Significant Zero Thermal Expansion Via Enhanced Magnetoelastic Coupling in Kagome Magnets

Abstract

with neither expansion nor contraction in response to different temperatures is urgently demanded in several fields, particularly in highly advanced modern applications such as telescopes, satellites, and semiconductors. [2,4] Thus far, ZTE materials such as Mn-based antiperovskites, [11,12] R 2 Fe 17 -based magnets, [13,14] LaFe 13−x Si x hydrides, [15] SnO 2 nanowires, [16] PbTiO 3 -Bi(Co,Ti)O 3 ferroelectric solid solutions, [17] and Tb(Co,Fe) 2 magnets [18] with different mechanisms have demonstrated excellent physical properties and unique advantages in practical applications. However, manipulation to obtain excellent NTE and ZTE within a broad temperature range is still challenging and limited for broad applications. Magnetic transition has been regarded as the desired mechanism for manipulating NTE based on a tunable magnetoelastic effect. The optimized NTE, but not yet yielding ZTE in Hf 1−x Ta x Fe 2 (Hf-Ta-Fe) magnets with excellent mechanical properties, [19][20][21][22][23] is obtained owing to the cell volume shrinkage during the ferromagnetic to antiferromagnetic (FM-AFM) transition. The induced weak PTE has exhibited magnetoelastic coupling; however, has not yet garnered considerable attention. Furthermore, Zero-thermal-expansion (ZTE) alloys, as dimensionally stable materials, are urgently required in many fields, particularly in highly advanced modern industries. In this study, high-performance ZTE with a negligible coefficient of thermal expansion a v as small as 2.4 ppm K −1 in a broad temperature range of 85-245 K is discovered in Hf 0.85 Ta 0.15 Fe 2 C 0.01 magnet. It is demonstrated that the addition of trace interstitial atom C into Ta-substituted Hf 0.85 Ta 0.15 Fe 2 exhibits significant capability to tune the normal positive thermal expansion into high-performance ZTE via enhanced magnetoelastic coupling in stabilized ferromagnetic structure. Moreover, direct observation of the magnetic transition between ferromagnetic and triangular antiferromagnetic states via Lorentz transmission electron microscopy, along with corresponding theoretical calculations, further uncovers the manipulation mechanism of ZTE and negative thermal expansion. A convenient and effective method to optimize thermal expansion and achieve ZTE with interstitial C addition may result in broadened applications based on the strong correlation between the magnetic properties and crystal structure.

A general strategy to significantly reduce thermal expansion and achieve high mechanical properties in iron alloys

“…Generally, transition metal elements with larger atomic radii exhibit low solubility in iron, and frequently engage with iron in a ratio of 1:2, resulting in Laves-type AFe 2 (A = transition metal elements) compounds. Intriguingly, Laves-type AFe 2 compounds occasionally exhibit excellent NTE 24 performance due to their complex magnetism and novel Kagome lattice 25 . This implies it is feasible to insuit form the Laves-type NTE phase by introducing a trace amount of transition metal elements into iron alloys.…”

Zero Thermal Expansion Effect and Enhanced Magnetocaloric Effect Induced by Fe Vacancies in Fe2Hf0.80Nb0.20 Laves Phase Alloys

“…Both coefficients, in absolute terms, are below 3 ppm/K, categorizing the Fe1.95 and Fe2.00 alloys as ZTE materials. The value of α V for the Fe1.95 alloy with a temperature span of 80 K is superior to most magnetic ZTE materials, such as Fe 2 Hf 0.85 Ta 0.15 C 0.01 18 (2.4 ppm/K), Mn 3 Zn 0.93 N (1.8 ppm/K), 26 Fe 2 Zr 0.8 Nb 0.2 (4.2 ppm/K), 37 TbCo 1.9 Fe 0.1 (1.44 ppm/K), 38 and Fe 2.5 Hf 0.80 Nb 0.20 (3.21 ppm/K). 24 The |α V | value of 1.2 ppm/K is also smaller than that of typical Invar alloys (4.5−7.5 ppm/K).…”

“…The hexagonal C14 structure Fe-based Laves phases stand out within the Laves phase family due to their remarkable sensitivity of crystal, magnetism, and electronic properties to compositional variations. − Among them, Fe 2 (Hf,Ta) alloys have garnered considerable attention due to the itinerant-electron metamagnetic transition from ferromagnetic (FM) to antiferromagnetic (AFM) state as the temperature increases. ,− This FM–AFM transition is attributed to a frustration effect, where the ordered magnetic moment of the Fe atom at the 2a site, situated within the middle layer of the Fe atom at the 6h site, vanishes as the temperature exceeds the transition temperature. − A significant research interest has been attracted in Fe-based Laves phase alloys including the mechanism underlying this metamagnetic transition ,− and related rich physical properties such as magnetocaloric effect, − negative thermal expansion (NTE) or zero thermal expansion (ZTE), ,− and magnetoresistance . A large adiabatic temperature change (3.5 K) from the metamagnetic transition was obtained at a magnetic field change of 2 T, which is comparable to the values for the two well-known MCE materials La­(Fe 0.88 Si 0.12 ) 13 H y and Mn x Fe 2– x P 1– y Si y .…”

An isotropic zero thermal expansion alloy with super-high toughness

“…Zero thermal expansion (ZTE) in alloys, is generally manipulated by rigorous spin-lattice-orbital coupling 1 – 4 , emerging in a variety of intermetallic compounds 5 – 9 , etc. Such compounds tend to be brittle because of their multiple covalent or ionic bonds and the lack of independent slip systems 10 – 12 .…”