Pressure-induced crystallization of a spin liquid

Mirebeau, I.; Goncharenko, I. N.; Cadavez-Peres, P.; Bramwell, S. T.; Gingras, Michel J. P.; Gardner, J. S.

doi:10.1038/nature01157

Cited by 188 publications

(159 citation statements)

References 21 publications

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“…The obtained samples were ground into powder then annealed at 800 • C in air for one day. Another stoechiometric sample, synthesized in 2004 using a similar procedure 12 and previously studied with neutrons 34,35 was also measured for comparison.…”

Section: Methodsmentioning

confidence: 99%

Mesoscopic correlations inTb2Ti2O7spin liquid

et al. 2015

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We have studied the spin correlations with k= ( 1 2 , 1 2 , 1 2 ) propagation vector which appear below 0.4 K in Tb2Ti2O7 spin liquid by combining powder neutron diffraction and specific heat on Tb2+xTi2−xO7+y samples with x=0, 0.01, -0.01. The k= ( 1 2 , 1 2 , 1 2 ) order clearly appears on all neutron patterns by subtracting a pattern at 1.2(1) K. Refining the subtracted patterns at 0.07 K yields two possible spin structures, with spin-ice-like and monopole-like correlations respectively. Mesoscopic correlations involve Tb moments of 1 to 2 µB ordered on a length scale of about 20Å. In addition, long range order involving a small spin component of 0.1 to 0.2 µB is detected for the x= 0 and 0.01 samples showing a peak in the specific heat. Comparison with previous single crystals data suggests that the ( 1 2 , 1 2 , 1 2 ) order settles in through nanometric spin textures with dominant spin ice character and correlated orientations, analogous to nanomagnetic twins.Rare earth pyrochlores with geometrical magnetic frustration are model compounds to investigate classical spin ice as well as quantum spin ice physics. The short range ordered ground states with large degeneracy give rise to a large variety of interesting phenomena such as magnetic monopoles 1,2 , first order transition 3 , or unconventional magnetoelastic excitations 4,5 . These frustrated ground states are highly sensitive to small perturbations and to the presence of defects. Already in the 80s, Villain 6 predicted that for an arbitrary small concentration of defects the spinel lattice with pyrochlore structure could switch its ground state from spin liquid to spin glass. More recently many studies focus on the role of a minute amount of defects in pyrochlores. The crystal structure of R 2 Ti 2 O 7 pyrochlores (where R 3+ is a rare earth ion, Ti 4+ is non magnetic) accommodates oxygen vacancies, small off-stoechiometries in the R 3+ or Ti 4+ lattice, "stuffing" or site inversion. Oxygen vacancies introduce Ti 3+ defects instead of Ti 4+ ions, modifying the R 3+ crystal field and inducing local distortions, with various consequences on the low temperature magnetic properties and spin ice physics. In classical spin ice Dy 2 Ti 2 O 7 , oxygen depletion or a low level Dy stuffing in the Ti sites strongly slows down the monopole dynamics at very low temperature 7,8 and affects the nonequilibrium macroscopic properties 9,10 . In the quantum spin ice Yb 2 Ti 2 O 7 , small off-stoechiometry clearly affects the magnetic ground state 11 . It appears that precise studies of the magnetic defects are needed to resolve controversies concerning these unconventional ground states.Among the pyrochlores, Tb 2 Ti 2 O 7 is one of the most complex, the subject of numerous investigations since the discovery of its spin liquid character in 1999. The Tb 3+ short range correlated moments fluctuate 12 down to 20 mK at the time scale of the muon probe (10 −6 s). The origin of these fluctuations has been highly debated [13][14][15][16][17][18] . Several mechanisms have been pr...

