  Monoclinic Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ compound exhibits unusual
magnetic properties with different field induced magnetic transitions. The
deuteride is ferrimagnetic at low temperature and the Er and Fe sublattices
present magnetic transitions at different temperatures. The Er moments are
ordered below T$_{Er}$=55 K, whereas the Fe moments remain ferromagnetically
coupled up to T$_{M0}$ = 66 K. At T$_{M0}$ the Fe moments display a sharp
ferromagnetic-antiferromagnetic transition (FM-AFM) through an itinerant
electron metamagnetic (IEM) behaviour very sensitive to any volume change.
Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ becomes paramagnetic above T$_N$=125 K. The
pressure dependence of T$_{Er}$ and T$_{M0}$ have been extracted from magnetic
measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures
decrease linearly upon applied pressure with dT$_{Er}$/dP=-126 and dTM0/dP=-140
K.GPa$^{-1}$ for a field of B=0.03 T. Both magnetic Er and ferromagnetic Fe
order disappear at P=0.44(4) GPa. However, under a larger applied field B=5 T,
dT$_{M0}$/dP=-156 K.GPa$^{-1}$ whereas dT$_{Er}$/dP=-134 K.GPa$^{-1}$ showing a
weaker sensitivity to pressure and magnetic field. At 2 K the decrease of the
saturation magnetization under pressure can be attributed to a reduction of the
mean Er moment due to canting and/or crystal field effect. Above T$_{M0}$ the
magnetization curves display a metamagnetic behaviour from AFM to FM state,
which is also very sensitive to the applied pressure. The transition field
B$_{trans}$, which increases linearly upon heating, is shifted to lower
temperature upon applied pressure with dT=-17 K between 0 and 0.11 GPa. These
results show a strong decoupling of the Er and Fe magnetic sublattices versus
temperature, applied field and pressure.
