Double symmetry breaking in TmFe4Ge2 compared to RFe4Ge2 (R=Y, Lu, Er, Ho, Dy) magnetic behaviour

作者：Schobinger Papamantellos P^*; Buschow K H J; Rodriguez Carvajal J

来源：Journal of Magnetism and Magnetic Materials, 2014, 355: 104-120.

DOI：10.1016/j.jmmm.2013.11.020

• Magnetic structure
• Neutron diffraction
• Rare earth alloy
• Magnetoelastic transition

TmFe4Ge(2) undergoes a double magneto-elastic first order transition at T-N,T-C where the high temperature (HT) tetragonal phase disproportionate into two distinct orthorhombic low temperature (LT) phases with commensurate and incommensurate magnetic wave vectors respectively:
P4(2)/mnm (HT) T-N, T-C -> Cmmm q(1) = (0, 1/2, 0) + Pnnm (q(2) = (0, q(y), 0), q(y) approximate to 2/11(LT)
Neutron diffraction shows the relative portions of the LT Cmmm and Pnnm competing phases change linearly with T. The amount of the majority IIT phase Nom (54% at 30 K) decreases linearly to 30% clown to 10 K in favour of the Cmmm phase that dominates the range 26-1.5 K. The Tm moments point along the c-axis in both phases while the Fe moments have canted arrangements. The mu(Tm) = 3.54(3) mu(B)/atom at 15 K is strongly reduced below the Tm3+ free ion value g(J)J = 7 mu(B) for the q(1) phase. The q(2) phase corresponds to a 3D canted sinusoidal arrangement. The results are summarised on a phase diagram and compared to the findings in RFe4Ge2 (R = Y, Lu, Er, Ho, Dy) that are reviewed. The multitude of transition paths occurring in those systems arise from the competing magnetoelastic mechanisms involving the R-crystal field anisotropy, the exchange interactions R-R, R-Fe, Fe-Fe of the two sublattices and their coupling to the lattice strain. The geometrical frustration emerging from the compact tetrahedral Fe arrangement with antiferromagnetic interactions leads to 2D and 3D canted, incommensurate and nonmagnetic states. The Cmmm transition is triggered by dominating R-R and R-Fe interactions becoming stronger at LT while the Pnnm phase is promoted by Fe-Fe and R-Fe interactions that prevail at HT. Included is also the magnetic structure of the ferromagnetic impurity phase Fe3Ge.

• 出版日期2014-4