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Section: Methodsmentioning

confidence: 99%

Mesoscopic correlations inTb2Ti2O7spin liquid

et al. 2015

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“…In fact, the application of high pressure to the spin liquid Tb 2 Ti 2 O 7 induces LRO. 17 Furthermore, the application of pressure on the MIT in pyrochlore oxides stabilizes it to a metallic state; the negative pressure dependence of the transition temperature (T MI ) has been observed in Cd 2 Os 2 O 7 (T MI = 226 K) 12 and Hg 2 Ru 2 O 7 (T MI = 107 K). 18 In particular, for Hg 2 Ru 2 O 7 , a Fermi liquid with an enhanced mass is realized above 6.5 GPa.…”

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Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B

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We report the pressure dependence of electrical resistance R(T) of a frustrated pyrochlore oxide Nd 2 Ir 2 O 7 , which shows a second-order metal-insulator transition (MIT) at 36 K. This MIT is monotonically suppressed by the application of pressure. The insulating phase disappears at around 10 GPa. Then, in the pressure-induced metallic state above 10 GPa, a new pressure-induced phase transition emerges at around 3 K, which is characterized by a resistance drop. The new phase transition is due to a ferromagnetic (FM) ordering, which is suggested to be an ordered spin ice (two-in two-out) state of the Nd moment via the RKKY interaction. We succeeded in observing the phase competition between the MIT and the FM ordering by the application of high pressure. Geometrical frustration in a magnetic material can lead to novel phenomena such as a macroscopic degeneracy in the ground state with no long-range ordering (LRO). Pyrochlore oxides A 2 B 2 O 7 have attracted great interest because their structure, 1 which includes corner-shared tetrahedra whose vertices are occupied by spins, may show a strong geometrical frustration such as spin ice 2,3 and spin liquid states. 4 Furthermore, in metallic pyrochlore oxides, a frustration originating from the pyrochlore lattice might also lead to novel types of electronic properties. In fact, 4d and 5d transition-metal pyrochlore oxides have been reported to show various transport properties such as superconductivity in Cd 2 Re 2 O 7 5 and AOs 2 O 6 (where A = K, Rb, and Cs), 6 15 The strongly frustrated state can be relieved by the application of a magnetic field and pressure. Applying a magnetic field is the easiest method to lower the symmetry of the system. Actually, the application of a magnetic field in the [111] direction to the spin ice state induces a Kagomé ice state, where the macroscopic degeneracy is partially reduced. 16 On the other hand, applying pressure is an effective method to drive more dramatic change in various physical parameters such as magnetic interactions, bandwidth, and electron correlations. In fact, the application of high pressure to the spin liquid Tb 2 Ti 2 O 7 induces LRO. 17 Furthermore, the application of pressure on the MIT in pyrochlore oxides stabilizes it to a metallic state; the negative pressure dependence of the transition temperature (T MI ) has been observed in Cd 2 Os 2 O 7 (T MI = 226 K) 12 and Hg 2 Ru 2 O 7 (T MI = 107 K). 18 In particular, for Hg 2 Ru 2 O 7 , a Fermi liquid with an enhanced mass is realized above 6.5 GPa. 18 Thus, the application of pressure to the strongly frustrated state can lead to a novel phase.A recent study on pyrochlore iridates Ln 2 Ir 2 O 7 has revealed the occurrence of MITs for Ln = Nd, Sm, and Eu at T MI of 36, 117, and 120 K, respectively. 19 These MITs are second-order transitions and involve a magnetic anomaly caused by 5d electrons from Ir 4+ . It should be noted that T MI increases with decreasing the ionic radius of Ln 3+ . Furthermore, the electrical conductivity of the iridates also depends ...

