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Extending the Growth Temperature-N Concentration Regime Through Pd Doping in Fe4N Thin Films

Rohit Kumar Meena, Akhil Tayal, Andrei Gloskovskii, Mukul Gupta

TL;DR

Fe4N is appealing for spintronic and magnetic storage applications due to its high magnetization and Curie temperature, but its growth is confined to a narrow Ts-Nc regime. The authors show that Pd doping extends this regime for Fe4N thin films, enabling single-phase formation over a wider nitrogen range and at lower temperatures; EXAFS indicates Pd substitutes corner Fe atoms, and magnetization remains largely preserved up to 13 at% Pd. Structural, magnetic, and spectroscopic analyses reveal that Pd incorporation expands the lattice and increases local disorder only at higher dopant levels, while the Fe4N electronic environment remains largely intact. This approach thus broadens the fabrication window for Fe4N thin films, providing a practical route to tailor synthesis and phase stability without significantly compromising magnetic performance.

Abstract

Fe4N is a well-known anti-perovskite compound exhibiting high magnetization, high chemical stability, low coercivity, high Curie temperature, and high spin-polarization ratio. Therefore, it is a viable candidate for applications in spintronic and magnetic storage devices. However, the Fe4N phase is formed in a narrow substrate temperature (Ts)-N concentration (Nc) regime in the phase diagram of Fe-N. It has been observed that a slight N deficiency will lead to impurity of alpha-Fe, and some N efficiency would result in epsilon-Fe3N phase. Through this work, it has been demonstrated that the doping of Pd can be suitably utilized to extend the Ts-Nc regime for the growth of Fe4N thin films. EXAFS analysis indicate that Pd atoms are substituting corner Fe atoms. Magnetization measurements reveal that the saturation magnetization reduces nominally with Pd doping up to 13 at.%. Therefore, it is foreseen that Pd doping is effective in extending the Fe4N phase formation regime without a significant impact on its structural, electronic, and magnetic properties.

Extending the Growth Temperature-N Concentration Regime Through Pd Doping in Fe4N Thin Films

TL;DR

Fe4N is appealing for spintronic and magnetic storage applications due to its high magnetization and Curie temperature, but its growth is confined to a narrow Ts-Nc regime. The authors show that Pd doping extends this regime for Fe4N thin films, enabling single-phase formation over a wider nitrogen range and at lower temperatures; EXAFS indicates Pd substitutes corner Fe atoms, and magnetization remains largely preserved up to 13 at% Pd. Structural, magnetic, and spectroscopic analyses reveal that Pd incorporation expands the lattice and increases local disorder only at higher dopant levels, while the Fe4N electronic environment remains largely intact. This approach thus broadens the fabrication window for Fe4N thin films, providing a practical route to tailor synthesis and phase stability without significantly compromising magnetic performance.

Abstract

Fe4N is a well-known anti-perovskite compound exhibiting high magnetization, high chemical stability, low coercivity, high Curie temperature, and high spin-polarization ratio. Therefore, it is a viable candidate for applications in spintronic and magnetic storage devices. However, the Fe4N phase is formed in a narrow substrate temperature (Ts)-N concentration (Nc) regime in the phase diagram of Fe-N. It has been observed that a slight N deficiency will lead to impurity of alpha-Fe, and some N efficiency would result in epsilon-Fe3N phase. Through this work, it has been demonstrated that the doping of Pd can be suitably utilized to extend the Ts-Nc regime for the growth of Fe4N thin films. EXAFS analysis indicate that Pd atoms are substituting corner Fe atoms. Magnetization measurements reveal that the saturation magnetization reduces nominally with Pd doping up to 13 at.%. Therefore, it is foreseen that Pd doping is effective in extending the Fe4N phase formation regime without a significant impact on its structural, electronic, and magnetic properties.
Paper Structure (7 sections, 7 figures, 2 tables)

This paper contains 7 sections, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Experimental Details
  3. Results and Discussion
  4. Structural Characterization
  5. Magnetic Properties:
  6. Electronic properties.
  7. Conclusion

Figures (7)

  • Figure 1: Crystal structure of Fe$_4$N. Fe atoms are shown in red, blue and N atom in green.
  • Figure 2: XRD pattern of Fe$_4$N thin films deposited on amorphous SiO$_2$ substrates at 673 K with RN$_2$ = 12, 13 and 14 $\%$ (a) and at RN$_2$ = 13 $\%$ with Ts = 673, 573 and 473 K (b) without doping. Further, XRD pattern of thin films at different Pd doping keeping RN$_2$ = 13 $\%$ and Ts = 673 K (c). Extension of RN$_2$ range from 12-16 $\%$ at fixed Ts = 673 K with doping (d) and comparison of undoped and Pd doped samples deposited at Ts = 673, 573, and 473 K at a fixed RN$_2$ = 13 $\%$ (e). N concentration (RN$-2$) and growth temperature (Ts) diagram depicting the phase regime where the formation of Fe$_4$N phase takes place for undoped and Pd doped samples (f).
  • Figure 3: M-H loops showing the Ms values for undoped and 5, 13, 24 at. $\%$ Pd doped Fe$_4$N samples.
  • Figure 4: XANES spectra taken at Fe L$_3$ and L$_2$ edge for undoped and 5, 13, 24 at. $\%$ Pd doped Fe$_4$N samples.
  • Figure 5: The moduli of Fourier transform (FT) of Fe K-edge EXAFS (a) and $\chi$(k)$\times$k$_3$ spectra (b) of undoped and 5, 13, 24 $\%$ Pd (at. Conc.) doped Fe$_4$N samples.
  • ...and 2 more figures