The magnetic system of the Mn1−xFexGe solid solution is ordered in a spiral spin structure in the whole concentration range of x ∈ [0 ÷ 1]. The close inspection of the small-angle neutron scattering data reveals the quantum phase transition from the long-range ordered (LRO) to short range ordered (SRO) helical structure upon increase of Fe-concentration at x ∈ [0.25 ÷ 0.4]. The SRO of the helical structure is identified as a Lorentzian contribution, while LRO is associated with the Gaussian contribution into the scattering profile function. The scenario of the quantum phase transition with x as a driving parameter is similar to the thermal phase transition in pure MnGe. The quantum nature of the SRO is proved by the temperature independent correlation length of the helical structure at low and intermediate temperature ranges with remarkable decrease above certain temperature TQ. We suggest the x-dependent modification of the effective RudermanKittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism to explain the quantum critical regime in Mn1−xFexGe. The cubic B20-type compounds (MnSi, etc) are well known for the incommensurate magnetic structures with a very long period appeared due to noncentrosymmetric arrangement of magnetic atoms. It is widely recognized that the helix spin structure is built on the hierarchy of interactions: ferromagnetic exchange interaction, antisymmetric Dzyaloshinskii-Moryia interaction (DMI), and the anisotropic exchange interaction [1,2]. It is also known that the substitution of manganese by iron in the isostructural solid solutions Mn 1−x Fe x Si suppresses the helical spin state [3]. The neutron scattering studies [4,5] together with magnetic data and specific heat measurements [3,6,7] discovered a quantum critical point (QCP) corresponding to the suppression of the spin spiral phase with long-range order (LRO) in Mn 1−x Fe x Si. This QCP located at x c1 ≈ 0.11 − 0.12 is, however, hidden by a short-range order of the spin helix (SRO) [5][6][7] that agrees well with the theoretical models [8,9]. This SRO phase, sometimes referred as chiral spin liquid [8], which is destroyed at the second QCP x c2 ≈ 0.24. Thus it has been shown that Mn 1−x Fe x Si undergoes a sequence of the two quantum phase transitions [7].The real breakthrough in understanding of the experimental facts mentioned above has been done via scrutinizing the Hall effect in Mn 1−x Fe x Si [10]. It was found that the substitution of Mn with Fe results rather in the hole doping opposite to the natural expectations on the electron doping. The two groups of the charge carriers contribute to the Hall effect and the ratio between them changes the sign of the Hall effect constants at x c1 ≈ 0.11, what is definitely associated with the QCP in these compounds. Despite the fact that the solid solutions of Mn 1−x Fe x Si are often considered as itinerant magnets [8,9], recent magnetic resonance and magnetoresistance studies [11,12] favor the alternative explanation based on the Heisenberg localized magn...