J. Vansummeren

On the precision of a susceptibility apparatus as deduced from measurements on superconducting vanadium

Abstract An apparatus for measuring static magnetic susceptibilities, based on a sensitive (10 −9 N) vacuum microbalance, has been adapted for measuring magnetic moments of small superconducting samples in small gradients of low fields. Data taken on vanadium at 3.2 K can be analysed for sample moments consisting of two parts: an induced one, proportional to the field; and a permanent one. The analyses of the data show that for a single sample on an undisturbed balance the relative precision on the forces at low temperatures can be better than 0.04 %. For coil positions ranging over 2 cm a good agreement is observed between the experimental and the calculated forces by fitting for one proportionality constant.

On an IC electronic balance control system and its impact on the calibration

Abstract The contribution deals with an “1974 integrated circuit” version of an electronic damping and nulling system, adapted to a torsion balance which now is more than twenty years old. The discussion of calibration results reveal that masses of about 0.5 mg, in certain cases, can be intercompared with a relative precision of 3 × 10 −5 , indicating that the balance sensibility is better than 2 × 10 −8 g. As the deflection sensitivity of the balance is 1.3 × 10 −4 deg/μg the position sensor on the balance can detect, over a few minutes, average displacements of about 4 × 10 −7 cm (i.e. ∼ 40 A).

Susceptibilities of superconducting vanadium measured following the faraday method

Abstract An apparatus for measuring static magnetic susceptibilities, based on a sensitive vacuum microbalance, has been used for studying the magnetic behaviour of small superconducting samples in small gradients of low fields. Forces on superconducting vanadium discs, cooled in fields ⩽ 10 mT, have been measured at 3 K following the Faraday method. It is observed that the sum of the magnitudes of the susceptibilities, related to i) the Meissner-Ochsenfeld effect and ii) the frozen-in currents, is equal within experimental error to the magnitude of the susceptibility at the induction of the moments at 3 K by generating similar fields.

Low temperature magnetic properties of solid DPPH

Abstract Magnetic susceptibility measurements are performed on DPPH-benzene complex and solvent-free DPPH in a temperature range of 300-2.2 K and in a field range of 6–20 kOe. The experimental values are quite different in these two cases and a pair model with a singlet-triplet state is proposed.

Magnetism of neutron-damaged alpha-quartz

Abstract Static magnetic susceptibilities have been measured on an α-quartz single crystal that had been irradiated with fast neutrons. Above 65 K, the radiation-induced paramagnetism obeys the Curie law, indicating the presence of non-interacting centres. The low-temperature measurements result in a field-dependent susceptibility comparable to the effect of the Brillouin saturation of non-interfacing centres. The average moment per centre, however, is higher than the one due to the spin only of single unpaired electrons, pointing to ferromagnetically coupled electron pairs. When the calculated susceptibility values, as obtained from the derived moments and concentrations using the Brillouin theory, are subtracted from the measured data, then the differences behave—over the whole temperature range—as the susceptibility of antiferromagnetically coupled electrons. On the same sample also, low-temperature 20.9 GHz ESR measurements have been carried out. The major resonance line is attributed to the E’ centre...

Magnetic interaction and spin diffusion in solvent-free DPPH

Abstract Susceptibility and ESR measurements are performed on single crystals of solvent-free 2,2-diphenyl-1-picrylhydrazyl (DPPH) in a temperature range of 1.5–300 K. The susceptibility measurements are explained by pair model ( 2 J k = -17.6 K ) but in contrast to previous powder data about 4% non-pairing paramagnetic centres are observed at low temperatures. As these centres probe the dynamics of the spin system the line width data may be explained by a low-dimensional diffusion model.

Magnetic moments measured at 78 K on an YBa2Cu3Ox superconducting ceramic disc

Abstract Static magnetic susceptibilities of an YBa(2)Cu(3)O(x) disc at 78 K, reveal the presence of magnetic moments, induced by low measuring fields. For higher fields the limited shielding capacity of the conductor allows flux penetration into the sample. The penetrated flux can be trapped in the disc yielding a permanent moment.

Amorphous Zr0.7Pd0.3 as a temperature reference near 2.5 K

Abstract The superconductive transition temperature of the high solidification rate material Zr 0.7 Pd 0.3 was used as a temperature reference to estimate the temperature deviation between the thermometer and the sample in the pan of a vacuum microbalance with 10 −9 N sensitivity. The latter system belongs to a set-up for measuring magnetic susceptibilities at low temperatures down to 2.2 K. The transition temperature of the amorphous Zr 0.7 Pd 0.3 sample was calibrated in a separate helium bath in good contact with the thermometer. In this bath the lambda transition point of liquid helium offered an additional check on the thermometer.

On the magnetic behaviour of superconducting lead discs

Abstract An apparatus for measuring static magnetic susceptibilities has been used for studying the magnetic behaviour of superconducting samples in gradients of low (⩽ 10 mT) magnetic induction fields. Forces on 3 mm diameter thin lead discs at temperatures down to 2.5 K have been measured with a sensitive (1 nN) vacuum microbalance. The interpretation of the data reveals that the three phenomena i) prohibition of flux penetration, ii) Meissner-Ochsenfeld flux expulsion and iii) flux trapping, occurring in lead are similar to those observed in vanadium (ref. 1). In the lead samples, however, saturation effects are revealed.

Magnetic susceptibilities measured on ceramic high-Tc superconducting discs☆

Abstract Static magnetic susceptibilities have been measured on ceramic high-Tc superconducting discs in magnetic induction fields between 1 and 9 mT. Data for a TlBaCaCuO ceramic compound at temperatures between 2.85 and 123 K are compared with those for YBa2Cu3O7 − x at 4.29 K. The susceptibility of the latter sample results in a critical induction field for flux penetration of 4 mT. For higher fields the flux penetrates the sample, resulting, in certain cases, in a permanent magnetic moment. The general magnetic behaviour of YBa2Cu3O7 − x is similar to that of the TlBaCaCuO compound. In the latter, persistent moments have been measured at 1 mT up to 80 K. Induced moments are observed up to 117 K, the critical temperature based on magnetic measurements.