Competing magnetic and structural states in multiferroic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>YM</mml:mi><mml:msub><mml:mi mathvariant="normal">n</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>at high pressure

The magnetic, structural, and vibrational properties of $\mathrm{YM}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and $30\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, respectively. Application of high pressure, $P&gt;1\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector $q=(1/2,0,{q}_{z}\ensuremath{\sim}1/4)$ and appearance of the commensurate AFM phase with $q=(1/2,0,1/2)$. This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with $q=(1/2,0,1/4)$ found in other $R\mathrm{M}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ compounds upon lattice compression. At $P\ensuremath{\sim}16\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and $R$-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of $R\mathrm{M}{\mathrm{n}}_{2}{\mathrm{O}}_{5}$ compounds.