Millisecond Dynamics of the Magnetocaloric Effect in a First‐ and Second‐Order Phase Transition Material

Abstract

The millisecond‐dynamics of the magnetocaloric effect in Gd and La‐Fe‐Si‐Mn, which exhibit first‐ and second‐order phase‐transitions, respectively, are investigated. Direct measurements of the adiabatic temperature change ΔT are obtained from modulation infrared thermometry with field‐cycling frequencies exceeding 1 kHz at amplitudes of up to 45 mT. The peak amplitude of ΔT(T) shows a dependence on sample thickness and decreases with increasing modulation frequency for both materials despite a frequency independent susceptibility of Gd. The adiabatic ΔT depends quadratically on the external field for Gd while La−Fe−Si−Mn shows a peculiar bucket‐shaped curve for temperatures below the peak maximum. A comparative study of non‐caloric samples shows that dissipative heating by eddy currents or magnetic hysteresis does not explain the observed behavior. The transient ΔT(t) instead suggests a mechanism involving strong temperature gradients at the ferromagnetic–paramagnetic boundaries and underlines the importance of further dynamical studies for a fundamental understanding of the magnetocaloric effect in first‐order materials.

Simultaneous direct measurement of the electrocaloric and dielectric dynamics of ferroelectrics with microsecond temporal resolution

“…proximate time-inversion symmetry, thus indicating only very weak irreversible processes 33 in accordance with the very narrow hysteresis loop of BZT (see also below). Fourth, the maximum temperature change ∆T max ex = max [∆T ex (t)] ≈ 450 mK for a field of 1.5 kV/mm is in very good agreement with reported values in literature [see also Figure 6(c)].…”

“…The direct measurement of the experimentally observed temperature change ∆T ex (t) with its dynamics is based on a large-bandwidth detection of the IR radiation emitted by the sample. [31][32][33] Simultaneously measured transients of the temperature change ∆T ex (t), the driving electric field E(t) and the induced polarization P(t) allow for a comprehensive characterization of the dynamics of the electrocaloric effect and the correlation with dielectric properties. The technique can also be used to quasi-continuously monitor fatigue of samples over many cycles of the driving electric field.…”

Heat capacity, thermal conductivity and magnetocaloric effect in Heusler alloy Ni-=SUB=-47-=/SUB=-Mn-=SUB=-40-=/SUB=-Sn-=SUB=-13-=/SUB=-

“…Indeed, on the one hand, the recent studies of dependence T (T, f ) for Gd in the magnetic field of 1.2 T showed a frequency stability of MCE value in the interval of 1−20 Hz [30]. On the other hand, paper [31] notes a slight decrease of amplitude T ad for Gd with an increase of the magnetic field modulation amplitude from 116 to 1184 Hz in the field of 33 mT. The frequency studies of MCE in various magnetocaloric materials show a complex pattern of MCE dependence on cyclic field frequency, even for materials with second-order phase transitions [30][31][32][33].…”

“…On the other hand, paper [31] notes a slight decrease of amplitude T ad for Gd with an increase of the magnetic field modulation amplitude from 116 to 1184 Hz in the field of 33 mT. The frequency studies of MCE in various magnetocaloric materials show a complex pattern of MCE dependence on cyclic field frequency, even for materials with second-order phase transitions [30][31][32][33]. While the dependence of T on magnetic field frequency near first-order phase transitions can be explained by growth and nucleation (phase transition kinetics), the situation is not so evident for second-order phase transitions.…”

Utilizing Incomplete Phase Transformation to Characterize Elastocaloric Effect of Shape Memory Alloys

“…Conventional vapor compression cooling technologies relying on gaseous refrigerant face more and more stress at atmosphere environment influences. Recently, solid-state refrigeration technologies based on caloric effects, such as magnetocaloric, [1] electrocaloric, [2] barocaloric, [3] and elastocaloric, [4] have drawn more attentions due to their potentially high efficiency and eco-friendliness. [5] As the most promising alternatives to conventional refrigeration from an energy savings standpoint, [6] elastocaloric cooling is still at the very beginning of development from the scientific and industrial perspectives.…”