  Multiferroics are a unique class of materials where magnetic and
ferroelectric orders coexist. The research on multiferroics contributes
significantly to the fundamental understanding of the strong correlations
between different material degrees of freedom and provides an energy-efficient
route toward the electrical control of magnetism. While multiple ABO3 oxide
perovskites have been identified as being multiferroic, their magnetoelectric
coupling strength is often weak, necessitating the material search in different
compounds. Here, we report the observation of room-temperature multiferroic
orders in multi-anion SrNbO3-xNx thin films. In these samples, the multi-anion
state enables the room-temperature ferromagnetic ordering of the Nb
d-electrons. Simultaneously, we find ferroelectric responses that originate
from the structural symmetry breaking associated with both the off-center
displacements of Nb and the geometric displacements of Sr, depending on the
relative O-N arrangements within the Nb-centered octahedra. Our findings not
only diversify the available multiferroic material pool but also demonstrate a
new multiferroism design strategy via multi-anion engineering.
