Neutron Diffraction Study Of Magnetic Order In Ndfe2al10

The orthorhombic compound NdFe2Al10 has been studied by powder and single- crystal neutron diffraction. Below TN = 3.9 K, the Nd3+ magnetic moments order in a double- k [k1 = (0, 3 4,0), k2 = (0, 1 4,0)] collinear magnetic structure, whose unit cell consists of four orthorhombic units in the b direction. The refinements show that this structure consists of (0 1 0) ferromagnetic planes stacked along b, in which the moments are oriented parallel to a (the easy anisotropy axis according to bulk magnetization measurements) and nearly equal in magnitude (similar to 1.7- 1.9 B). The alternating eight- plane sequence providing the best agreement to the data turns out to be that which yields the lowest exchange energy if one assumes antiferromagnetic near- neighbor exchange interactions with J1 J2, J3. With increasing similar to temperature, the single- crystal measurements indicate the suppression of the k2 component at T = 2.7 K, supporting the idea that the anomalies previously observed around 2- 2.5 K result from a squaring transition. In a magnetic field applied along the a axis, the magnetic Bragg satellites disappear at Hc = 2.45 T, in agreement with earlier measurements. Comparisons are made with related magnetic orders occurring in CeT2Al10 (T = Ru, Os) and TbFe2Al10.