L. G. Rubin

Low‐temperature thermometry in high magnetic fields. V. Carbon‐glass resistors

The characteristics of carbon‐glass resistance thermometers for temperatures from 2.15 to 320 K and in magnetic fields of up to 19 T are described. The results from nine thermometers made from six different batches of raw material are combined to produce mean values that may be used to correct a ’’typical’’ thermometer at 19 T to within ±0.1% in temperatures between 30 and 320 K, and to within ±1% between 2.15 and 30 K. All nine sensors show a small orientation dependence of their magnetoresistance at 77 K; two out of four tested have an experimentally significant dependence at 4.2 K. The temperature error corresponding to the magnetoresistance of a miniature precision platinum resistance thermometer at 19 T is less than for carbon‐glass sensors above 77 K. New recommendations are made for the optimum use of low‐temperature thermometers in high magnetic fields.

Low temperature thermometry in high magnetic fields. VII. Cernox™ sensors to 32 T

This article describes the behavior of Cernox™ zirconium oxynitride film temperature sensors from Lake Shore Cryotronics, Inc. in magnetic fields up to 32 T at temperatures between 2 and 286 K. Results from a number of sensors with different dimensionless temperature sensitivities and from different production batches are analyzed and compared with previous results on carbon-glass sensors that extend to 19 T. In that field range, the Cernox™ sensors appear to be a real alternative to carbon glass. Furthermore, the magnitude of their uncorrected error, ΔT/T, is smaller than other sensors at most temperatures in fields less than 20 T, and their temperature correctabilities appear to apply to off-the-shelf sensors with dimensionless temperature sensitivities in the range of −0.74 to −1.9. The sensors show a negligible (<0.05%) orientation dependence of their ΔR/R at 78 K; at 4.2 K, that dependence can be as high as ∼0.7% at 20 T.

Low temperature thermometry in high magnetic fields. III. Carbon resistors (0.5–4.2 K); thermocouples.

The magnetoresistance of 1/2 W, grade 1002, Speer carbon resistors with nominal room temperature resistances of 100, 200, and 470 Ω and of 1/8 W, 10 Ω, Allen‐Bradley resistors was measured at various temperatures between 0.5 K and 4.2 K in static magnetic fields up to 140 kG. In this temperature range the maximum magnetic field induced temperature error of these thermometers amounts to 14%. The Allen‐Bradley unit is to be preferred over the Speer resistors for use as a thermometer in a magnetic field for the following reasons: it has a more reproducible and regular magnetic field dependence, greater temperature sensitivity, and its much smaller physical size facilitates its incorporation in experimental apparatus where dimensions are restricted. One drawback of the 10 Ω Allen‐Bradley resistor is its relatively high impedance at the lowest temperatures. In addition, the effects of magnetic fields up to 150 kG on the characteristics of Chromel P/Au+0.07 at.% Fe and Chromel P/constantan (type E) thermocouple...

Studies of a Glass‐Ceramic Capacitance Thermometer in an Intense Magnetic Field at Low Temperatures

The effect of an intense magnetic field on an 1100‐type capacitance thermometer (made from an SrTiO3 glass‐ceramic crystallized at 1100°C) was accurately measured at five temperatures between 1.5 and 4.2 K. At each manostatically maintained temperature, the capacitance changes were measured five times between B=0 and B=14 T, and it was found that these changes did not exceed the measurement uncertainty, ±0.3 pF≅±1 mK. Similar results were obtained on a second 1100‐type thermometer. Some suggestions are made for the use of this type of thermometer in magnetic field experiments.

Low Temperature Thermometry in High Magnetic Fields. II. Germanium and Platinum Resistors

The effect of static magnetic fields up to 210 kG on the characteristics of commercial germanium and platinum resistance thermometers was measured at various temperatures in the range 3.5–78 K. Measurements of the transverse (sample current I normal to magnetic field H) and longitudinal (I∥H) magnetoresistance were carried out on both types of thermometers. A description is given of the dc resistance measuring technique used in these experiments. This method is a semiautomatic potentiometric scheme which increases the speed of measurement while maintaining high resolution and reasonable accuracy. The magnetoresistance of the germanium sensors was found to be large and orientation dependent over the temperature range investigated. These effects preclude the use of germanium elements, as presently fabricated, for temperature sensors in a high magnetic field environment. In the case of platinum resistance thermometers, the magnetoresistance at temperatures above 30 K is small enough so that it becomes practi...

A Technique for the Rapid Measurement of Thermoelectric Power

A new technique is described for rapid measurement of the thermoelectric power of rod‐shaped specimens over a wide temperature range. The apparatus utilizes sensitive commercial dc amplifier for the sample and temperature gradient voltages and a multiple‐point recorder for sampling these voltages as well as the sample temperature signal. The technique eliminates spurious thermal emfs in the leads and is based upon on‐the‐run recording of the sample and temperature gradient voltages as the temperature gradient slowly increases. As a test of this technique, the thermopower of pure nickel was measured between 4.2 and 300 K and the results are compared with other measurements using conventional techniques.

Low‐temperature thermometry in high magnetic fields. VI. Industrial‐grade Pt resistors above 66 K; Rh–Fe and Au–Mn resistors above 40 K

The characteristics of twelve industrial‐grade and one precision platinum resistance thermometers for temperatures from 66 to 300 K and in magnetic fields up to 19 T are described. The results from the 13 models from nine suppliers are combined to produce mean values that may be used to correct any of those thermometers for effects of a magnetic field parallel to its long axis. The correctability error at 19 T is less than ±0.3% between 66 and 110 K and less than ±0.1% above 110 K. Magnetoresistance data for Rh–Fe and Au–Mn resistance thermometers are also presented.

Magnetoresistance of carbon‐glass thermometers at liquid helium temperatures

The low‐temperature behavior of carbon‐glass thermometers in intense magnetic fields is described. At 15 T, the field‐induced error is 0.3 K at 4.2 K and 0.08 K at 2.1 K. An empirical equation is presented which fits the positive magnetoresistance data to better than 0.1% in the liquid‐helium range. No significant (<0.1%) orientation dependence was found at either 4.2 or 77 K.

Some practical solutions to measurement problems encountered at low temperatures and high magnetic fields

For the measurement of temperatures between 1 K and 300 K, there are available a wide variety of sensors and several dc, ac, and pulse techniques. The choice of measurement system depends on a number of factors, including the required precision, cost, speed of response, sensor size and availability, and the effect of high magnetic fields. When the most significant of those factors have been identified and quantified, it should then be possible to select the thermometer(s) that best meet those requirements. To aid in the selection procedures, some pertinent characteristics of a number of useful thermometers are presented. A brief discussion of high magnetic field sensors useful at low temperatures is included.

Characterization of two commercially available Hall effect sensors for high magnetic fields and low temperatures

A series of measurements were performed on two groups of transverse‐configuration Hall effect sensors, each group consisting of devices available from a particular commercial supplier. The Hall voltage output of the probes was measured as a function of magnetic field to 18 T at temperatures of 300, 77, and 1.5–4.2 K; at the same time, the probes were subjected to a program of abrupt thermal cycling and magnetic field cycling. With the aid of computer analysis of the data the following conclusions could be drawn: (1) the outputs of one group of probes were linear with magnetic field within a worst‐case value of ∼±1% up to 8 T, and for the second group, to within ±0.5% up to 8 T and ±1.4% up to 18 T; (2) statement (1) was true for any of the selected temperatures; in general, variations of sensor output with temperature proved to be an unimportant factor; (3) the degree of measurement repeatability between thermal cycles varied somewhat from probe to probe within a group, but was significantly different bet...