United States

Nanocomposite magnets composed of Nd&lt;sub&gt;2&lt;/sub&gt;Fe&lt;sub&gt;14&lt;/sub&gt;B and α-Fe nanoparticles are not only expected to increase the (&lt;i&gt;BH&lt;/i&gt;)&lt;sub&gt;max&lt;/sub&gt; 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)]&lt;sub&gt;5&lt;/sub&gt; 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.

2022 Joint MMM-INTERMAG

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

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.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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.

poster

Bayesian optimization is a well-developed machine learning field for black box function optimization. In Bayesian optimization a surrogate predictive model, here a Gaussian process, is used to approximate the black box function. The estimated mean and uncertainty of the surrogate model are paired with an acquisition function to decide where to sample next. Bayesian optimization with Gaussian processes can be used for structure-property relationship optimization in materials systems with second order phase transitions or gradual disordering without a distinct phase transition. In this study we applied this technique to known ferromagnetic thin film materials such as ferromagnetic (Fe100−y Gay)1−xBx (x=0–21 & y=9–17) and (Fe100−y Gay)1−xCx (x=1–26 and y=2–18) to demonstrate optimization of structure-property relationships, specifically the dopant concentration or stoichiometry effect on magnetostriction and ferromagnetic resonance linewidth. These systems both experience gradual disordering without distinct phase transition with increase in boron and carbon concentration, thus are great case systems for Bayesian optimization with Gaussian processes. We have shown that using simulated Bayesian optimization methods to guide experiments, the number of samples required to statistically determine the optimum was reduced by 50% compared with traditional research methods. Our results suggest that Bayesian optimization can be used to save time and resources to optimize ferromagnetic films. This method is transferrable to other ferromagnetic material structure-property relationships, providing an accessible implementation of machine learning to magnetic materials development.

Application of Bayesian Optimization and Regression Analysis to Ferromagnetic Materials Development

Currently, anisotropic magnetoresistive (AMR) sensors are actively used in many promising areas, such as automotive industry, geomagnetic navigation, biomedicine, etc. This is due to the fact that AMR sensors have quite good sensitivity to the magnetic field, high reliability, thermal stability, resistance to harsh environment and low cost. An important role in the fabrication of magnetoresistive elements of AMR sensors is played by the magnetic characteristics of thin ferromagnetic films at the nanoscale, which, in turn, depends on their internal crystal structure, controlled by the parameters of the technological process [1]. In this work, we experimentally analyzed the dependence of the key magnetic properties (coercivity, AMR coefficient, and magnetic anisotropy field) of a 30 nm permalloy (Ni80Fe20) thin film on its grain size controlled by the substrate temperature during magnetron sputtering (Figure 1). It was shown that both the AMR coefficient and the magnetic anisotropy field tend to reach a constant level of 2.25% and 5 Oe, respectively, with an increase in the grain size. In turn, the dependence of the permalloy film coercivity on the grain size has a minimum in the region of about 8 nm and sharply increases at a smaller thickness, which corresponds to the assumed behavior of NiFe from previous studies [2]. The results obtained are important for the development of magnetic nanostructures for a new generation of highly sensitive magnetoresistive sensors based on the AMR effect [3]. This work was performed with the financial support of the Foundation for Assistance to Small Innovative Enterprises in Science and Technology (FASIE) (contract No. AAAA-A20-120111290020-5) using the equipment of MIET Core Facilities Center «MEMSEC».

![](https://assets.underline.io/uploads/markdown_image/1/image/a8ea0939bc9bcdd7c425fcf114f38ae9.jpg)

Figure 1. (a) Coercivity (anisotropy field) and (b) AMR coefficient as a function of the grain size of 30 nm permalloy film.

