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1

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Calibration of a helical resonator for microwave dielectric and conductivity measurements of metals (2001)

Song, K. J. ; Castner, T. G.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 72 (2001), S. 1760-1769

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: The helical resonator (HR) is a useful resonant structure for the measurement of the microwave conductivity and dielectric response, but must be calibrated to obtain absolute values of these quantities. This has been accomplished by the measurement of frequency shifts and Q changes of thin disk samples of the metals Cu, Al, and Au and high purity Si and the use of the formula for (f−f0)/f due to Bethe and Schwinger. The measurements were made at 293, 77, and 50 K for the HR modes n=1–7(124 MHz–1.44 GHz). The results demonstrate the largest uncertain in the calculated values of Δf/f result from the z-axis variation of the E and H fields because of the helix short leading to large uncertainties in the stored energy U. The large dielectric response of the metals with their large values of dielectric "constant" −(ωpτeff)2 larger than 104 allows neglect of the Ez component contribution to Δf/f. However, uncertainties in the value of the T-independent τeff in the skin depth regime require the absolute calibration with high purity Si with cursive-epsilon∼11.7 at T=77 K. The calibration is accurate to ±15%. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1347379

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2

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The electromagnetic modes of a helical resonator (1996)

Diehl, Robert ; Wheatley, David M. ; Castner, T. G.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 67 (1996), S. 3904-3913

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: The electric fields of the helical resonator, both of the fundamental frequency and the odd harmonics up to the eleventh, have been probed using metallic copper and heavily doped Si:P disks by measuring the relative frequency shift Δf/f and the change in quality factor Δ(1/Q) with a network analyzer after insertion of the disk as a probe mounted on a dielectric support rod which could be translated along the z axis of the helix with a micrometer drive. The magnetic field component Hz was probed using the paramagnetic free radical DPPH and a simple transmission electron spin resonance (ESR) spectrometer. The Δf/f results were compared with calculated results using the Bethe–Schwinger expression and the plasma result for the change in dielectric response, while the Δ(1/Q) results were compared with a standard loss expression. The results, except for the role of the short but including the metallic disk thickness and diameter dependence, agree with the fields given by Pierce for an infinite helical current sheet, when adapted to the standing wave form. The ESR results demonstrate the optimum position for a paramagnetic sample. The ESR amplitude versus probe insertion depth is in qualitative agreement with an expression by Wilmshurst et al., but also exhibits an unexplained sign change. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1147291

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3

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Novel tunable reentrant microwave cavity (1988)

Migliuolo, M. ; Castner, T. G.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 59 (1988), S. 388-390

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: A cylindrical reentrant cavity is discussed that features a tunable resonant frequency. The tuning range can, in principle, be as large as a factor of 3, but the present design achieved only a 28% tuning range. Such a system could be utilized where it is necessary to tune the resonant frequency over a limited range, as in magnetic resonance experiments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1140216

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4

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Spin-lattice relaxation of the O2 − molecule-ion in the potassium halides (1970)

Castner, T. G.

Springer

The European physical journal 12 (1970), S. 104-130

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ISSN: 1434-6036

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Description / Table of Contents: Zusammenfassung Die Spin-Gitter Relaxation (SGR) des O2 −-Molekül-Ions in den Kalium Halogeniden wurde experimentell und theoretisch untersucht. Die SGR Rate wurde mit verschiedenen Methoden zwischen 1,32°K und 36°K mit Hilfe eines 3 cm-ESR Spektrometers gemessen. Die Resultate zeigen, daß ein Einphononenprozeß mit einer großen Anisotropie fürT〈2°K vorherrscht.T 1 ist am größten für das Magnetfeld parallel zur Molekülachse. Detaillierte Rechnungen zeigen, daß ein neuer SGR Prozeß, nämlich Phononen induzierte Libration der Molekülachse, wahrscheinlich den Fall des parallelen Feldes erklären kann. Der Van Vleck SGR Prozeß kann den Fall des senkrechten Feldes erklären.

Abstract: Résumé Une étude expérimentale et théorique a été faite sur la relaxation spin réseau (RSR) de la molécule O2 − dans les halogénures de potassium. On a mesuré le taux de relaxation par plusieurs methodes entre 1.32°K et 36°K avec un 3 cm-ESR spectromètre. Les résultats indiquent qu'un processus à un phonon avec une large anisotropie domine pourT〈2°K.T 1 est beaucoup plus long pour le champs magnétique parallel à l'axe moléculaire. Des calculs détaillés indiquent qu'un noveau type de RSR processus où la libration de l'axe moléculaire est causé par les phonons peut probablement expliquer le cas du champs parallel. Un processus du type Van Vleck décrit le cas du champs perpendiculaire.

