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Thermal annealing influence on structural, magnetic, electronic, and mechanical properties of offstoichiometric Ni40Cu10Mn35Ti15 all-d-metal Heusler alloy Vinicius G. de Paula, Leonardo S. de Oliveira, Anibal A. Mendes Filho, Carlos T. Rios, Jose A. Souzaa) Universidade Federal do ABC, Santo André, SP 09210-580, Brazil a) Address all correspondence to this author. e-mail: [email protected] Received: 8 May 2020; accepted: 31 July 2020

We have synthesized off-stoichiometric Ni40Cu10Mn35Ti15 all-d-metal Heusler alloy with a B2 cubic crystal structure by an arc melting process and investigated its structural, magnetic, electronic, thermal, and mechanical properties under the influence of a single-step thermal annealing. The compound exhibits an antiferromagnetic ordering accompanied by thermal hysteresis indicating a first-order magneto-structural transition. Curie–Weiss molecular field analysis reveals the presence of ferromagnetic interactions competing with long-range antiferromagnetic ordering. Thermal annealing leads to the appearance of a heat capacity sharp peak around antiferromagnetic transition. Electrical resistivity measurements display abrupt changes close to the magnetostructural transition revealing the strong coupling among spin, lattice, and charge degrees of freedom characteristic of a martensitic transition (MT). We have also evaluated its mechanical properties from microhardness measurements, and the results indicate that this alloy exhibits ductile behavior. The occurrence of MT associated with improved ductility is an essential combination for technological application as shape-memory alloys.

Introduction Heusler alloys form an important class of magnetic materials with potential technological applications in several fields [1]. Usually, they are formed of two transition metals and another element from III–V groups of the periodic table. They have attracted much attention due to their multifunctional character showing shape-memory behavior [2], magnetocaloric, magnetoresistance, and thermoelectric effects [3,4,5,6,7]. Besides strong orbital hybridization, these properties are also a consequence of strong coupling among lattice, spin, orbital, and charge degrees of freedom [8]. Particularly, in conventional X2YZ Heusler systems strong p–d orbital hybridization among d and p states from X and Z atoms, respectively, is closely related to the appearance of a magneto-structural transition, known as a martensitic transition (MT) [9]. However, recent theoretical simulations [10,11,12,13] have predicted that all-d-metal Heusler alloys, containing only transition metals, could also exhibit MT. From an experimental point of view, few all-d-metal alloys have been synthesized so

© Materials Research Society 2020

far. Most of these systems are off-stoichiometric variations of Ni–Mn–Ti series. For example, Ni50Mn35Ti15 alloy is an offstoichiometry full Heusler alloy which was synthesized by introducing low valence Ti atoms into binary NiMn alloy [14] and presents an antiferromagnetic transition