Magnetic Thermometers Research Articles

Magnetic Characterization of Electrodeposited Pt1−xNix Alloy Films: Influence of Deposition Potential and the Presence of Boric Acid

Pt1-xNix (x = 0.25 to 0.92) thin films were examined for possible application as magnetic thermometers. The alloys were prepared by potentiostatic electrodeposition from aqueous chloride-based solutions in the presence and absence of 0.5 mol dm−3 B(OH)3. Alloy composition was controlled by the deposition potential with the Ni concentration increasing towards more reducing potentials. Films with x > 0.45 were ferromagnetic with the magnetization at 300 K increasing with nickel content. Magnetization vs temperature (M vs T) at 8 kA m−1 (100 Oe) showed an increase in the Curie temperature from less than 200 K to above 400 K for the alloys investigated. For films deposited at potentials >−0.6 V vs the saturated calomel electrode (SCE), boric acid had negligible effect on the magnetization at the maximum applied field in M vs H measurements. In contrast, for depositions at more reducing potentials <−0.6 V vs SCE the presence of boric acid resulted in diminished magnetization. This effect was attributed to elevated incorporation of oxygen (up to ∼4 atomic %), along with boron incorporation of about 400 μmol mol−1.

Theoretical Studies of Electronic Paramagnetic Resonance g Factors for La2Mg3(NO3)12⋅24H2O

Lanthanum magnesium double nitrate (LMN) crystals can be used as material for adiabatic demagnetization, magnetic thermometers and a proton spin-polarized target in both physics and polarized neutron diffraction. In the past years, the double nitrates doped with transition metal or rare earth ions have been studied by experimental and theoretical methods. For instance, the electronic paramagnetic resonance (EPR) g factors of the Ce3+ ions in La2Mg3(NO3)12⋅24H2O crystal were measured decades ago. But until now, these useful experimental results have not been theoretically explained. In this work, The EPR g factors of the trigonal Ce3+ centers in La2Mg3(NO3)12⋅24H2O are theoretically studied from the perturbation formulae of the EPR parameters for a 4f1 ion under the trigonal symmetry crystal field. The used crystal parameters are obtained from the superposition model and the local structure of the studied crystal. The calculated results are reasonably constant to the observed values. The results are discussed.

Applications of garnet single crystals {Yb} 3Al 5O 12, {Er xY 1−x} 3Al 5O 12 and {Ce xY 1−x} 3Al 5O 12 for magnetic thermometers and magnetic cooling

Applications of garnet single crystals {Yb} 3Al 5O 12, {Er xY 1−x} 3Al 5O 12 and {Ce xY 1−x} 3Al 5O 12 for magnetic thermometers and magnetic cooling

3He-melting-curve thermometry

Precise measurements of theP-T relation along the melting curve of3He have been made for 8≲T≲330 mK. The results are in excellent agreement with other precise data for temperatures near the extremes of this range. A best-fit relation is provided which describes the melting curve to within ±1 mbar between the superfluid A transition and the pressure minimum. Detailed descriptions of the melting curve and magnetic thermometers used for the calibration are also given.

Application of magnetization measurements in iron to high temperature thermometry

It is proposed to use iron whiskers as elements for magnetic thermometers. The sharpness and reproducibility of the large second harmonic response that occurs just as the centre of the whisker saturates depends upon temperature through Ms(T). As a thermometer the whisker has a built-in fixed point which is reproducible to parts in 106. A one point calibration is needed to determined the demagnetizing factor. Suggestions are made for incorporating magnetic thermometers into thermocouples and resistance thermometers.

Very-low-temperature static magnetic properties of certain metals possibly useful as magnetic thermometers

The static magnetization of pure Al and Tl, and of Pt containing 70 ppm Fe, has been measured over the temperature range 10–400 mK. It is shown that the temperature-dependent magnetism of pure Al and Tl can be attributed to nuclear magnetism only, with calculated Curie constants 6.9×10−8 and 1.7×10−8 K, respectively. The magnetization of Pt containing 70 ppm Fe in a magnetic field of 10 Oe was found to obey a Curie-Weiss law over the entire temperature range studied. The adequacy of Cu, Al, Tl, and Pt as magnetic thermometers in the millidegree temperature region is discussed.

Measurements of Demagnetizing Factors and Their Application to Magnetic Thermometry

Shape corrections for several cerous magnesium nitrate magnetic thermometers have been measured, both for powders and for composites of oriented single crystals, in an attempt to establish a suitable geometry for a magnetic thermometer accurate to ∼1% at temperatures down to 0.02°K. The results indicate that this accuracy is available with either a spherical composite of oriented single crystals. or with a powder in the form of a right circular cylinder with ratio (length/diameter)=0.92. In either case it is imperative that the density be uniform within the sample. The results are compared with theoretical computations, where applicable, and with the results of other techniques.