Magnetic Flux Dynamics in HTS Bulks with Levitation Techniques

The discovery of high-temperature superconductors (HTS) has led to understanding that, in order to explain and utilize the phenomenon, completely new physical approaches should be introduced at all scales: microscopic, mesoscopic, macroscopic. Leaving first two scales beyond the scope of the present paper, we focus in the upper limit of the last scale, the study of the magnetic flux dynamics in HTS bulks—the dynamics of the ‘compact vortex structures’. A new direction in the experimental superconducting physics, the investigation of HTS bulks with levitation techniques, which has been elaborated during last years to effectively explore the subject, as well as the new fundamental and applied results obtained there from are overviewed here.Відкриття високотемпературних надпровідників (ВТНП) призвело до розуміння того, що задля пояснення та використання цього явища на всіх рівнях: мікроскопічному, мезоскопічному та макроскопічному, має бути створено принципово нові фізичні підходи. Полишаючи перші два рівні поза увагою даної роботи, ми детально розглядаємо верхню границю останнього — дослідження динаміки магнітного потоку в масивних ВТНП, динаміки «компактових вихорових структур». Дана робота — це огляд нового напрямку експериментальної фізики надпровідників — дослідження масивних ВТНП левітаційними методами — що його було вироблено останнім часом для вивчення зазначеної проблеми, а також тих нових фундаментальних та практичних результатів, що було тут отриманоОткрытие высокотемпературных сверхпроводников (ВТСП) привело к пониманию того, что для объяснения и использования этого явления необходимо создание принципиально новых физических подходов на всех уровнях: микроскопическом, мезоскопическом, макроскопическом. Оставляя первые два уровня за рамками данной работы, мы сфокусировали внимание на верхнем пределе последнего — исследовании динамики магнитного потока в массивных ВТСП, динамики «компактных вихревых структур». Данная работа — это обзор нового направления экспериментальной физики сверхпроводников, которое было выработано за последние годы, а также тех новых фундаментальных и прикладных результатов, которые были здесь получены

Electronic structure and magneto-optical Kerr effect in the compound UCuP₂

The optical and magneto-optical (MO) spectra of the fernary compound UCuP₂ are investigated from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method and density-functional theory in the local spin-density approximation. Within a band-like description of the 5f electrons, good agreement with the measured MO spectra is obtained. The origin of the Kerr rotation in the compound is examined

X-RAY AND AUGER ELECTRON MICROANALYSIS IN STUDY OF THE CONTACT ZONE OF STEELS UNDER FRICTION

L'étude de la structure fine des spectres d'émission X du fer et de l'oxygène ainsi que les données de la spectrométrie Auger permettent de réfuter les hypothèses anciennes sur la formation de solutions solides sursaturées ou de composés définis métal-oxygène aux interfaces de frottement des aciers dans l'eau. On suppose que les atomes d'oxygène sont piégés par les défauts de la surface de contact.The study of fine structure of emission X-ray spectra of iron and oxygen in combination with Auger electron spectra data refute the earlier suppositions about forming the oversaturated solid solutions or chemical compounds of oxygen with metal in the contact zone of steels under sliding friction in water. Oxygen atoms are supposed to disposed in defects of desorganized boundary material

Electronic Structure and Martensitic Transformation in a ZrRh Alloy

Experiments have revealed that equiatomic ZrRh alloy exhibits, upon cooling or heating, a structural transformation of the martensitic type from B2 to B19’ and vice versa, involving a hysteresis of the order 200°C and a shape memory effect. On the basis of the electronic structure calculation for the B2 phase of the ZrRh alloy, it is suggested that a reason for the structural instability of this ZrRh phase possessing a high-symmetry can be presence of a flat region near the Fermi level in the dispersion law

Magneto-optical spectroscopy of d- and f-ferromagnetic materials: recent theoretical progress

The current status of theoretical understanding of the optical and magneto-optical (MO) spectra of 3d, 4f and 5f compounds is reviewed. Energy band theory based upon the local spin-density approximation (LSDA) describes the optical and MO spectra of transition metal compounds reasonably well. Examples which we examine in detail are XPt₃ compounds (with X= 3dV, Cr, Mn, Fe, and Co) in the AuCu₃ structure, ternary Heusler alloys NiMnSb, PdMnSb, PtMnSb, and MnBi compound. The LSDA, which is capable of describing the spectra of transition-metal alloys with high accuracy, does not suffice for lanthanide compounds having a correlated 4f shell. A satisfactory description of the optical spectra could be obtained by using a generalization of the LSDA, in which explicitly f electron Coulomb correlations are taken into account (LSDA+U approach). As examples of this group we consider CeSb and CeBi. For CeSb a record Kerr angle of 90╟ was very recently reported, 90╟ is the absolute maximum value that can be measured. It is two orders of magnitude larger than the values that are commonly measured for transition-metal compounds, and about one order of magnitude larger than values maximally achieved for other lanthanide and actinide compounds. A third group consist of uranium 5f compounds. In those compounds where the 5f electrons are rather delocalized, the LSDA describes the MO spectra reasonably well. As examples of this group we consider UAsSe and URhAl. Particular difficulties occur for the uranium compounds where the 5f electrons are neither delocalized nor localized, but more or less semilocalized. Typical examples are US, USe and UTe. The semilocalized 5f`s are, however, not inert, but their interaction with conduction electrons plays an important role. Recently achieved improvements for describing such compounds are discussed

