Crossing the ballistic-ohmic transition via high energy electron irradiation

P.H.M. and M.D.B. received PhD studentship support from the UK Engineering and Physical Science Research Council via Grant No. EP/L015110/1. C.P. and P.J.W.M. are supported by the European Research Council under the European Union's Horizon 2020 research and innovation programme (Microstructured Topological Materials Grant No. 715730). E. Z. acknowledges support from the International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM). Irradiation experiments performed on the SIRIUS platform were supported by the French National Network of Accelerators for Irradiation and Analysis of Molecules and Materials (EMIR&A) under Project No. EMIR 2019 18-7099.The delafossite metal PtCoO2 is among the highest-purity materials known, with low-temperature mean free path up to 5 μm in the best as-grown single crystals. It exhibits a strongly faceted, nearly hexagonal Fermi surface. This property has profound consequences for nonlocal transport within this material, such as in the classic ballistic-regime measurement of bend resistance in mesoscopic squares. Here, we report the results of experiments in which high-energy electron irradiation was used to introduce pointlike disorder into such squares, reducing the mean free path and therefore the strength of the ballistic-regime transport phenomena. We demonstrate that high-energy electron irradiation is a well-controlled technique to cross from nonlocal to local transport behavior and therefore determine the nature and extent of unconventional transport regimes. Using this technique, we confirm the origins of the directional ballistic effects observed in delafossite metals and demonstrate how the strongly faceted Fermi surface both leads to unconventional transport behavior and enhances the length scale over which such effects are important. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Publisher PDFPeer reviewe

Determination of ferrite nanoparticles size inside the polymer matrix

В работе для изучения морфологии поверхности был использован модифицированный композит на основе гумата натрия, поливинилового спирта и магнитной жидкости с функционализацией дисперсной фазы ионами никеля. Показано, что структурные единицы композита имеют сферическую форму и состоят из агрегатов с размерностью от 18 до 100 нм.In our work for surfаce morphology study we used modified composite on the basis of sodium humate, polyvinyl alcohol and magnetic fluid with disperse phase functionalization by nickel ions. It was demonstrated that composite structural units have spherical shape and consist of aggregates with sizes from 18 to 100 nm.Работа выполнена при поддержке МОН Республики Казахстан (грант № 4864/ГФ4)

The Influence of Magnetic Inhomogeneous State on Thermopower and Magnetothermopower in Sm0.55Sr0.45MnO3 Manganites

Thermopower α and magnetothermopower ∆α/α were studied in the single-crystal Sm0.55Sr0.45MnO3 samples, containing clusters of following three types: ferromagnetic clusters with the Curie temperature TC = 134 K, A-type antiferromagnetic clusters with the Neel temperature TNA ≤ TC and CE-type antiferromagnetic clusters with the TNCE = 240 K. Temperature dependence of α and ∆α/α have extrema in the TNCE-region: large maximum on α(T) and sharp minimum on {∆α/α}(T). Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field H = 13,2 kOe. As will be shown below thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order (CO), displacing oxygen ions. Modified crystalline lattice inside clusters causes change of thermopower in them. This thermopower influences on the voltage drop on sample at measurement of thermopower and, consequently, on the effective value α of the whole sample. Enclosure of the magnetic field in the TNCE, which accelerates the destruction of the CE-type antiferromagnetic order, causes sharp decrease of total thermopower. This means that the CE-type antiferromagnetic clusters with CO order are the main contributors to the thermopower of the whole sample

The Influence of Magnetic Inhomogeneous State on Thermopower and Magnetothermopower in Sm

Thermopower α and magnetothermopower ∆α/α were studied in the single-crystal Sm0.55Sr0.45MnO3 samples, containing clusters of following three types: ferromagnetic clusters with the Curie temperature TC = 134 K, A-type antiferromagnetic clusters with the Neel temperature TNA ≤ TC and CE-type antiferromagnetic clusters with the TNCE = 240 K. Temperature dependence of α and ∆α/α have extrema in the TNCE-region: large maximum on α(T) and sharp minimum on {∆α/α}(T). Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field H = 13,2 kOe. As will be shown below thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order (CO), displacing oxygen ions. Modified crystalline lattice inside clusters causes change of thermopower in them. This thermopower influences on the voltage drop on sample at measurement of thermopower and, consequently, on the effective value α of the whole sample. Enclosure of the magnetic field in the TNCE, which accelerates the destruction of the CE-type antiferromagnetic order, causes sharp decrease of total thermopower. This means that the CE-type antiferromagnetic clusters with CO order are the main contributors to the thermopower of the whole sample

Controlled Introduction of Defects to Delafossite Metals by Electron Irradiation

The delafossite metals PdCoO$_{2}$, PtCoO$_{2}$ and PdCrO$_{2}$ are among the highest conductivity materials known, with low temperature mean free paths of tens of microns in the best as-grown single crystals. A key question is whether these very low resistive scattering rates result from strongly suppressed backscattering due to special features of the electronic structure, or are a consequence of highly unusual levels of crystalline perfection. We report the results of experiments in which high energy electron irradiation was used to introduce point disorder to the Pd and Pt layers in which the conduction occurs. We obtain the cross-section for formation of Frenkel pairs in absolute units, and cross-check our analysis with first principles calculations of the relevant atomic displacement energies. We observe an increase of resistivity that is linear in defect density with a slope consistent with scattering in the unitary limit. Our results enable us to deduce that the as-grown crystals contain extremely low levels of in-plane defects of approximately $0.001\%$. This confirms that crystalline perfection is the most important factor in realizing the long mean free paths, and highlights how unusual these delafossite metals are in comparison with the vast majority of other multi-component oxides and alloys. We discuss the implications of our findings for future materials research