Pub Date : 1988-08-01DOI: 10.1088/0305-4608/18/8/017
R. Richter, H. Eschrig
LCAO-CPA theory is applied to substitutionally disordered ferromagnetic BCC FeCo alloys. Calculations are based on charge and spin self-consistent LCAO parameters determined for the pure component metals within the local spin density functional theory. Effects of charge and spin self-consistency on the alloy magnetisation are treated in an ad hoc manner. Mechanisms determining the concentration dependence of the local magnetic moments are explained. The correlation of magnetic moment formation and maintenance of local charge neutrality is discussed. At Fe sites the exchange splitting is enhanced by a hybridisation-driven local reoccupation within the spin sub-bands. This causes the observed increase of the Fe moment by about 30%. Numerical results are presented for the saturation magnetisation, local magnetic moments, d-band population and specific heat coefficient as functions of concentration. Qualitative agreement was obtained with available experimental data. Numerical results for the concentration dependence of the total and component density of states are shown. Quite different degrees of disorder are found for both spin states. The majority spin states are typical rigid-band-like, whereas a strong influence of alloy disorder on the minority spin states is observed. This causes a strong broadening of the minority spin Bloch spectral functions and Fermi surface.
{"title":"Spin-polarised electronic structure of disordered BCC FeCo alloys from LCAO-CPA","authors":"R. Richter, H. Eschrig","doi":"10.1088/0305-4608/18/8/017","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/017","url":null,"abstract":"LCAO-CPA theory is applied to substitutionally disordered ferromagnetic BCC FeCo alloys. Calculations are based on charge and spin self-consistent LCAO parameters determined for the pure component metals within the local spin density functional theory. Effects of charge and spin self-consistency on the alloy magnetisation are treated in an ad hoc manner. Mechanisms determining the concentration dependence of the local magnetic moments are explained. The correlation of magnetic moment formation and maintenance of local charge neutrality is discussed. At Fe sites the exchange splitting is enhanced by a hybridisation-driven local reoccupation within the spin sub-bands. This causes the observed increase of the Fe moment by about 30%. Numerical results are presented for the saturation magnetisation, local magnetic moments, d-band population and specific heat coefficient as functions of concentration. Qualitative agreement was obtained with available experimental data. Numerical results for the concentration dependence of the total and component density of states are shown. Quite different degrees of disorder are found for both spin states. The majority spin states are typical rigid-band-like, whereas a strong influence of alloy disorder on the minority spin states is observed. This causes a strong broadening of the minority spin Bloch spectral functions and Fermi surface.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"30 1","pages":"1813-1825"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83618454","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/002
G. Ackland, M. Finnis, V. Vítek
The second moment approximation of tight-binding theory gives an electronic band energy per atom which has the form of the square root of a pairwise sum of squared hopping integrals. This functional form for the dependence of the energy on local coordination has been the basis of empirical non-pairwise force models for transition and noble metals. Hitherto, it appeared to be valid only for a half-filled band. By introducing the assumption that the atoms keep the same charge in all environments, the authors show that the square root function is appropriate for all band fillings.
{"title":"Validity of the second moment tight-binding model","authors":"G. Ackland, M. Finnis, V. Vítek","doi":"10.1088/0305-4608/18/8/002","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/002","url":null,"abstract":"The second moment approximation of tight-binding theory gives an electronic band energy per atom which has the form of the square root of a pairwise sum of squared hopping integrals. This functional form for the dependence of the energy on local coordination has been the basis of empirical non-pairwise force models for transition and noble metals. Hitherto, it appeared to be valid only for a half-filled band. By introducing the assumption that the atoms keep the same charge in all environments, the authors show that the square root function is appropriate for all band fillings.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"98 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73328847","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/024
H. Szymczak, R. Z̊uberek, A. Pajączkowska
The EPR spectrum of Gd3+ ions diluted (0.5% and 0.1%) in powdered samples of the high-Tc(Tc-92 K) superconductor Y1Ba2Cu3Ox has been measured at X-band in the temperature range 4.2-300 K. It was shown that the EPR spectrum exhibits significant changes in g-shift, thermal broadening and intensity well below Tc. The results are analysed in terms of existing theoretical models.
