  At ambient pressure (P) and below 5.5 K, olivine-type Mn2GeO4 hosts a
multiferroic (MF) phase where a multicomponent, i.e., multi-k magnetic order
generates spontaneous ferromagnetism and ferroelectricity (FE) along the c
axis. Under high P the FE disappears above 6 GPa, yet the P evolution of the
magnetic structure remained unclear based on available data. Here we report
high P single crystal neutron diffraction experiments in theMF phase at T = 4.5
K.We observe clearly that the incommensurate spiral component of the magnetic
order responsible for FE varies little with P up to 5.1 GPa. With support from
high P synchrotron x-ray diffraction measurements at room temperature (T), the
P driven suppression of FE is proposed to occur as a consequence of a crystal
structure transition away from the olivine structure. In addition, in the low T
neutron scattering experiments an emergent nonhydrostatic P component, i.e., a
uniaxial stress, leads to the selection of certain multi-k domains. We use this
observation to deduce a double-k conical magnetic structure for the ambient P
ground state, this being a key ingredient for a model description of the MF
phase.
