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While tetragonal MnAl with the L10-type structure (P4/mmm #123) is metastable, it displays good intrinsic hard magnetic properties such as large magnetization (Ms=110 emu/g), high magnetocrystalline anisotropy field (HA=40 kOe), and moderate Curie temperature (Tc=600 K),1 which make it highly attractive as a sustainable rare-earth free permanent magnet. However, the metastable behavior of the MnAl L10-phase promotes the formation of structural defects that degrade its intrinsic magnetic properties such as the local magnetocrystalline anisotropy (MCA). In this work, we study the effects of a partial replacement of Al by Ga on the stability of the L10-phase, and both the magnetization and the MCA using a first-principles density functional calculation. We find that increasing the Ga content, enhances the phase stability while the total magnetic moment per formula unit (f.u.) remains almost unchanged. The site-, atomic- and spin-resolved MCA has been estimated by evaluating the spin-orbit coupling energy using a second-order perturbation approximation. Structural distortion, chemical effects and different spin components in Mn(Al1-xGax) all contribute to the MCA. The site- and atomic-resolved MCA calculations show that the MCA energy (MAE) mainly comes from the Mn atoms. With increasing Ga content, the MAE at both Mn and Al(Ga) sites increases and the total MAE increases from 0.2 meV/f.u. for x=0 to 0.34 meV/f.u for x=1 (Fig. 1). However, the structural distortion induced by the partial replacement of Al by Ga reduces the MCA. The spin-resolved MCA and band structure calculations indicate that the microscopic origin of high MCA is mainly associated with the spin flipping behavior near the Fermi level, induced by the spin-orbit coupling. The derived effective magnetic anisotropy field increases from 37 kOe (x=0) to 46 kOe (x=1), in agreement with experiments. Doping with Ga improves the stability of the L10 structure and enhances the magnetic anisotropy field, which facilitates the development of high coercivity Mn-Al based permanent magnets.&lt;br&gt;
**References:**&lt;br&gt; 1 L Pareti, F. Bolzoni, F. Leccabue, A.E. Ermakov, J. Appl. Phys. 59, 3824 (1986)&lt;br&gt;

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/2686cbc73adcf807336315c2b6ddbdee.png)&lt;br&gt;
Fig. 1 Dependence of MAE on Ga content, x, in Mn(Al1-xGax).&lt;br&gt;

MMM 2022

Constituent contribution to the magnetocrystalline anisotropy in Mn(Al1 xGax)

While tetragonal MnAl with the L10-type structure (P4/mmm #123) is metastable, it displays good intrinsic hard magnetic properties such as large magnetization (Ms=110 emu/g), high magnetocrystalline anisotropy field (HA=40 kOe), and moderate Curie temperature (Tc=600 K),1 which make it highly attractive as a sustainable rare-earth free permanent magnet. However, the metastable behavior of the MnAl L10-phase promotes the formation of structural defects that degrade its intrinsic magnetic properties such as the local magnetocrystalline anisotropy (MCA). In this work, we study the effects of a partial replacement of Al by Ga on the stability of the L10-phase, and both the magnetization and the MCA using a first-principles density functional calculation. We find that increasing the Ga content, enhances the phase stability while the total magnetic moment per formula unit (f.u.) remains almost unchanged. The site-, atomic- and spin-resolved MCA has been estimated by evaluating the spin-orbit coupling energy using a second-order perturbation approximation. Structural distortion, chemical effects and different spin components in Mn(Al1-xGax) all contribute to the MCA. The site- and atomic-resolved MCA calculations show that the MCA energy (MAE) mainly comes from the Mn atoms. With increasing Ga content, the MAE at both Mn and Al(Ga) sites increases and the total MAE increases from 0.2 meV/f.u. for x=0 to 0.34 meV/f.u for x=1 (Fig. 1). However, the structural distortion induced by the partial replacement of Al by Ga reduces the MCA. The spin-resolved MCA and band structure calculations indicate that the microscopic origin of high MCA is mainly associated with the spin flipping behavior near the Fermi level, induced by the spin-orbit coupling. The derived effective magnetic anisotropy field increases from 37 kOe (x=0) to 46 kOe (x=1), in agreement with experiments. Doping with Ga improves the stability of the L10 structure and enhances the magnetic anisotropy field, which facilitates the development of high coercivity Mn-Al based permanent magnets. 
**References:** 1 L Pareti, F. Bolzoni, F. Leccabue, A.E. Ermakov, J. Appl. Phys. 59, 3824 (1986) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/2686cbc73adcf807336315c2b6ddbdee.png) 
Fig. 1 Dependence of MAE on Ga content, x, in Mn(Al1-xGax).

