Phase transformations in the Mn-Ge system and in Ge x Mn1 − x diluted semiconductors

Solid-state synthesis, structural and magnetic properties of CoPd films

“…For example, solid state reactions in Pt/Co [39], Cu/Au [40], and Pd/Fe [41] films start at the order-disorder transition temperatures in the Pt-Co, Cu-Au, and Pd-Fe systems, whereas in Ni/Ti [42], Au/Cd [43], Al/Ni [44,45], and Mn/Fe [46] films, these reactions start at the reverse martensitic transition temperatures A s in the Ni-Ti, Au-Cd, Al-Ni, and Mn-Fe systems, respectively. This rule also holds true for other struc tural transformations [47][48][49][50][51][52][53]. On this basis, we can assume the existence of a structural phase transition at a temperature of ~400°C in the region of the equi atomic composition of the Co-Pd system.…”

“…In [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53], it was shown that solid state reactions in bilayer thin films start at minimum temperatures T K of the solid phase structural transformation of the first phase (T in = T K ) formed in the reaction products. For example, solid state reactions in Pt/Co [39], Cu/Au [40], and Pd/Fe [41] films start at the order-disorder transition temperatures in the Pt-Co, Cu-Au, and Pd-Fe systems, whereas in Ni/Ti [42], Au/Cd [43], Al/Ni [44,45], and Mn/Fe [46] films, these reactions start at the reverse martensitic transition temperatures A s in the Ni-Ti, Au-Cd, Al-Ni, and Mn-Fe systems, respectively.…”

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

“…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].…”