  We investigated the magnetic phase diagram of single crystals of
SrNdFeO$_{4}$ by measuring the magnetic properties, the specific heat and the
dielectric permittivity. The system has two magnetically active ions, Fe$^{3+}$
and Nd$^{3+}$. The Fe$^{3+}$ spins are antiferromagnetically ordered below 360
K with the moments lying in the ab-plane, and undergo a reorientation
transition at about 35-37 K to an antiferromagnetic order with the moments
along the c-axis. A short-range, antiferromagnetic ordering of Nd$^{3+}$ along
the c-axis was attributed to the reorientation of Fe$^{3+}$ followed by a
long-range ordering at lower temperature [S. Oyama {\it et al.} J. Phys.:
Condens. Matter. {\bf 16}, 1823 (2004)]. At low temperatures and magnetic
fields above 8 T, the Nd$^{3+}$ moments are completely spin-polarized. The
dielectric permittivity also shows anomalies associated with spin configuration
changes, indicating that this compound has considerable coupling between spin
and lattice. A possible magnetic structure is proposed to explain the results.
