Magnetic order, magnetic correlations, and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7

Abstract

Er2Ti2O7 is believed to be a realization of an XY antiferromagnet on a frustrated lattice of corner-sharing regular tetrahedra. It is presented as an example of the order-by-disorder mechanism in which fluctuations lift the degeneracy of the ground state, leading to an ordered state. Here we report detailed measurements of the low temperature magnetic properties of Er2Ti2O7, which displays a second-order phase transition at TN ≃ 1.2 K with coexisting short-and long-range orders. Magnetic-susceptibility studies show that there is no spin-glass-like irreversible effect. Heatcapacity measurements reveal that the paramagnetic critical exponent is typical of a 3-dimensional XY magnet while the low-temperature specific heat sets an upper limit on the possible spin-gap value and provides an estimate for the spin-wave velocity. Muon spin relaxation measurements show the presence of spin dynamics in the nanosecond time scale down to 21 mK. This time range is intermediate between the shorter time characterizing the spin dynamics in Tb2Sn2O7, which also displays long-and short-range magnetic order, and the time scale typical of conventional magnets. Hence the ground state is characterized by exotic spin dynamics. We determine the parameters of a symmetry-dictated Hamiltonian restricted to the spins in a tetrahedron, by fitting the paramagnetic diffuse neutron scattering intensity for two reciprocal lattice planes. These data are recorded in a temperature region where the assumption that the correlations are limited to nearest neighbors is fair.

Holographic antiferromagnetic quantum criticality andAdS2scaling limit

“…The detailed measurements of the low-temperature magnetic properties of compound and the analysis of these experimental data leads to the conclusion that the ground state is characterized by exotic spin dynamics [36,37], which is vanishing at the Néel's temperature, T N ¼ 1.2 K, via a second-order phase transition. There the co-existence of both the short-and long-range orders has been suggested.…”

“…The local crystal field (CF) of a trigonal D 3d point symmetry at the erbium sites splits the 16-fold degenerate state into eight doublets. Considering the sum of all these spin doublets associated with the single ion as a single total spin we note that these total spins are ordered in noncoplanar structure on the vertex-sharing tetrahedra [36,37]. The compound has a strong local XY-type anisotropy of magnetic moments arising due to the large orbital momentum of Er 3þ ions, L ¼ 6.…”

“…In spite on the crystal anisotropy both phase diagrams are similar to each other. Muon spin relaxation measurements show the presence of spin dynamics in the nanosecond time scale down to 21 mK, that also illustrates the long-and short-range magnetic order, and the time scale not typical of conventional magnets [37]. Therefore, we will be interested to test the predictions of our holographic model to describe such exotic AF state, which is difficult to characterize by any other and conventional means.…”

“…To understand the role of magnetic frustrations in establishing long-range order is now one of the main challenges of condensed matter physics. They play probably an important role in the formation of the nontrivial antiferromagnetic non-coplanar structure observed [36,37].…”

Phase Competition in the Palmer-Chalker XY Pyrochlore Er2Pt2O<

“…Given that the lattice parameter of Er 2 Pt 2 O 7 differs by less then 0.5% from its titanate analog, it is surprising that the transition temperature is so substantially reduced. This dramatic reduction in T N occurs despite minimal structural modifications and a larger Curie-Weiss [12], Er2Ti2O7 [13], and Er2Pt2O7, filled in circles from [14] and open circles from our study. The latter two samples magnetically order with TN = 1.4 K and 1.2 K, respectively.…”