Pub Date : 2002-05-01DOI: 10.1080/13642810208224374
Jai Singh, T. Aoki, K. Shimakawa
Abstract Applying the effective-mass approach, the energy eigenvalues of excitonic states in amorphous semiconductors are derived. It is shown that Wannier–Mott-type excitons can indeed be formed in amorphous solids. The results show that the occurrence of the double photoluminescence (PL) lifetime distribution peak, fast and slow, in hydrogenated amorphous silicon (a-Si: H) and hydrogenated amorphous germanium (a-Ge: H) can unambiguously be assigned to radiative recombinations from singlet and triplet excitonic states respectively. The dependence of PL peaks on the temperature and generation rate in a-Si: H and a-Ge: H is also discussed. The approach is general and simple and can be applied to study the charge-carrier transport and PL properties in any amorphous solid.
{"title":"Excitonic contribution to photoluminescence in amorphous semiconductors","authors":"Jai Singh, T. Aoki, K. Shimakawa","doi":"10.1080/13642810208224374","DOIUrl":"https://doi.org/10.1080/13642810208224374","url":null,"abstract":"Abstract Applying the effective-mass approach, the energy eigenvalues of excitonic states in amorphous semiconductors are derived. It is shown that Wannier–Mott-type excitons can indeed be formed in amorphous solids. The results show that the occurrence of the double photoluminescence (PL) lifetime distribution peak, fast and slow, in hydrogenated amorphous silicon (a-Si: H) and hydrogenated amorphous germanium (a-Ge: H) can unambiguously be assigned to radiative recombinations from singlet and triplet excitonic states respectively. The dependence of PL peaks on the temperature and generation rate in a-Si: H and a-Ge: H is also discussed. The approach is general and simple and can be applied to study the charge-carrier transport and PL properties in any amorphous solid.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86574714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208218351
Zhongchun Wang, V. Kugler, U. Helmersson, E. Evangelou, Nikos Konofaos, S. Nakao, P. Jin
Abstract SrTiO3 (STO) thin films were deposited on p-type Si(100) substrates by rf magnetron sputtering at various substrate temperatures, and their structural and electrical properties were investigated without post-deposition annealing. The thickness of the films was in the range from 300 to 500 nm while the deposition temperature was varied between room temperature and 550°C. Compositional and structural characterizations included X-ray diffraction, Rutherford back-scattering spectroscopy and variable-angle spectroscopic ellipsometry. Metal-insulator-semiconductor diodes with the configuration of Al/STO/p-Si/Al were fabricated and characterized by capacitance-voltage, current-voltage and admittance spectroscopy measurements. Depending on the substrate temperatures, the dielectric constant of the films varied between 60 and 120 and the loss factor between 0.019 and 0.051 at 100 kHz. All films showed high charge storage capacity, varying between 1.9 and 3μm cm−2. However, the films deposited at 200°C showed the lowest density of bulk trapped charges (150 nC cm−2) and interface states ((1.2–6.1) × 1011 cm−2 eV−1), and are therefore considered to be the most suitable for device applications.
