Electronic and Optical Properties of RCuGe Compounds (R = Dy, Ho)
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tronic and Optical Properties of RCuGe Compounds (R = Dy, Ho) Yu. V. Knyazeva, *, A. V. Lukoyanova, b, Yu. I. Kuzmina, S. Guptac, and K. G. Sureshc aMikheev
Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620108 Russia bUral Federal University, Yekaterinburg, 620075 Russia c Department of Physics, Indian Institute of Technology (Bombay), Mumbai, 400076 India *e-mail: [email protected] Received March 19, 2020; revised April 10, 2020; accepted May 27, 2020
Abstract—Results are presented from investigating the electronic structure and optical properties of DyCuGe and HoCuGe compounds. Spin-polarized calculations of the band structure are made using the local spin density approximation that allows for strong electronic correlations in the 4f-shells of rare earth ions. The optical properties of these alloys are studied in a broad range of wavelengths via ellipsometry. The calculated electron densities of states are used to interpret the experimental energy dependences of optical conductivities in the region of interband light absorption. DOI: 10.3103/S1062873820090191
INTRODUCTION Interest in studying the properties of RTX intermetallides (where R is a rare earth metal and T and X are d- and p-elements) has grown considerably in recent years, due to the great potential of their wide application and their broad range of physical and chemical characteristics [1–3]. A great many such alloys have been synthesized and studied. It has been shown that the uniqueness of their physical properties depends on the hybridization of the 4f-electrons of rare earth metals (REM) with electrons of the transition metal. This type of compound includes equiatomic intermetallides RCuGe (R = Dy, Ho) with hexagonal crystal structure. The study of magnetic properties in [4] showed that these materials are antiferromagnets (AFM) below Néel temperature TN, which is 6.0 K for DyCuGe and 6.1 K for HoCuGe. These compounds are characterized by strong magnetocaloric and magnetoresistive effects whose maximum values are reached near the temperatures of magnetic ordering [5]. In this work, we studied the electronic structure of these compounds by performing ab initio calculations of the band spectrum of these compounds and investigating their optical properties experimentally. CALCULATING ELECTRONIC STRUCTURE DyCuGe and HoCuGe compounds crystallize with a hexagonal LiGaGe-type crystal structure (P63ms spatial symmetry group). The lattice parameters were determined in [5]. The electronic structure
of these intermetallides was calculated using the LSDA + U approach [6], which corrects for strong electronic correlations in the 4f-shells of rare earth ions in the electron spin density approximation. The TB-LMTO-ASA software package [7] was used in our calculations. The AFM ordering of the magnetic moments of REM atoms was modeled in accordance with the experiment [4]. To allow for the strong electronic correlations within this approach, we used the following values of the Coulomb U and exchange J interaction paramete
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