Study of the magnetic properties of nano-thin permalloy films depending on the grain size

Vibration of the core during the operation of medium-frequency transformer is the main electromagnetic noise source, which will cause environmental noise pollution and even influence the reliability of the transformer [1-2]. At present, the research on vibration and noise of silicon steel under multiple conditions is developing rapidly. However, the measurement of magnetic properties, vibration and noise of ultra-thin oriented silicon steel are not complete [3]. Therefore, a real-time vibration and noise measurement platform based on a triaxial acceleration sensor is built in this paper to measure the magnetic properties, vibration and noise of ultra-thin oriented silicon steel simultaneously, as shown in Fig.1. The vibration and noise of amorphous, GT-050 and GT-100 ultra-thin grain-oriented silicon steel core under sinusoidal, square and rectangular waveforms are compared and analyzed. The calculation formula of the vibration acceleration under non-sinusoidal excitation is also deduced. In addition, the effect of dead time on vibration and noise is analyzed. Part of the results are shown in Fig. 2. It can be seen that the vibration of the core increases with the increase of frequency and magnetic flux density. The vibration and noise under non-sinusoidal excitation are much greater than that under sinusoidal excitation. The vibration amplitude in the lamination direction is larger than other directions. By comparison, ultra-thin oriented silicon steel has higher saturation magnetic flux density, lower loss and lower vibration noise than amorphous alloys. The measurement data in this paper can provide a basis for material selection for medium-frequency electrical equipment designers.

![](https://assets.underline.io/uploads/markdown_image/1/image/e21eaf43663686cf2289451e7a3f2600.jpg)

Fig. 1. Real-time measurement platform for transformer core vibration and noise

![](https://assets.underline.io/uploads/markdown_image/1/image/33cf023dda74693ab975e58f0efc3c3b.jpg)

Fig. 2. Vibration acceleration of GT-100 under different excitations and directions

Measurement and Analysis of Vibration and Noise Characteristics of Medium-Frequency Transformer Core Under Non-Sinusoidal Voltage Excitation

Rapidly solidified amorphous wires with diameters below 1 μm have opened up new miniaturization opportunities for sensing devices and created new application possibilities [1]. Here we report on an in-depth study of magnetization switching in nearly zero magnetostrictive (Co0.94Fe0.06)72.5Si12.5B15 amorphous wires with diameters between 300 and 450 nm, prepared by an improved variant of glass-coated melt spinning. Hysteresis loops were measured using a method developed specifically for thin wires [2]. All samples were magnetically bistable, exhibiting a rectangular axial loop. Hence, magnetization reversal takes place by depinning and subsequent propagation of a single domain wall when the applied field H reaches the value of the switching field, H*. We measured the domain wall velocity at various values of H, starting from H = H* up to the maximum employed value, Hmax = 10 000 A/m. The most remarkable results are shown in Fig. 1, which illustrates both the switching field and the domain wall velocity vs. sample diameter. Both exhibit strongly nonlinear variations with the diameter. Also, the slopes of the curves are always opposite to one another. The nonlinear shape of wall velocity vs. sample diameter is maintained even at larger fields, up to H = Hmax. The maximum wall velocity at H = H*, i.e. 1450 m/s, was observed for a sample with 410 nm in diameter. Domain wall velocity increases monotonically with applied field for all samples. Fig. 2 shows the field dependence of domain wall velocity for the 410 nm sample, with a maximum of nearly 4000 m/s at H = Hmax. The nonlinear effects have been attributed to the nonlinear distribution of intrinsic frozen-in stresses, that are inherent to the rapid solidification preparation process. The results allow one to accurately control and tailor the magnetic behavior of these ultrathin magnetic wires for specific applications. Work supported by the Romanian Executive Unit for Financing Higher Education, Research, Development and Innovation (UEFISCDI) through project PN-III-P4-ID-PCE-2020-1856 MaDWallS (contract no. PCE1/01.02.2021).

![](https://assets.underline.io/uploads/markdown_image/1/image/a970aba3063dffb28164de150a42efa1.jpg)

Fig. 1. Switching field & wall velocity vs. sample diameter.

![](https://assets.underline.io/uploads/markdown_image/1/image/00e3b06de01dbc5ecfa81be5b8357d0f.jpg)

Fig. 2. Domain wall velocity vs. applied field for a 410 nm in diameter sample.

