Magnetoresistance hysteresis in the superconducting state of kagome CsV_(3)Sb_(5)

The hysteresis of magnetoresistance observed in superconductors is of great interest due to its potential connectionwith unconventional superconductivity.In this study,we perform electrical transport measurements on kagome superconductorCsV_(3)Sb_(5)nanoflakes and uncover unusual hysteretic behavior of magnetoresistance in the superconducting state.This hysteresis can be induced by applying either a large DC or AC current at temperatures(T)well below the superconductingtransition temperature(T_(c)).As T approaches T_(c),similar weak hysteresis is also detected by applying a smallcurrent.Various scenarios are discussed,with particular focus on the effects of vortex pinning and the presence of timereversal-symmtery-breaking superconducting domains.Our findings support the latter,hinting at chiral superconductivityin kagome superconductors.

Linear magnetoresistance and structural distortion in layered SrCu_(4-x)P_(2) single crystals

We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.

Magnetic Switching Dynamics and Tunnel Magnetoresistance Effect Based on Spin-Splitting Noncollinear Antiferromagnet Mn_(3)Pt

In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust against external magnetic field,etc.However,unlike ferromagnetic orders,which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions,the antiferromagnetic order(i.e.,Néel vector)cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets.Recently discovered spin-splitting noncollinear antiferromagnets,such as Mn_(3)Pt with momentum-dependent spin polarization due to their special magnetic space group,make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions.Through first-principles calculations,we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn_(3)Pt/perovskite oxides/Mn_(3)Pt antiferromagnetic tunnel junctions.We also reveal the switching dynamics of Mn_(3)Pt thin film under magnetic fields using atomistic spin dynamic simulation.Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.

Negative magnetoresistance in the antiferromagnetic semimetal V_(1/3)TaS_(2)

Intercalated transition metal dichalcogenides(TMDCs)attract much attention due to their rich properties and potential applications.In this article,we grew successfully high-quality V_(1/3)TaS_(2) crystals by a vapor transport method.We measured the magnetization,longitudinal resistivityρxx(T,H),Hall resistivityρxy(T,H),as well as performed calculations of the electronic band structure.It was found that V_(1/3)TaS_(2) is an A-type antiferromagnet with the Neel temperature T_(N)=6.20 K,and exhibits a negative magnetoresistance(MR)near T_(N).Both band structure calculations and Hall resistivity measurements demonstrated it is a magnetic semimetal.

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.

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

Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67（Ca0.65Ba0.35）0.33MnO3 and xPd-La0.67（Ca0.65Ba0.35）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.

Enhancement of room-temperature magnetoresistance in La_(0.5)Sm_(0.2)Sr_(0.3)MnO_3/(Ag_2O)_(x/2)

La0.5Sm0.2Sr0.3MnO3/（Ag2O）x/2 （x = 0.00, 0.04, 0.08, 0.25, 0.30） samples were prepared by the solid-state reaction method, and their transport behaviors, transport mechanism, and magnetoresistance effect were studied through the measurement and fitting of p-T curves. The results show that the element Ag takes part in reaction when the doping amount is small. Ag is mainly distributed at the grain boundary of the host material and is in metallic state when the doping amount is relatively large; then the system becomes a two-phase composite. A small amount of Ag doping can apparently increase grain-boundary magnetoresistance induced by the spin-dependent scattering. The resistivity of the sample doped with 30 mol% Ag is one order of magnitude smaller than that of low-doped samples, and its magnetoresistance in the magnetic field of 0.5 T and at 300 K is strengthened apparently reaching 9.4%, which is connected not only with the improvement of the grain-boundary structure of the host material but also with the decrease of material resistivity.

Magnetoresistance enhancement and temperature stability of magnetoresistance in La_(1-x)(Sr_(1-y)Na_y)_xMnO_3

A series of the samples La_(1-x)(Sr_(1-y)Na_y)_xMnO_3(y=0.0,0.2,0.4,0.6,0.8,1.0) were prepared by the solid-state reaction method.Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La_(1-x)(Sr_(1-y)Na_y)_xMnO_3 with unchanged Mn^(3+)/Mn^(4+) ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction(XRD) patterns,resistivity-temperature(ρ-T) curves and magnetoresistance-temperature(MR-T) curves.The results indicate that with the increase of Na doping amount,the peak value of MR increases,and it increases from 12.4% for y=0.2 to 50.6% for y=1.0 in the magnetic field B=0.8 T;ρ-T curves exhibit the double-peak phenomenon,which comes from the competition between the resistivity of surface phase and that of body phase;for the sample of y=0.8,MR increases slowly from 8.3% to 9.4% in the temperature range from 259 to 179 K,and MR is so stable in such a wide temperature range,which provides reference for the research on the temperature stability of MR.

