Thermodynamic and Relaxation Processes near Curie Point in Gadolinium

TL;DR

This study introduces an experimental method to measure magnetic phase transition rates in gadolinium near its Curie point by observing susceptibility changes, providing insights into relaxation dynamics and power limits of magnetocaloric devices.

Contribution

The paper presents a novel experimental approach for determining magnetic transition rates using susceptibility measurements near the Curie point of gadolinium.

Findings

Relaxation time of gadolinium's magnetic susceptibility can be modeled with Landau-Khalatnikov equation.

Linear approximation of susceptibility relaxation is inadequate above 291.3 K.

Estimated power restrictions for gadolinium-based magnetocaloric refrigerators.

Abstract

An experimental method is suggested for the determination of the rate of magnetic phase transitions. The method is based on the measurement of the change of magnetic susceptibility of a ferromagnetic sample in the vicinity of the phase transition in response to an abrupt change of the sample temperature. This paper describes the measurement of the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (Tc = 292 K). It was found that the relaxation time of the magnetic susceptibility of gadolinium in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value gamma = 3.9x10-8 cm3/(ergxs). The linear approximation does not fit well in the range from 291.3 to 293.2 K. The fundamental restriction of specific power of the magnetocaloric refrigerator (made by gadolinium plates) was estimated.