Epitaxial thin-film Pd 1-x Fe x alloy: a tunable ferromagnet for superconducting spintronics
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Published online 28 October 2020 | https://doi.org/10.1007/s40843-020-1479-0
Epitaxial thin-film Pd1-xFex alloy: a tunable ferromagnet for superconducting spintronics 1
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Alireza Esmaeili , Igor V. Yanilkin , Amir I. Gumarov , Iskander R. Vakhitov , Bulat F. Gabbasov , 1* 2 1,3 Roman V. Yusupov , Dmitriy A. Tatarsky and Lenar R. Tagirov ABSTRACT Thin epitaxial films of the palladium-rich Pd1−xFex alloy were synthesized and extensively studied as a tunable ferromagnetic material for superconducting spintronics. The (001)-oriented MgO single-crystal substrate and the composition range of x = 0.01–0.07 were chosen to support the epitaxial growth and provide the films with magnetic properties spanning from very soft ferromagnet for memory applications to intermediately soft and moderately hard for the programmable logic and circuit biasing, respectively. Dependences of the saturation magnetization, Curie temperature and three magnetic anisotropy constants on the iron content x were obtained for the first time from the analyses of the magnetometry and ferromagnetic resonance data. The experimental results were discussed based on existing theories of dilute ferromagnetic alloys. Simulation of the hysteresis loops within the Stoner-Wohlfarth model indicates the predominant coherent magnetic moment rotation at cryogenic temperatures. The obtained results were compiled in a database of magnetic properties of a palladium-iron alloy in a single-crystal thin-film form considered as a material for superconducting spintronics. Keywords: palladium-iron alloy, thin epitaxial films, magnetization, magnetic anisotropy, superconducting spintronics
INTRODUCTION Conventional complementary metal–oxide–semiconductor (CMOS)-based electronics is already approaching its physical limits [1–5], so the end of conventional Moore’s law scaling [6] is really near. Approaches beyond the Moore suggest various solutions comprising new materials and devices, more efficient architectures and packaging, and new models of calcula-
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tions [4,5]. One of them pushes forward heterogeneous multi-chip architectures/packages where every kind of calculations is performed by a specialized processor based on optimal device physics. Forefront in the high-end supercomputing is associated with superconducting Josephson-junction technology [7– 10], which offers up to two orders increase in the clock frequency (100 GHz and beyond) and six orders reduction in the energy dissipation per bit operation— incredible gain against present semiconductor processors [11,12]. Requirement of the cryogenic cooling may seem complicated; however, it should not be a scare, thanks to the development of close-cycle refrigeration. The superconducting single flux quantum (SFQ) Josephson logic technology [13] was implemented in the US Cryogenic Computing Complexity (C3) Program [14,15], aiming to demonstrate a route towards the supercomputing system with the total performance of up to 1000 PFLOPS utilizing sub-ns access time Josephson magnetic random access memory (M
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