Neodymium-based magnets are used dominantly in the industry due to their exceptional magnetic properties. However, because of regulations and environmental harm on rare earth elements, it is unsustainable to use Nd-Fe-B. Fe16N2 is proposed as an alternative to rare-earth-based magnets, as it shows a giant magnetic energy product and abundance of its elements. Here we demonstrate an improvement to our previously published low-cost synthesis method to produce highly coercive Fe16N2 flakes and a consolidation method to form it into a permanent magnet. The synthesis path begins with deforming iron powder into iron flakes by surfactant-assisted ball milling. Iron flakes are heat treated under air to achieve a porous morphology to increase Fe to Fe16N2 conversion yield. Porous flakes are reduced under Ar/H2 gas flow, followed by a low-temperature nitridation process under ammonia gas. Synthesized Fe16N2 flakes exhibit saturation magnetization up to 180 emu/g and coercivity up to 1.1 kOe. (Fig .1) Rietveld analysis of the X-ray diffraction measurement of flakes shows up to 93% volumetric fraction of Fe16N2 phase. To consolidate Fe16N2 cold press method is used. Consolidated flakes do not indicate any trace of phase decomposition, hence a solid Fe16N2 magnet is produced. (Fig.2.) A cost-effective method to bulk produce Fe16N2 magnet could be sustainable for next-generation magnet applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/7ddd89cc469ea3d817f2c1579f38fe63.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/32a762515db256c1caccd2c387137c01.jpg)

Fe16N2 Permanent Magnet Production by High-Pressure Consolidation

The key to a healthy and extended life is the early detection of diseases; abnormal cells, viruses, and bacteria could be detected in the early stages by analyzing various body fluids. To ease the detection and expedite the process, portable test kits that do not require hospitals and/or specialists have been developed. In that matter, biosensors are being developed with the capability of trapping bio-entities inside the microfluidic channels via magnetic field gradients. This work presents an innovative, easy-to-apply, and cost-efficient technique for developing at-home disposable rapid test kits with well-organized patterned arrays of Nd-Fe-B flakes in the PDMS matrix (Fig.1). Nd-Fe-B flakes (HC = 1.5 kOe) (Fig.2) were synthesized by surfactant-assisted ball milling technique (at 700 rpm for 12 hours) with an average lateral dimension of 10 μm and an average thickness of 100 nm. The ball to powder weight ratio was chosen as 10:1. Dispersant and surfactant were heptane and oleic acid, respectively. Up to 0.1 %, solid content concentration was aligned and decorated to a gingham pattern. The microfluidic channel was prepared by photolithographic method with 3 layers (50 μm each) of UV-sensitive blue dry film which was developed in Na2CO3 bath (10% (w/v)). Two individual PDMS pieces (microfluidic channel and Nd-Fe-B/PDMS region) were bonded by a two-part epoxy to finalize the Nd-Fe-B/PDMS patch. In order to test the trapping system, Fe nanoparticles were synthesized. Fe nanoparticles were synthesized by the Y-junction method in the presence of NaBH4 and FeCl2 under Ar/H2 gas flow. Synthesized particles have an average size of 92 nm. Subsequently, Fe NPs suspended in DMSO or DI water were flown inside the microfluidic channel. A high trapping efficiency (&gt;90%) of Fe nanoparticles was observed. The developed device can be a game-changer for biosensors.

![](https://assets.underline.io/uploads/markdown_image/1/image/ffed951d44910ae56aa7145ea13fbf28.jpg)

Figure 1. Patterned Nd-Fe-B/PDMS patch.

![](https://assets.underline.io/uploads/markdown_image/1/image/8935f7f33f5fcf0d7450fad1dce203b3.jpg)

Figure 2. Hysteresis loop of Nd-Fe-B/PDMS patch with 0.1 solid content ratio.

