μSR study of the triangular Ising antiferromagnet ErMgGaO4

Abstract

We present a detailed magnetic study of the triangular antiferromagnet ErMgGaO4. A point charge calculation under the single ion approximation reveals a crystal field ground state doublet with a strong Ising-like behavior of the Er 3+ moment along the c axis. Magnetic susceptibility and specific heat measurements indicate no presence of magnetic transitions above 0.5 K and no evidence of residual entropy as temperature approaching zero. Zero field (ZF) µSR measurements shows no sign of static uniform or random field and longitudinal field (LF) µSR measurements exhibit persistent spin fluctuations down to our lowest temperature of 25 mK. Our results provide evidence of a quantum spin liquid state in the triangular antiferromagnet ErMgGaO4.A quantum spin liquid (QSL) is a state of matter in which spins are highly entangled and do not show magnetic order down to zero temperature [1]. QSL's are of great current interest both from a fundamental physics point of view and for possible applications in quantum computation [2]. Geometrically frustrated magnets (where competing magnetic interactions cannot be simultaneously satisfied) are excellent candidate materials for QSL behavior since magnetic order is suppressed in them by the frustration [3][4][5]. Such frustration frequently arises from antiferromagnetically coupled spins located on triangle-based lattices (stacked triangular, kagome, pyrochlore), and can lead to a highly degenerate ground state without magnetic order. The previously studied quasi-two dimensional triangular layered material YbMgGaO 4 (with YbFe 2 O 4 -type structure) has been attracting considerable interest as a potential quantum spin liquid candidate [6][7][8][9][10][11][12].YbMgGaO 4 has a Curie-Weiss temperature of ∼ -4 K but shows no sign of long-range order down to 30 mK [6,7,9,10]. Its magnetic specific heat in zero field shows a broad hump at 2.4 K instead of sharp λ-type peak which would be expected for a well-defined second order phase transition. The magnetic excitation spectra appears as a broad continuum in inelastic neutron scattering measurements, which has been taken as an evidence for a QSL state [7,10]. Particularly, the anisotropic exchange interactions between rare earth ions are found to be playing a crucial role in stabilizing such spin liquid ground state [6-10], although an alternative explanantion in terms of the random Ga/Mg site mixing has also been proposed [11]. Such exchange interactions associated with spin orbit coupling strongly depends on rare earth ions. It has also been found, particularly, in rare earth pyrochlores (R 2 B 2 O 7 with R = rare earth, B = non-magnetic cation), that the interplay of exchange couplings, dipolar interactions, and single ion anisotropy leads to spin glasses [5,13], spin liquids [14-16], spin ices [17], order-by-disorder [18, 19], magnetic moment fragmentation [20,21], and conventional long-range magnetic ordering [22]. These observations indicating different rare earth ions can result in much different ground states, motivating the sea...

Crystal Synthesis and Frustrated Magnetism in Triangular Lattice CsRESe2 (RE = La–Lu): Quantum Spin Liquid Candidates CsCeSe2 and CsYbSe2

“…This feature was also found in other frustrated Dy compounds. , These suggest possible spin-glass state in CsDySe 2 . AC susceptibility of CsErSe 2 increases with lowering temperature down to 0.4 K. Similar behavior has been observed in the previously reported compounds, AErSe 2 (A = Na and K) and ErMgGaO 4 , , suggesting a possible spin liquid ground state.…”

Stripe antiferromagnetic ground state of ideal triangular lattice KErSe$_2$

“…Besides the Ce/Yb materials, Er based compounds are also attractive in the search for quantum magnetism and several compounds have already been discovered which seem promising. In ErMgGaO 4 there have been several reports of a possible QSL ground state with no apparent long-range order down to the lowest measured temperature [38,39]. Similarly, NaErSe 2 , KErSe 2 and CsErSe 2 all exhibit easy-plane magnetic anisotropy with no longrange magnetic order or spin freezing in heat capacity and magnetization measurements down to 0.42 K [27,40,41].…”

Synthesis, magnetization, and heat capacity of triangular lattice materials NaErSe2 and KErSe2

“…However, the existence of Ga/Mg disorders may drive the system to another state [32,36,37,[40][41][42][43]. Replacing Yb by Er also reveals possible QSL behavior [44,45]. This encourages research on rare earth materials with the ideal frustrated triangular structures.…”