Rare-earth transition metal thin films hold great potential for implementation in devices at the micro and nanoscale 1-3. While Nd2Fe14B and Pr2Fe14B share almost the same intrinsic magnetic properties (Ms, Ku…), Nd2Fe14B has a limited use for low temperature applications (i.e. aerospace) due to the spin reorientation that occurs at 135 K 4. This limitation can be overcome using Pr2Fe14B, whose magnetization direction remains along the c-axis until 4.2 K 4. The understanding and optimization of these systems is of great importance when attempting their integration in novel miniaturized devices 5. In this study, high coercivity PrFeB thin films of 100 nm have been fabricated by magnetron sputtering. The effect on the substrate temperature (Ts) in the structure and morphology and its resulting impact on the magnetic properties has been evaluated.
Our research stablishes the optimum Ts to be 600oC where a highly textured growth of Pr2Fe14B is achieved according to the X-Ray Diffraction (XRD) analysis (Fig. 1a). Pr2Fe14B crystalline phase is accompanied by a Pr-rich phase that can be identified in all the XRD patterns. The role that these Pr-rich areas play in the magnetism of these systems has also been thoroughly studied by Energy Dispersive X-Ray Spectroscopy (EDX) (Fig. 1c). Regardless of Ts, all films present strong perpendicular magnetic anisotropy (Fig.2c,d) which is in good accordance with the c-axis oriented preferential growth. Out of plane coercivities up to 14 kOe have been obtained at RT. Atomic and Magnetic Force Microscopy (AFM and MFM, respectively) have also been used to determine influence of Ts on the roughness and magnetic domains (Fig 2a,b).
References:
1 X. Liu, T. Okumoto, M. Matsumoto, A. Morisako. J. Appl. Phys. 97, 10K301 (2005).
2 T.-S. Chin, J. Magn. Magn. Matter. 209, 75-79 (2000).
3 A. Bollero, V. Neu, V. Baltz et al., Nanoscale, 12, 1155-1163 (2020).
4 TT. B. Lan, G.C. Hermosa and A.C. Sun, J. Phys. Chem. Solid. 144, 109506 (2020).
5 H2020 FET-OPEN project “UWIPOM2”: https://cordis.europa.eu/project/id/857654.

Acknowledgements:
Authors acknowledge financial support from EU through the H2020 FET Open UWIPOM2 project (Ref. 857654). J. S-M. acknowledges financial support from Comunidad de Madrid (PEJD-2019-PRE/IND-17045).

Fig. 1. a) XRD pattern of PrFeB thin films grown at different Ts, b) Scanning electron microscopy (SEM) image of a PrFeB film grown at 600oC, c) EDX mapping of a PrFeB film with a Ts = 600oC showing the distribution of Pr and Fe (c.1) Prdistribution (c.2) Fe distribution (c.3). The scale bar is 800 nm in all cases.

Fig. 2. a) AFM and b) MFM image of a PrFeB film grown at 600oC, c) Out of plane and d) In Plane room temperature hysteresis loops with a maximum applied field of 20 kOe for PrFeB thin films grown at different Ts.