Incipient ferromagnetism in Tb2Ge2O7: application of chemical pressure to the enigmatic spin-liquid compound Tb2Ti2O7.

After nearly 20 years of study, the origin of the spin-liquid state in Tb2Ti2O7 remains a challenge for experimentalists and theorists alike. To improve our understanding of the exotic magnetism in Tb2Ti2O7, we synthesize a chemical pressure analog: Tb2Ge2O7. Substitution of titanium by germanium results in a lattice contraction and enhanced exchange interactions. We characterize 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 liquidlike correlations dominate in this system at 3.5 K. However, below 1 K, the liquidlike correlations give way to intense short-range ferromagnetic correlations with a length scale similar 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.

Phase diagram and magnetic structures of the Co-bearing dugganites Pb3TeCo3A2O14 (A = V, P).

Exhibiting rich magnetic behaviour and potentially multiferroic properties, the dugganites, a Te(6+) containing subgroup of the langasite series, are an attractive family of compounds for future study. It was recently shown that Pb-bearing members of the dugganite series undergo distortions away from the P321 symmetry that is characteristic of the langasites. Here, we detail the consequences these distortions have on the magnetism exhibited by Pb3TeCo3V2O14 and Pb3TeCo3P2O14, solving the magnetic structures of both compounds with respect to a new supercell. Using neutron scattering and magnetic susceptibility measurements, we show that small applied magnetic fields can seriously perturb the delicate magnetic states in both of these systems. This is further demonstrated by presenting how doping P(5+) onto the nonmagnetic V(5+) site completely changes the magnetic structure from either of the end series members. Finally, it is shown using inelastic neutron scattering and magnetic susceptibility measurements that Pb3TeCo3V2O14 can be characterized using a model for isosceles trimers, which do not exist in the previously reported P321 subcell.

Successive phase transitions and extended spin-excitation continuum in the S=1/2 triangular-lattice antiferromagnet Ba3CoSb2O9.

Using magnetic, thermal, and neutron measurements on single-crystal samples, we show that Ba3CoSb2O9 is a spin-1/2 triangular-lattice antiferromagnet with the c axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the c axis. A pronounced extensive neutron-scattering continuum above spin-wave excitations, observed below T(N), implies that the system is in close proximity to one of two spin-liquid states that have been predicted for a 2D triangular lattice.

High pressure route to generate magnetic monopole dimers in spin ice.

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas, like monopole dimerization, critical phase separation, or charge ordering. However, all known spin ices have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, where none of these interesting phenomena occur. Here we use high-pressure synthesis to create a new monopole host, Dy(2)Ge(2)O(7), with a radically altered chemical potential that stabilizes a large fraction of monopole dimers. The system is found to be ideally described by the classic Debye-Huckel-Bjerrum theory of charge correlations. We thus show how to tune the monopole chemical potential in spin ice and how to access the diverse collective properties of magnetic monopoles.

Absence of long-range magnetic ordering in the pyrochlore compound Er2Sn2O7.

The low temperature behaviour of powder Er2Sn2O7 samples has been studied by magnetic susceptibility, heat capacity, and neutron scattering experiments. We report here the absence of magnetic ordering down to 100 mK. Anomalies in the heat capacity can be accounted for through an analysis of the crystal field spectrum observed by inelastic neutron scattering spectroscopy. These new measurements on Er2Sn2O7 suggest a new lower bound for the frustration index of f = |Θ(CW)|/T(N) = 14/0.1 = 140, placing this compound into a highly frustrated regime.

Use of the malleus handle as a landmark for localizing the round window membrane.

Localization of the round window membrane is desirable in order to allow a more direct application of medication to the inner ear. A new procedure has been developed to deliver direct, near-continuous inner ear perfusion to the round window with the Silverstein MicroWick. In this office procedure, the wick is inserted through a tympanostomy tube into the round window niche. Accurate localization of the round window is a necessary component of this procedure. In an effort to ascertain the precise location of the round window, we examined 25 cadaveric human temporal bones and measured the distance from the umbo to the round window in each sample. We found that the round window was an average of 3.44 mm (+/- 0.68) from the umbo and was situated at an average angle of 113.2 degrees (+/- 9.8) from the long process of the malleus. Our simple and reliable determination of the relationship between the malleus handle and the round window niche allows for the accurate placement of the Silverstein MicroWick and other devices.

Pediatric laser-assisted tympanostomy.