Notes: Abstract An experimental and theoretical study of the spin-lattice relaxation (SLR) of the O2 − molecule-ion in the potassium halides has been made. The SLR rate was measured by several methods between 1.32°K and 36°K with a 3 cm. ESR spectrometer. The results indicate a one phonon process with a large anisotropy dominates forT〈2°K.T 1 is much longer for the magnetic field parallel to the molecular axis. Detailed theoretical calculations indicate a new SLR process, namely phonon-induced libration of the molecular axis, can probably explain the field parallel case. The Van Vleck SLR process can account for the field-perpendicular case.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02422373

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The paramagnetic line width in Cu(HCOO)2·4H2O (1968)

Seehra, Mohindar S. ; Castner, T. G.

Springer

The European physical journal 7 (1968), S. 185-200

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ISSN: 1434-6036

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Description / Table of Contents: Résumé Nous avons mesuré par ESR (9 et 36 GHz) la largeur de raie paramagnetique de Cu(HCOO)2·4H2O le long des axes principaux. Celle-ci dépend linéairement de la température entre 70°K et 273°K. Endessous de 70°K la pente change légèrement. L'augmentation rapide de la largeur de raie près deT N indique un ferromagnétisme faible. La largeur de raie extrapoliée à 0°K indique un fort rétrécissement d'échange. Nous avons observé un effet dû au volume et nous l'expliquons quantitativement. Nous considérons plusieurs méchanismes dépendant de la temperature et conduisant à l'élargissement de la raie. Nous suggérons que la linéarité observée est dûe à la modulation phononique de l'interaction de Moriya-Dzyaloshinsky.

Abstract: Zusammenfassung Die Linienbreite der paramagnetischen Resonanz von Cu(HCOO)2·4H2O wurde im Temperaturbereich von 20°K bis 273°K bei 9 GHz und 36 GHz entlang den Hauptachsen untersucht. Eine ungewöhnliche lineare Temperaturabhängigkeit wird zwischen 70°K und 273°K beobachtet. Unterhalb 70°K findet eine kleine Neigungsänderung statt. Die rasche Verbreitung der Linie in der Nähe vonT N deutet auf einen schwachen Ferromagnetismus hin. Die zu 0°K extrapolierte paramagnetische Linienbreite zeigt ausgeprägte Austauschverschmälerung. Eine Abhängigkeit von der Größe der Kristallprobe wird beobachtet und quantitativ erklärt. Verschiedene Ursachen für die temperaturabhängige Linienverbreitung werden untersucht. Es wird vorgeschlagen, daß die Phononmodulation der Moriya-Dzyaloshinsky Wechselwirkung für die lineare Temperaturabhängigkeit verantwortlich ist.

Notes: Abstract The paramagnetic ESR line width of Cu(HCOO)2·4H2O has been investigated in the temperature range 20°K to 273°K at 9 GHz and 36 GHz along the principal axes. An unusual linear temperature dependence is observed between 70°K and 273°K. Below 70°K a slight slope change occurs. The rapid line broadening nearT N shows evidence of weak ferromagnetism. The extrapolated 0°K paramagnetic line width shows strong exchange narrowing. An observed „sample size effect” is quantitatively explained. Various temperature-dependent line broadening mechanisms are considered. It is proposed that phonon modulation of the Moriya-Dzyaloshinsky interaction accounts for the linear process.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02422859

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6

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The low-frequency, low-temperature dielectric behavior of n-type germanium below the insulator-metal transition (1980)

Castner, T. G. ; Lee, N. K. ; Tan, H. S. ; [et al.]

Springer

Journal of low temperature physics 38 (1980), S. 447-473

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ISSN: 1573-7357

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Dielectric constant and ac conductance measurements of a number of n-type Ge samples (mostly Sb-doped) have been made with a low-frequency, three-terminal capacitance bridge between 4.2 and 0.011 K. From the concentration dependence of the low-temperature asymptotic values of the dielectric constant the value of the polarizability of the Sb donor has been determined to be αSb = (7.3 ± 1.0) × 106 »3. When employed with a new theory of the polarizability enhancement α D (N)/α D (0) and the Clausius-Mossotti expression, a calculated value of N c,calc = 2.5 × 1017/cm3 is obtained for the onset of metallic behavior for Ge:Sb. Although much larger than the current value of 1 × 1017/cm accepted in the literature, a correction of the neutral donor densities employing room-temperature resistivities and the Sze-Irvine curve rather than Hall coefficient data as applied to the transport data of Fritzsche shows N c,expt ≈ (1.9 ± 0.1) × 1017/cm. Data on ultra high-purity Ge samples yield a host dielectric constant ɛGe = 15.40−0.08 +0.01 (after a Kramers-Kronig analysis correction to remove a hopping conductivity contribution to ɛ), in excellent agreement with the value of 15.36 determined by Faulkner from the positions of the 2p and 3p levels of the Sb shallow donors. The data demonstrate the importance of the Kramers-Kronig analysis in obtaining values of ɛ(N) without any conductivity contribution. The ac conductance data are also briefly discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00114337

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