{"title":"Paramagnetic resonance of Gd3+ ions in the high-Tc superconductor Y1Ba2Cu3Ox","authors":"H. Szymczak, R. Z̊uberek, A. Pajączkowska","doi":"10.1088/0305-4608/18/8/024","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/024","url":null,"abstract":"The EPR spectrum of Gd3+ ions diluted (0.5% and 0.1%) in powdered samples of the high-Tc(Tc-92 K) superconductor Y1Ba2Cu3Ox has been measured at X-band in the temperature range 4.2-300 K. It was shown that the EPR spectrum exhibits significant changes in g-shift, thermal broadening and intensity well below Tc. The results are analysed in terms of existing theoretical models.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"17 1","pages":"1889-1892"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85646336","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/019
Junchu Cao, Fu-sui Liu, Chong-yu Wang
The electronic structure of Mg-reinforced nickel-based superalloys has been studied. By setting up models for the mechanism of Mg in nickel-based superalloys, the local density of states, charge transfer, structural energy, and Fermi level of the systems have been calculated with Haydock's recursion method (1972, 1975). The difference in structural energy of clusters including Mg and its neighbours in between systems in model I and model II shows that Mg prefers and stabilises gamma ' phases. The amount of charge transfer of Mg in the gamma ' phase of a nickel-based superalloy indicates that Mg tends to enter a gamma ' phase.
{"title":"Electronic structure of the γ'+γ phase in nickel-based superalloys","authors":"Junchu Cao, Fu-sui Liu, Chong-yu Wang","doi":"10.1088/0305-4608/18/8/019","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/019","url":null,"abstract":"The electronic structure of Mg-reinforced nickel-based superalloys has been studied. By setting up models for the mechanism of Mg in nickel-based superalloys, the local density of states, charge transfer, structural energy, and Fermi level of the systems have been calculated with Haydock's recursion method (1972, 1975). The difference in structural energy of clusters including Mg and its neighbours in between systems in model I and model II shows that Mg prefers and stabilises gamma ' phases. The amount of charge transfer of Mg in the gamma ' phase of a nickel-based superalloy indicates that Mg tends to enter a gamma ' phase.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"3 1","pages":"1839-1847"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91202571","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/005
V. Vaks, N. Zein, V. Kamyshenko
The cluster field method (CFM) described earlier is applied to the calculation of the correlation function Kij=K(ri-rj) and short-range order parameters aij in alloys. The method generalises the previous approaches of Krivoglaz (1957) and Clapp and Moss (1966, 1968) to the case of realistic values of the interaction constants Vij, which are not small, as compared with the temperature T. The cluster expansions for the matrix elements Sij=(K-1)ij are presented, which converge rapidly at normal values of the 'virial' parameter c(1-c)fij where c is the mean site occupation number and fij=exp(-Vij/T)-1 is the Mayer function. The sum rule aij=1 is usually fulfilled in the CFM with good accuracy, unlike in the previous approximate methods. The method enables the authors to estimate quantitatively the interaction constants Vij from the diffuse scattering data. This is illustrated by using the data of Lefebvre et al. (1981) for Ni0.765Fe0.235. The results show that the conventional Clapp-Moss approximation underestimates Vij by 30-40%. Applications to interstitial alloys are illustrated by calculating Kij for the NbHx-type alloys.