Nd-Fe-B Based Magnetophoretic Microfluidic Device with High Trapping Efficiency

* Corresponding Author: ozan.akdogan@eng.bau.edu.tr Magnetically actuated milli swimmers/robots, especially in biomedical field, are used in many applications such as cargo delivery and sensing applications. In this study, magnetically actuated small-scale swimmers have been developed by using Fe flakes embedded in photocurable polymeric resin. Our future aim will be to merge the developed small-scale swimmers with minimally invasive biomedical applications. The 3D printed structures were fabricated using a photocurable polymeric resin acquired from Wanhao (China). In addition to monomers and oligomers, the chemical composition of this resin includes a photo initiator that responds to a certain wavelength of UV light (405nm) to change the polymerization conformation of the resin into a solid state. Then, structures were printed by using the Anycubic Photon digital light processing (DLP) 3D printer with an exposure time of 10 seconds and a layer thickness of 0.05 mm. Different sizes and shapes of (length of the ship1, ship2 and square, 5.6 mm, 2.7 mm and 0.6mm, respectively) the magnetically actuated swimmers were 3D printed; two ellipsoid shaped swimmers with different sizes and a cubic shaped swimmer. An ellipsoid and cubic shape were chosen for its unique morphology that gives it hydrodynamic superiority over traditional spheres [1]. The combination of polymeric materials such as resins with magnetic particles expand the robot’s functionality [2]. The Fe flakes have been previously tested with functional polymer composites for extrusion-based 3D printing [3]. In this study, Fe flakes (100-200nm thickness and ~10μm lateral size) were incorporated into the photocurable resin to actuate robots in response to the magnetic field. The X-Ray Diffraction and vibrating sample magnetometer analysis of Fe flakes showed that Fe flakes have BCC crystal symmetry and soft ferromagnetic response, respectively. (Fig 1a and b). A 0.2 g of Fe flakes and 40 ml of the polymeric resin were mixed to synthesize 0.5% wt/vol concentration. The printed structures were cured by UV light exposure. The incorporated Fe flakes were visualized by a light microscope (Fig.1c, d and e). The movement characteristics of the swimmers in a magnetic field gradient were tested by a homemade electromagnetic setup with a maximum field of 336 Gauss. The 3D printed magnetic structures’ movement speed in DI water were calculated experimentally as 12.27±1.89 mm/s, 11.92±1.9mm/s and 8.29±1.5mm/s for milli ship1, milli ship 2 and sub-mm square, respectively. The theoretical swimming speed values were calculated according to the equations below; the magnetic force acting on the robots by a gradient, in which m and B are the magnetic moment and the field, respectively (3) and the drag force (Stoke’s Law), in which, η, the viscosity of DI water (8.9x10-4 Pa.s), R and v are the hydrodynamic radius and velocity of the objects, respectively (4). Fm = ▽ (m . B) [3] Fd= 6π η R v [4] Theoretical speeds calculated for milli ship1, milli ship2 and sub-mm square were 13.54 mm/s, 9.9 mm/s and 10 mm/s, respectively. The different shaped milli swimmers were actuated by electromagnetic system and tracked (Fig.2). Magneto-responsive robots movement abilities will be tested against specific obstacles with different shapes and magnetic materials as well. Acknowledgements This work was supported by BAP.2019-03.11(Bahcesehir University).

**References:**

1. Carrasco, B. et al., Hydrodynamic Properties of Rigid Particles: Comparison of Different Modeling and Computational Procedures., Biophysical Journal, 76, 3044–3057, (1999) 2.Song, S. W., Jeong, Y. & Kwon, S., Photocurable polymer nanocomposites for magnetic, optical, and biological applications., IEEE J. Sel. Top. Quantum Electron. 21, 324–335, (2015) 3.Zirhli, O. et al. Fabrication and Characterization of Fe16N2 Micro-Flake Powders and Their Extrusion-Based 3D Printing into Permanent Magnet Form., Adv. Eng. Mater. 22, (2020) 4. Pankhurst, Q. A. et al., Applications of magnetic nanoparticles in biomedicine., J. Phys. D. Appl. Phys. 36, 167-181, (2003) 5. L.D. Landau, I.Akhiezer, M.Lifshitz, Chapter XV-Viscosity, General Physics, 341-366, (1967)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/fcd27136415135330892ad5e005270ef.png)
Figure 1. a) VSM and b) XRD analysis of Fe flakes given. Light microscopy image of Fe flakes nanoparticle distribution 3D-printed structures c) Milli square. d) Milli ship. e) Texture of printed structures.

![](https://assets.underline.io/uploads/markdown_image/1/image/66e69fa67a75757fe051df0e36d11fd7.jpg)
Figure2. The swimming pathway of structures in the DI water are shown in the figure respectively. a) Square, b) Ship 1 and c) Ship 2 (0.6 mm 5.6 mm, 2.7 mm, respectively). d) The swimming trajectory snapshots of robots under the magnetic field.

 Development and characterization of magnetically actuated milli-robots by Stereolithography

**Session chairs:** Adrian Quesada, Institute of Ceramics and Glass (CSIC) and Alberto Bollero, IMDEA Nanociencia



DOC - Non-Rare Earth Permanent Magnet Materials and Nanocomposites I

technical paper

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Fe16N2 Permanent Magnet Production by High-Pressure Consolidation

Nd-Fe-B Based Magnetophoretic Microfluidic Device with High Trapping Efficiency

Development and characterization of magnetically actuated milli-robots by Stereolithography

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