OBJECTIVE: To evaluate effectiveness of laser-assisted tympanostomy in treatment of pediatric patients with chronic otitis media with effusion. STUDY DESIGN: Retrospective review of 23 pediatric patients who received office laser-assisted tympanostomy. METHODS: A CO2 laser attached to an operating microscope with a microscope laser adaptor device or the handheld Oto-LAM (Needham, MA) was used to perform all of the tympanostomies. The average diameter of tympanostomy was 2 mm; on average, 13.6 W was applied for 0.13 seconds. RESULTS: Laser-assisted tympanostomy was performed on 37 pediatric ears (patient age range, 2-16 y) for the diagnosis of chronic otitis media with effusion. Average follow-up time was 4.7 weeks. At the time of the follow-up examination, 46% of the ears had no evidence of fluid and required no further intervention. Forty-nine percent of the ears required placement of pressure equalization tubes. The average SRT improved from 30.8 dB preoperatively to 21.03 dB postoperatively. CONCLUSIONS: Laser-assisted tympanostomy appears to be an effective treatment for chronic otitis media with effusion in pediatric patients.

Intraoperative facial nerve monitoring: a comparison between electromyography and mechanical-pressure monitoring techniques.

OBJECTIVES: To examine the hypothesis that for intraoperative facial nerve monitoring, an EMG monitor is more sensitive than a mechanical-pressure monitor. To compare the threshold sensitivity of the two facial nerve monitoring methods-mechanical-pressure versus EMG--by using them simultaneously during surgery. To assess and compare their true- and false-positive responses in otologic and neurotologic procedures. SETTING: A tertiary referral private otology/neurotology practice. STUDY DESIGN: Prospective case-controlled study. PATIENTS AND METHODS: The facial nerve of 46 consecutive patients undergoing various otologic and neurotologic procedures was stimulated intraoperatively using a pulsed constant-current. Facial responses were monitored using the Silverstein WR-S8 Monitor/Stimulator and the Brackmann EMG System simultaneously. The threshold (i.e., minimal) current level required to elicit a response from each monitor was recorded. Monitor responses to facial nerve manipulation (including false-positive responses) were assessed by continuous recording of all responses, using the Wiegand Monitoring System, and noting the causative event for each response. RESULTS: The EMG monitor responded to lower current threshold (p < 0.001) in every surgical procedure and for every nerve segment studied. However, the average threshold difference was <0.05 mAmps and in clinical practice, when using above threshold stimulation, becomes negligible. In posterior fossa surgery, the EMG monitor showed higher sensitivity by responding earlier to various manipulations of the bare facial nerve. The EMG had more false-positive responses than the mechanical-pressure monitor. CONCLUSIONS: In otologic surgery, if monitoring is required, the mechanical-pressure monitor is used. In neurotologic surgery, both monitors are used simultaneously.

Use of a new device, the MicroWick, to deliver medication to the inner ear.

A new procedure for delivering medication directly to the inner ear has been developed. This delivery system, called the MicroWick, involves the use of a small wick that is inserted through a tympanic membrane vent tube into the round window niche. Once the wick has been inserted, the patient can self-administer eardrops into the ear canal, where they are absorbed by the wick and transported to the round window membrane and to the inner ear fluids. Inserting the wick is a minor procedure that is performed in the office. This paper describes the indications for and use of the MicroWick.

Direct round window membrane application of gentamicin in the treatment of Meniere's disease.

OBJECTIVE: To evaluate the effectiveness of the round window membrane (RWM) Gelfoam gentamicin technique in patients with Meniere's disease who were unresponsive to medical management or in whom surgical therapy failed. STUDY DESIGN: Protocol 1, single intratympanic gentamicin infusion; protocol 2 (the best method), 2 infusions, 5 days apart with reevaluation at 1 month; and protocol 3, multiple infusions 1 to 4 weeks apart. PATIENTS: In total, 32 patients (19 male, 13 female) were enrolled in the study. The mean age was 65 years (range 34 to 94 years). Seven of these patients were surgical salvage cases. INTERVENTIONS: Laser-assisted otoendoscopy with a 1.7-mm otoendoscope (Smith-Nephew Richards, Memphis, TN) was performed first. If the RWM was obscured by mucosa or adhesions, these were cleared before placing a 2 x 3 mm piece of dry Gelfoam against the RWM. Buffered gentamicin (26.7 mg/mL) was then injected into the middle ear (0.2 to 0.3 mL). RESULTS: Overall, vertigo was controlled in 75% of the patients after the completion of the treatment, with subtotal vestibular ablation in two thirds of patients. Hearing was preserved in 90% of the patients (within 15 dB pure-tone average or 15% speech discrimination score), tinnitus improved in 48%, and aural pressure improved in 62.5%.

