Specific heat and magnetocaloric effect of the Mn5Ge3 ferromagnet

Magnetocaloric refrigerant with wide operating temperature range based on Mn5−Ge3(Co,Fe) composite

“…1 indicate that the spectra from all three alloys were indexed to a hexagonal phase (space group P6 3 /mcm) without any impurity phases. Lattice parameters obtained by the least-square fitting from the XRD spectrum for Mn 5 Ge 3 were a = 0.720 nm and c = 0.505 nm which were in agreement with the literature values [19]. The substitution of the Mn sites with Fe atoms changed the lattice parameters to a = 0.720 nm and c = 0.502 nm, leading to a slight decrease in the unit cell volume ($0.4%).…”

“…For magnetic refrigeration to be economically competitive against the conventional cooling system, however, low-cost and non-toxic magnetic refrigerant with small thermal hysteresis still needs to be identified. Mn 5 Ge 3 with Curie temperature, T C close to room temperature at 296 K, is capable of generating maximum magnetic entropy change, |DS M | of 7-9 J kg À1 K À1 under an applied field of 5 T near room temperature [19,20]. Although |DS M | for Mn 5 Ge 3 is substantially inferior compared to those of the abovementioned giant MCE materials, Mn 5 Ge 3 is relatively cheap and non-toxic and does not produce thermal hysteresis unlike Heusler alloy-based refrigerants.…”

Solid-state synthesis and characterization of ferromagnetic Mn5Ge3 nanoclusters in GeO/Mn thin films

“…Hysteresis loops after annealing at both 250°C and 300°C possess the ratio M r /M S = 0.55 (where M r is magnetic remanence) similar to the Stoner-Wolfarth curve with M r /M S = 0.5, which describes a random assembly of noninteracting single-domain ferromagnetic particles with uniaxial anisotropy [27]. It is known that for Mn 5 Ge 3 the magnetocrystalline anisotropy constant K 1 = 3.0×10 5 erg/cm 3 [28] and the exchange stiffness parameter A ex = 1 × 10 −7 erg/cm [29], and therefore the exchange length L ex = (A ex /K 1 ) 1/2 is ~ 6 nm. From this it follows that for the majority of noninteracting Mn 5 Ge 3 (Mn 5 Ge 3 O y ) nanoclusters the intercluster distances must be more than 6 nm.…”

“…Our findings are in good agreement with previously published results of the formation of Ge nanoclusters in GeO film by annealing [30][31][32][33][34][35] and an important contribution is the detection of the low initiation temperature T in = 180°C of reaction (1). Figure 8a shows the photoelectron Ge 3d spectra of as-deposited GeO film (1,2) and that after annealing at 300ºC (3,4) collected before (1,3) and after etching with Ar + ions to remove an oxidized surface layer (2,4). The binding energy of 31 eV for the main peak, along with the atomic ratio O/Ge slightly above 1, indicate that a nearly stoichiometric GeO oxide was fabricated in the as-deposited sample underneath the surface of the GeO 2 (Figure 8b) [36].…”

“…In recent years, the synthesis features and structural, electronic and magnetic properties of ferromagnetic Mn 5 Ge 3 films have been intensively studied for future applications in spintronics [1][2][3][4][5]. An important advantage of Mn 5 Ge 3 is a sufficiently high spin polarization [6,7] and epitaxial growth on Ge (111) and Ge (001) substrates by solid-phase epitaxy [8][9][10][11].…”