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.

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.

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.

Research of Colossal Magnetoresistance in La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3 (0.00x0.15)

The extraordinary colossal magnetoresistance (CMR) behavior in Mn-site doped system La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3 (0.00x0.15) was reported. It was found that the substitution with Cr on Mn sites introduces an additional bump in zero-field resistivity. With increasing Cr content, this additional bump grows up drastically while the original resistivity peak associated with magnetic order transition diminishes gradually. Under the applied magnetic field, both bumps of resistivity are deeply compressed, which leads to the appearance of two peaks in CMR response. As a result, the temperature range of CMR response is significantly broadened, spanned from the lowest to near room temperature. These results suggest that Mn-site element substitution could be a potent way of tuning CMR response.

MAGNETIC PROPERTIES AND COLOSSAL MAGNETORESISTANCE OF La1-xSrxMn0.88Fe0.12O3

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Irreversible Colossal Magnetoresistance in La_(0.58)Dy_(0.09)Ca_(0.33)MnO_3

The representative sample La0.58Dy0.09Ca0.33MnO3 of Dy doped La0.67Ca0.33MnO3 rare-earth manganites was investigated. The most important effect of Dy doping is to introduce the magnetoimpurity and form the spin clusters which induce dramatically large CMR in La0.58Dy0.09Ca0.33MnO3. The fitting results of field-induced resistivity decrease to the Brillouin function indicate that the CMR is caused by the spin dependent hopping between spin clusters. It is the magnetic field that reduces the size of spin clusters and induces a field-induced irreversible CMR behaviour.

Possible Origins for Paramagnetic-ferromagnetic and Insulator-metal Transitions as well as Colossal Magnetoresistance in Manganites

Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach.

Transport-magnetism Correlation and Colossal Magnetoresistance in Mixed-valent Manganites

A phenomenological model based on phase separation between ferromagnetic metallic and paramagnetic insulating domains was applied to analyze the electrical transport and colossal magnetoresistance for mixed-valent manganites of RE_(2/3)AE_(1/3)MnO_3. The results show that the model can yield results in agreement with experimental observations in these manganites. The present approach provides a simple picture to visualize the reason that the temperature dependence of resistance (with and without applied magnetic fields) in these compounds has the peculiar shape, without invoking any complicated concept.

Dielectric Properties of Colossal Permittivity Materials： An Update

During the last 10 years, a lot of interests have been devoted to the so-called CDC （colossal dielectric constant） materials. The first materials exhibiting this behavior were the perovskite-based ceramics on the CCTO （CaCuaTi4012） composition. Relative dielectric permittivity can attain values up to （or even larger than） 105. Nevertheless, their dielectric losses are too high, the lower values ranging 10%, in a narrow frequency range, thus limiting their applications. The underlying physical mechanisms at the origin of the CDC are still under study. The analysis of broadband impedance spectroscopy measurements leads most of the authors to propose an interracial polarization mechanism （at the electrodes or at internal barriers）, there is a limited number of complementary electrical characterization techniques, which, up to now, comfort the proposed interracial polarization mechanisms. In the present work, I-V and time-domain polarization are used to characterize these materials. One of the main results is the observation of a non-symmetrical response of these materials related to the direction of the polarization. These results are observed for both macroscopic level on bulk polycrystalline material and within individual grains of the same samples. These results do not fit current accepted models for polarization for CDC materials.

Colossal permittivity and ultralow dielectric loss in Nb-doped SrTiO_(3) ceramics

Defect engineering has been applied to prepare materials with modifiable dielectric properties.SrTiNbxO3(x=0,0.003,0.006,0.009,0.012)ceramics were synthesized using the traditional solid-state reaction method and sintered in a reducing atmosphere.All samples show excellent dielectric properties with giant permittivity(>3.5×10^(4))and low dielectric loss(<0.01).SrTiNb0.003O3 ceramic exhibits a colossal permittivity of 4.6×10^(4)and an ultralow dielectric loss of 0.005(1 kHz,room temperature)as well as great temperature stability in the range of(−60)–160℃.The mechanism of the presented colossal permittivity(CP)properties is investigated by conducting X-ray photoelectron spectroscopy(XPS)and analyzing activation energies.The results indicate that the introduction of Nb5+and the reducing sintering atmosphere together generated the formation of Ti^(3+)and V_(O)^(**).These defects further form Ti-V_(O)^(**)-Ti'_(Ti)defect dipoles,contributing to the coexisting giant permittivity and low dielectric loss in Nb-doped SrTiO_(3)(STN)ceramics.

Magnetocaloric and Colossal Magnetoresistance Effect in Layered Perovskite La_(1.4) Sr_(1.6)Mn_2O_7

Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature （T C =120 K）,which can be associated with the existence of two-dimensional short range ferromagnetic order.Additionally,the curvilinear shape of-△S M for layered perovskite is quite different from that of the Ln 1-x A x MnO 3 probably arising from magnetocrystalline anisotropy.At the same time,a wide peak of colossal magnetoresitance effect near T C is found in the layered provskite La 1.4 Sr 1.6 Mn 2 O 7.