{"title":"Characteristics of SrTiO3 thin films deposited on Si by rf magnetron sputtering at various substrate temperatures","authors":"Zhongchun Wang, V. Kugler, U. Helmersson, E. Evangelou, Nikos Konofaos, S. Nakao, P. Jin","doi":"10.1080/13642810208218351","DOIUrl":"https://doi.org/10.1080/13642810208218351","url":null,"abstract":"Abstract SrTiO3 (STO) thin films were deposited on p-type Si(100) substrates by rf magnetron sputtering at various substrate temperatures, and their structural and electrical properties were investigated without post-deposition annealing. The thickness of the films was in the range from 300 to 500 nm while the deposition temperature was varied between room temperature and 550°C. Compositional and structural characterizations included X-ray diffraction, Rutherford back-scattering spectroscopy and variable-angle spectroscopic ellipsometry. Metal-insulator-semiconductor diodes with the configuration of Al/STO/p-Si/Al were fabricated and characterized by capacitance-voltage, current-voltage and admittance spectroscopy measurements. Depending on the substrate temperatures, the dielectric constant of the films varied between 60 and 120 and the loss factor between 0.019 and 0.051 at 100 kHz. All films showed high charge storage capacity, varying between 1.9 and 3μm cm−2. However, the films deposited at 200°C showed the lowest density of bulk trapped charges (150 nC cm−2) and interface states ((1.2–6.1) × 1011 cm−2 eV−1), and are therefore considered to be the most suitable for device applications.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80865027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208224366
P. Levy, Kuising Wang, P. Dederichs, C. Heide, Shufeng Zhang, L. Szunyogh
Abstract In conventional calculations of transport in magnetic tunnel junctions, one usually assumes that the transverse momentum of the tunnelling electrons is conserved and that the itinerant electron states are orthogonal to localized states. However, in most of the junctions studied, there is diffuse scattering in both the bulk of the electrodes and the barrier so that the transverse momentum is not conserved, and there are processes that couple localized states at the electrode-barrier interface to the itinerant states in the bulk of the electrodes. While it is in principle possible to include these effects, it leads to lengthy calculations. Here we propose an approximate scheme in which we do not take explicit account of either of the effects mentioned above, but in which we calculate the tunnelling through all the states that exist at the electrode-barrier interfaces. We compare the k∥-resolved density of states and tunnelling currents across a junction in our approximate scheme with that found using the Landauer formalism in the ballistic limit.
{"title":"An approximate calculation for transport in magnetic tunnel junctions in the presence of localized states","authors":"P. Levy, Kuising Wang, P. Dederichs, C. Heide, Shufeng Zhang, L. Szunyogh","doi":"10.1080/13642810208224366","DOIUrl":"https://doi.org/10.1080/13642810208224366","url":null,"abstract":"Abstract In conventional calculations of transport in magnetic tunnel junctions, one usually assumes that the transverse momentum of the tunnelling electrons is conserved and that the itinerant electron states are orthogonal to localized states. However, in most of the junctions studied, there is diffuse scattering in both the bulk of the electrodes and the barrier so that the transverse momentum is not conserved, and there are processes that couple localized states at the electrode-barrier interface to the itinerant states in the bulk of the electrodes. While it is in principle possible to include these effects, it leads to lengthy calculations. Here we propose an approximate scheme in which we do not take explicit account of either of the effects mentioned above, but in which we calculate the tunnelling through all the states that exist at the electrode-barrier interfaces. We compare the k∥-resolved density of states and tunnelling currents across a junction in our approximate scheme with that found using the Landauer formalism in the ballistic limit.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83871618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208224369
A. Zaoui, F. H. Hassan
Abstract The present paper aims to study the electronic structure of semiconductors with d valence electrons such as CuX (X = Cl, Br or I). The full-potential linearized augmented-plane-wave method has been employed within the generalized gradient approximation for the exchange-correlation potential. The structural parameters have been obtained for the fundamental state of each CuX. Also, the role of d electrons and the contribution of every atomic orbital to the electronic structure are detailed and explained. From the obtained band structures, the electron (hole) valence and conduction effective masses are deduced. Our findings are compared with experimental and previous theoretical studies.
{"title":"Application of the full-potential linear augmented-plane-wave method to the study of electronic properties in semiconductors with d valence electrons","authors":"A. Zaoui, F. H. Hassan","doi":"10.1080/13642810208224369","DOIUrl":"https://doi.org/10.1080/13642810208224369","url":null,"abstract":"Abstract The present paper aims to study the electronic structure of semiconductors with d valence electrons such as CuX (X = Cl, Br or I). The full-potential linearized augmented-plane-wave method has been employed within the generalized gradient approximation for the exchange-correlation potential. The structural parameters have been obtained for the fundamental state of each CuX. Also, the role of d electrons and the contribution of every atomic orbital to the electronic structure are detailed and explained. From the obtained band structures, the electron (hole) valence and conduction effective masses are deduced. Our findings are compared with experimental and previous theoretical studies.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85257390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208224373
K. Ziegler
Abstract The Hubbard model is used as a starting point for a study of an electronic system with spin ½. Using a functional integral representation at half-filling it is demonstrated that the spin degeneracy is equivalent to dynamic Ising spins coupled to the fermions. A magnetic phase transition of the model is related to a transition of the Ising spins from a paramagnetic to an antiferromagnetic phase. A metal-insulator transition in the paramagnetic phase can be described within this approach by the Green's function of non-interacting fermions, coupled to Ising spins. This picture is compared with the earlier Ising spin representation of the Hubbard model by Hirsch and discussed in terms of a small hopping amplitude.
