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). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/955034a15cdb0a0f619d8946ed3387f8.png) 
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. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/10cb6499fc26bfe27947f0693ed28999.png) 
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.

High coercive PrFeB Films with Strong Perpendicular Magnetic Anisotropy

Rare earth/transition metal permanent magnets have gained significant interest due to their outstanding performance, which has made them key materials for many applications. The most well-known compounds Nd2Fe14B, SmCo5, and Sm2Co17 combine a large energy density, high Curie temperature, and a large magnetocrystalline anisotropy (MCA). Besides, SmCo5 exhibits the highest known uniaxial MCA1. Due to their importance, a detailed understanding of their hysteresis behavior has come into the focus of research2.
Since the extrinsic magnetic properties of magnetic materials depend on their complex defect and nanostructure, we follow the strategy to disentangle intrinsic and extrinsic properties as well as the effect of specific defects by investigating SmCo5 and Sm2Co17 phases in thin film model systems grown by molecular beam epitaxy (MBE). 
The Sm-Co system, when grown as thin films in a certain parameter range, undergoes a phase decomposition into a nanocomposite of SmCo5 and Sm2Co17 phases. Due to the structural similarity of the two phases, it is challenging to discriminate their phase contributions. Extended X-ray absorption fine structure (EXAFS) analysis combined with transmission electron microscopy (TEM) allows the unambiguous quantification of the nano-domain phase decomposition in the thin films3. 
In this work, we have studied the behavior of the magnetic anisotropy of Co and Sm using - for the first time, to our knowledge - angle-dependent X-ray magnetic circular dichroism (XMCD) at Sm M4,5 and Co L2,3 edges in 1.9 Tesla external applied field. SmCo5 and Sm2Co17 thin films have been grown onto Al2O3 substrates and pre-characterized by X-ray diffraction (XRD) and superconducting quantum interface device (SQUID). XMCD and X-ray absorption spectroscopy (XAS) gave access to element-specific information and have been complemented by detailed atomistic spin dynamics (ASD) calculations. 
Element-specific hysteresis curves demonstrate strong coupling between Sm and Co, however, the spectroscopy indicates different saturation behavior. The XMCD spectra for the Sm M4,5 edges show surprisingly only a minor angle dependence. Using ASD simulations, we estimate the exchange field at the Sm site to be of the order of -200 T. 
**References:** [1] K. J. Strnat & R. M. W. Strnat, J. Magn. Magn. Mater. 100, 36 (1991). 
[2] O. Gutfleisch et al., Adv. Mater. 23, 821 (2011). 
[3] S. Sharma et al., ACS Appl. Mater. Interfaces 13, 32415 (2021).

Element specific magnetocrystalline anisotropy of Sm

Using molecular beam epitaxy, a nanoscale thin film magnet of c-axis-oriented Sm2Co17 and SmCo5 is stabilized. While typically in the prototype Sm(Co,Fe,Cu, Zr)7.5−8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm−Co system is shown. A detailed analysis of the extended X-ray absorption fine-structure confirmed the coexistence of Sm2Co17 and SmCo5 with 65% Sm2Co17 and 35% SmCo5. The SmCo5 phase is stabilized directly on an Al2O3 substrate up to a thickness of 4 nm followed by a matrix of Sm2Co17 intermixed with SmCo5. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm2Co17 and SmCo5 with coherent interfaces results in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm2Co17 and SmCo5 phases at the nanoscale is reflected in the observed magneto-crystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophase magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets.

Epitaxy Induced Highly Ordered Sm2Co17−SmCo5 Nanoscale Thin Film Magnets

LOB: Thin Films and Surface Effects

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**Session chair:** Hossein Sepehri-Amin, National Institute for Materials Science


DOA - Rare-earth Hard Magnetic Materials

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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High coercive PrFeB Films with Strong Perpendicular Magnetic Anisotropy

Element specific magnetocrystalline anisotropy of Sm

Epitaxy Induced Highly Ordered Sm2Co17−SmCo5 Nanoscale Thin Film Magnets

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