Scaling of anomalous Hall effects in facing-target reactively sputtered Fe₄N films

Abstract

The anomalous Hall effect (AHE) in the reactively sputtered epitaxial and polycrystalline γ'-Fe4N films is investigated systematically. The Hall resistivity is positive over the entire temperature range. The magnetization, carrier density and grain boundary scattering have a major impact on the AHE scaling law. The scaling exponent γ in the conventional scaling of ρAH ∝ ρ(γ)(xx) is larger than 2 in both the epitaxial and polycrystalline γ'-Fe4N films. Although γ > 2 has been found in heterogeneous systems due to the effects of the surface and interface scattering on AHE, γ > 2 is not expected in homogenous epitaxial systems. We demonstrated that γ > 2 results from residual resistivity (ρxx0) in γ'-Fe4N films. Furthermore, the side-jump and intrinsic mechanisms are dominant in both epitaxial and polycrystalline samples according to the proper scaling relation.

Field-Free Deterministic Magnetization Switching with Ultralow Current Density in Epitaxial Au/Fe4N Bilayer Films

“…Note that the ordinary contributions to the Hall resistivity arising from Lorentz force have been extracted. The obtained ρ AH – H z curves are opposite the previous report, which might be caused by different measurement circuits. However, in identical measurement configurations and circuits, the sign of the anomalous Hall coefficient R AH (which is defined as ρ AH = R AH M z , where M z is the normal component of magnetization) is opposite that of Mn 4 N-based antiperovskite compounds, , that is, positive (negative) M z generates negative (positive) ρ AH in Fe 4 N films, while positive (negative) M z generates positive (negative) ρ AH in Mn 4 N-based antiperovskite compounds.…”

“…Here, we report field-free deterministic magnetization switching in epitaxial Au/Fe 4 N bilayer films grown by PA-MBE on MgO substrates. Fe 4 N has a high Curie temperature, saturation magnetization, and spin polarization and a large negative spin polarization of the electrical conductivity, which are all of technological importance and fundamental interest. − However, Fe 4 N as a switchable ferromagnetic layer in SOT-induced magnetization switching has rarely been reported so far. In this work, owing to the special magnetic anisotropies of Fe 4 N, field-free switching with ultralow threshold current density was obtained in the simple bilayer films.…”

Bending Strain-Tailored Magnetic and Electronic Transport Properties of Reactively Sputtered γ′-Fe4N/Muscovite Epitaxial Heterostructures toward Flexible Spintronics

“…In flexible spintronics, the magnetic and electronic transport properties of the ferromagnetic films are mainly tailored via applying the bending strains (>1.0%), − which is larger than the piezoelectric strain (<0.2%) in PbZr x Ti 1‑ x O 3 . , However, the integration of epitaxial films on flexible organic substrates is quite difficult due to the lower fabrication temperatures (<300 °C) and lattice mismatch. − Meanwhile, the large strain-induced magnetization and resistance change are also not easy to achieve because most of the ferromagnetic films deposited on flexible substrates are polycrystalline or amorphous. The poor lattice symmetry, low anisotropy, and complicated grain boundaries in the polycrystalline or amorphous films, such as flexible polycrystalline Fe 81 Ga 19 and amorphous Co 40 Fe 40 B 20 films, ,− make them have a weaker response to the strains, which can result in a smaller modulation on the magnetic and electronic transport properties than that in the epitaxial films. , Since, the epitaxial films can effectively transfer the strain from the substrate, the epitaxial ferromagnetic films with a large magnetization, anisotropy magnetoresistance (AMR), and anomalous Hall resistivity are more desirable. − Meanwhile, the muscovite simplified as “mica” [KAl 2 Si 3 AlO 10 )­(OH) 2 ] has been paid much attention to achieve a large strain due to its large stretchability. − The melting point of mica is as high as 1300 °C, which is necessary to fabricate the epitaxial ferromagnetic films. ,,, …”

Bending strain tailored exchange bias in epitaxial NiMn/ γ ′-Fe4N bilayers

“…Owing to poor lattice symmetry, low anisotropy, and grain boundaries in polycrystalline or amorphous films, 11,18 the strain effects on the magnetic and electronic transport properties are smaller than those in epitaxial films because the epitaxial films can effectively transfer the strain from substrates. 19,20 Therefore, flexible epitaxial antiferromagnetic/ferromagnetic (AFM/FM) bilayers are more suitable to tailor EB. Muscovite (mica) [KAl 2 Si 3 AlO 10 )(OH) 2 ] has been used as the substrate to produce a large strain by bending due to its large stretchability 21,22 and high melting point of 1300 C. 23,24 Here, c 0 -Fe 4 N is selected as the ferromagnetic layer due to its large ductility, 25,26 a high Curie temperature of 767 K, and a large saturation magnetization of 1440 emu/cm 3 .…”