Temperature dependence of spin-cluster resonance intensity in RbFeCl3·2H2O

The spin-cluster resonance intensity is observed as a function of temperature in the pseudo-one-dimensional canted Ising metamagnet RbFeCl3·2H2O. For T 0.7 TN a pure one-dimensional Ising model gives a good description of the observed intensities. For T TN the intensity decreases rapidly as a function of temperature due to the destruction of the local ordering around a spin-cluster. The measured value of the intrachain interaction Ja/k of -36 K is in good agreement with earlier measurements on spin-cluster excitations

The influence of thermal conduction on the field dependence in spin-lattice relaxation experiments

It is demonstrated that heat transfer in magnetic samples and the surrounding liquid helium leads to a field dependence of the observed relaxation time in low-frequency relaxation measurements which deviates strongly from that of the intrinsic spin-lattice relaxation

Spin-lattice relaxation in potassium chromium alum

A comparison is made between the results of low-frequency relaxation measurements on potassium chromium alum placed in liquid helium and in vacuum, respectively. It is found that only a part of the lattice oscillations is involved in the spin-lattice relaxation process. The spin-lattice relaxation time was found after correcting the time constants of the vacuum measurements by experimental shortening factors. The differences between the spin-lattice relaxation time and the time constants from the liquid-helium measurements can be explained for the greater part by the finite thermal conductivity of the liquid helium

Introduction of ramp-type technology in HTS quasiparticle injection devices

Injection of quasiparticles with an energy larger than the superconducting gap into a superconducting strip results in breaking of Cooper-pairs and hence the suppression of the superconducting properties. Experiments using planar injection devices made of HTS materials with various barrier materials showed current gains varying from 2 up to 15 at 77 K. By changing the junction size and therefore the superconducting volume the current gain could be increased. A further reduction of the junction volume is very difficult using the planar device geometry. However, by applying the ramp-type technology it is possible to reduce the junction volume by at least one order of magnitude and a further increase in current gain is expected. Another advantage of this technology is the formation of in-situ barriers and electrodes and hence a better control of the junction characteristics should be possible, also the compatibility with the processes involved making RSFQ devices can be interesting for later applications. We have fabricated ramp-type injection devices, using various types of barriers. Characterization of these devices has been performed and the results of these experiments will be presented and discussed

Controlled preparation of all high-Tc SNS-type edge junctions and DC SQUIDs

High-Tc SNS-type Josephson junctions and DC SQUIDs were successfully fabricated using hetero-epitaxially grown multilayers of YBa2Cu3Ox and PrBa2Cu3Ox. These layers are c-axis oriented and hence edges of the multilayers give rise to a current flow in the ab-plane between the electrodes of a Josephson junction. The necessary structuring was done by Ar ion beam etching. The individual junctions exhibit a supercurrent up to 80 K. The IcRn-product of these junctions usually has a lower limit of 8 mV at 4.2 K. Voltage modulation of the first DC SQUIDs can be observed up to 66 K. Details on the fabrication and measurements are presented

High quality YBa2Cu3Ox ultra-thin films and Y/Pr/Y multilayers made by a modified RF-magnetron sputtering technique

High quality ĉ-axis oriented thin and ultra-thin films have been grown in situ on (100) surfaces of ZrO2, SrTiO3 and MgO. Sharp transitions were observed with Tc,zero of 87–91 K for films thicker than 70 Å. On atomically polished MgO substrates films as thin as 15 Å revealed a full transition to superconductivity above 45.5 K. The critical current density at 77 K was found to be strongly dependent on film thickness. A maximum value was found for a 100 Å film with 8 × 106A/cm2 at 77 K. Also, YBCO/PBCO/YBCO multilayer thin films have been fabricated in situ by the same technique. The epitaxy is maintained throughout the whole multilayer system. The superconducting properties of YBa2Cu3Ox layers do not change compared to single layers. Interdiffusion and possible chemical reaction close to the interfaces can be neglected.\ud \u

Relaxation phenomena in CsCoCl3·2 H2O

Dynamic susceptibility measurements have been performed on a single crystal of CsCoCl3·2H2O at liquid temperatures by means of a Hartshorn mutual inductance bridge. At the magnetic phase transition a maximum in τabs(H) has been observed. A jump in τabs(T) has been found at the λ-point of liquid helium

Environmental influence on the observed relaxation behaviour of two chromium systems

EPR recovery curves were measured for KCr alum and ruby with 2.7% chromium. A considerable influence of the heat transport properties of the bath is observed. Taking care of this influence a spin relaxation time τ = (0.7 ± 0.2) ms could be observed for ruby and a spin-lattice relaxation time T1 ∝ T-1. For KCr alum an anomalous behaviour of T1 was observed which may be due to a phonon bottleneck