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Effects of La3+ and Li1+ co-substitution on structural and magnetic properties of M-type strontium hexaferrite have been studied by using crystallographic and magnetic measurements. Stoichiometric Sr1-xLaxFe12-x/2Lix/2O19 (x=0, 0.25, 0.4, 0.5, and 0.6) samples have been prepared by the conventional ceramic method using La2O3, SrCO3, Fe2O3, and Li2CO3 powders with repeated sinterings at 1250 °C for 24 hours.
XRD patterns showed that when x > 0.6, LaFeO3, SrFeO3-δ, and other spinel ferrite coexisted along with the M-type hexaferrite. Lattice parameters deduced from the GSAS refinement shows that both a and c decrease with increasing x, but the change in c is more outstanding (Table 1). Variations of the saturation magnetization Ms and the coercivity Hc with x was obtained from room temperature VSM measurement as in Table 1. Whereas the Ms decreases slightly with x, the Hc increases with the La3+ - Li1+ co-substitution throughout the doping range examined. Effective magnetic anisotropy constants K are calculated as well from the hysteresis curves using the law of approach to saturation method. K shows slight decrease with increasing x as listed in Table 1. 
XPS scan shows the Li 1s peak at ~56 eV (Fig. 1(a)). Apparently, monovalent Li1+ is non-magnetic. In view of the facts that Li1+ in the lithium ferrite (LiFe5O8) preferentially occupies the octahedral site and that the M-type hexaferrite has the spinel S-block in its structure, the decreasing trend of Ms with x strongly suggests that Li+1 ions preferentially replace Fe3+ ions either at 12k or 2a sites (rather than the 4f2 site in R-block). Non-magnetic substitution at those sites is known to give rise to negative contribution to Ms. Finally, Mössbauer spectra show gradual decrease in 2a intensity, in support of the octahedral 2a site preference of Li1+ in M-type hexaferrite (Fig. 1(b)). 
**References:** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/df4dab457afcb7e5118c6d0fedb9652a.png) 
Table 1. Various structural and magnetic parameters for Sr1-xLaxFe12-x/2Lix/2O19 (x=0, 0.25, 0.4, 0.5, and 0.6) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/05367f421b43d801d81539c55a4d55eb.png) 
Figure 1. (a) A comparison of Li 1s XPS scan for Sr1-xLaxFe12-x/2Lix/2O19 (x=0.25 and 0.5) and (b) 57Fe Mössbauer spectrum for Sr0.4La0.6Fe11.7Li0.3O19 taken at room temperature.

Structural and magnetic characterizations of La3+ and Li1+ co substituted M

The magnetization of Mn4C with face centered cubic structure increases with the increase of temperature within a certain temperature range, which means that Mn4C may be applied to the field requiring high working temperature of magnetic materials through further research and development. Unfortunately, Mn4C is a metastable phase [1-3], so it is difficult to synthesize high-purity Mn4C. 
High-purity Mn4C powders was prepared by melt spinning, grinding and magnetic separation in this paper. It is found that high cooling rate is beneficial to obtain high-purity Mn4C material. Moreover, compared with argon gas as the grinding medium, grinding Mn4C melt-spun strips in alcohol solution is not only conducive to refining the size of the ground particles, but also conducive to improving the dispersion of the particles. Therefore, Mn4C powders with higher purity can be obtained after magnetic separation (see Fig. 1).
The magnetization of Mn4C powders remained unchanged with the increase of temperature in the range of 2 K -50 K, but increased with the increase of temperature in the range of 50 K to 300 K (see Fig. 2). This may be because there is a spin glass state in Mn4C powders. At low temperature, the spins are frozen, but the frozen spins are gradually thawed with the increase of temperature. Further investigation is in progress. 
Crystal and magnetic structure of Mn4C powders was investigated by variable temperature neutron diffraction technique. The magnetization change of Mn4C with temperature should be mainly due to its own magnetic phase transition, and is closely related to the antiparallel arrangement of the magnetic moments of Mn atoms at the symmetrical crystal positions 1a and 3c in the Mn4C lattice. The total magnetic moment of crystal cells increases with the increase of temperature. 
**References:** 1. Si, PZ, Qian, HD, Ge, HL,et al. Applied physics letters, 2018, 112(19):192407. 
2.Park ,J, Qian, HD, Si, PZ, et al. Journal of magnetism and magnetic materials, 2021, 527:167765. 
3. Tagawa, Y and Motizuki, K. Journal of physics-condensed matter, 1991, 3(12): 1753-1761 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/65df04ba198f154c12183b9b3f6c217e.png) 
Fig.1 XRD patterns of Mn4C obtained by (a) arc melting, (b) Suction casting, (c) melt spinning technology (50m/s),and (d) grinding and magnetic separation of the same strips as (c) in alcohol solution. (a) (b) and (c) are both heat treated and ground and magnetically separated in argon. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e3091542db36f8e069365c557c6f6f8e.png) 
Fig.2 (a) Variation of magnetization of Mn4C powder with temperature under different magnetic field; (b) Hysteresis loops of Mn4C powders at 2K-300K