{"title":"On the cluster method in the theory of short-range order in alloys","authors":"V. Vaks, N. Zein, V. Kamyshenko","doi":"10.1088/0305-4608/18/8/005","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/005","url":null,"abstract":"The cluster field method (CFM) described earlier is applied to the calculation of the correlation function Kij=K(ri-rj) and short-range order parameters aij in alloys. The method generalises the previous approaches of Krivoglaz (1957) and Clapp and Moss (1966, 1968) to the case of realistic values of the interaction constants Vij, which are not small, as compared with the temperature T. The cluster expansions for the matrix elements Sij=(K-1)ij are presented, which converge rapidly at normal values of the 'virial' parameter c(1-c)fij where c is the mean site occupation number and fij=exp(-Vij/T)-1 is the Mayer function. The sum rule aij=1 is usually fulfilled in the CFM with good accuracy, unlike in the previous approximate methods. The method enables the authors to estimate quantitatively the interaction constants Vij from the diffuse scattering data. This is illustrated by using the data of Lefebvre et al. (1981) for Ni0.765Fe0.235. The results show that the conventional Clapp-Moss approximation underestimates Vij by 30-40%. Applications to interstitial alloys are illustrated by calculating Kij for the NbHx-type alloys.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"12 1","pages":"1641-1661"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87159670","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/013
P. Oppeneer, A. Lodder, R. Griessen
The contribution of resonant modes (band modes) to the electron scattering in dilute interstitial Pd-hydrogen alloys is investigated computationally. The interaction of Bloch electrons with the vibrating defect is treated in the adiabatic approximation. Electron scattering from a frozen defect is described by a KKR-Green function method which accounts for all defect-induced multiple scattering effects. It appears that the combined oscillations of a hydrogen atom together with surrounding Pd atoms give rise to a considerable enhancement of the scattering quantities. It is conjectured that the measured isotope effects in the de Haas-van Alphen quantities of Pd(H), Pd(D) and Pd(T) can be attributed to differences in the resonant modes of the isotopes. The occurrence of a resonant mode depends critically on the Pd-hydrogen force constants, which are, due to anharmonicity, different for the three isotopes.
{"title":"Resonant vibrations of hydrogen isotopes in Pd: their contributions to the electron-defect scattering","authors":"P. Oppeneer, A. Lodder, R. Griessen","doi":"10.1088/0305-4608/18/8/013","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/013","url":null,"abstract":"The contribution of resonant modes (band modes) to the electron scattering in dilute interstitial Pd-hydrogen alloys is investigated computationally. The interaction of Bloch electrons with the vibrating defect is treated in the adiabatic approximation. Electron scattering from a frozen defect is described by a KKR-Green function method which accounts for all defect-induced multiple scattering effects. It appears that the combined oscillations of a hydrogen atom together with surrounding Pd atoms give rise to a considerable enhancement of the scattering quantities. It is conjectured that the measured isotope effects in the de Haas-van Alphen quantities of Pd(H), Pd(D) and Pd(T) can be attributed to differences in the resonant modes of the isotopes. The occurrence of a resonant mode depends critically on the Pd-hydrogen force constants, which are, due to anharmonicity, different for the three isotopes.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"122 1","pages":"1743-1759"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81142483","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/007
S. Lai
The temperature dependences of the liquid structure factors of caesium metal have been determined using a Monte Carlo simulation technique. The calculation adopts the generalised non-local model pseudopotential theory developed recently by Li et al. (1986) to construct the interionic pair potential. The author finds that the latter pair potentials are rather accurate and, with proper choice of the asymptotic pair correlation function, are capable of reproducing highly reliable liquid structure factors at various temperatures.
利用蒙特卡罗模拟技术确定了金属铯的液态结构因子对温度的依赖关系。计算采用Li et al.(1986)最近发展的广义非局域模型赝势理论来构造离子间对势。作者发现，后一种对势是相当精确的，只要选择适当的渐近对相关函数，就能够在不同温度下再现高度可靠的液体结构因子。
{"title":"Monte Carlo simulation of the structure of liquid Cs at different temperatures","authors":"S. Lai","doi":"10.1088/0305-4608/18/8/007","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/007","url":null,"abstract":"The temperature dependences of the liquid structure factors of caesium metal have been determined using a Monte Carlo simulation technique. The calculation adopts the generalised non-local model pseudopotential theory developed recently by Li et al. (1986) to construct the interionic pair potential. The author finds that the latter pair potentials are rather accurate and, with proper choice of the asymptotic pair correlation function, are capable of reproducing highly reliable liquid structure factors at various temperatures.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"15 1","pages":"1673-1680"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74792898","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/020
A. Szász, L. Watson, L. Kertész, J. Kollár
Changes in the electronic density of states (DOS) caused by plastic deformation and hydrostatic pressure in dilute Al-Mg-Si alloys are examined. Significant changes in the DOS were observed which depended on the mechanical treatment of the alloy. The observations are compared with the DOS of the same alloy in metastable states.
