We have investigated a series of high performance metal-matrix composites (MMCs), in order to improve mechanical and thermal properties of such composites. To fabricate such composites, we have used spark plasma sintering (SPS) process. Using this processing, we would minimize or avoid some risks in damaging filler surfaces during processing. In this article, also introduced are various kinds of MMCs, metal/intermetallic laminate materials, fiber reinforced composites and particle dispersed heat dissipative materials. These composites have been fabricated using various methods, such as, vacuum hot pressing, diffusion bonding and metal infiltration, and their physical properties are shown and well documented. In the article, MMCs fabricated by our SPS method is compared to those fabricated by other fabrication methods. This review article leads to strong indications regarding fabrication techniques for making better MMCs.

Me-substituted W-type ferrites (AMe₂Fe₁₆O₂₇ with A = Sr, Ba, …, and Me = Co, Ni, Zn, Mg, …) can be obtained by standard solid state reaction but always contain secondary phases. Phase stability of SrMe₂Fe₁₆O₂₇ with Me = Co, Ni, Zn, and Mg sintered in various oxygen pressures of p_O2 = 0.2, 1, 10 and 387 atm were investigated using X-ray diffraction analysis, wavelength-dispersive X-ray (WDX) analysis, and transmission electron microscopy (TEM). WDX analysis revealed that the W-type ferrites are described as SrMe_2-δFe_16+δO₂₇ because Fe³⁺ is partially reduced to Fe²⁺ even when synthesis is initiated from SrMe₂Fe₁₆O₂₇. Increasing the oxygen pressure suppresses the reduction of Fe³⁺ and the formation of the secondary phases. In addition, TEM analysis shows that the SrCo₂Fe₁₆O₂₇ single crystal is free of stacking faults. We conclude that the single-phase formation of the Me-substituted W-type ferrites is hampered by the discrepancy between initial and actual chemical composition caused by the appearance of Fe²⁺.

We studied a solid-solution system of the transition-metal pnictide, Y₂(Mn_xFe_1−x)₁₂P₇, with the Zr₂Fe₁₂P₇-type structure, which has two kinds of transition metal sites: three tetrahedral sites and a pyramidal site. We successfully obtained polycrystalline samples of Y₂(Mn_xFe_1−x)₁₂P₇ in the range of 0 ≦ x ≦ 0.9. The lattice parameter along the a-axis monotonically increases with the Mn substitution, while that along the c-axis is nearly constant. ⁵⁷Fe Mössbauer spectroscopy shows that Mn atoms prefer to occupy the pyramidal site. At x = 0.25, the site-ordered compound, Y₂Mn₃Fe₉P₇, was obtained, where Mn atoms occupy the pyramidal site and Fe atoms occupy the tetrahedral sites. The magnetization of Y₂Mn₃Fe₉P₇ exhibits an anomaly at approximately 60 K, suggesting presence of an antiferromagnetic transition, which originates from the magnetic moment of Mn at the pyramidal site.

Ferromagnetic spin fluctuations in itinerant-electron magnetic compounds RCo₉Si₄ (R = Y, La) were investigated by using magnetization and ⁵⁹Co-NMR measurements. YCo₉Si₄ is an itinerant ferromagnet, while LaCo₉Si₄ is a nearly ferromagnetic metal. In YCo₉Si₄, the field dependence of the magnetization is well described by Takahashi’s spin-fluctuation theory for weak itinerant ferromagnets. In both YCo₉Si₄ and LaCo₉Si₄, the magnetic susceptibility, the Knight Shift and 1/T₁T show a similar temperature dependence, which suggests that the ferromagnetic spin fluctuation is dominant in these compounds. The difference in the magnetic ground state of these compounds is possibly attributed to the fact that the energy scale of the ferromagnetic spin fluctuation in LaCo₉Si₄ is larger than that in YCo₉Si₄.