Study on preparation, structure and magnetic properties of high purity Mn4C

Structural changes and evolution taking place in ferrites with increasing processing temperature are crucial from their performance point of view. Three M-type hexaferrites were prepared using solid-state reaction at 650-1250 °C: SrFe12O19 (SrM), BaFe12O19 (BaM), and CaFe12O19 (CaM). The evolution of phases was studied with X-ray powder diffraction and thermogravimetry investigation. The structural studies reveal that the formation M-type phase begins at 820, 850, and 1200 °C, respectively, and different mid-phases of SrFe3-x, BaFe2O4, and CaFe2O4 were formed. The structural studies in all cases were successfully refined using the P63/mmc (No.194) space group but Ca2+ shrank the hexaferrite crystal lattice. Their magnetic properties were studied with respect to their composition and microstructure by scanning electron microscopy (SEM). The different phase evolution leading to the different magnetic properties of M-type hexaferrite were discussed in the present work. 
**References:** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/36c0fa25d7625bed31a1e2e1bc6aa2e9.png) 
Table 1 The phase evolution with the temperature of SrM, BaM and CaM

Understanding of the Phase Evolution with Temperature in Pure SrM, BaM and CaM

Permanent magnets are an essential material in many electrification technologies, such as electric vehicles and Air mobility. So, Many efforts have paid for enhanced magnetic flux density and robust high temperature for electrification technologies application.
As a representative example, efforts are being made to reduce the negative temperature coefficient coercive force and use less rare earth by developing NdFeB magnet.
Among the rare-earth-free magnets candidates, MnBi alloy have been regarded as one of the most attractive candidates with promising magnetic properties and the positive temperature coefficient coercivity . The theoretical (BH)max value at room temperature of the LTP MnBi is about 17 MGOe and can reach a high real value of 6.5 MGOe at 400 K . This magnetic performance of the LTP MnBi is can be replace NdFeB magnets in high-temperature magnet applications. 
This study has been developed based on Density functional theory(DFT) calculation and experimental. First, thermodynamic calculations were used for MnBi lattice modeling to select substitutable elements for Mn and Bi lattice sites, and then DFT calculations were used to predict magnetic moments. The MnBi-X alloy candidate material selected through prediction was manufactured using the melt spinning method. A vibratory sample magnetometer (VSM) was used to evaluate the magnetic properties and a trial and error method was used to finally optimize the MnBi alloy composition.
MnBi-Sb magnetic powder has a comparative advantage over ferrite magnets and has the same performance as rare earth bonded magnets. (magnetic flux density 4kG, coercive force 9kOe and coercive force coefficient 0.68~0.91%/K) 
**References:** 1. Yang-Ki Hong, AIP Advances., 3, 052137 (2013) 
2. S. Kavita, Journal of Magnetism and Magnetic Materials., Vol. 377, P. 485(2014) 
3. C. Curcio,Physics Procedia., Vol. 75, P. 1230 (2015) 
4. Sumin Kim, Journal of Alloys and Compounds., vol 708, p1245 (2017) 
5. A.M. Gabay, Journal of Alloys and Compounds., vol. 792, p.77 (2019) 
6. Truong Xuan Nguyen, Physica B., vol. 552, p.190, (2018) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/051728167f485b8fd0af85cfee9ba719.png) 
Fig. 1 X-Ray Diffraction (XRD) data of the Mn-Bi-Sb alloys. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/5eb252ebecb83a90c3e1dc96146b4583.png) 
Fig. 2 Analysis of M-H curve in Mn-Bi-Sb alloys.

