Neutron spectroscopic study of crystal field excitations in Tb₂Ti₂O₇ and Tb₂Sn₂O₇

Journal Article · Tue Apr 01 00:00:00 EDT 2014 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.89.134410· OSTI ID:1132958

Zhang, J. ^[1]; Fritsch, Katharina ^[1]; Hao, Z. ^[2]; Bagheri, B. V. ^[2]; Granroth, Garrett E ^[3]; Jiramongkolchai, P. ^[4]; Cava, R. J. ^[4]; Schiffer, P ^[5]; Gaulin, Bruce D. ^[1]

---

1. McMaster Univ., Hamilton, ON (Canada)
2. Univ. of Waterloo, Ontario (Canada)
3. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
4. Princeton Univ., Princeton, NJ (United States)
5. Penn State Univ., University Park, PA (United States)

We present time-of-flight inelastic neutron scattering measurements at low temperature on powder samples of the magnetic pyrochlore oxides Tb₂Ti₂O₇ and Tb₂Sn₂O₇. These two materials possess related, but different ground states, with Tb₂Sn₂O₇ displaying "soft" spin ice order below T_N approx 0.87 K, while Tb₂Ti₂O₇ enters a hybrid, glassy-spin ice state below T_g approx 0.2 K. Our neutron measurements, performed at T = 1.5 K and 30 K, probe the crystal field states associated with the J = 6 states of Tb³⁺ within the appropriate Fd3-barm pyrochlore environment. These crystal field states determine the size and anisotropy of the Tb³⁺ magnetic moment in each material's ground state, information that is an essential starting point for any description of the low temperature phase behavior and spin dynamics in Tb₂Ti₂O₇ and Tb₂Sn₂O₇. While these two materials have much in common, the cubic stanate lattice is expanded compared to the cubic titanate lattice. As our measurements show, this translates into a factor of approx 2 increase in the crystal field bandwidth of the 2J +1 = 13 states in Tb₂Ti₂O₇ compared with Tb₂Sn₂O₇. Our results are consistent with previous measurements on crystal field states in Tb₂Sn₂O₇, wherein the ground state doublet corresponds primarily to mJ = {vert_bar}+-5> and the first excited state doublet to mJ = {vert_bar}+-4>. In contrast, our results on Tb₂Ti₂O₇ differ markedly from earlier studies, showing that the ground state doublet corresponds to a significant mixture of mJ = {vert_bar}+-5>, mJ = {vert_bar}+-4> and mJ = {vert_bar}+-2>, while the first excited state doublet corresponds to a mixture of mJ = {vert_bar}+-4>, mJ = {vert_bar}+-5> and mJ = {vert_bar}+-1>. We discuss these results in the context of proposed mechanisms for the failure of Tb₂Ti₂O₇ to develop conventional long range order down to 50 mK.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1132958
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 89, Issue 13; ISSN 1098-0121
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS