Non-collinear antiferromagnetism to compensated ferrimagnetism in Ti(Fe1−xCox)2 (x = 0, 0.5 and 1) alloys: experiment and theory

Abstract

The manifestation of the structural and magnetic properties of Co substituted TiFe₂ is investigated using powder X-ray diffraction, magnetization and density functional theory calculations. The alloys TiFe₂ and TiFeCo crystallize in the hexagonal structure (P6₃/mmc) with a reduction in the lattice parameters of TiFeCo (by about 0.51% in a and 0.64% in c) when compared to TiFe₂. On the other hand, TiCo₂ crystallizes in the cubic structure (Fdm). A structural transition from hexagonal to cubic is anticipated for a composition with x ∈ [0.5, 1]. The non-collinear antiferromagnetic (AFM) spin structure (formed by 6h Fe atoms) of TiFe₂ with Néel temperature T_N ∼ 275 K is reported at zero magnetic field H. Meanwhile, a magnetic field-induced collinear antiferromagnetic spin structure is suggested by magnetization measurements and supported by density functional theory calculations. The magnetization of TiFeCo shows a weak-ferromagnetic (FM)-like transition around 204 K, followed by a broad hump at 85.5 K and H = 200 Oe. Ferromagnetic interactions are weakened, causing the hump to disappear due to the possible transfer of electrons between Fe and Co. TiCo₂ shows compensated ferrimagnetism with magnetization of the order of 10⁻⁵μ_B f.u.⁻¹ and a linear increase of M with H at 5 K. The presence of a non-collinear AFM spin structure in TiFe₂, a reduced magnetic moment in TiFeCo due to the charge transfer between Co and Fe, and compensated ferrimagnetism in TiCo₂ promise a rich phase diagram of Ti(Fe_1−xCo_x)₂ alloys and the possible potential of these alloys for use in spintronics applications.