Development of Mn based Permanent Magnet Material for Electric Motor

Magnetic dead layers (MDLs) can be formed at the interface of ferromagnetic (FM) and non-magnetic thin films as a result of interfacial diffusion typically during the fabrication process [1][2], causing degradation of magnetic layers’ properties, such as the magnetic moment and exchange coupling. For patterned films it also poses thermal stability problems due to a decrease in the magnetic anisotropy energy, leading to a reduction in thermal activation energies [3]. 

X-Ray reflectometry (XRR) has been used in conjunction with polarised neutron reflectometry (PNR) to investigate the formation of magnetic dead layers in Co70Fe30 thin films with Ta interfaces in addition to sample degradation over time. The rate at which the Ta diffuses into the Co70Fe30 layer differs between the top and bottom interfaces resulting in MDLs of different thicknesses, 3.04Å and 1.87Å respectively as indicated in figure 1(b). It is clear that the formation of magnetic dead layers has resulted in a loss of magnetisation in the thin Co70Fe30 layer. 

This is of particular technological importance for spintronic devices in which the magnetic properties at the interfaces are crucial. Ta has been known to provide very good adhesion between the substrate and the soft FM layer. It is also widely used as a passivation layer to prevent oxidisation in air [4]. Our results show that this is not the case, with Ta unsuitable as a seed due to the formation of MDLs and not viable as a capping layer due to oxygen passivation over time as shown by XRR in figure 2. 
**References:** [1] T. L. Monchesky and J. Unguris, Phys. Rev. B 74, 24130 (2006). 

[2] K. Oguz et al., J. Appl. Phys. 103, 07B526 (2008). 

[3] M. Tokaç et al., AIP Advances 7, 115022 (2017). 

[4] H. S. Jung et al., J. Appl. Phys., Vol. 93, No. 10, (2003). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/4fa86217a7c805ccc7036f26a1a59ed3.png) 
Fig. 1. (a) PNR measurements, raw data shown as points while the fitted simulated data is indicated by a solid line. (b) Depth profiles of nuclear and magnetic scattering length density (SLD) for the sample structure in the schematic above. MDLs have been introduced in the interfaces between the top and bottom interfaces of the CoFe layer. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/072c7007a6575d080bf1a6ca3cc9fc39.png)
 
Fig. 2. XRR curves for the sample structure denoted in the inset above. Sample A was measured as soon as deposited whilst sample B was measured 15 months later which has clearly degraded over time as seen on the fringes and as well as the differences in thickness of the sample.

Interface Degradation in Magnetic Multilayer Stacks Characterised by X Ray Reflectometry and Polarised Neutron Reflectometry

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

Hole doped La2/3Sr1/3MnO3 (LSMO) is an auspicious candidate for spintronic applications due to its high spin polarization [1] and colossal magnetoresistance [2]. However, the growth of LSMO thin films on silicon, and other substrates important for applications, is extremely challenging due to their structural incompatibility and high reactivity with oxygen. 
Here, we demonstrate the possibility to grow strain-free LSMO thin films on silicon substrates with magnetic, magneto-optical and optical properties comparable to epitaxial layers grown on SrTiO3 (STO). This growth was achieved using a two-dimensional Ca2Nb3O10 nanosheet (NS) seed layer which induces epitaxial stabilization of LSMO. The 20 and 40 nm thick films of LSMO were grown by pulsed laser deposition with identical conditions for both the silicon and STO substrates. X-ray diffraction characterization of the samples confirmed strained epitaxial LSMO layers on STO and relaxed fibre textured films with unified out-of-plane orientation on Si with NS seed layer. Magnetization measurements, shown in Fig. 1, revealed smaller saturation magnetization for samples grown on Si. This might be attributed to the textured nature of the samples. However, these samples exhibit a higher Curie temperature by more than 10 K, which is the result of strain relaxation. For a closer insight into the electronic structure of the material a combination of spectroscopic ellipsometry and magneto-optical spectroscopy experiments were performed. The results allowed to derive the full permittivity tensor of the material in the spectral range from 1.5 to 5 eV. The spectral dependence of the off-diagonal element of the permittivity tensor, shown in Fig. 2, revealed striking similarity between the LSMO samples grown on STO and Si. Three electronic transitions around 1.9, 2.9, and 3.5 eV were identified in the spectra, suggesting the main contribution to the optical response arises from Mn states [3]. 
**References:** 1 M. Bowen, M. Bibes, A. Barthélémy, et al., Appl. Phys. Lett., Vol. 82, p.233–235 (2003) 
2 A.P. Ramirez, J. Phys.: Condens. Matter, Vol. 9, p.8171–8199 (1997) 
3 M. Zahradník, T. Maroutian, M. Zelený, et al., Phys. Rev. B, Vol. 99, p.195138 (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e466a8c107bf99ccb2449812508ecd27.png) 
Fig. 1: Temperature dependent magnetization of LSMO samples on STO and Si in saturation. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/883d8cb08244cf7b151eed0cd2e1fbb5.png) 
Fig. 2: Spectral dependence of the off-diagonal element of the permittivity tensor of LSMO samples on Si and STO.

