Tunable Gilbert damping and magnetization in B-rich ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{B}}_{x}$ thin films

Tunable Gilbert damping and magnetization in B-rich ${Fe}_{1 - x} B_{x}$ thin films

Mohammad M. Qaid, Camillo Ballani, Frank Syrowatka, Tobias Peters, Günter Reiss, Gregor Buettel, Uwe Hartmann, and Georg Schmidt

Phys. Rev. Materials 8, 034404 – Published 15 March 2024

Abstract

Gilbert damping and saturation magnetization are of critical importance for magnetic thin films in spintronic devices. Using complementary techniques, including ferromagnetic resonance (FMR), superconducting quantum interference device (SQUID) measurements, and energy dispersive x-ray spectroscopy, we demonstrate that Gilbert damping and magnetization in ${Fe}_{1 - x} B_{x}$ thin films can be tuned by controlling the B concentration $x$ . At low B concentration, FMR and SQUID measurements show a strong reduction of the magnetic damping and the saturation magnetization, respectively. A very low magnetic damping of around $3.8 \times 10^{- 3}$ is measured at $x = 25 %$ , which is among the lowest damping values reported so far for a conducting ferromagnet. This tunability of magnetic properties will be useful for fabricating thin films with low damping that can be used in high-performance spintronic devices.

Received 12 May 2022
Revised 24 January 2024
Accepted 28 February 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.034404

Physics Subject Headings (PhySH)

Ferromagnetism Magnetic anisotropy Magnetic coupling Magnetic phase transitions Magnetic susceptibility Magnetism Magnetization dynamics Magnetization switching Micromagnetism Spin dynamics Spin waves Spintronics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Mohammad M. Qaid and Camillo Ballani

Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, D-06120 Halle, Germany

Frank Syrowatka

Interdisziplinäres Zentrum für Materialwissenschaften, Martin-Luther-Universität Halle-Wittenberg, Nanotechnikum Weinberg, Heinrich-Damerow-Strasse 4, D-06120 Halle, Germany

Tobias Peters and Günter Reiss ^*

ForLab MagSens, Physics Department, Bielefeld University, D-33501 Bielefeld, Germany

Gregor Buettel and Uwe Hartmann

Institute of Experimental Physics, Saarland University, D-66041 Saarbruecken, Germany

Georg Schmidt ^†

Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, D-06120 Halle, Germany and Interdisziplinäres Zentrum für Materialwissenschaften, Martin-Luther-Universität Halle-Wittenberg, Nanotechnikum Weinberg, Heinrich-Damerow-Strasse 4, D-06120 Halle, Germany

^*https://www.physik.uni-bielefeld.de/experi/d2/index.html; reiss@physik.uni-bielefeld.de
^†Corresponding author: georg.schmidt@physik.uni-halle.de

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Vol. 8, Iss. 3 — March 2024

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Figure 1
EDX characterization for the ${Fe}_{1 - x} B_{x}$ films. (a) EDX spectrum of the different films indicating the gradual change in the B peaks due to increasing B target concentration. (b) Tilted view of the layers for one of the ${Fe}_{1 - x} B_{x}$ films indicating the layer sequence along the film. The rectangular boxes are from the EDX measurements made only for selecting small regions to show their spectrum. (c)–(f) EDX elemental maps of Ru, Fe, B, and O in the layer stack. The Ru mapping illustrates the element counts from the layer side and the surface because of the sample tilting position. Scale bar: 100 nm.
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Figure 2
SEM top view images for ${Fe}_{1 - x} B_{x}$ films showing the change in morphology with increasing B concentration. (a)–(f) show the Fe, ${Fe}_{95} B_{5}$ , ${Fe}_{90} B_{10}$ , ${Fe}_{90} B_{10}$ -cosp, ${Fe}_{85} B_{15}$ , and ${Fe}_{70} B_{30}$ films, respectively. Scale bar: 100 nm.
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Figure 3
(a) X-ray diffraction patterns for the Fe, ${Fe}_{95} B_{5}$ , and ${Fe}_{80} B_{20}$ samples. (b) X-ray reflectometry measurements and fittings for the same samples.
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Figure 4
Results from SQUID magnetometry with the magnetic field applied in plane. (a) The hysteresis loops of ${Fe}_{1 - x} B_{x}$ films with different compositions show a change in saturation magnetization and coercive field. (b) Zoom of the hysteresis loops for better visualization of $μ_{0} H_{c}$ . (c) $μ_{0} M_{s}$ and (d) $μ_{0} H_{c}$ extracted from the hysteresis loops and plotted as a function of $x$ for the different ${Fe}_{1 - x} B_{x}$ samples. The inset in (d) shows the variation of $μ_{0} H_{c}$ within the B composition range $x = 10 % - 30 %$ . The open squares are the main samples, which include all ${Fe}_{1 - x} B_{x}$ series except ${Fe}_{1 - x} B_{x}$ -MgO and ${Fe}_{1 - x} B_{x}$ -cosp samples.
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Figure 5
FMR and magnetic damping measurements for ${Fe}_{1 - x} B_{x}$ thin films. (a) FMR measurement configuration. (b) FMR curves for one ${Fe}_{1 - x} B_{x}$ sample measured by sweeping $μ_{0} H_{ext}$ at different microwave frequencies. (c) Dependence of the resonance frequency on the resonance field for one ${Fe}_{1 - x} B_{x}$ film fitted according to Kittel's equation. (d) Linewidth-frequency dependence $μ_{0} Δ H (f)$ extracted from FMR. A linear fit of these data is used to determine the Gilbert damping. (e) The effective magnetization $μ_{0} M_{eff}$ extracted using Kittel's equation. (f) Inhomogeneous broadening and (g) magnetic damping, both extracted from the linewidth-frequency dependence. (h) Anisotropy field $μ_{0} H_{ani}$ change with $x$ . The open squares indicate the results of the samples sputtered only from alloy targets. The open circles and triangles at 10% and 20% represent the cosputtered ${Fe}_{90} B_{10}$ and MgO- ${Fe}_{80} B_{20}$ , respectively. The lines in (e)–(g) are only guides to the eye.
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Figure 6
MFM images within zero field of five elliptical and three circular structures fabricated from ${Fe}_{80} B_{20}$ samples with a thickness of (a) 40 nm and (b) 20 nm with a maximum width of the short axis of 2 $µ m$ and the long axis decreasing gradually from 4 to 2.4 $µ m$ , with the three in the lower right being nominally circular.
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Physical Review Materials

Tunable Gilbert damping and magnetization in B-rich Fe1−xBx thin films

Mohammad M. Qaid, Camillo Ballani, Frank Syrowatka, Tobias Peters, Günter Reiss, Gregor Buettel, Uwe Hartmann, and Georg Schmidt

Phys. Rev. Materials 8, 034404 – Published 15 March 2024

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Tunable Gilbert damping and magnetization in B-rich ${Fe}_{1 - x} B_{x}$ thin films