Influence of an MgTiTaON Inserted Layer on Magnetic Properties and Microstructure of FePtAgC Films

The FePt film above 10 nm critical lattice relaxation thickness was prepared and the ultrathin MgTiTaON layer was interleaved in between FePt film and the multilayer stack is FePt(6 nm)/[MgTiTaON(1 nm)/FePt(4 nm)]2. Next, the FePt films were co-sputtered with (Ag, C) segregants during deposition and the layer stacks is FePt(6 nm)(Ag, C)(x vol %)/[MgTiTaON (1 nm)/FePt(4 nm)(Ag, C) (x vol %)]2 (x = 0, 10, 20, 30, 40). After high temperature deposition at 470 °C, the granular FePt(Ag, C, MgTiTaON) film illustrated perpendicular magnetization and the out-of-plane coercivity (Hc) was increased with (Ag, C) segregants and the highest Hc is 18.3 kOe when x = 40. From cross-section images, the FePt layer are more continuous with 0 and 10 vol% (Ag, C) segregants and changed to an island structure when the (Ag, C) segregants increase to 20–40 vol %. The FePt grains were grown in separated islands in 20, 30 vol % (Ag, C) and changed to dense columnar-like morphology in 40 vol%. The second nucleated grains which contribute the in-plane magnetization are found in FePt (Ag, C) (40 vol %) film. The FePt islands are reached by inserting the ultrathin MgTiTaON layer and the island heights of FePt(Ag, C) (30, 40 vol %) are around 31–38 nm and the aspect ratios are 0.6–0.8.

Magnetic Properties and Microstructure of FePt(BN, Ag, C) Films

The microstructure and magnetic properties of FePt(BN, Ag, C) granular films grown on the MgTiON intermediate layer with and without the MoC inserting layer were studied. Without the MoC inserting layer, the 6 nm thick FePt film is continuous, which favors the domain wall motion magnetization reversal process and shows a lower out-of-plane coercivity (Hc) value of 6.7 kOe. The FePt(BN, Ag, C) granular film was grown in ball- and square-like grains with an almost vertical contact angle, and the out-of-plane coercivity (Hc) was increased to 15.5 kOe. When the MoC with a thickness of 3 nm was capped on the MgTiON intermediate layer, the FePt grains with and without (BN, Ag, C) segregants were both formed in large trapezoidal islands with a low contact angle morphology. The out-of-plane Hc value changed from 14.9 to 13.2 kOe and the reduced coercivity was due to larger grain sizes and a lower ordering degree of the FePt(BN, Ag, C) film.

Nonvolatile modulation of electronic structure and correlative magnetism of L10-FePt films using significant strain induced by shape memory substrates

Tuning the lattice strain (εL) is a novel approach to manipulate the magnetic, electronic and transport properties of spintronic materials. Achievable εL in thin film samples induced by traditional ferroelectric or flexible substrates is usually volatile and well below 1%. Such limits in the tuning capability cannot meet the requirements for nonvolatile applications of spintronic materials. This study answers to the challenge of introducing significant amount of elastic strain in deposited thin films so that noticeable tuning of the spintronic characteristics can be realized. Based on subtle elastic strain engineering of depositing L10-FePt films on pre-stretched NiTi(Nb) shape memory alloy substrates, steerable and nonvolatile lattice strain up to 2.18% has been achieved in the L10-FePt films by thermally controlling the shape memory effect of the substrates. Introduced strains at this level significantly modify the electronic density of state, orbital overlap and spin-orbit coupling (SOC) strength in the FePt film, leading to nonvolatile modulation of magnetic anisotropy and magnetization reversal characteristics. This finding not only opens an efficient avenue for the nonvolatile tuning of SOC based magnetism and spintronic effects, but also helps to clarify the physical nature of pure strain effect.