Magnetic structure ofYb2Pt2Pb: Ising moments on the Shastry-Sutherland lattice

Abstract

Neutron diffraction measurements were carried out on single crystals and powders of Yb 2 Pt 2 Pb, where Yb moments form two interpenetrating planar sublattices of orthogonal dimers, a geometry known as ShastrySutherland lattice, and are stacked along the c axis in a ladder geometry. Yb 2 Pt 2 Pb orders antiferromagnetically at T N = 2.07 K, and the magnetic structure determined from these measurements features the interleaving of two orthogonal sublattices into a 5 × 5 × 1 magnetic supercell that is based on stripes with moments perpendicular to the dimer bonds, which are along (110) and (−110). Magnetic fields applied along (110) or (−110) suppress the antiferromagnetic peaks from an individual sublattice, but leave the orthogonal sublattice unaffected, evidence for the Ising character of the Yb moments in Yb 2 Pt 2 Pb that is supported by point charge calculations. Specific heat, magnetic susceptibility, and electrical resistivity measurements concur with neutron elastic scattering results that the longitudinal critical fluctuations are gapped with E 0.07 meV. DOI: 10.1103/PhysRevB.93.104419 Much attention is focused on coupled spin-dimer systems, where frustrated magnetic interactions can lead to spin liquid ground states [1,2]. The Shastry-Sutherland lattice (SSL), consisting of planes of orthogonal dimers with intradimer exchange J and interdimer exchange J , is of particular interest as it has been exactly solved [3] to show that the ground state is ordered antiferromagnetically (AF) for J /J less than a critical value (J /J ) C and otherwise has a singlet ground state with gapped magnetic excitations. Insulating SrCu 2 (BO 3 ) 2 is an example of the SSL dimer liquid ground state [4][5][6]. Here, frustrated exchange interactions tend to localize singlet and triplet dimers into complex ordered superstructures at high fields [7][8][9], resulting in quantized plateaus in the magnetic field B dependence of the magnetization M(B) [10][11][12].Most SSL systems are magnetically ordered, where the closure of the singlet dimer gap yields a nonzero magnetization that makes AF order possible even for B = 0. The metallic RB 4 (R = Ho,Er,Tm,Tb) compounds order AF with period-doubling Néel ground states with Ising-like moments oriented perpendicular to the SSL planes [13][14][15][16]. In metallic The neutron diffraction measurements presented here demonstrate that the in-plane Ising-like Yb moments in Yb 2 Pt 2 Pb have a remarkably complex magnetic structure, with a commensurate superlattice of ordered stripes consisting of moment-bearing and magnetically compensated Yb pairs with moments perpendicular to the (110) and (−110) dimer bonds. The magnetic cell contains 200 Yb atoms, whose Ising character results in the formation of two independent and orthogonal sublattices that are separately polarized by magnetic fields along either (110) or (−110). The persistence of AF order in the surviving AF sublattice shows that the two orthogonal bonds of the B = 0 SSL are effectively decoupled in magnetic field, leading to a un...

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

“…However, we find that the absolute value of the resistivity parallel to the chains is markedly smaller than the one perpendicular to them due to the one dimensional character of the spin excitations. This agrees with the experimental measurements for Yb 2 Pt 2 Pb, which show an anisotropic resistivity linear in T at intermediate magnetic fields [13,15]. arXiv:1712.01884v2 [cond-mat.str-el] 19 Mar 2018 2 Model The neutron-scattering experiments in Yb 2 Pt 2 Pb can be described by a model of weaklyinteracting, anisotropic spin S=1/2 chains [12] in terms of exact expressions of the XXZ spin-1/2 chain Hamiltonian with moderate Ising anisotropy leading to a small excitation gap ∆.…”

“…Here, we will study the situation when this gap closes due to an external magnetic field and the spins enter a Luttinger liquid phase. Due to the dipolar origin of the interchain coupling its effect in the absence of order becomes negligible [13,15]. The low-energy spin-spin correlation functions take a universal form and do not depend on the exact microscopic model.…”

Synthesis and crystal structure of La21Cr8−2a Al b Ge7−b C12 [a = 0.22 (2) and b = 0.758 (19)]

“…In the simplest case, this phenomenon occurs when three antiferromagnetic exchange-coupled Ising spins are arranged on the vertices of an equilateral triangle, their counterbalanced interactions thereby precluding the transition to mutually energetically favorable magnetic order. The ability to tune the onset of order via geometric frustration has been shown to lead to a variety of intriguing properties, including magnetic monopoles (Pan et al, 2016), spin ice states (Hirschberger et al, 2015;Huang et al, 2016), tricritical phenomena (McNally et al, 2015), and quantum criticality (Miiller et al, 2016), with applications ranging from neural networks (Grass et al, 2016), to quantum computing (Katzgraber et al, 2015), to unconventional superconductivity (Glasbrenner et al, 2015). Over the last decades, a class of materials known as pyrochlores has provided a rich ground for studying magnetic frustration due to geometric degeneracies arising from their vertex-linked, regular tetrahedral building blocks (Gardner et al, 2010).…”

Spinon confinement and a sharp longitudinal mode in Yb2Pt2Pb in magnetic fields

“…It is clear that the XXZ Hamiltonian (1) is an appropriate description for Yb 2 Pt 2 Pb despite the large and orbitally dominated moment of the Yb ions. Due to their Kramers doublet ground state of almost pure |J, m J = |7/2, ±7/2 , the Yb moments have a pseudospin S = 1/2 character [26,29]. Rather than quenching the quantum spin dynamics, the strong Ising magnetic anisotropy imposed by the crystal electric field acting on the f −orbital wave function instead singles out the longitudinal excitation channel in two orthogonal sublattices of 1D chains with moments oriented along the (110) and (110) crystal directions.The essential features of the quantum continuum can be understood by noting that each spinon carries spin 1/2, and so the angular momentum selection rules dictate that neutron scattering in Yb 2 Pt 2 Pb measures two-spinon states where the total spin is zero, with one spinon in each spin state, ±1/2.…”

“…In zero field, there is a five by five periodicity to the order in the tetragonal a − b plane, evidenced by neutron diffraction peaks that index as q HH = 0.2 rlu [ Fig. 4(A)] [29]. When the gap ∆ S closes at µ 0 H = 0.5 T, those peaks move from q L = 1 rlu to incommensurate positions along q L [Fig.…”