Y.I. Spichkin

Field dependence of the adiabatic temperature change in second order phase transition materials: Application to Gd

The field dependence of the adiabatic temperature change ΔTad of second order phase transition materials is studied, both theoretically and experimentally. Using scaling laws, it is demonstrated that, at the Curie temperature, the field dependence of ΔTad is characterized by H1/Δ. Therefore, as the magnetic entropy change ΔSM follows a H(1−α)/Δ power law, these two dependencies coincide only in the case of a mean field model. A phenomenological construction of a universal curve for ΔTad is presented, and its theoretical justification is also given. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory (extrapolations in field or temperature), for enhancing the resolution of the data and as a simple screening procedure for the characterization of materials.

Elastic properties of a high purity gadolinium single crystal

Abstract The temperature dependence of Youngs modulus ( E c and E b ) and the internal friction have been measured in a high-purity gadolinium single crystal along the c - and b - axis in the temperature range of 4.2–350xa0K at the frequencies of 800–1200xa0Hz. At 4.2xa0K the values of E c and E b are equal to 7.25×10 11 and 6.14×10 11 dyn/cm 2 , respectively. The lattice part of Youngs modulus has been calculated. The origin of Youngs modulus anomalies at the Curie temperature and in the temperature region near 140xa0K are discussed.

Magnetocaloric Effect at the Field‐Induced First Order Transition in Rare Earth Metals and Alloys

On the basis of a thermodynamic approach the magnetocaloric effect (MCE) arising at the first order transition in the heavy rare earth metals Tb, Dy, Er and Tb0.5Dy0.5 alloy is considered. The main contributions to the MCE (exchange, magnetoelastic, anisotropic and that due to magnetic energy) were calculated in the temperature interval corresponding to the first order transition. It was shown that the model adequately describes the MCE and gives results which are in accord with direct experimental measurements.

Rotating-sample magnetometer for measuring crystal field parameters

A method of measuring crystal field parameters by means of a rotating-sample magnetometer is presented. The measurement is performed by registering 2nd, 4th and 6th harmonics of the signal that is proportional to magnetization change due to rotation of the sample in a magnetic field. Experimentally measured temperature dependence of the amplitudes of these harmonics is used to determine the crystal field parameters within the framework of the theoretical model proposed in [. The signal is detected by a digital lock-in amplifier, while temperature is controlled by a PID controller. The sample and pickup coils are located in the bore of a Halbach permanent magnet. The measurements are fully automated. Magnitude of the expected signal was estimated. Test measurements of magnetization of the Tb single crystal along a axis (in the easy crystallographic plane a-b) in the permanent magnetic field 2.7 T at room temperature were performed. The results show that sensitivity of the instruments and the proposed design of the equipment allows us to determine crystal field parameters of heavy rare-earth metals. Testing of the control software showed that computer-device communications and execution of the software blocks are correct.