{"title":"The Hubbard model, spin degeneracy and Ising spins","authors":"K. Ziegler","doi":"10.1080/13642810208224373","DOIUrl":"https://doi.org/10.1080/13642810208224373","url":null,"abstract":"Abstract The Hubbard model is used as a starting point for a study of an electronic system with spin ½. Using a functional integral representation at half-filling it is demonstrated that the spin degeneracy is equivalent to dynamic Ising spins coupled to the fermions. A magnetic phase transition of the model is related to a transition of the Ising spins from a paramagnetic to an antiferromagnetic phase. A metal-insulator transition in the paramagnetic phase can be described within this approach by the Green's function of non-interacting fermions, coupled to Ising spins. This picture is compared with the earlier Ising spin representation of the Hubbard model by Hirsch and discussed in terms of a small hopping amplitude.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85428090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208218356
N. Bertolino, J. Garay, Umberto Anselmi-Tamburini, Z. Munir
Abstract The influence of high dc currents (up to 1019 A cm−2) on the interaction between thin Au-Al layers was investigated over the temperature range 400-500°C. In contrast with earlier diffusion couple results, only four of the five intermetalllic compounds in this system were observed, in both the absence and the presence of a current at all levels. The intermetallics Au5 Al2 and Au2 Al were the dominant products while AuAl and AuAl2 were relatively insignificant. The latter showed little change, growing only to a total thickness of a few micrometres, regardless of the magnitude of the current density and time of annealing. While the sequence of formation of the different intermetallics was not affected by the current, the incubation time and rate of growth of the layers were strongly influenced. The incubation time for the appearance of a measurable product layer was markedly reduced by the current, by nearly two orders of magnitude in some cases. The effect of the current on the nucleation of the product phases was investigated through the use of ‘pre-nucleated’ samples. The results are discussed in light of the effect of the current on atomic flux (electromigration) and on the formation of defects and compared with recent observations on field effects in multilayer systems.
在400-500°C的温度范围内，研究了高直流电流(高达1019 A cm−2)对薄Au-Al层相互作用的影响。与早期的扩散偶的结果相比，在没有电流和在所有水平上存在电流的情况下，该系统中只有四种金属间化合物被观察到。金属间化合物Au5 Al2和Au2 Al是主要产物，而AuAl和AuAl2相对不显著。后者的变化不大，仅增长到几微米的总厚度，无论电流密度的大小和退火时间。虽然不同金属间化合物的形成顺序不受电流的影响，但层的孵育时间和生长速度受到强烈影响。出现可测量产品层的孵化时间因电流而显著减少，在某些情况下减少了近两个数量级。通过使用“预成核”样品，研究了电流对产物相成核的影响。讨论了电流对原子通量(电迁移)和缺陷形成的影响，并与最近在多层体系中观察到的场效应进行了比较。
{"title":"High-flux current effects in interfacial reactions in Au–Al multilayers","authors":"N. Bertolino, J. Garay, Umberto Anselmi-Tamburini, Z. Munir","doi":"10.1080/13642810208218356","DOIUrl":"https://doi.org/10.1080/13642810208218356","url":null,"abstract":"Abstract The influence of high dc currents (up to 1019 A cm−2) on the interaction between thin Au-Al layers was investigated over the temperature range 400-500°C. In contrast with earlier diffusion couple results, only four of the five intermetalllic compounds in this system were observed, in both the absence and the presence of a current at all levels. The intermetallics Au5 Al2 and Au2 Al were the dominant products while AuAl and AuAl2 were relatively insignificant. The latter showed little change, growing only to a total thickness of a few micrometres, regardless of the magnitude of the current density and time of annealing. While the sequence of formation of the different intermetallics was not affected by the current, the incubation time and rate of growth of the layers were strongly influenced. The incubation time for the appearance of a measurable product layer was markedly reduced by the current, by nearly two orders of magnitude in some cases. The effect of the current on the nucleation of the product phases was investigated through the use of ‘pre-nucleated’ samples. The results are discussed in light of the effect of the current on atomic flux (electromigration) and on the formation of defects and compared with recent observations on field effects in multilayer systems.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79711339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208218350
H. Zrouri, J. Hugel, C. Chaib, J. Gasser, L. Roubi
Abstract The resistivities and thermopowers of the liquid 3d transition-metal series have been investigated within Ziman's formula based on a spin-polarized approach. This implies the existence of atomic magnetic moments and the use of a two-band conduction model for the resistivity. The calculated resistivities are the lowest obtained until now within the Ziman scheme and better agreement with experiment has been found than with the classical non-polarized calculations. In spite of the improvement with respect to the non-magnetic results, the thermoelectric power values do not attain the degree of agreement observed for the resistivities.