Nonlinear Effects in the Magnetization Switching of Nearly Zero Magnetostrictive Amorphous Submicron Wires

NdFeB sintered magnet shows the highest energy product ((BH)max) at room temperature of all developed magnetic materials, but the drastic decrease in magnetic anisotropy field (HA) of Nd2Fe14B (2:14:1) phase with rising temperature limits its application at high temperature [1]. In recent years, the grain boundary diffusion (GBD) has been reported to be an effective method to significantly enhance coercivity (iHc) with minor sacrificing remanence (Br), and also to reduce the usage of heavy rare earth (HRE) elements simultaneously [2]. The formation of core-shell structure, the distribution of HRE only at the surface of 2:14:1 phase, through GBD of HRE-containing alloys, could inhibit the nucleation of reverse domain, and thus enhance iHc [3]. In this work, the dual-alloy (DA) sintering method together with GBD treatment are adopted to further enhance coercivity and modify the magnetic properties of NdFeB sintered magnets. (BH)max of 51.4 MGOe and iHc of 14.9 kOe are obtained for the original NdFeB magnet made by sintering Ce85Al15 doped NdFeB powders. Magnetic isolation due to the distribution of Ce and Al at grain boundary increases of the coercivity effectively, yet few Ce entering into grain interior decreases Br, (BH)max, and Curie temperature slightly. In addition, coercivity of the above magnets can be further enhanced to 22.7-25.1 kOe by GBD with different amount of Tb70Cu30 powders. The clear core-shell structure, which consists of (Nd, Tb)2Fe14B phase with higher HA as the shell and Nd2Fe14B phase as the core, is observed. CeAl helps to form continuous and smooth grain boundary. The diffusion source of TbCu could infiltrate into the magnet along such smooth grain boundary and form homogeneous core-shell structure. As a result, coercivity are remarkably enhanced from 14.9 kOe for DA sintered magnet with 2 wt.% CeAl to 25.1 kOe for the magnet GBD with TbCu. Most importantly, various levels of the NdFeB magnets, such as 52M, 35-50SH, and 45UH, could be attained by simply modifying the amounts of CeAl for DA sintered magnets and/or GBD with TbCu powders.

Magnetic properties of Ce85Al15 doped NdFeB sintered magnet by grain boundary diffusion of Tb70Cu30 powders

In order to reveal the demagnetization mechanism of NdFeB magnets and establish the relationship between microstructure and magnetic property, this paper focuses on the structural change of magnetic domain and the demagnetization behavior of NdFeB magnets under various demagnetization factors. Temperature, constant demagnetizing field and alternating demagnetizing field are applied to NdFeB magnets by high and low temperature alternating test chamber, demagnetization test device, programmable DC power supply and programmable AC power supply. Demagnetization test device is made up of 2000 turns copper winding winded on a laminated hollow rectangular steel core. Magnetic properties of the studied material are determined by magnetic domain size, amplitude and open-circuit remanence. The magnetic domain structure and open-circuit remanence are measured by atomic force microscope and Tesla meter. When the sample is demagnetized, the open-circuit remanence of the measuring point in the magnetization direction decreases, and the open-circuit remanence of the measuring point perpendicular to the magnetization direction increases. In the domain imaging, the domain size in the magnetization direction becomes fine and the amplitude decreases, while the domain size perpendicular to the magnetization direction expands and the amplitude increases. The change of magnetic domain structure is consistent with the macroscopic demagnetization law. As the domain size decreases, the number of domains increases and the area of domain wall increases. As a transition region with weak magnetism, the increase of domain wall area will lead to the decrease of macro magnetic properties. When the alternating demagnetizing field is 1000Hz at 140 °C, the remanence losses in the magnetization direction reaches 47.9%, and the domain size increases from 2.35 μm reduced to 1.15 μm. This work is helpful to understand the demagnetization mechanism of NdFeB magnets.

![](https://assets.underline.io/uploads/markdown_image/1/image/6e029230f24bf115f2a0be497a2d004f.jpg)

Magnetic domain of NdFeB magnet demagnetized by an alternating magnetic field with frequency of 1000Hz at 140 °C.

![](https://assets.underline.io/uploads/markdown_image/1/image/a78fa86255ef22db4c513685daf75636.jpg)

Open-circuit remanence losses and domain size of NdFeB magnets demagnetized by multiple levels of alternating fields and temperatures.