Magnetic, optical and magneto optical properties of strain

β-Mn type CoZnMn is one of chiral magnets and is reported to host Bloch skyrmions above room temperature [1]. CoZnMn epitaxial thin films are attractive for the device application, however, there is no report on the fabrication of the epitaxial film, although polycrystalline CoZnMn films were reported in the previous study [2]. Here, we report CoZnMn epitaxial films grown on MgO(001) single crystal substrates. [Co-Zn(10 – t nm)/Mn(t nm)]15 multilayers were prepared by rf magnetron sputtering of Co-Zn composite target and Mn target. The multilayers were grown on 10 nm-thick W buffer layer. The total thickness of the multilayers was kept constant at 150 nm, and the Mn composition was controlled by varying the Mn layer thickness t. The composition of Co-Zn layer was estimated to be Co/Zn = 0.8 by energy dispersive x-ray spectroscopy. 10 nm-thick W capping layer was deposited on the multilayers. After the deposition, the multilayers were annealed at 300 °C in vacuum to obtain the CoZnMn alloy. Crystal structure was characterized by x-ray diffraction. Figure 1(a) shows a reciprocal space mapping of the sample for t = 2 nm in the plane parallel to MgO(130), where Qy and Qz are parallel to MgO[310] and MgO[001], respectively. In the figure, β-Mn type CoZnMn 103, 104 and 204 diffraction spots were observed, indicating the epitaxial growth of β-Mn type CoZnMn film with (001) orientation. Figure 1(b) shows φ scan profile for β-Mn type CoZnMn 103 diffractions. 8 peaks were observed in the in-plane scanning even though β-Mn type CoZnMn has 4-fold symmetry, which means the existence of twinned crystal grains with CoZnMn[100]//MgO[310] and CoZnMn[100]//MgO[3 -1 0] in the film. Although there exists twin crystals in the film, β-Mn CoZnMn (001) film was successfully fabricated on a MgO single crystal substrate. 
**References:** [1] Y. Tokunaga et.al., Nat. Comm. 6, 7638 (2015). 
[2] Ishikawa et.al., The 66th JSAP Spring Meeting, 9p-PB1-15 (2019). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ec451b1f310d93f08abb3bea2a1cb469.png) 
Fig. 1 (a) Reciprocal space mapping of the CoZnMn film in the plane parallel to MgO(130). (b) φ scan for β-Mn type CoZnMn 103 diffractions.