Outcomes after laser stapedotomy with and without preservation of the stapedius tendon.

Our goal was to investigate the postoperative differences in hearing between patients who had their stapedius tendon sacrificed and those whose stapedius tendon was preserved during laser stapes surgery for otosclerosis. To that end, we performed a retrospective review by mailing extensive questionnaires to patients who had been operated on between 1994 and 1997. We also performed routine and special audiometric testing to augment the subjective data. Seventy-nine of 124 questionnaires (64%) were returned. Of the respondents, 75 patients had undergone additional pre- and/or postoperative audiometric testing, including tests to evaluate "hearing in noise" and to determine the "uncomfortable loudness level" (dynamic range). We found no statistically significant differences between the two groups with respect to their subjective responses and their audiologic test results. The responses to the questionnaire indicated that in most cases, hearing was improved by stapes surgery. We conclude that the stapedius tendon should be preserved whenever possible during stapes surgery, provided that it does not jeopardize the exposure or outcome.

A morphological and morphometric study of the peripheral process of the human vestibular nerve following posterior cranial fossa neurectomy.

Three vestibular nerve specimens removed at transmeatal neurectomy were studied in order to understand better retrograde degeneration and regeneration after vestibular neurectomy in the posterior cranial fossa. In two cases this procedure followed retrolabyrinthine retrosigmoid posterior fossa vestibular neurectomy. The subjects, three patients with Menière's disease, were compared with one another and two autopsy controls with no known otological problem. The specimens were obtained at the distal end of the internal auditory canal and transversely sectioned. Many collapsed Schwann cell basement membranes were observed. The ratio of small-diameter nerve fibres increased significantly after neurectomy. Onion bulb formation around myelinated nerve fibres with small diameters and Schwann cell proliferation around the soma of vestibular ganglion cells reflected remyelination. We conclude that peripheral processes of vestibular nerve fibres can undergo retrograde degeneration and subsequent regeneration after transection of the central process.

A reevaluation of the 512-Hz Rinne tuning fork test as a patient selection criterion for laser stapedotomy.

OBJECTIVE: This study aimed to challenge the classical hypothesis that a negative preoperative 512-Hz Rinne tuning fork test (bone conduction greater than air conduction) is a necessary condition to allow consistent objective and subjective hearing improvement with surgery for otosclerosis. STUDY DESIGN: The study design was retrospective (chart review and questionnaire). SETTING: The study was conducted at a Florida Ear and Sinus Center at Sarasota, Florida, a tertiary otology-neurotology referral center. PATIENTS: Patients who underwent primary laser stapedotomy with equivocal (air=bone) preoperative 512-Hz Rinne test results participated. INTERVENTION: KTP laser stapedotomy was performed. MAIN OUTCOME MEASURES: Audiologic measurements of air-bone gap closure and patient assessment of hearing improvement and satisfaction were conducted. RESULTS: The air-bone gap was closed to within 10 dB in all cases. There were no complications. Eighteen patients were questioned about their results. Hearing improvement was subjectively described as "excellent" or "good" by 17 (94%), and 16 (89%) thought the surgery was "absolutely" worthwhile. CONCLUSIONS: The preoperative 512-Hz Rinne test results need not be negative to achieve significant air-bone gap closure and subjective appreciation of improved hearing.

Preservation of the stapedius tendon in laser stapes surgery.

OBJECTIVES/HYPOTHESIS: The stapedius tendon is routinely transected during stapes surgery. The objective of this study was to evaluate the technique of stapedial tendon preservation during stapes surgery and to compare results of these cases with cases where the stapedial tendon was not preserved. STUDY DESIGN: Retrospective study. METHODS: Four groups of patients were evaluated. Two groups had undergone stapes surgery with preservation of the stapedial tendon. One of these groups underwent a laser stapedotomy minus prosthesis (laser STAMP) procedure, while the other group had a prosthesis inserted. The other two groups had undergone laser stapedotomy with one of two different prostheses being used. Audiometric data were obtained and reviewed both preoperatively and at approximately 6 weeks postoperatively. RESULTS: All groups had overall successful results demonstrating that stapedial tendon preservation is technically possible and does not compromise outcomes. CONCLUSIONS: Based on the results, it is recommended that the stapedius tendon be preserved whenever possible during laser stapes surgery. Reasons justifying its preservation are discussed.