Neutron diffraction study of magnetic order inNdFe2Al10

Abstract

The orthorhombic compound NdFe2Al10 has been studied by powder and single-crystal neutron diffraction. Below TN = 3.9 K, the Nd 3+ magnetic moments order in a double-k [k1 = (0,, 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 (≈ 1.7 − 1.9µB). The alternating 8-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 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.

Temperature-Dependent Cycloidal Magnetic Structure in GdRu2Al10Studied by Resonant X-ray Diffraction

“…Interestingly, the q value seems to start from nearly 0.75 just below T N1 = 17.5 K. Note that q ∼ 0.75 is a value commonly observed in other RT 2 Al 10 compounds such as NdFe 2 Al 10 and SmRu 2 Al 10 . 15,16) The similar result for GdRu 2 Al 10 seems to show that q ∼ 0.75 is the fundamental propagation vector of the RKKY interaction in the RT 2 Al 10 system. It is also noteworthy that the temperature dependence of the q value is very similar to that of the order parameter.…”

“…[12][13][14] In isostructural NdFe 2 Al 10 and SmRu 2 Al 10 , on the other hand, the magnetic structure is described by q = (0, 3/4, 0) and its third harmonic of (0, 1/4, 0), reflecting the squaring up. 15,16) The high-temperature phase of SmRu 2 Al 10 is an incommensurate phase with q = (0, 0.759, 0). There is also a case of q ≃ (0, 0.798, 0) as in TbRu 2 Al 10 .…”

Incommensurate-commensurate magnetic phase transition inSmRu2Al10

“…The magnetic structure found in NdFe 2 Al 10 , however, is a square-wave like structure described by double-q components, q 1 = (0, 3/4, 0) and q 3 = (0, 1/4, 0) = 3q 1 +τ 020 . 21 This is different from the simple antiferromagnetic arrangement of up and down moments in CeRu 2 Al 10 , and seems to reflect the real nature of the RKKY interaction in the RT 2 Al 10 (R=rare earth) compounds. A similar magnetic structure is also reported in TbFe 2 Al 10 , where the q-vector is (0, 4/5, 0).…”

“…8 is consistent with the magnetic structure factor of the ABABBABA arrangement, which is the same as that of NdFe 2 Al 10 . 21 In the ABABBABA arrangement, the Sm moments at the jth lattice point, µ 1/4,j and µ 3/4,j on the z = 1/4 and z = 3/4 layer, respectively, are written as …”

“…21, let us calculate and compare the exchange energies of the C-and IC-phase. We take 100 unit cells, corresponding to the magnetic unit cell of the IC-structure with q 1 = (0, 0.76, 0), calculate the total exchange energy, and convert it to the energy per four unit cells, corresponding to the magnetic unit cell of the C-phase.…”