Laboratory of Magnetism

Institute of Physics, Slovak Academy of Sciences, 84511 Bratislava, Slovakia

Work Information

The laboratory of magnetism facilitates experimental material-research of soft magnetics. The measuring setups are adapted for materials prepared into the toroidal or the ribbon form. The range of methods in function to the date of this issue comprises:

Hysteresisgraph:
- provides automated recording of repetitive or single-shot a.c. hysteresis loops using equidistant sampling with numeric integration and/or analog integration method. Characteristic parameters as losses (to 100 kHz), dynamic coercivity, remanence, saturation induction, etc. are evaluated simultaneously.

Amplitude permeability (or susceptibility measured on open samples):
- PC controlled set-up enables investigated B, J or m, c vs H variation in range 0.001 ¸ 800 A/m or 0.1 to 4000A/m. The same vs f variation in the range 10 Hz to 0.3 MHz.

Disaccommodation of the permeability:
- the variable set-up enables to trace magnetic aftereffects from 0.5 s as H variation (f is from 10 Hz to 1 kHz).

Incremental permeability:
- The primary of Helmholtz coils is energized by a dc current to provide the field H_dc. The longitudinal incremental permeability is evaluated from the impedance of a pick-up coil fitted to the Helmholtz pair. Using a 770 Hz sine ac excitation, we use the constant B_ac mode; this of course reverted to a constant H_ac by approaching saturation with the field H_dc. Low ac fields with a maximum of 0.4 mT and 0.3 A/m respectively.

Sample preparation and technology:
The investigated materials come in form of as-cast ribbons. The following refers to toroids and strips (maximal long 10 cm):

· Toroid construction: winding the core under controlled stress, encapsulation or box-protection after thermal treatment.

· Thermal treatment at Ar atmosphere to 600°C of toroids or strips.

· Thermo-magnetic treatment with axial field (for strips) up to 550 A/m, other conditions as above one.

The density measurement of small samples (thin metallic ribbons):
The density determination is performed by the buoyancy method (Archimedes' principle) in a liquid. The method attains resolution better than 0.5% around r ~ 8 g/cm³ for nonporous metallic samples as small as 0.005 cm³.