Low-field magnetoresistance of (1-x)La_(0.6)Dy_(0.1)Sr_(0.3)MnO_3/0.5x (Sb_2O_3) composite system under different sintering temperatures of matrix

A series of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x(Sb2O3)(x=0.15) samples were prepared by the solid-state reaction method, and the influence of sintering temperature of the matrix on low-field magnetoresistance of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x (Sb2O3) was studied through the measurements of X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) image, resistivity-temperature (ρ-T) curves, and magnetoresistance-temperature (MR-T) curves. The results indicate that for the samples with low sintering temperature of the matrix, lowfield magnetoresistance effect appears on the whole temperature range and can be explained by grain boundary effect; for the sample with high sintering temperature of the matrix, intrinsic magnetoresistance peak appears on the high-temperature range, low-field magnetore-sistance effect appears on low temperature range, and the magnetoresistance in the magnetic field of 0.2 T and on the comparatively large temperature range between 280 K and 225 K hardly changes with temperature and remains at 4.8%, which can be explained by the competition between the intrinsic magnetoresistance induced by double-exchange function inside grains and the tunneling magnetoresis-tance (TMR) induced by grain boundary effect. The temperature stability of magnetoresistance is beneficial to the practical applications of MR.

Effect of nano-oxide layers on the magnetoresistance of ultrathin permalloy films

Ta/NiFe/Ta ultrathin films with and without nano-oxide layers （NOLs） were prepared by magnetron sputtering followed by a vacuum annealing process. The influence of NOLs on the magnetoresistance （MR） ratio of ultrathin permalloy films was studied. The results show that the influence of grain size and textures on the MR ratio becomes weak when the thickness of the NiFe layer is below 15 nm. A higher MR ratio was observed for the thinner （〈 15 nm） NiFe film with NOLs. The MR ratio of a 10 nm NiFe film can be remarkably enhanced by NOLs. The enhanced MR ratio for these ultrathin films can be attributed to the enhanced specular reflection of conduction electrons.

Abnormal electric transport property and magnetoresistance stability of La-Sr-K-Mn-O system

The perovskite samples La1-x（Sr1-yKy）xMnO3 （y = 0.0, 0.2, 04, 0.6, 0.8） were prepared by the solid-state reaction method with comparatively low sintering tem- perature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The p-T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator-metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ2 on the electric transport property of perovskite manga- nites is larger than that of the radius of A-site ions （rA）. In the temperature range below 225 K, MR increases contin- uously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the com- paratively wide temperature range near 250 K, the MR- T curves of all the samples are comparatively fiat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresis- tance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresis- tance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at （7.92 ±0.36） % in the very wide temperature range of 225-275 K, and this is a goodreference for the preparation of this kind of sample with practical application value in the future.

Research progress in anisotropic magnetoresistance

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.

Electric transport properties and temperature stability of magnetoresistance of composite system between La_(8/9)Sr_(1/45)Na_(4/45)MnO_3 and Sb_2O_3

The samples ofLa8/9Sr1/45Na4/45MnO3 （LSNMO）/x/2（Sb2O3） were prepared by the solid-state reaction method. The electric transport properties and the temperature stabil-ity of magnetoresistance （MR） of the samples were studied through the measurements of X-ray diffraction patterns, resistivity-temperature （ρ-T） curves, mass magnetization-temperature （σ-T） curves, and magnetoresistance-temper-ature （MR-T） curves. The results indicate that the p-Tcurves of the original material LSNMO show two peaks, and the phenomenon of two peaks of ρ-T curves disappears for the composite samples, which can be explained by a competition between surface-phase resistivity induced by boundary-dependent scattering and body-phase resistivity induced by paramagnetism-ferromagnetism transition. For all the sam-ples in the low temperature range, MR increases continu-ously with the decrease of temperature, which shows a characteristic of low-field magnetoresistance. However, MR basically keeps the same in the high temperature range. The paramagnetism-ferromagnetism transition is observed in the high temperature range due to a composite between perov-skite manganite and insulator, which can enhance the tem-perature of MR appearance in the high temperature range and make it to appear near room temperature. For the sample with x = 0.12, MR remains constant at the value of 7.5 % in the temperature range of 300-260 K, which achieves a tem-perature stability of MR near room temperature. In addition,for the sample with x = 0.16, MR is above 6.8 % in the high temperature range of 318-252 K （△T = 66 K）. MR almost remains constant in this temperature range, which favors the practical application of MR.

Analytical Descriptions of Magnetic Properties and Magnetoresistance in n-Type HgCr_2Se_4

We present a detailed investigation of magnetic properties of colossal magnetoresistance material HgCr2Se4. While spontaneous magnetization and zero-field magnetic susceptibility are found to follow asymptotic scaling laws for a narrow range of temperatures near the critical point, two methods with connections to the renormalization group theory provide analytical descriptions of the magnetic properties for much wider temperature ranges. Based on this, an analytical formula is obtained for the temperature dependence of the low field magnetoresistance in the paramagnetic phase.

