Presentation Information
[O13-5]A high throughput study of element substitution in NdFeB-based films combined with heavy rare-earth diffusion
*William Rigaut1, Pierre Le Berre1, Lukas Fink1, Richard Haettel1, Stephane Grenier1, Alex Kovacs2, Harald Oezelt2, Thomas Schrefl2, Thibaut Devillers1, Nora M. Dempsey1 (1. Univ. Grenoble Alpes, CNRS, Institut NEEL (France), 2. Department for Integrated Sensor Systems, University for Continuing Education Krems (Austria))
Keywords:
Magnetic Thin Film,High-Throughput Characterization,Permanent Magnet
Combinatorial studies based on the preparation and characterization of compositionally graded thin films are being used for the screening and optimization of a range of functional materials [1], including hard magnetic FePt [2] and NdFeB-based [3] films. In the case of NdFeB-based magnets, element substitution and processing strategies such as heavy rare-earth (HRE) diffusion are critical for enhancing coercivity while reducing reliance on expensive and scarce elements [4].
Here we present a study of RE-TM films based on the 2-14-1 high-anisotropy phase, deposited by magnetron sputtering onto thermally oxidized Si substrates of diameter 100 mm, using in-house prepared targets of diameter 76 mm. Ta buffer and capping layers (thickness = 10 nm) were deposited to prevent interdiffusion with the substrate and oxidation, respectively. High throughput characterization of both structural and magnetic properties was carried out at approximately 300 positions per substrate, using a number of techniques operated in scanning mode, including Energy Dispersive X-Ray (EDX) spectroscopy, mechanical profilometry, X-Ray Diffraction (XRD) and Magneto-Optic Kerr effect (MOKE) magnetometry. More detailed measurements were carried out on select samples using SQUID-VSM and Scanning Electron Microscopy.
Initially, an extensive parametric study was carried out using a Nd-Fe-B target, to characterize the impact of a number of processing parameters (target-substrate distance, target off-set angle, sputtering power, film thickness, deposition temperature, annealing conditions) on cross wafer variations in composition, film thickness, lattice parameters and magnetic properties. Then NdLaCeFeB films were deposited using a “camembert” style target (Figure 1a) comprised of three parts (NdFeB, CeFeB, LaFeB) of equal size, and processed under the optimum conditions established in the initial parametric study. It is interesting to note that the EDX maps shown in Figure 1 reveal that the composition spread in the different rare earths is not equal, with the maximum content decreasing from 11% for La, to 7% for Nd and 5% for Ce. This happens despite the fact that all three parts of the target had the same rare earth content, and films made with the NdFeB target at the same target-substrate distance are homogeneous in composition across the full wafer. The origins of the observed variations in rare earth content will be discussed in more detail. Furthermore, diffusion of heavy rare-earth elements (Dy and Tb) was investigated to show its impact on coercivity enhancement. This was achieved by sputtering very thin layers from a Dy80Tb20 target, onto NdFeB and NdLaCeFeB films, prior to deposition of the Ta capping layer. Comparison of measurements made on NdFeB and NdLaCeFeB films, both with and without heavy rare-earth diffusion, provide insight into the combined effects of element substitution and diffusion. Finally, results from machine learning analysis performed on our data sets using PLS regressors and PCA analysis (WAVEBASE), will be presented.
[1] ML Green et al., J. Appl. Phys. 113 (2013) 231101
[2] Y. Hong et al., J. Mater. Res. Technol. 18 (2022) 1245
[3] Kovacs et al., Front. Mater. 9 (2023) 1094055
[4] H. Sepehri-Amin et al., J. Appl. Phys. 107, 09A745 (2010)
Here we present a study of RE-TM films based on the 2-14-1 high-anisotropy phase, deposited by magnetron sputtering onto thermally oxidized Si substrates of diameter 100 mm, using in-house prepared targets of diameter 76 mm. Ta buffer and capping layers (thickness = 10 nm) were deposited to prevent interdiffusion with the substrate and oxidation, respectively. High throughput characterization of both structural and magnetic properties was carried out at approximately 300 positions per substrate, using a number of techniques operated in scanning mode, including Energy Dispersive X-Ray (EDX) spectroscopy, mechanical profilometry, X-Ray Diffraction (XRD) and Magneto-Optic Kerr effect (MOKE) magnetometry. More detailed measurements were carried out on select samples using SQUID-VSM and Scanning Electron Microscopy.
Initially, an extensive parametric study was carried out using a Nd-Fe-B target, to characterize the impact of a number of processing parameters (target-substrate distance, target off-set angle, sputtering power, film thickness, deposition temperature, annealing conditions) on cross wafer variations in composition, film thickness, lattice parameters and magnetic properties. Then NdLaCeFeB films were deposited using a “camembert” style target (Figure 1a) comprised of three parts (NdFeB, CeFeB, LaFeB) of equal size, and processed under the optimum conditions established in the initial parametric study. It is interesting to note that the EDX maps shown in Figure 1 reveal that the composition spread in the different rare earths is not equal, with the maximum content decreasing from 11% for La, to 7% for Nd and 5% for Ce. This happens despite the fact that all three parts of the target had the same rare earth content, and films made with the NdFeB target at the same target-substrate distance are homogeneous in composition across the full wafer. The origins of the observed variations in rare earth content will be discussed in more detail. Furthermore, diffusion of heavy rare-earth elements (Dy and Tb) was investigated to show its impact on coercivity enhancement. This was achieved by sputtering very thin layers from a Dy80Tb20 target, onto NdFeB and NdLaCeFeB films, prior to deposition of the Ta capping layer. Comparison of measurements made on NdFeB and NdLaCeFeB films, both with and without heavy rare-earth diffusion, provide insight into the combined effects of element substitution and diffusion. Finally, results from machine learning analysis performed on our data sets using PLS regressors and PCA analysis (WAVEBASE), will be presented.
[1] ML Green et al., J. Appl. Phys. 113 (2013) 231101
[2] Y. Hong et al., J. Mater. Res. Technol. 18 (2022) 1245
[3] Kovacs et al., Front. Mater. 9 (2023) 1094055
[4] H. Sepehri-Amin et al., J. Appl. Phys. 107, 09A745 (2010)
