Neutron scattering studies of the spin-5/2 antiferromagnetic linear trimer substance SrMn₃P₄O₁₄

We studied the spin-5/2 antiferromagnetic (AF) linear trimer substance SrMn₃P₄O₁₄ using neutron powder diffraction and inelastic neutron scattering (INS) techniques. We determined the magnetic structure below T_N1 = 2.2(1) K. Ordered magnetic moments have x and z components. The angle between two neighboring moments in the trimer is 164 or 166° at 1.5 K, indicating that the intra-trimer (J₁) interaction is AF as expected. The propagation vector is expressed as k = [0, k_y, 0]. The value of k_y is 0.317 at 1.5 K, indicating an incommensurate magnetic structure. The value of k_y changes abruptly between 1.7 and 1.8 K and reaches values close to 0.33 above 1.8 K, indicating another phase transition at T_N2 = 1.75(5) K. We observed plural magnetic excitations. The peak positions are 0.46, 0.68 and 1.02 meV. Our INS results are consistent with those expected in the trimer model. We evaluated the J ₁ value as 0.29 meV (3.4 K).