Multiple transition phenomena in divalent Eu compound EuAl4 with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of TCDW = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector qCDW ¼ ð0; 0; δcÞ with δc ∼ 0.19. In contrast, magnetic peaks appear at q2 ¼ ðδ2; δ2; 0Þ with δ2 = 0.085 in a magnetic-ordered phase at 13.5 K below TN1 = 15.4 K. By further cooling to below TN3 = 12.2 K, the magnetic ordering vector changes into q1 ¼ ðδ1; 0; 0Þ with δ1 = 0.17 at 11.5 K and slightly shifts to δ1 = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at TN2 = 13.2 K and TN4 = 10.0 K. The structural modulation below TCDW with qCDW is characterized by the absence of the superlattice peak in the (0 0 l) axis. As a similar CDW transition was observed in SrAl4, the structural modulation with qCDW could be mainly ascribed to the displacement of Al ions within the tetragonal ab-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa4. This could stem from different electronic structures with the CDW transition between two compounds.
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