Evolution of incommensurate spin order with magnetic field and temperature in the itinerant antiferromagnet GdSi

Abstract

GdSi exhibits spin-density-wave (SDW) order arising from the cooperative interplay of sizeable local moments and a partially nested Fermi sea of itinerant electrons. Using magnetotransport, magnetization, and nonresonant magnetic x-ray diffraction techniques, we determine the H-T phase diagrams of GdSi for magnetic fields up to 21 T, where antiferromagnetic order is no longer stable, and field directions along each of the three major crystal axes. While the incommensurate magnetic ordering vector that characterizes the SDW is robust under magnetic field, the multiple spin structures of this compound are highly flexible and rotate relative to the applied field via either canting or spin-flop processes. The antiferromagnetic spin densities always arrange themselves transverse to the applied magnetic field direction. The phase diagrams are delineated by two types of phase boundaries: one separates a collinear from a planar spin structure associated with a lattice structural transition, and the other defines a spin flop transition that is only weakly temperature dependent. The major features of the phase diagrams along each of the crystal axes can be explained by the combination of local moment and global Fermi surface physics at play.

Linear magnetoresistance in the low-field limit in density-wave materials

“…1 detailed ρ ( T , H ) data on the density-wave systems GdSi, SrAl 4 , and Cr, in addition to comparisons to NbSe 3 and (PO 2 ) 4 (WO 3 ) 8 derived from the literature. GdSi and Cr have SDWs driven by Fermi surface nesting with Néel transitions at T N = 54.5 and 311.5 K, respectively (14–18). SrAl 4 develops a CDW state below T CDW = 245 K (19), with no confounding contributions from spin order.…”

“…SrAl 4 develops a CDW state below T CDW = 245 K (19), with no confounding contributions from spin order. All of the SDW and CDW ordering wave vectors are incommensurate: Q ∼ (0, 0.483, 0.092) in GdSi (14–16), Q ∼ (0.952, 0, 0) in Cr (18), and Q ∼ (0, 0, 0.11) in SrAl 4 (19). GdSi turns into a field-induced ferromagnet at H c = 20.7 T (15), while the SDW in Cr extends to beyond 16 T (17).…”

“…Black solid and dashed lines are even-parity linear (∼| H |) and quadratic fits to the data, respectively. GdSi undergoes a first-order spin-flip transition at ∼3 T for both H||a and H||c (15). Hence we focus on its MR behavior under the H||b geometry where the spin canting under field is continuous.…”

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

“…A similar temperature dependence of the q vector has also been reported in GdSi, GdNi 2 B 2 C, and GdPd 2 Al 3 . [29][30][31][32] Note that when the magnetic anisotropy is taken into account, the temperature dependence of the q vector becomes more complicated, as observed in rare-earth metals. 26) When there is a uniaxial anisotropy, a squaring up occurs and the third harmonic peak develops with decreasing temperature.…”

Helical Ordering of Spin Trimers in a Distorted Kagome Lattice of Gd3Ru4Al12Studied by Resonant X-ray Diffraction

“…20) The temperature dependence of q below T 1 is similar to that of the magnetic order parameter, which implies that the development of the order parameter causes a modification in the RKKY interaction and changes the resultant q value. 21,25,26) In summary, we have performed resonant X-ray diffraction experiment on Gd 3 Ru 4 Al 12 with a distorted kagome lattice of Gd, where successive antiferromagnetic transitions of spin trimer, composed of ferromagnetically coupled S =7/2 spins, have been suggested. We constructed a model structure using the irreducible representation of the observed propagation vector q = (0.27, 0, 0), so that the trimer formation and the results of polarization analysis are explained consistently.…”