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 w...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.展开更多
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 mang...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.展开更多
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 addi...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.展开更多
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,...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.展开更多
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 cluste...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.展开更多
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 pa...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.展开更多
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 man...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.展开更多
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 CC...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.展开更多
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 sint...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.展开更多
基金financially supported by the Ministry of Science and Technology(MOST)NSF of China through the research projects(2018YFA03057001,11820101003)+2 种基金CAS Project for Young Scientists in Basic Research(YSBR-030)support of Beijing Nova program(2020133)the Youth Innovation Promotion Association of CAS(2020007).
文摘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.
基金supported by the National Natural Science Foundation of Chinathe National Basic Research Program of China(Grant Nos.2012CB922003,2011CBA00102,and 2009CB929502)
文摘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.
文摘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.
基金This work was supported by the National Science Foundation Grant No.DMR 1905277.
文摘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.
文摘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.
基金Funded by the National "973" Project of China (No.2006CB921606)the Foundation from the Ministry of the National Education (Nos. 309020and 20060487011)
文摘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.
文摘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.
文摘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.
基金This work was supported by the National Key R&D Program of China(Grant No.2021YFB3800601)the Basic Science Center Project of the National Natural Science Foundation of China(Grant No.52388201).
文摘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.
