## 2 Materials and Methods  
For the realisation of a high filling density in the HIP capsule, Al, Fe, Co, and Ni are used in spherical powder form [24; 25]. Al, Ni, and Fe have particle sizes of 45 \(\upmu\)m to 150 \(\upmu\)m. To integrate the influence of the particle size, a Co powder with a 300 \(\upmu\)m particle size was chosen. As the focus of the following investigations is on the ferromagnetic properties of the materials, the properties are listed in Table 1.  
First, the powders are mixed with a 3D shaker mixer for 1 h according to the composition in Table 2. Because HIP is only used for the characterisation of the Al-particle composites and in order not to eliminate the good deformation properties of Al, 10 mass-% of ferromagnetic particles were initially selected. As no magnetic feedback could be generated, 30 mass-% was subsequently selected. The 30 mass-% is the maximum percentage of magnetic particles, as even 10 mass-% significantly reduces the plastic deformation properties of the Al, which this study verifies. The 3D shaker mixer achieves effective mixing of the powders through the interaction of rotation, translation, and inversion during the mixing process. The powder is filled into stainless steel HIP containers, precompacted, evacuated, and sealed. An HIP system essentially consists of an insulating jacket, a furnace, and a pressure chamber, see Figure 2a. Up to three hip capsules are placed in the HIP chamber, and after sealing, it is flooded with argon. Surrounded by this inert gas atmosphere, the capsules are heated to 500 \({}^{\circ}\)C, whereby the pressure increases because of heating, see Figure 2b, and they act uniformly on the entire outside of the capsule to ensure compression over the entire cross-section. A pressure of 1200 bar was selected for test numbers one to four, and 1100 Pa was selected for test numbers five to seven. After the heating phase, the temperature and pressure are kept constant for 3 h, and then the cooling phase begins. After HIP, the specimens have a diameter of 50 mm and a height of 100 mm, with the cover and base removed because of deformation [30; 31]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **Lattice** & **Magnetic** & **Saturation** & **Curie Temperature** \\  & **Structure** & **Permeability \(\upmu\)** & **Polarisation \(\mathbf{J_{5}}\) [T]** & \(\mathbf{T_{C}}\) [\({}^{\circ}\)C] \\ \hline Fe & bcc & 250–680 & 2.15 & 1043 \\ \hline Co & hcp & 80–200 & 1.76 & 1393 \\ \hline Ni & fcc & 280–2500 & 0.61 & 631 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Magnetic properties of Fe, Co, and Ni [26; 27; 28; 29]. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Test Number**} & **Material** & **Mass Fractions [\%]** \\ \hline
1 & Al & 100 \\ \hline
2 & Al & 90 \\  & Fe & 10 \\ \hline
3 & Al & 90 \\  & Co & 10 \\ \hline
4 & Al & 90 \\  & Ni & 10 \\ \hline
5 & Al & 70 \\  & Fe & 30 \\ \hline
6 & Al & 70 \\  & Ni & 30 \\ \hline
7 & Al & 70 \\  & Co & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material composition of the hipped samples. The microstructure and magnetic properties of the resulting hipped materials are examined for their magnetic properties. Barkhausen noise analysis is used for the detection of the magnetic characteristics. The Barkhausen noise analysis detects the jumps in magnetisation caused by the irreversible Bloch walls movement from the 180\({}^{\circ}\) Bloch walls. To induce Bloch wall jumps, the material is subjected to time-periodic remagnetisation, whereby a ferromagnetic material passes through a hysteresis process, see Figure 3a. The abrupt changes in magnetisation induce voltage pulses in the magneto-inductive sensor, which is located in the testing head of the measuring instrument, see Figure 3b. The testing head is placed on the material surface and acts as a transmitter and receiver of the magnetic signals.