LTHMFL - High Magnetic Fields Laboratory

In this laboratory we have a 4He / 3He (0.3-300 K) Oxford Cryostat that is equipped with a 18 Tesla magnet, and a second 4He with a 10 Tesla magnet. In these cryostats we can measure resistivity, magneto resistance, thermoelectric power and Hall Effect, with suitable homemade probes.

Cryostat (0.3 K-300 K) with a 18 T magnet

Cryostat with a 18 T magnet.Among the several low temperature and high magnetic field facilities available, the cryostat with 18 T magnet offers the most extreme conditions and is specially dedicated to electrical transport measurements. Two different inserts can be fitted in this cryostat allowing either a temperature range from 1.6 K up to 300 K (4He flow) or from 0.3 K up to 300 K (3He cryostat).

The 4He insert is easy to use and various types of probe can be fitted. Our probes have been used for magnetotransport measurements in quasi-1D or 2D materials, in intermetallic compounds and in High Tc superconductors. A very precise rotating sample holder was built here at the CTN to measure the variation of the magnetoresistance as a function of the angle between the magnetic field and the cristallographic axis or the electrical current. The angle is measured by a Hall sensor, the resolution is better than 0.01º. The rotation is obtained by an endless screw moved at room temperature by a step-by-step motor controlled by computer. This probe allows resistivity, magnetoresistivity and Hall Effect measurements vs angle, vs temperature or vs magnetic field (1.6 K-300 K; 0-18 T). This probe was used to determine the anisotropy parameter in High Tc multilayers as a function of the angle between the magnetic field and the a,b plane (Fig. 1). A rotating cantilever magnetometer was installed, allowing magnetisation measurements up to 18 T in various directions.
The 3He insert is equipped with a rotating sample holder (0.02º precision, manually operated) for resistivity, magnetoresistivity and Hall Effect. This probe was used to study localisation effects and Shubnikov-de Haas oscillations in quasi-2D materials (Fig. 2).

Figure 1: Electrical transport at very low temperature Magnetoresistance of a quasi-two-dimensional compound at 0.3 K. The Fourier transform of these oscillations (Shubnikov-de Haas effect) allows the determination of the Fermi surface.

Figure 2: Variation of the critical field of the superconductor Covellite (CuS) with temperature.

Responsible Researcher: Elsa Branco Lopes

Access to the equipment:

This equipment is available to scientific community on the basis of research cooperation and co-authorship of publications in peer-reviewed international scientific journals and Conference presentations.