Alternate Monatomic Layer Deposition Research Articles

Magnetic Anisotropy and Chemical Order of Artificially Synthesized L10-Ordered FeNi Films on Au–Cu–Ni Buffer Layers

L10-FeNi films were grown by alternate monatomic layer deposition on Au–Cu–Ni buffer layers at several substrate temperatures (Ts), and the relation between the uniaxial magnetic anisotropy energy (Ku) and the long-range chemical order parameter (S) was investigated. A large Ku of (7.0 ±0.2) ×106 erg/cm3 and S of 0.48 ±0.05 were obtained. The value of Ku was larger than those reported previously for artificially synthesized FeNi films. It was first found that both Ku and S increased with Ts, and Ku was roughly proportional to S.

Magnetic Anisotropy and Chemical Order of Artificially Synthesized L10-Ordered FeNi Films on Au–Cu–Ni Buffer Layers

L10-FeNi films were grown by alternate monatomic layer deposition on Au–Cu–Ni buffer layers at several substrate temperatures (Ts), and the relation between the uniaxial magnetic anisotropy energy (Ku) and the long-range chemical order parameter (S) was investigated. A large Ku of (7.0 ±0.2) ×106 erg/cm3 and S of 0.48 ±0.05 were obtained. The value of Ku was larger than those reported previously for artificially synthesized FeNi films. It was first found that both Ku and S increased with Ts, and Ku was roughly proportional to S.

L10-ordered FeNi film grown on Cu-Ni binary buffer layer

An FeNi film with a metastable L10-ordered phase was fabricated by an alternate monatomic layer deposition. An Fe monolayer and a Ni monolayer were alternately grown on a Cu0.6Ni0.4 binary buffer layer. A (001) L10-FeNi superlattice peak, which indicates the formation of a L10 phase, was clearly observed by an X-ray diffraction. A long-range order parameter S of L10-FeNi was estimated to be 0.5 ± 0.1. It was found that the film has a uniaxial magnetic anisotropy along c-axis by magnetization measurement. The uniaxial magnetic anisotropy energy Ku was evaluated to be (5.0 ± 0.1) × 106 erg/cc.

Artificial Fabrication and Order Parameter Estimation of L10-ordered FeNi Thin Film Grown on a AuNi Buffer Layer

Epitaxial L10-ordered FeNi thin films were artificially fabricated on a nonmagnetic AuNi buffer layer by using an alternate monatomic layer deposition. A uniaxial magnetic anisotropy energy of the FeNi layer was estimated to be 5.8 × 106 erg/cm3 from magnetization measurements, which is the largest energy among values reported on FeNi thin films grown on nonmagnetic buffers. A long-range order parameter of the FeNi layer was estimated to be 0.330 from a grazing incidence X-ray diffraction (GI-XRD) using synchrotron radiation. We also investigated the relation between the ratio of c-axis lattice constant to a-axis lattice constant (c/a ratio) and the uniaxial magnetic anisotropy energy of FeNi thin films grown on several buffer layers. The uniaxial magnetic anisotropy energy monotonically increased with the increase in the c/a ratio, whereas the anisotropy had no clear relation with the long-range order parameter. Not only the improved long-range order parameter but optimized c/a ratio in FeNi are expected to lead to the enhancement of the perpendicular magnetic anisotropy.

Characterization of Cu buffer layers for growth of L1-FeNi thin films

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

Structure and magnetic properties for L1 0-ordered FeNi films prepared by alternate monatomic layer deposition

Alternate monatomic layer (ML) deposition technique has been used to fabricate a metastable L1 0-ordered phase of FeNi alloys. The films were prepared by alternating Fe (0 0 1) and Ni (0 0 1) MLs on MgO (0 0 1) substrates at various temperatures T S in the range between 80 and 400 °C. It has been found that the degree of long-range order S evaluated by X-ray diffraction increases with T S, and it has a maximum at T S=240 °C. With further increase of T S, S shows a drastic decrease, and almost disappears at T S=280 °C. 280 °C is close to the order–disorder transformation temperature in the thermal equilibrium. The variation of K u shows the same tendency as that of S, suggesting the formation of L1 0-ordered FeNi alloy in the range of T S=200–260 °C. Maximum values of S=0.6±0.2 and K u=6.3×10 6 (erg/cm 3) are obtained at T S=240 °C.

Growth of L10 ordered FePt alloy films at reduced temperatures

In this work, polycrystalline fct(001) FexPt1−x alloy thin films (with x ≈ 50 at%) have been successfully grown at reduced temperatures by dc magnetron sputtering, via two different deposition methods: a conventional cosputtering and an alternate monatomic layer (AML) deposition process. The FePt films were grown on MgO(100) substrates, with and without a Pt fcc(100) buffer layer (∼55 nm), at substrate temperatures (TS) ranging from 200 °C to 600 °C. For FePt alloy grown directly on MgO, the X-ray diffraction (XRD) analysis shows the presence of the fct(001) phase and long-range chemical order parameter (S) of 0.31, in the film prepared by AML deposition at 400 °C. For FePt alloy grown on Pt/MgO substrates, the XRD data reveal the presence of the fct(001) phase, with S ≈ 0.41, in the films deposited at TS = 300 °C by both methods. In the samples with the Pt buffer layer pre-deposited at high TS (500 °C), the presence of the fct(001) phase and high chemical order (S = 0.88) is observed for the alloy prepared by AML deposition at 400 °C. Hysteresis measurements, using Vibrating sample magnetrometry, show the presence of perpendicular magnetic anisotropy and perpendicular coercivity of 1.4 kOe for the FePt films with the definite fct(001) phase. The experimental results demonstrate the feasibility to grow FePt films with ordered fct(001) phase at moderate TS. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced coercivity of L10 ordered FePt thin films fabricated by alternate monatomic layer deposition on stepped Pt(0 0 1)

Abstract L10 ordered FePt(0 0 1) thin films were prepared by alternating Fe and Pt monatomic layers on stepped Pt(0 0 1) surfaces at reduced temperature. The clear enhancement of coercivity has been observed due to the introduction of steps, which is considered to contribute to pinning domain walls.

Structural and magnetic properties of Fe/noble metal monatomic multilayers equivalent to L10 ordered alloys

Alternate monatomic layer deposition by MBE is proposed as a new method to prepare L10 ordered alloys. A highly-ordered single crystal of Fe-Pt alloy was obtained. Furthermore, the L10 ordered structure was artificially fabricated for an Fe-Au alloy although it does not exist in the equilibrium phase diagram. The magnetic properties of the ordered Fe-Pt and Fe-Au alloys are described.