Ferromagnetic resonance of facing-target sputtered epitaxial γ′-Fe₄N films: the influence of thickness and substrates

Abstract

The microstructure and high frequency properties of facing-target sputtered epitaxial γ′-Fe 4 N films were investigated in detail. It was found that the eddy current in ultrathin γ′-Fe 4 N films is too small to influence the ferromagnetic resonance (FMR) linewidth, where the linewidth is mostly determined by intrinsic damping and the two-magnon scattering (TMS) process. In relatively thick films, the TMS process can significantly affect the linewidth due to the roughness on the sample surface. However, the TMS process in a thin film is quite weak because of its smooth surface. The Gilbert damping constant of about 0.0135 in our γ′-Fe 4 N films is smaller than the experimental value in the previous work. Moreover, substrates can also influence the FMR linewidth of the γ′-Fe 4 N films by the TMS process. Besides, the resonance field of polycrystalline γ′-Fe 4 N film is larger than the epitaxial ones because of the lack of a magnetic anisotropic field, but the linewidth of the polycrystalline γ′-Fe 4 N film is smaller.

Magnetoelectric coupling in γ′-Fe4N/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 multiferroic heterostructures

“…Based on Bragg's law, the calculated lattice constant is c = 3.792 Å, which is consistent with the value (3.795 Å) of bulk γ 0 -Fe 4 N. 31 The calculated lattice constant indicates that the growth of the γ 0 -Fe 4 N films is fully relaxed due to the misfit dislocations at the interface, which has also been observed at the γ 0 -Fe 4 N/MgO interface. 32 In Fig. 1(b), the γ 0 -Fe 4 N(011) and (022) peaks appear at 33.40°and 70.18°.…”

“…The easy axis of γ 0 -Fe 4 N films is along the [100] direction and the hard axis is along the [110] direction. 32 In Fig. 5, the magnetization switching of γ 0 (011) along the [01-1] direction becomes easier by applying an electric field of 10 kV/cm at t ≥ 12 nm because the easy axis turns into the hard axis under the electric field due to the SSE-induced MEC.…”

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 .…”

Emergence of Room Temperature Magnetotransport Anomaly in Epitaxial Pt/γ′-Fe4N/MgO Heterostructures toward Noncollinear Spintronics

“…Moreover, one-step saturation is shown in Figure c,d (see blue arrow), indicating that the OP moments of Pt­(3 nm)/γ′-Fe 4 N/MgO heterostructures saturate sharply at a small H z due to the existence of noncollinear spin textures. However, the ρ xy sign reversals have not been observed in any single γ′-Fe 4 N films. , ρ xy sign reversals can be attributed to the competition between the magnetic proximity effect and the spin Hall effect, − which is independent on the noncollinear spin textures of the γ′-Fe 4 N layer. Specifically, as the γ′-Fe 4 N thickness decreases to 4 nm at 300 K, a contrast hump appears in the nonmonotonic ρ xy – H z curve of Pt­(3 nm)/γ′-Fe 4 N­(4 nm)/MgO heterostructures at 30–35 kOe (Figure c).…”

“…Epitaxial γ′-Fe 4 N­( t 1 ) ( t 1 = 5 and 30 nm) films were directly deposited on MgO substrates at 450 °C by facing target sputtering from a pair of Fe targets (99.99%). The details for epitaxial γ′-Fe 4 N film growth on MgO substrates can be found in our previous work. − Pt films from a pair of Pt (99.95%) targets were deposited on the top of γ′-Fe 4 N layer at room temperature, where sputtering pressure of Ar (99.999%) gas was 0.5 Pa with an Ar flow rate of 100 sccm and a sputtering power of 18 W. The film thickness was measured with a Dektak 6M surface profiler and calibrated by transmission electron microscopy (TEM).…”