E. Gažo

Košice nuclear demagnetization refrigerator

Abstract A nuclear demagnetization refrigerator with diffusion-welded copper nuclear stage has been constructed and successfully operated. The stage consists of 80 mol of copper and is capable, starting from an initial magnetic field of 6.4 T, of cooling the superfluid 3 He-B down to temperatures of ~280 μK in a single-walled experimental cell. The apparatus is currently used to study the magnetic relaxation processes in superfluid 3 He.

Diffusion-welded laminar nuclear stage

Abstract A nuclear cooling stage has been constructed from diffusion-welded copper sheets. We describe details of the technology and the design.

Transport properties of variously doped SmB6

Abstract SmB6 is a heavy fermion semiconductor with a narrow energy gap at the Fermi level, often denoted also as Kondo insulator, which has recently been considered to be a topological Kondo insulator, the first strongly correlated electron system to exhibit topological surface conduction states. In this contribution we have investigated the electrical transport properties of single crystalline SmB6 samples having various surfaces, of single crystalline SmB6 doped with various concentrations of lanthanum, europium, ytterbium and strontium, and of samarium deficient (i.e. doped with metal vacancies) Sm1-xB6 sintered samples with the aim to study the influence of miscellaneous doping and sample surfaces on the electronic states in the narrow energy gap of this material. The received results show rather complex resistivity vs. temperature ρ(T) and resistance vs. magnetic field ρ(H) behaviours as a function of wide range La doping and as a function of doping with different elements and vacancies. These results are discussed within the framework of the electronic structure of SmB6 observed in recent angle resolved photoemission spectroscopy as well as in other (above all transport properties) investigations, which exhibit surface electronic states in the narrow energy gap of this material.

Coherently Precessing Spin Structure in 3He-B High-Resolution Quantum Amplifier

We present results of the study of surface oscillation modes of coherently precessing nuclear spins in the superfluid 3He-B known as a homogeneously precessing domain (HPD). HPD represents the first macroscopic experimental manifestation of magnetic superfluidity phenomenon. The measurements showed that HPD is extremely sensitive to longitudinal perturbations and it behaves as tuned (by magnetic field gradient) quantum amplifier that allows to measure very small changes of magnetic field with very high relative resolution, of the order of 10-7.

Rotating magnetocaloric effect and unusual magnetic features in metallic strongly anisotropic geometrically frustrated TmB 4

We have investigated the rotating magnetocaloric effect (R-MCE) of TmB4 - an anisotropic magnetic system with geometrical frustration of Shastry-Sutherland type. The R-MCE was obtained from detailed temperature dependencies of heat capacity in various magnetic fields of a single crystalline sample for crystal axes orientations c || B and c ⊥ B. The received results exhibit rather complex distributions of positive and negative entropy ΔS(T, B) and temperature ΔT(T, B) differences below and above TN when the direction of the magnetic field changes between directions c || B and c ⊥ B. The calculated results were confirmed by direct R-MCE measurements which, moreover, show an interesting angular dependence of R-MCE in the ordered phase, which seems to be related with the change of the effective magnetic field along the c axis during sample rotation. Thus, our study presents a new type of magnetic refrigerant with a rather large R-MCE for low temperature magnetic refrigeration, and points to further interesting magnetic features in the ordered phase of this frustrated system.

Low-frequency dynamics of HPD at low pressures

Abstract Experimental study of low-frequency oscillation modes of a domain wall between the homogeneously precessing domain (HPD) and the stationary domain (SD) in superfluid 3He–B is presented. Measurements were performed in the temperature range from 0.5Tc to 0.8Tc and at a pressure of 2.7 bar. The small signal of the low-frequency domain wall oscillations on the high-frequency background (the HPD excitation) was measured using an RF-detector and a low-frequency filter in combination with a low-frequency lock-in amplifier. This technique makes it possible to study fine effects of the HPD low-frequency oscillation modes which may be associated with the influence of the texture.

Simple fix-point device for temperature scale definition below 1 K

Abstract We present the design, properties of a very simple and very easy to make fix-point device (FPD) for temperature scale definition below 1 K. The FPD consists of five superconductors Mo, Zn, Zr, Ti and AuIn 2 allowing thus to fix the temperature scale from 0.915 K down to 200 mK.

Magnetic dissipation in superfluid3He-B in the transition regime to nonhydrodynamic conditions

We have applied the so-called HPD spectroscopy, i.e. the NMR of the homogeneously precessing domain (HPD) in superfluid3He-B, to study the magnetic relaxation processes down to 0.3Tc. The power absorbed by HPD from cw NMR rf-field was divided into several contributions corresponding to different relaxation processes. From these contributions nonhydrodynamic corrections to spin diffusion and Leggett-Takagi (L-T) relaxation were extracted for a pressure of 6 bar. Below 0.45Tc a large absorption term linear with the HPD length and increasing with the falling temperature was observed. This term could be associated with an instability of coherent precession in the nonhydrodynamic regime. The process of the HPD formation in the nonwetting regime, forT<0.37Tc, was observed and described, leading to a new possibility to determine thed-constant of the surface energy.

Domain wall dynamics of the coherent quantum precession domain in3He-B

Dynamics of the domain wall (DW) separating the homogeneously precessing domain (HPD) and a stationary domain in thin channel has been studied. Measurements were performed at 0.65Tc (29 bar) and 0.7Tc (11 bar). Transformation of the spectroscopic DW to non-spectroscopic one was observed. The results are analysed in terms of the theory developed for the non-spectroscopic behaviour of the DW.