Facility
General Layout
A schematic overview of the pulsed field experimental facilities is shown in Fig 1.
Each room has its own functionality, and is centrally connected to the data acquisition system.
Capacitor bank
At the core of the facility is a user-friendly 5 kV, 600 kJ capacitor bank. This bank allows polarity
switching, firing with thyristors or a mechanical switch, selection up to 4 coils and automatic integrated
inductance (L) / resistance (R) measurements for coil monitoring. The charger unit can operate completely
floating, which in fact allows reversing the polarity of the magnetic field while keeping the inside of
the coil related to the ground potential.
For the next generation of coils, operating at higher fields (~70 Tesla) an additional 10 kV, 500 kJ
capacitor bank is installed.
Cryogenics
For the high temperature region, gas flow cryostats allow stable temperatures between T =
4.2 K and T = 300 K. The cryostats are built in house; they are used in transport experiments
on high temperature superconductors (Cu-Oxides) and giant magnetoresistance materials (Mn-Oxides)
and photoluminescence experiments on semiconductor nanostructures.
For the low temperature range a 3He and a dilution fridge are installed.
The 3He system is equipped with an elegant plastic insert, which enables sample
changing within an hour. The base temperature of this system is T=350 mK. A commercial
dilution fridge has been purchased from Air Liquide (TBT);
it is equipped with a B = 40 T magnet (presently at the LNCMP-Toulouse).
The base temperature of this system is T ~ 50 mK. The mixing chamber is entirely made out
of plastic material. The low temperature systems are mainly used for studying spin -
Peierls materials, quantum oscillations (dHvA, SdH) on organic conductors and quantum
magnetic -phase - transitions.
For photoluminescence (PL) experiments 4He bath cryostats have been
developed with ultra small tails (Ø<8 mm), allowing the use of small bore magnets with
fields up to B=70 T.
Measuring probes and optical sources
Photoluminescence
For photoluminescence experiments, two solid-state lasers (l=532 nm, 100 mW
and 5 W) and an argon laser (l = 275 nm - 530 nm) are used to generate wavelengths
from the ultra violet to the visible light range. Three spectrometer/detector systems are available
featuring an intensified-CCD (l=400nm - 850 nm), an electron-multiplying CCD (l=400 nm - 1000 nm) and an InGaAs diode array (l=0.9 mm - 1.7 mm).
Transport measurements
Sample holders for magneto-resistance and Hall effect
measurements have been constructed.
Magnetization measurements
Magnetization measurements are performed using a
coupled-coils magnetometer. The small detector coil has two parts, wound in opposite directions. The
total number of windings is approximately 1000 turns. The magnetic moment sensitivity of this assembly is
about 10-2 emu in fields above 20 Tesla, and up to 10-4 emu for lower fields. The
sample can be removed in-situ after the experiment, which allows an easy method of compensation.