X-ray and Magnetoresistance Measurements of Electrodeposited Cu-Co Granular Films

Granular CoxCu1-x alloy films were prepared by electrodeposition at room temperature directly onto semiconducting Si substrate. X-ray diffraction (XRD) revealed that the as-deposited films formed single phase metastable fcc alloy structure. The fcc lattice parameter α was found to decrease linearly with increasing Co concentration x in the studied range. The giant magnetoresistance (GMR) of the films was improved after annealing. Pure Co fcc diffraction peaks were observed in the diffractogram of the annealed sample, indicating phase separation occurred upon annealing. The optimal annealing temperature was 450℃. The maximum of magnetoresistance (MR) ratio 8.21% was obtained for the Co20Cu80 thin film after annealing at 450℃ for 1 h. The saturation field decreased upon annealing in the MR curves of Co20Cu80 film.

Colossal magnetoresistance in manganites and related prototype devices

We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb：SrTio3 p-n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.

Colossal negative magnetoresistance from hopping in insulating ferromagnetic semiconductors

Ferromagnetic semiconductor Ga_(1–x)Mn_(x)As_(1–y)P_(y) thin films go through a metal–insulator transition at low temperature where electrical conduction becomes driven by hopping of charge carriers.In this regime,we report a colossal negative magnetoresistance(CNMR)coexisting with a saturated magnetic moment,unlike in the traditional magnetic semiconductor Ga_(1–x)Mn_(x)As.By analyzing the temperature dependence of the resistivity at fixed magnetic field,we demonstrate that the CNMR can be consistently described by the field dependence of the localization length,which relates to a field dependent mobility edge.This dependence is likely due to the random environment of Mn atoms in Ga_(1-x)Mn_(x)As_(1-y)P_(y) which causes a random spatial distribution of the mobility that is suppressed by an increasing magnetic field.

Enhancement of room-temperature magnetoresistance in La_(0.6)Dy_(0.1)Sr_(0.3)MnO_3/Ag_x

The samples of La0.6Dy0.1Sr0.3MnO3/（Ag2O）x/2（x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30） were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature（M-T） curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is comparatively large, Ag as metallic state mainly deposits on the grain boundary of La0.6Dy0.1Sr0.3MnO3, and then the system forms a two-phase composite.When the Ag doping amount is 30% mole ratio, the resistivity of the sample is one order of magnitude smaller than that of low doped samples, and its peak of magnetoresistance at 292 K and in the magnetic field of 0.2 T strengthens apparently and reaches 16.3%, which is over 7 times as large as 2.2% of La0.6Dy0.1Sr0.3MnO3.The two-phase composite system of magnetoresistance based on perovskite manganite consists of two parts：intrinsic magnetoresistance and extrinsic magnetoresistance.However, extrinsic magnetoresistance comes from spin-dependent scattering（SDS） and spin-polarized tunneling（SPT）.Magnetoresistance near TC increases due to the contribution of intrinsic magnetoresistance and extrinsic magnetoresistance formed by SDS, and magnetoresistance at low temperature is extrinsic magnetoresistance formed by SPT.

Enhancing low-field magnetoresistance of La0.67Ca0.33MnO3 films deposited on anodized aluminium-oxide membranes

In this paper we report a new method to fabricate nanostructured films, La0.67Ca0.33MnO3 （LCMO） nanostructured films have been fabricated by using pulsed electron beam deposition （PED） on anodized aluminium oxide （AAO） membranes, The magnetic and electronic transport properties are investigated by using the Quantum Design physics properties measurement system （PPMS） and magnetic properties measurement system （MPMS）. The resistance peak temperature （Tp） is about 85 K and the Curie temperature （To） is about 250 K for the LCMO film on an AAO membrane with a pore diameter of 20nm. Large magnetoresistance ratio （MR） is observed near Tp. The MR is as high as 85% under 1 T magnetic field. The great enhancement of MR at low magnetic fields could be attributed to the lattice distortion and the grain boundary that are induced by the nanopores on the AAO membrane.

Colossal negative magnetoresistance in spin glass Na(Zn,Mn)Sb

We report the study of magnetic and transport properties of polycrystalline and single crystal Na(Zn,Mn)Sb,a new member of“111”type of diluted magnetic materials.The material crystallizes into Cu2Sb-type structure which is isostructural to“111”type Fe-based superconductors.With suitable carrier and spin doping,the Na(Zn,Mn)Sb establishes spin-glass ordering with freezing temperature(Tf)below 15 K.Despite lack of long-range ferromagnetic ordering,Na(Zn,Mn)Sb single crystal still shows sizeable anomalous Hall effect below Tf.Carrier concentration determined by Hall effect measurements is over 1019 cm-3.More significantly,we observe colossal negative magnetoresistance(MR≡[ρ(H)−ρ(0)]/ρ(0))of-94%in the single crystal sample.