Measuring Nuclear Magnetization in Strong Magnetic Fields
Akira Harita, Takashi Tayama, Takahiro Onimaru, Toshiro Sakakibara
Institute for Solid State Physics, University of Tokyo, Kashiwa, 277-8581, Japan
27Al nuclear spin magnetization has been measured in magnetic fields up to 10 T, by use of a capacitive Faraday magnetometer installed in a dilution refrigerator. The sample employed in the experiment was an Al0.98Si0.02 alloy, prepared from high purity (6N) elements. The Si doping was essential in suppressing the de Haas-van Alphen oscillations of conduction electrons. Magnetic force acting on the sample was detected by a force-sensing parallel plate capacitor. Field gradient of 8 T/m was generated independently of central fields, by use of a special superconducting solenoid equipped with gradient coils. Fine Curie law was observed at temperatures below 1 K down to ~ 50 mK in magnetic fields ranging from 2 T to 10 T, with the Curie constant in good agreement with the calculated value. The measurement opens a new route towards primary thermometry in low temperature and high magnetic field region.
Current sensing noise thermometry from 4.2 K to below 1 mK using a DC SQUID preamplifier
A. Casey, B.P. Cowan, H. Dyball, J. Li, C.P. Lusher, V. Maidanov, J. Nyéki, J. Saunders, Dm. Shvarts
Department of Physics, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK
We are using a DC SQUID to perform current sensing noise thermometry, by measuring the thermal noise currents in a resistor cut from copper foil. The temperature is obtained from the Nyquist formula. This is a practical thermometer for use from 4.2 K to below 1 mK, with a percentage precision independent of temperature. Using a 0.34 mW resistor, the thermometer had an amplifier noise temperature TN of 8 mK. A precision of 1.5% was obtained in 200 s. The thermometer was in good agreement with the PLTS-2000 3He melting curve scale down to 4.5 mK. It can be used to significantly below 1 mK, and the performance down to the lowest temperatures will be discussed.
High resolution scanning probe microscopy at low temperatures and high magnetic fields
Markus Maier, Mathias Fenner, Andreas Bettag, Albrecht Feltz, Thomas Berghaus
OMICRON NanoTechnology GmbH, 65232 Taunusstein, Germany
Reduced surface mobility of species and minimised thermal drift are well known to be key advantages of LT SPM. Beside STM, full AFM capabilty gives access to physical phenoma in insulators, magnetic materials and many others. A complete UHV and high magnetic field compatible system design will be presented considering important design criteria for sample/sensor exchange and 3D coarse positioning. Furthermore, an effective isolation against external vibrations is another major aspect that will be discussed. Recent MFM results at high magnetic fields and high resolution STM measurements will be reported.
A Millikelvin T-Scale in High Magnetic Fields based on 3He Melting Pressure
Hiroshi Fukuyamaa, K. Yawatab, D. Itoc, H. Ikegamic, H. Ishimotoc
aDepartment of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
bInstitute of Physics, University of Tsukuba, 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-0006, Japan
cInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan
We propose a new millikelvin temperature scale (3.5 mK £ T £ 250 mK), which can be used in high magnetic fields ( B £ 14 T), based on the melting pressure of 3He. The melting pressure in magnetic fields was measured with a 3He melting curve thermometer (MCT) located in zero-field with the least temperature gradient. The scale is defined by an equation which gives a pressure decrease due to application of B at fixed T. The estimated accuracies are ±0.1 % and ±0.4 % above and below 10 mK, respectively, besides uncertainties in zero-field 3He MC T-scales we stand for. It is useful to calibrate other more easily handled thermometers such as RuO resistance thermometers in situ of high fields.