Magnetic Domain Structure and Remanence Losses of NdFeB Magnets Under the Influence of Demagnetization Factors

Because the degree of vibration in the permanent magnet synchronous motor (PMSM) is dependent on the magnetization distribution in the permanent magnet. The accurate estimation of magnetization distribution at the previous stage of the practical design eliminates the manufacturing of PMSM with poor performance. To nondestructively estimate the magnetization distribution in the permanent magnet, some numerical methods using the magnetic flux density measured on the outside region of the permanent magnet have been proposed [1], [2]. Because there are countless combinations of magnetization distribution in the permanent magnet, these methods can effectively remove the non-physical distributions. However, since those performances depend on the parameter tunings, the non-physical distributions cannot be completely removed. Then, the deep learning-based estimation method is proposed. In this paper, the deep feedforward neural network is applied to the estimation method. The network is configured by the framework of Keras [3], which is the python-based library of deep learning. The number of network layers is set to 9 layers. The number of neurons in the input layer is set to 344, which is identical to the summation of x- and y- direction of magnetic flux density on 172 measuring points on the outside of the 2-D permanent magnet model. The number of neurons in the output layer is set to 816, which is identical to the number of cells for the magnetization. The target distribution of magnetization is focused on the parallel orientation. The training data are generated by changing the angle of parallel direction every 0.01 degree within [0, 360] with the uniform intensity of magnetization. The weighted coefficients are determined by AdaGrad [4]. The input data (magnetic flux density) is generated by Biot-Savart law, and the 5 % error of the magnetization intensity is superposed on all data, as shown in Fig. 1. While the non-physical distribution tends to be estimated using the conventional methods [1], [2], the practical distribution is estimated using the proposed deep learning system, as shown in Fig. 2. The complicated magnetization distributions in 3D field will be estimated in the full paper.

![](https://assets.underline.io/uploads/markdown_image/1/image/7c8243f47a10aa08684a096da45db3f1.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/37d9c1618dae2eb45dea4d383d086e70.jpg)

Deep Learning-based Estimation Method of Magnetization Distribution in Permanent Magnet

The 2:17-type Sm-Co sintered magnet has excellent magnetic properties, which is widely used in aviation modern high-tech fields [1-2]. It was reported that the cell size increased with increasing isothermal aging time [3]. The effect of Fe-rich content on the phase structure and element distribution was rarely discussed. In this study, the phase structure, elementals distribution and magnetic properties of Fe-rich magnets were studied. The magnets with nominal composition Sm(Co0.91-xFexCu0.07Zr0.02)7.6 (x=0.22, 0.30, 0.35) were prepared, and the corresponding final magnets were named Fe0.22, Fe0.30 and Fe0.35. At the solid solution, the 2:17H phase, 2:17R phase and Zr-rich(1:3R) phase diffraction peaks are detected in the Fe0.30 and Fe0.35 magnet, while the Fe0.22 magnet bears typic 1:7H phase. Furthermore, the characteristic peaks [Fig. 1(a)] of 2:17H, 2:17R and 1:3R phases enhanced with the increase of Fe content, indicating that the high Fe content is not conducive to obtain homogeneous solid solution resulting in poor magnetic properties. The powder XRD patterns [Fig. 1 (b)] of three final magnets are almost the same, except the 1:3R phase can be detected in the Fe0.30 and Fe0.35 magnets. Fig. 2 shows the elemental distribution of the Fe0.22 and Fe0.35 magnets. Compared with the uniform element distribution of Fe0.22 magnet [Fig. 2(a-e)], there are large-sized Sm and Cu enrichment in Fe0.35 magnet, as marked in Fig. 2 (g) and (f). The enrichment regions in Fe0.35 magnet consumes a lot of Sm and Cu, leading to the destruction of the continuity of the cell wall and incomplete cellular structure which is revealed by TEM results. The poor cellular structure should be the main reason for the low coercivity of the Fe0.35 magnet. Our results confirmed that the 1:7H main phase in the solid solution was destroyed with too large Fe content. In addition, enrichment of Cu and Sm elements and incomplete cell structure formed for the large Fe content magnet, resulting in poor magnetic properties.