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“…Another theoretical construct that attempts to account for the lack of static order in Tb 2 Ti 2 O 7 is a quantum spin ice state [11][12][13][14][15]. A third proposed scenario is that the non-Kramers doublet ground state of Tb 2 Ti 2 O 7 is split into two non-magnetic singlets through a symmetry reducing structural distortion [16][17][18].Other studies sought to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 by focusing on mechanisms of its destruction, such as: external pressure [19], magnetic fields [18,20,21], and a combination of the two [22]. Partial antiferromagnetic order is induced in Tb 2 Ti 2 O 7 with external hydrostatic pressures of 8.6 GPa, resulting in a 1% compression of the lattice [19].…”

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Incipient Ferromagnetism inTb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin-L

et al. 2014

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The origin of the spin liquid state in Tb2Ti2O7 has challenged experimentalists and theorists alike for nearly 20 years. To improve our understanding of the exotic magnetism in Tb2Ti2O7, we have synthesized a chemical pressure analog, Tb2Ge2O7. Germanium substitution results in a lattice contraction and enhanced exchange interactions. We have characterized the magnetic ground state of Tb2Ge2O7 with specific heat, ac and dc magnetic susceptibility, and polarized neutron scattering measurements. Akin to Tb2Ti2O7, there is no long-range order in Tb2Ge2O7 down to 20 mK. The Weiss temperature of −19.2(1) K, which is more negative than that of Tb2Ti2O7, supports the picture of stronger antiferromagnetic exchange. Polarized neutron scattering of Tb2Ge2O7 reveals that at 3.5 K liquid-like correlations dominate in this system. However, below 1 K, the liquid-like correlations give way to intense short-range ferromagnetic correlations with a length scale related to the Tb-Tb nearest neighbor distance. Despite stronger antiferromagnetic exchange, the ground state of Tb2Ge2O7 has ferromagnetic character, in stark contrast to the pressure-induced antiferromagnetic order observed in Tb2Ti2O7.Geometrically frustrated pyrochlores, R 2 M 2 O 7 , exhibit a diverse array of exotic magnetic behaviors [1]. The ground states in these materials are dictated by a complex, and often delicate balance of exchange, dipolar, and crystal field energies. Tb 2 Ti 2 O 7 is one of the most remarkable of these frustrated pyrochlores; strong antiferromagnetic exchange and Ising-like spins led to predictions of an antiferromagnetic Néel state below ∼1 K for this material [2]. However, experimental studies revealed a lack of static order or spin freezing in Tb 2 Ti 2 O 7 down to 70 mK [3,4], and more recently 57 mK [5]. Subsequently, enormous efforts have been undertaken to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 .A further complication in Tb 2 Ti 2 O 7 is the coupling of magnetic and lattice degrees of freedom [6][7][8][9]. It has been suggested that hybridized magnetoelastic excitations may be responsible for the suppression of magnetic order in Tb 2 Ti 2 O 7 [10]. Another theoretical construct that attempts to account for the lack of static order in Tb 2 Ti 2 O 7 is a quantum spin ice state [11][12][13][14][15]. A third proposed scenario is that the non-Kramers doublet ground state of Tb 2 Ti 2 O 7 is split into two non-magnetic singlets through a symmetry reducing structural distortion [16][17][18].Other studies sought to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 by focusing on mechanisms of its destruction, such as: external pressure [19], magnetic fields [18,20,21], and a combination of the two [22]. Partial antiferromagnetic order is induced in Tb 2 Ti 2 O 7 with external hydrostatic pressures of 8.6 GPa, resulting in a 1% compression of the lattice [19]. Another means of destroying the spin liquid state is chemical pressure: substitution of the non-magnetic titanium cation for an iso-electronic cation w...

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Pressure-induced crystallization of a spin liquid

Cited by 188 publications

References 21 publications

Mesoscopic correlations inTb2Ti2O7spin liquid

Mesoscopic correlations inTb2Ti2O7spin liquid

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B

Incipient Ferromagnetism inTb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin-L

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Pressure-induced crystallization of a spin liquid

Cited by 188 publications

References 21 publications

Mesoscopic correlations inTb2Ti2O7spin liquid

Mesoscopic correlations inTb2Ti2O7spin liquid

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2OSakata1, Kagayama2, Shimizu3 et al. 2011Phys. Rev. B

Incipient Ferromagnetism inTb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin-L

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Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O
Sakata
¹
,
Kagayama
²
,
Shimizu
³

et al. 2011
Phys. Rev. B