## 2 Materials and Methods  
(Mn\({}_{55}\)Al\({}_{45}\))\({}_{100\times}\)C\({}_{x}\) powders, where x = 0 (MnAl-C0), 1 (MnAl-C1), 2 (MnAl-C2), and 3 (MnAl-C3), were firstly prepared according to the procedure described in a previous work [21]. In summary, an induction heating tube with argon flow of 5 L/min was used to heat Mn flakes (purity 99.9%), Al granules (purity 99.995%), and C (purity 99.09%) at 1450 \({}^{\circ}\)C. After 3 minutes, the power supplied to the heating coils was switched off, allowing the gradual cooling to room temperature. The obtained alloys were ground into powders and subsequently annealed in a tube furnace (Carbolite GHA12/300) under argon atmosphere. In this work, three different annealing temperatures of 450, 500, and 550 \({}^{\circ}\)C were investigated in order to increase the \(\tau\)-MnAl, whereas the annealing time was kept constant at only 20 min to minimize decomposition of \(\tau\)-MnAl, as suggested by [PERSON] et al. [15]. The ferromagnetic \(\tau\) phase in annealed MnAl-C powders was separated from other nonmagnetic phases by using a magnetic field. A sheet of hard ferrite was slowly dragged to attract the magnetic portion from the annealed powders distributed on a sheet of paper. This process was repeated several times until the magnetic and nonmagnetic portions were thoroughly discriminated. Both portions were then examined by field-emission scanning electron microscope (FESEM: Zeiss Merlin Compact, Carl Zeiss Microscopy GmbH, Germany) with the energy-dispersive X-ray spectroscopy (EDS: Oxford Aztec, Oxford Instruments, UK). The phases in MnAl-C powders before and after the magnetic separation were characterized by a single crystal X-ray diffractometer (XRD, Rigaku SuperNova diffractometer with a HyPix 3000 detector, Rigaku Corporation, Poland) using Cux radiation (\(\lambda\) = 1.54184 A). Data reduction, scaling and absorption corrections were performed using CrysAlisPro software in the micro powder mode. Crystalline phases present in the XRD patterns were quantified by Rietveld refinement via XPowder12 software. This software indexed the set of diffraction peaks by searching and matching with the Predicted Powder Diffraction Database (P2D2). The phase components were calculated using the least squares statistical method and the pattern intensity ratio (PIR) scale factor. The quantitative analysis is based on database records with increased accuracy by the addition of background subtraction and inclusion/exclusion elements selected from the periodic table. The quality of data related to the 2 \(\theta\) correction fitting was assessed by the value of the R-factor. In addition, the full width of the intensity distribution at half of the maximum intensity (\(\beta\)) of the major \(\tau\)-MnAl peak was used to determine the crystallite size (d) according to the Scherrer formula [22]:  
\[\text{d}=\frac{0.94\lambda}{\beta\cos\theta} \tag{1}\]  
where \(\lambda\) is the wavelength of K\(\alpha\). Composites were prepared by loading PLA with MnAl-C powders collected from the magnetic separation. From the preliminary assessment of mechanical characteristics, the MnAl-C0/PLA composition of 60/40 wt% was selected. Firstly, PLA powders were dissolved in 20 mL toluene (6% _w/w_) at 120 \({}^{\circ}\)C. The solution was stirred by using a 500 rpm rotating magnetic bar for 1 h. MnAl-C0 powders were then added before heating and stirring continued for another 1 h in order to achieve homogeneous dispersion in the polymeric matrix. Once heating and stirring were terminated, the temperature was cooled down to room temperature. The residual toluene was removed by allowing evaporation for 24 h, and pieces of bulk MnAl-C0/PLA composites were finally obtained. Magnetic properties of MnAl-C powders and MnAl-C/PLA composites were measured at room temperature using a vibrating sample magnetometer (VSM). Loose powders and small granules were loaded in specially designed capsules, which locked the sample in place with a built-in screw.