Defect engineering of rutile TiO_(2) ceramics:Route to high voltage stability of colossal permittivity

Donor-acceptor co-doped rutile TiO_(2) ceramics with colossal permittivity(CP)have been extensively investigated in recent years due to their potential applications in modern microelectronics.In addition to CP and low dielectric loss,voltage stability is an essential property for CP materials utilized in high-power and high-energy density storage devices.Unfortunately,the voltage stability of CP materials based on codoped TiO_(2) does not catch enough attention.Here,we propose a strategy to enhance the voltage stability of co-doped TiO_(2),where different ionic defect clusters are formed by two acceptor ions with different radii to localize free carriers and result in high performance CP materials.The(Ta+Al+La)co-doped TiO_(2) ceramic with suitable La/Al ratio exhibits colossal permittivity with excellent temperature stability as well as outstanding dc bias stability.The density functional theory analysis suggests that La^(3+)Al^(3+)V_(0)Ti^(3+)defect clusters and Ta^(5+)-Al^(3+)pairs are responsible for the excellent dielectric properties in(Ta+Al+La)co-doped TiO_(2).The results and mechanisms presented in this work open up a feasible route to design high performance CP materials via defect engineering.

Hole-pinned defect-dipoles induced colossal permittivity in Bi doped SrTiO3 ceramics with Sr deficiency

Bi doped SrTiO3 ceramics with Sr deficiency,i.e.Sr1-1.5xBixTiO3(x=0,0.01,0.05,0.1),were prepared via conventional solid-state reaction route.A colossal permittivity(CP)over 104 with low dielectric loss less than 0.05wasobtained in x=0.05 Sr1-1.5xBixTiO3 ceramics.In addition,the dielectric constant is maintained at a value greater than 104 in the range of 102-105 Hz and almost frequency independent.Phase structure analysis and density functional theory calculations suggest that the Bi·Sr-V"Sr-Bi·Sr defect complex with hole-pinned defect-dipoles maybe responsible for the high-performance CP properties.This work gives a new way to achieve high performance CP materials in ABO3 perovskite ceramics.

The size effect on transport properties of colossal magnetoresistance materials La_(0.67)Ca_(0.33)MnO_3

High quality La0.67Ca0.33MnO3 (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO3(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2 and 1.5 μm,the insulator-to-metal transition temperature (TP) keeps un-changed compared with the film. For the micro-bridges with width of 1 μm,the TP shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm,the insulator-to-metal transition disappears. The magnetoresistance be-havior of these micro-bridges was studied,and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced.

ANALYSES OF WAGNER'S MODEL

To achieve a better understanding of the effects of the colossal magnetoresistivity in the mixed valence manganites,the model of a negative magnetoresistivity scaling proposed by Wagner et al is explored in both mathematical and physical analyses.The inconsistency in Wagners model is discussed and corrected. The behaviors of the large spin polarons in Nd 0.52 Sr 0.48 MnO 3 film at T c are studied and analyzed.The results show that only through necessary corrections can Wagners model become self consistent. A further exploration of the nature of the magnetically aligned clusters will make the model more convincing.

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.

La_(0.67)Sr_(0.33)Co_(1-x)Fe_xO_3 体系的输运行为(英文)

研究了Co位Fe掺杂对La0.67Sr0.33Co1-xFexO3体系的电输运性质和巨磁效应的影响。结果表明:电阻率在低掺杂(x≤0.1)时显示金属性输运行为,而在高掺杂(x=0.2,0.3)时则显示半导体行为。而且,Fe掺杂削弱了Tc处的MR峰值,但增加了低温下T≤Tc的MR值。La0.67Sr0.33Co1-xFexO3体系的磁电阻的起源可由外加磁场导致的自旋态转变来解释。

First Principles Study of the Electronic and Magnetic Properties of Ce Doped SrMnO3

The electronic and magnetic properties of Ce doped SrMnO3 have been investigated us- ing the pseudo-potential plane wave method within the generalized gradient approximation method by first principles. The different Mn-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6 octahedron, which associates with a structural phase transition from cubic symmetry （Pm3m） to tetragonal symmetry （I4/mcm）, and the Jahn- Teller ordering stabilizes a chain like （C-type） antiferromagnetie ground state. The electronic structures indicate that SrMnO3 and Sr1-xCexMnO3 （z=0.125 and 0.25） are semiconductor and metallic, respectively. The doping of SrMnO3 with cerium induces simultaneously a decrease in the electrical resistivity, which can be attributed to the formation of Mn3＋ as a result of charge compensation. The density of states and charge density map present that hybridization exists between some of O bands with those of Mn and Ce bands, the bonding between Sr and O is mainly ionic. Density of states and magnetic moment calculations show that the formal valence state of the Ce ion is trivalence.

Influence of the substitution of Sm, Gd, and Dy for La in La_(0.7)Sr_(0.3)MnO_3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

A series of La0.7-xSmxSr0.3MnO3, La0.7-xGdxSr0.3MnO3, and La0.7-xDyxSr0.3MnO3 （x=0.00, 0.10, 0.20, 0.30） samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance （MR） was studied through measurements of M-T curves and p-T curves. The results showed that： lattice distortion induced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric properties of pcrovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.

Resistivity and critical temperature of （Lal-xPrx）0.7Ca0.3MnO3

An empirical formula of the critical temperature that is concentration dependent for polycrystalline （La1-xPrx）0.7Ca0.3MnO3 is presented in this paper. With this formula, the temperature dependence of resistance is simulated for various values of x by using the random resistor network model and the Monte Carlo method. The hysteresis effect in p-T curves is reasonably explained. The simulation results are in good agreement with the relevant experimental measurements.