{"title":"Electronic transport properties in the liquid 3d transition-metal series","authors":"H. Zrouri, J. Hugel, C. Chaib, J. Gasser, L. Roubi","doi":"10.1080/13642810208218350","DOIUrl":"https://doi.org/10.1080/13642810208218350","url":null,"abstract":"Abstract The resistivities and thermopowers of the liquid 3d transition-metal series have been investigated within Ziman's formula based on a spin-polarized approach. This implies the existence of atomic magnetic moments and the use of a two-band conduction model for the resistivity. The calculated resistivities are the lowest obtained until now within the Ziman scheme and better agreement with experiment has been found than with the classical non-polarized calculations. In spite of the improvement with respect to the non-magnetic results, the thermoelectric power values do not attain the degree of agreement observed for the resistivities.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78352298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208218355
S. A. El-Hakim
Abstract This work deals with the determination of the magnitude of the fractal dimension, from the analysis of the temperature dependence of the dc conductivity in the temperature range 1.5–300 K in germanium, disordered by large fluences of fast reactor neutrons, with the radiation defect concentration making it an insulator near the metal–insulator transition. From the reduced activation energy method and the percolation theory of hopping conductivity, the dielectric constants of the samples are calculated. The localization radius is determined. The obtained fractal dimensions are found to satisfy the scaling theory. The value determined for the exponent t is 1.7.
{"title":"An experimental determination of the fractal dimension at the metal—insulator transition in germanium ‘doped’ by radiation defects","authors":"S. A. El-Hakim","doi":"10.1080/13642810208218355","DOIUrl":"https://doi.org/10.1080/13642810208218355","url":null,"abstract":"Abstract This work deals with the determination of the magnitude of the fractal dimension, from the analysis of the temperature dependence of the dc conductivity in the temperature range 1.5–300 K in germanium, disordered by large fluences of fast reactor neutrons, with the radiation defect concentration making it an insulator near the metal–insulator transition. From the reduced activation energy method and the percolation theory of hopping conductivity, the dielectric constants of the samples are calculated. The localization radius is determined. The obtained fractal dimensions are found to satisfy the scaling theory. The value determined for the exponent t is 1.7.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75203036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208218353
J. C. Phillips
Abstract What is the microscopic interaction responsible for high temperature superconductivity? Here data on temporal relaxation of T c and the room temperature conductivity in YBa2Cu3O6+x after abrupt alteration by light pulses or pressure changes are analysed. The analysis proves, independently of microscopic details, that only electron-phonon interactions can cause high-temperature superconductivity in the cuprates; all other dynamic interactions are excluded by experiment.
