Evidence for two distinct spin relaxation mechanisms in  hot  spin ice Ho2Ti2O7

Ehlers, Georg; Cornelius, A. L.; Fennell, T.; Koza, Michael Marek; Bramwell, S. T.; Gardner, J. S.

doi:10.1088/0953-8984/16/11/010

Cited by 88 publications

(108 citation statements)

References 32 publications

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“…Our magnetic neutron diffraction experiments indicate that below a magnetic ordering temperature of 1.6 K, the magnetic unit cell is comprised of eight formula units, with the magnetic spins ordered in a spiral arrangement along the four-fold symmetry axis of the tetragonal cell. We find no evidence of strong magnetic frustration in the magnetization, but the ac susceptibility reveals two possible spin relaxation mechanisms, similar to what is observed in Ho 2 Ti 2 O 7 [12].…”

Section: Introductionsupporting

confidence: 78%

“…7). However, as we will show below, the low temperature ac susceptibility data of Ho 2 Ge 2 O 7 display signatures of spin freezing resembling the behavior observed in the spin ice system Dy 2 Ti 2 O 7 [10][11] and Ho 2 Ti 2 O 7 [12].…”

Section: Resultssupporting

confidence: 55%

“…Although the anisotropic magnetic dc susceptibility has been previously reported [6], no field-dependent measurements exist to date. In addition, the spin freezing that has been observed in the isotypical systems R 2 Ti 2 O 7 for R = Dy [10][11] or Ho [12][13], in which the Ising character of Ho and Dy and the crystal field are critical to the observed spin relaxations, motivated us to perform a study of the frequency-and field-dependent anisotropic ac susceptibility in Ho 2 Ge 2 O 7 . In the present study we confirm and further characterize the highly anisotropic magnetic properties.…”

Section: Introductionmentioning

confidence: 99%

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Structure and magnetic properties of theHo2Ge2O7pyrogermanate

et al. 2008

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We report the anisotropic magnetic properties of Ho 2 Ge 2 O 7 determined from dc and ac magnetization, specific heat and powder neutron diffraction experiments. The magnetic lanthanide sublattice, seen in our refinement of the tetragonal pyrogermanate crystal structure, is a right-handed spiral of edge-sharing and corner-sharing triangles; the local Ho-O coordination indicates that the crystal field is anisotropic. Susceptibility and magnetization data indeed show that the magnetism is highly anisotropic, and the magnetic structure has the Ho moments

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Section: Introductionsupporting

confidence: 78%

Section: Resultssupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

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Structure and magnetic properties of theHo2Ge2O7pyrogermanate

et al. 2008

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“…Examples of observed phenomenology include spin ice [1], spin glass [2,3], and spin liquid [4] behaviors as well as long-range magnetic order [5,6,7,8,9,10,11] and perhaps some novel type of hidden order [12]. A common trend observed in all of these systems is an apparent persistence of spin dynamics down to the lowest temperatures as revealed by muon spin relaxation (µSR) [3,4,7,8,9,11,12], Mössbauer spectroscopy [13] and neutron spin echo [1] experiments. The origin of persistent spin dynamics (PSDs) is a major open question in the study of highly frustrated insulating magnetic oxide materials [5].…”

mentioning

confidence: 99%

Evidence for Gapped Spin-Wave Excitations in the FrustratedGd2Sn2O7Pyrochlore Antiferromagnet from Low-Temperature Specific Heat Measurements

et al. 2007

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We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low-energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material.In the insulating R 2 M 2 O 7 magnetic pyrochlores, the rare-earth ions (R 3+ ) sit on a lattice of cornersharing tetrahedra, resulting in geometrical frustration for antiferromagnetic nearest-neighbor exchange between Heisenberg spins. As such, these materials display a wide variety of interesting and unusual behaviors. Examples of observed phenomenology include spin ice [1], spin glass [2,3], and spin liquid [4] behaviors as well as long-range magnetic order [5,6,7,8,9,10,11] and perhaps some novel type of hidden order [12]. A common trend observed in all of these systems is an apparent persistence of spin dynamics down to the lowest temperatures as revealed by muon spin relaxation (µSR) [3,4,7,8,9,11,12] Perhaps what is most perplexing, is that PSDs have been found in pyrochlores, such as Gd 2 Ti 2 O 7 (GTO) [9,11] and Gd 2 Sn 2 O 7 (GSO) [7,8,13], which, according to neutron scattering experiments [6,10], display long-range magnetic order below a critical temperature T c = 0.74 K for GTO [6] and T c = 1.0 K for GSO [10]. This is highly unusual since conventional wisdom suggests that collective magnon-like excitations, hence spin dynamics, should freeze out in the limit of zero temperature. Similarly, the Gd 3 Ga 5 O 12 antiferromagnetic garnet (GGG), which displays rather extended magnetic correlations below 140 mK [14] that are now theoretically rationalized [15], also exhibits PSDs below 100 mK [16]. It is tempting to speculate that the unusual low-energy excitations giving rise to PSDs may result from a remnant of the high frustration that these systems possess and the lack of long-range order that would occur were it not for perturbatively small exchange interactions beyond nearest-neighbor [17], dipolar interactions [18,19] or single-ion anisotropy [20].We see Gd 2 Sn 2 O 7 (GSO) as a key system to investigate in seeking to convincingly demonstrate, via measurements of the low temperature magnetic specific heat, C m (T ), the existence of unconventional low-energy excitations, as suggested by the observation of PSDs. Previous C m measurements on this material between 350 mK and 800 mK (see Fig. 1) were found to be parametrized by a C m (T ) ∼ T 2 law [5]. Such a temperature dependence of C m is unusual since conventional antiferromagnetic magnon excitations without a gap lead to C m (T ) ∼ T 3 or, with an anisotropy energy gap ∆, to C m (T ) ∼ exp(−∆/T ). Such an unconventional C m (T ) behavior further argues for the existe...

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“…For example, spin ices and spin glasses do meet these criteria at low temperature [28,29]. The relative change of α between pixels and time bins can also be calculated from the instrument geometry without any ambiguity, because α is simply the in-plane angle of the Q vector.…”

Section: Polarization Analysis With Detector Coverage Out Of Planementioning

confidence: 99%

Neutronxyz– polarization analysis at a time-of-flight instrument

Ehlers

Stewart

Deen

et al. 2015

EPJ Web of Conferences

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Abstract. When implementing a dedicated polarization analysis setup at a neutron time-of-flight instrument with a large area detector, one faces enormous challenges. Nevertheless, significant progress has been made towards this goal over the last few years. This paper addresses systematic limitations of the traditional method that is used to make these measurements, and a possible strategy to overcome these limitations. This will be important, for diffraction as well as inelastic experiments, where the scattering occurs mostly out-of-plane.

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Evidence for two distinct spin relaxation mechanisms in hot spin ice Ho₂Ti₂O₇

Cited by 88 publications

References 32 publications

Structure and magnetic properties of theHo2Ge2O7pyrogermanate

Structure and magnetic properties of theHo2Ge2O7pyrogermanate

Evidence for Gapped Spin-Wave Excitations in the FrustratedGd2Sn2O7Pyrochlore Antiferromagnet from Low-Temperature Specific Heat Measurements

Neutronxyz– polarization analysis at a time-of-flight instrument

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