{"title":"On the electronic density of states of age-hardening aluminium alloys","authors":"A. Szász, L. Watson, L. Kertész, J. Kollár","doi":"10.1088/0305-4608/18/8/020","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/020","url":null,"abstract":"Changes in the electronic density of states (DOS) caused by plastic deformation and hydrostatic pressure in dilute Al-Mg-Si alloys are examined. Significant changes in the DOS were observed which depended on the mechanical treatment of the alloy. The observations are compared with the DOS of the same alloy in metastable states.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"35 1","pages":"1849-1853"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79787492","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/003
Z. Fang, Zhang De
The characteristics of the aging internal friction and modulus associated with the non-equilibrium phase transformation were investigated in an as-quenched eutectoid Al-Zn alloy. It was observed that the loss of stability in the lattice during spinodal pretransition did not induce any localised soft modulus effect and there were two aging internal friction peaks during the phase transition. These results are discussed.
{"title":"Internal friction and modulus associated with non-equilibrium diffusion-type phase transformation in an Al-Zn alloy","authors":"Z. Fang, Zhang De","doi":"10.1088/0305-4608/18/8/003","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/003","url":null,"abstract":"The characteristics of the aging internal friction and modulus associated with the non-equilibrium phase transformation were investigated in an as-quenched eutectoid Al-Zn alloy. It was observed that the loss of stability in the lattice during spinodal pretransition did not induce any localised soft modulus effect and there were two aging internal friction peaks during the phase transition. These results are discussed.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80103377","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 : 1988-08-01DOI: 10.1088/0305-4608/18/8/022
B. Chenevier, O. Laborde, M. Bacmann, D. Fruchart, R. Fruchart, J. Puértolas
Electrical resistivity and magnetoresistivity measurements were performed on MnRhAs between 4.2 K and 300 K. The reveal an anisotropic behaviour and strong anomalies giving evidence for changes in the magnetic ordering. The anomalies are most pronounced in measurements along the hexagonal easy axis. The resistivity curve recorded in the ferromagnetic state (160
在4.2 K ~ 300 K范围内对MnRhAs进行了电阻率和磁电阻率测量。显示出各向异性行为和强烈的异常，为磁有序的变化提供了证据。这种异常在沿六边形易轴的测量中最为明显。当外加磁场大到足以翻转初始AF结构时，在铁磁状态(160
{"title":"Resistivity and magnetoresistivity up to 18 tesla of single crystals MnRhAs","authors":"B. Chenevier, O. Laborde, M. Bacmann, D. Fruchart, R. Fruchart, J. Puértolas","doi":"10.1088/0305-4608/18/8/022","DOIUrl":"https://doi.org/10.1088/0305-4608/18/8/022","url":null,"abstract":"Electrical resistivity and magnetoresistivity measurements were performed on MnRhAs between 4.2 K and 300 K. The reveal an anisotropic behaviour and strong anomalies giving evidence for changes in the magnetic ordering. The anomalies are most pronounced in measurements along the hexagonal easy axis. The resistivity curve recorded in the ferromagnetic state (160<T<200 K) coincides well with that measured at lower temperatures, when the applied magnetic field is large enough to flip the initial AF structure. It can be concluded that the resistivity of the two phases (F and AF) would be equal near 78 K. When the temperature is increased above the magnetic ordering temperature (TN=238 K), rho (T) reaches an almost constant value. This could result from the superposition of a weak electron-phonon interaction term and the contribution of the paramagnetic scattering of the conduction electrons.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"14 1","pages":"1867-1875"},"PeriodicalIF":0.0,"publicationDate":"1988-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84628988","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}
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