  Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry
and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm
magnetism exhibiting complex magnetic behavior at low temperatures with four
consecutive magnetic phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich
magnetic phase diagram of this compound reflects the specific features of the
Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and
the first excited multiplet J = 7/2 in conjunction with strong crystal field
influence. Consequently, a significantly reduced Sm magnetic moment in
comparison with the theoretical Sm3+ free-ion value is observed. Despite the
strong neutron absorption by natural samarium and the small Sm magnetic moment
(~ 0.2 {\mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3,
0) of the phase existing in the temperature interval 12.5 - 4.3 K. This
observation classifies the SmPd2Al3 compound as a magnetically frustrated
system. The complex magnetic behavior of this material is further illustrated
by kinetic effects of the magnetization inducing rather complicated magnetic
structure with various metastable states.
