Session S12: Measurements and Sensors in High Magnetic Fields

Wide Range Ceramic Metal-Alloy Thin Film Thermometers for High Magnetic Fields

Many thermal measurements in high magnetic fields require thermometers that are sensitive over a wide temperature range, are low mass, have a rapid thermal response, and have a minimal, easily correctable magnetoresistance. Here we report the development of a new granular-metal oxide ceramic composite (cermet) for this purpose formed by co-sputtering of the metallic alloy nichrome Ni0.8Cr0.2 and the insulator silcon dioxide SiO2. The resulting thin films are sensitive enough to be used from room temperature down to below 100 mK in magnetic fields up to at least 35 tesla. The maximum magnetic-field induced fractional error in temperature ΔT/T over this temperature range is 2%.   

High Field Measurements of Quantum Materials with In-Situ Tunable Strains

Electronic material properties are closely linked to the properties of the underlying crystal lattice. For instance, ferroelectric materials break spatial inversion symmetry and ferromagnetic materials break time reversal symmetry. Consequently, deforming the crystal lattice with strain can have large effects on the electronic behavior of materials. In this talk, I will discuss an in-situ tunable strain technique that is compatible with extreme magnetic field environments (both DC and pulsed magnetic fields). Measurements will be shown on a prototypical electron doped iron pnictide superconductor, Ba(Fe_1-xCo_x)₂As₂, where  strain can be used as a conjugate field for electronic order and in the Weyl semimetal Mn₃Sn where strain tunes the topologically driven anomalous Hall effect.   

High Temperature Thermocouple Use in Strong Magnetic Fields

Thermomagnetic processing of materials at high temperatures and in high magnetic fields requires an understanding of in situ temperatures experienced by the samples/workpieces. Here, the performance of Type-K thermocouples is compared to Type-N and Type-S alternatives in two different thermomagnetic processing configurations, one with rf induction coils and the other with resistance heating elements. The results will be reported for studies spanning magnetic fields up to 9 T and temperatures up to 1000 C.   

Achieving High Static Pressures in Pulsed Magnetic Fields

Extreme pressure allows for creation of materials with desirable properties and behaviors that do not normally exist under ambient conditions, such as high-temperature superconductivity, high-energy density phases, and electronic topological phase transitions. The combination of extreme condition pathways, such as the application of pressure in conjunction with the ability to apply high magnetic fields allows for both a deeper understanding of the underlying fundamental behaviors of a given system, as well as the ability to access properties not measurable without the use of both, such as magnetotransport measurements of high superconducting crtical transition temperature materials. However, the constraints imposed by both of these techniques makes these measurements considerably more difficult when combined. 

In this contributed talk, I will discuss some of the difficulties imposed by applying large pulsed magnetic fields in conjunction with high, static pressures applied using the diamond anvil cell (DAC), as well as progress made in cell design in pulsed fields. I will also discuss our recent success measuring a cerium hydride sample synthesized under high pressures and measured in pulsed fields, in which both the upper critical field limit, H_C2, and Hall measurements were able to be measured at 1.2 MBar and fields up to 59 T.   

Development of a Standalone Sample Thermometer Based on Quartz Tuning Forks

There is a growing demand within the user program across the Maglab and within the cryogenic industry for thermometers capable of simultaneous operation at ultra-low temperatures down to and below 1 mK and in high magnetic fields. To this end we have developed a thermometer design based upon a tuning fork encapsulated in a small volume containing ³He [1] and demonstrated compatibility with these extreme conditions. Here we discuss the next stages in the design of this thermometer.

We present measurements of the viscosity of liquid ³He and the typical mixture of ³He and ⁴He found in a dilution refrigerator as measured by a variety of quartz tuning forks. We present an enhanced hydrodynamic description of the resonator in both cases, based on drawing together existing models in different temperature regimes. The mixture has a significantly lower viscosity, which is advantageous to the sensitivity of the tuning fork measurement. Thus, we discuss the feasibility of using a cell containing a small volume of such mixture as a sample thermometer. We further detail the use of an array of tuning forks as a diagnostic tool for the mixture level, temperature and location of the phase boundary within the mixing chamber of a dilution refrigerator.