{"title":"Electron-phonon interactions cause high-temperature superconductivity","authors":"J. C. Phillips","doi":"10.1080/13642810208218353","DOIUrl":"https://doi.org/10.1080/13642810208218353","url":null,"abstract":"Abstract What is the microscopic interaction responsible for high temperature superconductivity? Here data on temporal relaxation of T c and the room temperature conductivity in YBa2Cu3O6+x after abrupt alteration by light pulses or pressure changes are analysed. The analysis proves, independently of microscopic details, that only electron-phonon interactions can cause high-temperature superconductivity in the cuprates; all other dynamic interactions are excluded by experiment.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88839969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-05-01DOI: 10.1080/13642810208224371
R. Troć, H. Noël, P. Boulet
Abstract The recent more thorough reinvestigation of the U–Ge system has finally established the existence of five compounds with the chemical formulae U5Ge4, UGe, U3Ge5, UGe2 and UGe3. Here we add another compound UGe2-x, existing in a homogeneity range of 0.30 < x > 0.35, and crystallizing in the defect tetragonal ThSi2-type structure. This compound is a ferromagnet with T c = 47 K. For all these compounds we have revised earlier measured magnetic properties and measured (often for the first time) the magnetotransport properties such as the electrical resistivity at 0T and in applied magnetic fields up to 8 T. We have found no superconducting properties for U5Ge4 down to 20 mK, which was claimed earlier. The most striking features found for both ferromagnets UGe2-x (ThSi2-type phase) and UGe2 (ZrGa2-type phase) are their temperature dependences of the magnetoresistivity (MR). At low temperatures the MRs for both these phases are large and positive which, above 10 and 15 K respectively, change sign to negative. The largest negative values of MR were found not at the corresponding Tc values but at the characteristic temperature T', which is an inflection point T iof the ρ(T) curve; this is attributed to be a measure of the spin fluctuation temperature Tsf.
最近对U-Ge体系进行了更深入的重新研究，最终确定了五种化合物的化学式为U5Ge4、UGe、U3Ge5、UGe2和UGe3。这里我们添加了另一种化合物UGe2-x，存在于0.30 < x > 0.35的均匀性范围内，并以缺陷四方thsi2型结构结晶。该化合物为铁磁体，温度为47k。对于所有这些化合物，我们已经修正了之前测量的磁性，并测量了(通常是第一次)磁输运特性，例如在0T和高达8 t的外加磁场下的电阻率。我们发现U5Ge4在20 mK以下没有超导性质，这是之前声称的。铁磁体UGe2-x (thsi2型相)和UGe2 (zrga2型相)最显著的特征是它们的磁电阻率(MR)的温度依赖性。在低温下，这两相的MRs都很大且为正，分别在10和15 K以上，MRs变为负。MR的最大负值不是在相应的Tc值处，而是在ρ(T)曲线的拐点T′处;这是自旋涨落温度Tsf的测量值。
{"title":"Magnetotransport of compounds in the U–Ge system","authors":"R. Troć, H. Noël, P. Boulet","doi":"10.1080/13642810208224371","DOIUrl":"https://doi.org/10.1080/13642810208224371","url":null,"abstract":"Abstract The recent more thorough reinvestigation of the U–Ge system has finally established the existence of five compounds with the chemical formulae U5Ge4, UGe, U3Ge5, UGe2 and UGe3. Here we add another compound UGe2-x, existing in a homogeneity range of 0.30 < x > 0.35, and crystallizing in the defect tetragonal ThSi2-type structure. This compound is a ferromagnet with T c = 47 K. For all these compounds we have revised earlier measured magnetic properties and measured (often for the first time) the magnetotransport properties such as the electrical resistivity at 0T and in applied magnetic fields up to 8 T. We have found no superconducting properties for U5Ge4 down to 20 mK, which was claimed earlier. The most striking features found for both ferromagnets UGe2-x (ThSi2-type phase) and UGe2 (ZrGa2-type phase) are their temperature dependences of the magnetoresistivity (MR). At low temperatures the MRs for both these phases are large and positive which, above 10 and 15 K respectively, change sign to negative. The largest negative values of MR were found not at the corresponding Tc values but at the characteristic temperature T', which is an inflection point T iof the ρ(T) curve; this is attributed to be a measure of the spin fluctuation temperature Tsf.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75032907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：