Fabrication of β Mn type CoZnMn(001) film on MgO single crystal substrate

Future embedded and standalone magnetic random access memory (MRAM) solutions require materials possessing bulk magnetocrystalline anisotropy at sub-10 nm feature sizes. FePd in its L10-ordered phase delivers MJ/m3 bulk anisotropy energy density (Ku) [1], large interlayer exchange coupling through Ru [2], Gilbert damping (α) below 0.008 [3] and robust compatibility across a range of Pt-group buffer layers [4]. Transitioning FePd films into mature spintronic applications requires a higher level of process control realize highly uniform microstructural, magnetic and magnetotransport properties. 
We demonstrate control of the orientation distribution of the c-axis in highly (001)-oriented L10 FePd. Using direct current magnetron sputtering on (001)-cut, polished MgO substrates, we explore an N2 substrate anneal, variation in the individual thicknesses of the Cr/Pt underlayer and post-anneal modules between layers. Each sample had an 8-nm-thick FePd layer grown at 350 °C and post-annealed at 500 °C, leading to a high degree of L10 ordering, with Ku ranging between 0.8 MJ/m3 and 1.1 MJ/m3 and α ranging from 0.0067 to 0.0133. Despite the relatively narrow spread in these key parameters, we observed a wide range of inhomogeneous linewidth broadening (µ0ΔH0) from ferromagnetic resonance measurements, ranging from below 0.01 T to nearly 0.2 T (Fig. 1(a)). Variation in µ0ΔH0 correlates with the FePd grain orientation distribution, as measured by x-ray diffraction rocking curve scans of the (002) Bragg peak (Fig. 1(b)). Our process controls enable varying the full-width-half-maximum (FWHM) of the (002) peak from 14 degrees down to nearly 2 degrees, leading to narrowing of the local anisotropy distribution and reduction in the µ0ΔH0 (Fig. 1(b) inset). These process improvements will deliver the large-scale uniformity needed to implement FePd-based MRAM solutions. 
**References:** [1] M. Futamoto et al., AIP Advances 6, 085302 (2016) 
[2] D.-L. Zhang et al., Phys. Rev. Appl. 9, 044028 (2018) 
[3] D.-L. Zhang et al., Appl. Phys. Lett. 117, 082405 (2020) 
[4] X. Wang et al., AIP Advances 11, 025106 (2021) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/aa4b6704bacd0147dba693b652175112.png) 
Figure 1: (a) FMR Linewidth versus frequency for three samples with inhomogeneous line broadening of 0.178 T (blue), 0.075 T (green) and 0.015 T (red). (b) Inhomogeneous line broadening versus FWHM of FePd(002) (Δω), with (inset) exemplary FePd(002) rocking curve scans of the red, blue and green star samples highlighted with colored markers in (a)

Control of grain orientation spread and inhomogeneous broadening in L10 phase FePd thin films with low damping and high perpendicular magnetic anisotropy

Exchange coupling in as-deposited and annealed magnetic trilayers Co80Fe20 (CoFe)/MgO/Co80Fe20 (CoFe) for MgO thickness spanning 0.45 to 4.5 nm has been studied. Unlike relevant existing results and theories, antiferromagnetic exchange coupling behavior was observed in annealed CoFe/MgO/CoFe with 2.7-nm MgO insulating barrier. Figure 1 shows in-plane minor hysteresis loops of the as-deposited and annealed CoFe/MgO/CoFe trilayer for MgO thickness spanning 1.8 to 4.5 nm, respectively. Interestingly, the shift of the hysteresis loop toward positive or negative field depends on the temperature. For the temperature range of 25 to 500 deg. C, the hysteresis loop is shifted to the negative and to the positive field for 600 deg. C as shown in Fig. 2(a) [1]. Figure 2(b) a transition from antiferromagnetic to nearly paramagnetic response to applied magnetic field was found around 520 deg. C—conceptually called as Neel temperature. Based on grazing incidence x-ray diffraction study, formation of CoO and CoFe2O4 were found at annealed CoFe/MgO interfaces [2], which indicates they act as antiferromagnetic sources giving rise to the exchange-coupled antiferromagnetic/ferromagnetic interface and then antiferromagnetic coupling across the magnetic trilayer [3]. 
**References:** [1] T. Ambrose et al., Phys. Rev. B 56, 83 (1997). 
[2] S. Grytsyuk et al., Eur. Phys. J. B. 85, 254. (2012). 
[3] J. Spray et al., J. Phys. D: Appl. Phys. 39, 4536 (2006). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/78800643a37d3cd33a576952b551a2d5.png) 
Fig. 1 Magnetic hystereis loops of (a) as-deposited and (b) annealed CoFe/MgO/CoFe films for MgO thickness spanning 1.8 to 4.5 nm. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/3a0ae8452ec77a8b35e2f1f3e85f1fe5.png) 
Fig. 2 (a) Temperature dependence of magnetic hysteresis loops of 4-nm CoFe/2.7-nm MgO/8-nm CoFe film annealed at 250 deg. C for 1 hour at the rotation angle 75 deg. (b) exchange coupling field of the same film as mentioned in (a).

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