[1] A. J. Woods, A. M. Donald, R. Gazizulin, E. Collin, L. Steinke; Developing compact tuning fork thermometers for sub-mK temperatures and high magnetic fields. J. Appl. Phys. 14 January 2023; 133 (2): 024501. https://doi.org/10.1063/5.0132492

  

Characterization of the Low Temperature Static Magnetic Properties of Cryogel®

While searching for a “new age” cryogenic insulating material for use in magnetic fields, the silica aerogel known as Cryogel^®x201 was identified for its performance at low temperatures [1]. The thermal conductivity of Cryogel^® has been reported [2], but the magnetic properties have not been characterized to date. Applications in high magnetic field instrumentation establish a necessity to fingerprint the magnetic properties of Cryogel^®. Using a commercial magnetometer, magnetization data, M(2 K ≤ T ≤ 300 K, B = 100 mT) and M(T = 2 K, −1 T ≤ B ≤ 7 T), were collected. These data sets were fit to a Brillouin function with a Curie-like background contribution to extract parameters, namely the spin value and the concentration of magnetic entities. Ultimately, this unexpected magnetic signal is conjectured to be associated with Fe₂O₃ nanoparticles.

[1] https://www.pacorinc.com/wp-content/uploads/Cryogel-x201-Datasheet.pdf

[2] V. Ilardi et al., IOP Conf. Ser.: Mater. Sci. Eng. 756 (2020) 012005, doi:10.1088/1757-899X/756/1/012005   

Quantum Current Sensor Integrating Quantum Anomalous Hall and Josephson Effects

Following the International System of Units (SI) redefinition, the units volt and ohm are directly realized via quantum-based standards (the Programmable Josephson Voltage Standard (PJVS) and the Quantum Hall Resistance Standard (QHRS), respectively). Direct realization of the ampere is then achievable through application of Ohm’s Law. However, direct integration of the PJVS and QHRS is challenging due to their vastly different magnetic field requirements. By leveraging the zero-field quantization of a quantum anomalous Hall (QAH) resistor in conjunction with a PJVS, we have demonstrated a direct realization of the Ampere with a quantum current sensor (QCS) in a single cryostat, precisely determining current over the range (9.33–252) nA. QCS accuracy was assessed by comparison to an indirect Ohm’s law measurement of the same current source, using both the QAH resistor and a PJVS-calibrated digital multimeter. The closest agreement, (1.46 +/- 4.28) x 10^-6 A/A, was found at 83.9 nA. In this talk, I will discuss the direct and indirect measurement results, as well as the integration of the QAH resistor and PJVS in a single cryostat.    

Diamond anvil cell based magneto-optical spectroscopy for quantum materials research

Quantum materials often exhibit exotic phases under extreme conditions such as low temperature, high magnetic field, and high pressure. Here, we report on the development of a magneto-optical setup that integrates a diamond anvil cell with a Quantum Design Physical Property Measurement System, enabling variable temperature (down to 2 K), high-pressure (up to 16 GPa) optical spectroscopy in a magnetic field (up to 14 T). Using topological material ZrTe₅ as an example, we showcase the capability of our setup. Specifically, we show the evolution of Raman peaks as a function of temperature, magnetic field, and pressure.   

High-sensitivity Magnetic Microscope using an Optically Pumped Magnetometer and Flux Guides

Various applications in neuroscience research require high-sensitivity magnetic microscope. To meet this demand, we recently proposed an original approach of combining a cm-size optically pumped magnetometer (OPM) with flux guides (FGs) in order to develop a compact, portable, high-sensitivity OPM-FG magnetic microscope. The OPM based on lasers and alkali-metal vapor cells is the most sensitive cryogen-free magnetic sensor, approaching femtotesla sensitivity with cm-scale resolution. The FG serves to transmit the magnetic flux from a microscopic source of magnetic field to the cm-size OPM to simultaneously improve the resolution and sensitivity. In this talk, we will describe our approach and present numerical tests of sensitivity and resolution. Our numerical tests show that an optimized OPM-FG has sufficient resolution and sensitivity for the detection of a small number of neurons, which would be an important milestone in neuroscience.   

Measurement of Phonon Angular Momentum via the Einstein-deHaas Effect, Fiber-Optic Interferometry, and a High-Q Oscillator

We report the design and use of a fiber-optic-interferometer

system to measure the predicted¹ macroscopic phonon angular

momentum. An oscillating magnetic field is applied to an

insulating ferromagnet attached to our single-crystal high-Q

double torsional oscillator. By the Einstein-de Haas effect,

oscillator displacement measurements between low

temperatures and those closer to the Debye temperature allow

extraction of the changing phonon angular momentum. A force

change of 5 x 10^-8 N was detected between 77 K and 300 K for a

1 mm³ MgZn ferrite sample. Our oscillator, with a resonance at

1.3 kHz, has a thermal noise limit on the order of 10^-14 N/√Hz,

allowing the possibility of high-accuracy detection. Competing

effects are being minimized; for example, induced eddy current

momentum can overwhelm the phonon effect for metallic

ferromagnets, and careful temperature-dependent studies are

required for force calibrations.