Magneto-optical spectroscopy of magnetic multilayers: Theory and experiment (A review)

Experimental and theoretical results on the optical and magneto-optical (MO) spectral properties of a series of Co/Cu, Co/Pd, Co/Pt and Fe/Au multilayers (MLS) are reviewed. Diagonal and off-diagonal components of the optical conductivity tensor have been determined in the photon energy range 0.8-5.5 eV from the polar and longitudinal Kerr rotation as well as ellipticity and the ellipsometry measurements. The conductivity tensor has been evaluated on the basis of self-consistent spin-polarized relativistic linear muffintin orbital (LMTO) band-structure calculations within the local spin-density approximation. The role of the spin polarization and the spin-orbit interaction in the formation of the magneto-optical Kerr effect (MOKE) spectra as inferred from first-principles calculations is examined and discussed. The high sensitivity of the MO properties to the interface structure is studied by ab initio modeling of the effects of the interface alloying, substitutional disorder, and the roughness at the interfaces. It is shown that the MOKE spectra of the MLS calculated using the LMTO method reproduce the experimental spectra only moderately well if ideal multilayer structure with sharp interfaces are assumed. It is shown that the MOKE spectra of the MLS can be adequately reproduced only by taking into account their real interface microstructure. The magneto-optical anisotropy (MOA) is studied both experimentally and theoretically for a series of Fen/Aun superlattices prepared by molecular beam epitaxy with n=1,2,3 of Fe and Au atomic planes of (001)orientation. The results of the LMTO calculations show that the microscopic origin of the large MOA is the interplay of the strong spin- orbit coupling on Au sites and the large exchange splitting on Fe sites via Au d-Fe d hybridization of the electronic states at the interfaces. The orientation anisotropy of the d orbital moment is calculated from first principles and analyzed on the basis of d orbital symmetry considerations. The relationship between the orbital moment anisotropy and the MOA is discussed. The reviewed results imply that the magneto-optical properties of multilayers with various compositions and structures can be quantitatively predicted from first-principles band-structure calculations. Such a possibility is important for basic research as well aplications. Experimental and theoretical results on the optical and magnetooptical (MO) spectral properties of a series of Co/Cu, Co/Pd, Co/Pt and Fe/Au multilayers are reviewed. Diagonal and off-diagonal components of the optical conductivity tensor have been determined in the photon energy range 0.8-5.5 eV from the polar and longitudinal Kerr rotation as well as ellipticity and ellipsometry measurements. The conductivity tensor has been evaluated on the basis of self-consistent spin-polarized relativistic linear muffin-tin orbital (LMTO) band-structure calculations within the local spin-density approximation. The role of the spin polarization and the spin–orbit interaction in the formation of the magnetooptical Kerr effect (MOKE) spectra as inferred from first-principles calculations is examined and discussed. The high sensitivity of the MO properties to the interface structure is studied by ab initio modeling of the effects of the interfacial alloying, substitutional disorder, and the roughness at the interfaces. It is shown that the MOKE spectra of the multilayered structures (MLS) calculated using the LMTO method reproduce the experimental spectra only moderately well if ideal MLS with sharp interfaces are assumed. It is shown that the MOKE spectra of the MLS can be adequately reproduced only by taking into account their real interface microstructure. The magnetooptical anisotropy (MOA) is studied both experimentally and theoretically for a series of Fen/Aun superlattices prepared by molecular beam epitaxy with n=1,2,3 Fe and Au atomic planes of (001) orientation. The results of the LMTO calculations show that the microscopic origin of the large MOA is the interplay of the strong spin-orbit coupling on Au sites and the large exchange splitting on Fe sites via Aud–Fe d hybridization of the electronic states at the interfaces. The orientation anisotropy of the d orbital moment is calculated from first principles and analyzed on the basis of d orbital symmetry considerations. The relationship between the orbital moment anisotropy and the MOA is discussed. The reviewed results imply that the magnetooptical properties of multilayers with various compositions and structures can be quantitatively predicted from first-principles band-structure calculations. Such a possibility is important for basic research as well as applications