The use of Nd-Fe-B magnets with Nd2Fe14B, which are used in high performance motors, is increasing. However, it is predicted that inexpensive Nd will become unavailable in near future, and there is a need to reduce the amount of Nd used and develop new magnets [1]. Exchange-coupled nanocomposite magnets consisting of magnetic hard and soft nanoparticles, NPs have been proposed as candidate [2]. The Sm(Fe0.8Co0.2)12 with ThMn12 structure has higher saturation magnetization, Ms, and uniaxial magnetocrystalline anisotropy, Ku than Nd2Fe14B and is expected to be a magnetic hard phase in the Fe-based system without Nd [3]. We investigate the effect of the direction of the α-Fe coating surface and the volume fraction of α-Fe, VFe on the demagnetization process and the maximum energy product, (BH)max of exchange-coupled Sm(Fe0.8Co0.2)12 /α-Fe nanocomposite NPs using LLG simulations [4]. Sm(Fe0.8Co0.2)12 NPs is as reference model #1. The nanocomposite NPs of Sm(Fe0.8Co0.2)12 coated with α-Fe on top/bottom, and both sides are model #2 and #3. For both # 2 and #3, α-Fe layer thickness is 1 nm ≤ tFe ≤ 7 nm. The size of NPs are x = y = 50 nm and z = 100 nm. The magnetic properties of Sm(Fe0.8Co0.2)12 and α-Fe were taken from references [3, 5-7]. The cell volume is 1 nm3. External field, Hex is applied parallel to c-axis of Sm(Fe0.8Co0.2)12 along to z-axis of NPs. Fig. 1 shows VFe dependence of (BH)max for #2 and #3. The (BH)max of #1 was 630 kJ/m3 , while the (BH)max of #2 and #3 with optimized tFe were larger, 636 kJ/m3 for #2 with VFe = 4 % (tFe = 2 nm) and 657 kJ/m3 for #3 with VFe = 12 % (tFe = 3 nm). Fig. 2 shows distribution of demagnetizing field, Hd at Hex = 0 T for #2 and #3. The Hd acting on top/bottom surfaces of NPs was larger for #2, which was coated on top/bottom surfaces with α-Fe, which is larger than Ms of Sm(Fe0.8Co0.2)12, than for #3, which was coated on sides with α-Fe. Therefore, remanence and (BH)max of #3 are larger than those of #2. From the above discussion, it is clear that side coating of magnetic soft phase is effective in increasing (BH)max of Sm(FeCo)12/α-Fe NPs. 
**References:** [1] S. Hirosawa, M. Nishino and S. Miyashita, Adv. Nat. Sci: Nanosci. Nanotechnol., 8, (2017) 013002. 
[2] R. Skomski and J. M. D. Coey, Phys. Rev. B, 48, (1993) 15812. 
[3] Y. Hirayama et al., Scripta Mater., 138, (2017) 62–65. 
[4] M. J. Donahue and D. G. Porter, “OOMMF User’s Guide, Version 1.0,” NISTIR 6376, National Institute of Standards and Technology, Gaithersburg, MD (Sept 1999). ; M. J. Donahue, D. G. Porter (2021), "OOMMF: Object Oriented MicroMagnetic Framework," https://nanohub.org/resources/oommf. (DOI: 10.21981/8RRA-5656). 
[5] Felix Jimenez-Villacorta and Laura H. Lewis, Chapter 7 "Advanced Permanent Magnetic Materials" Nanomagnetism, edited by J. Gonzalez (OCP Publishing Group) (2014). 
[6] D. Ogawa, T. Yoshioka et al., J. Magn. Magn. Mater., 497, (2020) 165965. 
[7] T. Fukazawa, H. Akai et al., J. Magn. Magn. Mater., 469, (2019) 296-301. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/3a61bed85d0536499bdd51d5c215ec21.png) 
Fig. 1 VFe dependence of (BH)max for #2 and #3. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a2b7eb05cc1ea092f5b586fe81fd43cf.png) 
Fig. 2 Hd distribution on the top surface and the cross-section of NPs for #2 and #3 at Hex = 0 T.

Maximum Energy Product of Exchange coupled Sm(FeCo)12/α

Nanocomposite magnets composed of Nd2Fe14B and α-Fe nanoparticles are not only expected to increase the (BH)max compared to Nd-Fe-B magnets [1], but also effective in reducing the use of HREs [2]. Recently, we have reported on NdFeB/Mo/FeCo multilayered magnet films formed by a two-step method [3]. However, long-time multi-step annealing (MSA) using a halogen lamp was necessary to realize this magnet film. It is well known that method using a laser is an excellent technique that can significantly reduce the process time and is expected to improve the magnetic properties. In this study, we report the formation of nanocomposite NdFeB/Mo/FeCo magnet films using infrared laser annealing (iLA) technique. The Nanocomposite [NdFeB(30 nm)/Mo(0.3 nm)/FeCo(5 nm)/Mo(0.3 nm)]5 multilayered magnet films were prepared by UHV sputtering [3] followed by iLA processing. It is equipped with a CW semiconductor laser with a wave length of 939.8 nm and a spot size of about 5 mm in diameter on surface of films. Fig. 1 shows in-plane magnetization curves of the multilayered films as-deposited and iLA processed at 760°C. Both films with and w/o Mo interlayer before iLA processing showed soft magnetism with small coercivity and weak perpendicular magnetic anisotropy (PMA). The PMA of the film with the Mo interlayer is larger than that of the film without the Mo interlayer. Magnetic properties of both films were drastic changed from soft magnetism with PMA to hard magnetism with in-plane magnetic anisotropy after iLA processed at 760°C. Coercivity of in-plane of iLA processed film with Mo interlayer was 10 kOe which was double of the film w/o Mo interlayer. After iLA process, we can see that the squareness of film was improved by the introduction of Mo interlayer. These results show that the iLA process is effective in forming in-plane anisotropic nanocomposite NdFeB/Mo/FeCo magnet films even though the processing time of the iLA process is 1/100 of the processing time of the MSA process [3].


![](https://assets.underline.io/uploads/markdown_image/1/image/4abf4bd1b86901df35a7bb50f4fa6b41.jpg)


An in-plane magnetization curves of [Nd-Fe-B/Mo(tMo = 0 nm, 0.3 nm)/FeCo]5 multilayered films as-deposited state and iLA processed at 760°C.

Infrared Laser Annealing of Nanocomposite Nd-Fe-B/Mo/FeCo Multilayered Magnet Films

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**Session Chair:** Julius de Rojas, *University of Durham*

KPC: Hard Magnetic Materials V: Rare-Earth Free Hard Magnetic Materials

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#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

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MMM 2022

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**Session chairs:** Emily Rinko, Iowa State University and Parashu Kharel, South Dakota State University



DPB - Non-Rare Earth Permanent Magnet Materials and Nanocomposites II

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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Masaru Itakura

2

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Maximum Energy Product of Exchange coupled Sm(FeCo)12/α

Infrared Laser Annealing of Nanocomposite Nd-Fe-B/Mo/FeCo Multilayered Magnet Films

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