![](https://assets.underline.io/uploads/markdown_image/1/image/c0ed8d5a60db8ed5927cb50958e1edd0.jpg)

Fig. 1 (a) and (b) the powder XRD patterns of final magnets and solid solution magnets with different Fe contents

![](https://assets.underline.io/uploads/markdown_image/1/image/ae847a024e473dd590c03713f82c09e3.jpg)

Fig. 2 Element distribution of (a)-(e) Fe0.22 and (f)-(j) Fe0.35 magnet

The Phase Structure and Properties of Fe-riched 2:17-type Sm-Co Sintered Magnets

RT12 compounds with the ThMn12 crystal structure have been recently studied as potential candidates for high-performance magnets, due to their low rare-earth content which are considered as critical elements. These compounds with high Fe content, are expected to be strong magnets, because of their large magnetization, high Curie temperature as well as strong uniaxial magnetocrystalline anisotropy when R=Sm. Arc-melted alloys with composition Sm1Fe10.5−xCoxMo1.5(x =0,1,2) were prepared with the tetragonal ThMn12 structure. The cast samples were first high-energy-ball-milled followed by hot-compaction at 650 degree celsius under 275 MPa. Annealing of compacted samples was done from 700 to 1000 degree celsius to optimize the magnetic properties. The effects of Co on the magnetic properties, including the Curie temperature, saturation magnetization, anisotropy field, and energy product, have been investigated. It was found that the Curie temperature shows a linear relationship with the Co substitution; an increasing Co content increases Ms but decreases Hc, The Sm1Fe10.5−xCoxMo1.5 alloy with x =1 has an Hc=2782 Oe and shows the highest energy product(2.63 MGOe) after annealing at 750 degree celsius for 48 h. This work was supported by the U.S. Department of Energy under Grant DE-FG02-90ER45413.

![](https://assets.underline.io/uploads/markdown_image/1/image/ac144c27ad737697673ba2a9f28002d2.jpg)

Table 2: Lattice parameters and magnetic properties of arc-melted alloys Sm1Fe10.5−xCoxMo1.5 at 300K, with x =0, 1, 2

![](https://assets.underline.io/uploads/markdown_image/1/image/d8abe03bb48bec5c706bc98217bb2394.jpg)

Table 2: Magnetic properties of hot compacted nanocrystalline Sm1Fe10.5−xCoxMo1.5 magnets, with x =0, 1, 2, annealed at 750 degree celsius

Magnetic properties of nanocrystalline Sm1Fe10.5−xCoxMo1.5 alloys with x =0,1,2

FePt nanoparticles (NPs) with fct (L10) structures have a wide promising application in high-density magnetic storage media, catalysis, and biomedicine [1, 2], because of their high magnetocrystalline anisotropy, catalytic activity, and good biocompatibility. Ag addition can promote ordering transition and directly obtain L10-FePt NPs with high structural ordering [3-5]. However, the ordering mechanism of the NPs by Ag addition and the ordering transition process are rarely reported. Herein, we report the direct synthesis of L10-FePt NPs by Ag addition. The ordering transition process was investigated, and the ordering mechanism was discussed. The metal precursors Pt(acac)2, Fe(acac)3, and AgAc were dissolved in HDA in the presence of HDD as reductant. And then the mixed solution was heated to 360 °C for 180 min. Finally, the product was collected by centrifugation with ethanol. The phase structure and magnetic properties of a series of products sampled at 360 °C for different reaction times (from 0 min to 180 min) are shown in Fig. 1 and Fig. 2, respectively. The precursors of Ag and Pt were firstly reduced, and form AgPt phase at beginning of the reaction. With reacting for 10 min, the precursor of Fe was reduced, and the FePt NPs were obtained. The products were mainly combined of elemental Ag and L10-FePt phases. The magnetic properties of the products changed from diamagnetic to ferromagnetic. With extending the reaction time, the both content of Ag and L10-FePt phases continuously increased. The coercivity of products enhanced from 0.9 kOe to 6.3 kOe with increasing the reaction time from 10 min to 180 min. These results indicate that Ag atoms are easy to migrate and enrich because of their low surface energy and high mobility. The Ag migration helps the formation of a large number of defects and vacancies in the crystal lattice, which can promote the rearrangement of atoms, and reduce the ordering transition barrier. Therefore, Ag addition can result into improvement of structural ordering of the FePt NPs.


![](https://assets.underline.io/uploads/markdown_image/1/image/81f76544f273f94ac19ed3a8359a5ab6.jpg)


Fig.1 The XRD patterns of products obtained at 360 °C for different reaction times

![](https://assets.underline.io/uploads/markdown_image/1/image/166d467e2867a3c4344affaf327827f5.jpg)


Fig. 2 The hysteresis loop of products obtained at 360 °C for different reaction times

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