Technische Universität Wien
Institut für Festkörperphysik
E138
Institut für Festkörperphysik

RESEARCH

Properties

Pulsed high magnetic fields

  • Pulsed field magnetometer

  • Industrial pulsed field magnetometer

  • "Austromag" high field installation - Quasistatic System

Pulsed field magnetometer
Field range up to 40 T in a bore of 25 mm.
Room temperature system: 10 T in a bore of 70 mm.
Power Supply 1: condensor battery C = 24 mF, Umax = 2500 V (W = 7 kJ)
Power Supply 2: condensor battery C = 14 mF, Umax = 8000 V (W = 440 kJ)
Pulse duration between 10 ms up to 100 ms.
Temperature range from 4.2 K up to 700 K.

Measurement: Temperature dependence of hysteresis, magnetic anisotropy, magnetic viscosity. The system is used to measure the temperature dependence of the hysteresis loop and the temperature dependence of the anisotropy field of hard magnetic materials going over a wide temperature range. The system was also adapted to measure “quasi-minor loops” with the exponentially decaying field.

Speciality:
The singular point detection (SPD) technique can be used to measure the anisotropy field, HA even for polycrystalline materials. The SPD technique is defined as observation of a singularity in derivatives of the magnetisation with respect to the applied field. The singularity occurs due to the rotation of the magnetisation vector from its easy axis into a hard direction when the applied field approaches the anisotropy field. The SPD technique is sensitive only to grains with hard axis in the same direction as the applied field that cause the singularity.

Block diagramm of pulsed magnetometer
Contact: R. Grössinger

Industrial pulsed field magnetometer
This Pulsed Field Magnetometer (PFM) was developed focusing on the industrial needs. The design was a manual loading system that could charge a 22.5 kJ capacitor bank (C = 5 mF) to 3000 V in approximately 25 seconds using phase controlled thyristors. The whole charging process, f/2f selection and the data acquisition is computer controlled using a Z80 microprocessor which is linked to the PC. The f/2f option (40 ms and 57 ms) can be used for correcting eddy current errors.

The signal is integrated with a stable analogue integrator with selectable time constants. The signals are connected to a 14 bit 5Msample/s two channel ADC card from Datel (model: PCI-416N) directly in the computer. For the data handling a C++ based computer program was written.

The system is capable of accepting samples up to 30 mm diameter and 10 mm length within a +/-1 % pickup homogeneity range. The maximum field is 5 T. It is calibrated with an absolute error in H and M of ± 1.5 %.

The system can be used for accurate hysteresis loop measurements on large samples at room temperature.

Recently a measuring device was developed for determining the magnetostriction using strain gauges with a 50 kHz strain gauge ridge. The sensitivity here is of ± 1 ppm.Additionally in a new experiment the magneto-electric coefficient can be measured.Also a pressure cell (p up to 20 kbar) can e used for measuring the pressure dependence of the hysteresis loop as well as of the anisotropy field.

Block diagramm of pulsed magnetometer
Contact: R. Grössinger

"Austromag" high field installation - Quasistatic System
The power for generating high magnetic fields comes directly from the line. A second cable of the total power supply of the T.U.Vienna can be used for this facility. The primary power is 16 MVA which is connectes the transformer to the 10 kV level. There the voltage is reduced to 2 x 840V which can be switched together either in sery or parallel or antiparallel. The ac-current is rectified by two bridges with 6 thyristors which can be regulated by varying the ignition angle a. The maximum dc-power is 10 MW over 1s, or 5 MW for 2s or 1 MW for 10s. With this thyristor regulator the current versus time profile can be free chosen - with 20 free points within the profile. Here particular field plateau’s are possible which are important for eddy current free measurements on metallic samples. The field versus time profile is selected using a graphical users interface.

The system allows – depending on the switching of the thyristor bridges- three types of pulses:

  1. parallel switching: 2 x Imax = 6800 A, Umax = 840 V – high current. Field -pulse with one polarity.
  2. Serial switching: Imax = 6800 A, 2 x Umax = 840 V – higher voltage; field pulse of one polarity; now used for generating the highest fields (40 T).
  3. Antipararllel switching: Imax = ± 6800 A, Umax =± 840 V. Bipolar pulse – necessary for real hysteresis measurements.

The system allows to generate fields up to 40 T in a bore of 25 mm with a pulse duration of up to 1s. The achievable temperature range goes from 4.2 K up to 800 K.

The system is used to measure: magnetization, magnetostriction, magnetoresistence, pressure effects (up to 10 kbar).

Extension: combination with 440 kJ battery – two coil system under construction – maximum field of 70 T is final goal.

Cooperations: IFW (Dresden) NHMFL (Tallahssee), LNCMP (Toulouse),NIMS (Tsukuba)...

Block diagramm of pulsed magnetometer
Contact: R. Grössinger