Solid state synthesis of Mn5Ge3 in Ge/Ag/Mn trilayers: Structural and magnetic studies

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

“…The TEM image of the Mn(50nm)/GeO(300nm) film after annealing at 300°C (Figure 5c) reliably demonstrates the doubling of the Mn-based layer thickness due to the migration of a considerable quantity of Ge atoms which arises due to reaction (1) in the Mn layer. This finding agrees well with our previous studies and suggests that Ge is the dominant diffusing species in the Mn 5 Ge 3 synthesis [16]. An increase in the annealing temperature up to 500°C leads to the oxidation of the Mn 5 Ge 3 and Nowotny Mn 5 Ge 3 Oy nanoclusters and further increases in the Mn-based layer as shown in Figure 5d.…”

“…As is known, thin-film solid-state reactions start when the temperature of a sample T S exceeds the initiation (formation) temperature T in (T S >T in ). For metallic thin-film reactions the initiation temperature T in can be below room temperature or even below 90 K [39,16]. Recently we showed that the initiation temperature of the Mn 5 Ge 3 compound is equal to T in (Mn 5 Ge 3 ) ~ 120°C [14][15][16] and the Ge is the sole diffusing species [16].…”

“…For metallic thin-film reactions the initiation temperature T in can be below room temperature or even below 90 K [39,16]. Recently we showed that the initiation temperature of the Mn 5 Ge 3 compound is equal to T in (Mn 5 Ge 3 ) ~ 120°C [14][15][16] and the Ge is the sole diffusing species [16]. As pointed out above the reaction between the Mn and GeO layers starts at T in (Mn/GeO) = 180°C which coincides with the initiation temperature T in (GeO → Ge+GeO 2 ) = 180°C of the disproportionation reaction (1) that produces Ge and GeO 2 , which exceeds the initiation temperature of Mn 5 Ge 3 (T in ~ 120°C).…”

“…Both dependences indicate the formation of the Mn 5 Ge 3 phase with a Curie temperature T C 1 ~ 300K [14 -16] and a second ferromagnetic phase with T C 2 ~ 360 -400K. Recently, we reported that in the 250°C -300°C temperature interval the migration of С and O impurity atoms into the octahedral interstitial sites of the Mn 5 Ge 3 lattice leads t o the formation of the Nowotny phase Mn 5 Ge 3 C x O y , with a Curie temperature T C ~ 350 -400K when annealing Mn/Ge bilayers [14,15] and Ge/Ag/Mn trilayers [16]. However, EDS analysis ( Table 1) shows a preferential presence of oxygen, which indicates that Mn 5 Ge 3 and Nowotny Mn 5 Ge 3 O y are the main phases formed in the Mn/GeO bilayers after annealing up to 300°C.…”

“…For epitaxial Mn 5 Ge 3 C x films the Curie temperature increases with the carbon concentration and reaches a maximum T C = 460K at x ~ 0.6 -0.7 [13]. The homogeneous distribution of oxygen and carbon in Mn 5 Ge 3 films obtained in a vacuum of 10 -6 mbar suggests that the increase in the Curie temperature and magnetization is due to the migration of gas C and O impurities to the Mn 5 Ge 3 lattice and the formation of the Novotny phase of Mn 5 Ge 3 C x O y [14][15][16]. Experimental studies have shown that N, C and O impurities, which are present even in ultra-high vacuum, are embedded in the Mn 5 Ge 3 lattice during precipitation or annealing and increase the magnetic and electrical properties [17][18][19][20].…”