and transport properties of Ga-, Ni-, and Fe-doped perovskite manganese oxides

A comparative study on magnetic and transport properties has been performed for B-site substituted perovskites La0.67Sr0.33Mn0.90B0.10O3 (B=Ga, Ni, and Fe). The doped samples show a notable decrease of the Curie Temperature, from 365 K of the undoped sample to 290 K (Ga), 292 K (Ni), and 265 K (Fe). Furthermore, the metal–semiconductor transition peaks in the doped samples shift to lower temperature, from above 300 K (undoped) to 212 K (Ga), 237 K (Ni), and 195 K (Fe). This considerable differences in magnetic and transport properties between doped and undoped samples and the diversity among the doped samples can be explained by the destruction of the partial double-exchange interactions and the exchange couplings between Mn and doped ions.