Giant low-field cryogenic magnetocaloric effect in polycrystalline LiErF4 compound

Antiferromagnetic LiErF4has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In the present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect(MCE) of polycrystalline LiErF4compound are investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I41/a space group. It exhibits an antiferromagnetic(AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy changes are 24.3 J/kg·K,33.1 J/kg·K, and 49.0 J/kg·K under the low magnetic field change of 0–0.6 T, 0–1 T, and 0–2 T, respectively. The giant MCE observed above Néel temperature TNis probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4compound an attractive candidate for the magnetic refrigeration at the ultra-low temperature.

Giant low-field reversible magnetocaloric effect at liquid helium temperature of niobium and iron co-substituted EuTiO_(3) compounds

Giant magnetocaloric effect(MCE)materials in the liquid helium temperature region have attracted a lot of attention in the field of low-temperature magnetic refrigeration(MR).In this study,a series of niobium(Nb)and iron(Fe)co-substituted EuTiO_(3) perovskites with cubic structure(space group pm3m)was successfully fabricated,and their magnetic properties as well as cryogenic magnetocaloric effects were investigated in detail.As expected,the introduction of Nb and Fe can significantly modulate the magnetic phase transition and magnetocaloric effect of the EuTiO_(3) compounds.With increasing Fe concentration,two local minima corresponding to the AFM-FM magnetic phase transition near 5.0 K and FM-PM transition near 10 K with no hysteresis in the thermomagnetic curves are observed,which is attributed to an enhancement of FM coupling.At the same time,the gradually widened-ΔSM-T curves and the two peaks with a broad shoulder lead to considerable refrigeration capacity(RC).With the field change ofΔH=2 T,the calculated values of-ΔS_(M)^(max) for the EuTi_(0.9375-x)Nb_(0.0625)Fe_(x)O_(3)(x=0.075,0.1,0.125,0.15)compounds are 24.2,17.6,14.5 and 14.0 J/(kg·K),respectively.The corresponding RC values were calculated to be 144.6,138.3,151.2 and 159 J/kg,respectively.Especially,the values of-ΔS_(M)^(max) for EuTi_(0.8625)Nb_(0.0625)Fe_(0.075)O_(3) are 8.6 and 15.1 J/(kg·K)under low field changes of 0.5 and 1 T,respectively.The giant low-field reversible magnetocaloric effect makes them attractive candidates for magnetic refrigeration in the liquid helium temperature region.

Magnetic properties and magnetocaloric effects in Eu(Ti,Nb,Mn)O_(3) perovskites

In perovskite EuTiO_(3),the magnetic characteristics and magnetocaloric effect(MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to ferromagnetic.In the present work,a series of Eu(Ti,Nb,Mn)O_(3) compounds,abbreviated as ETNMO for convenience of description,was fabricated and their crystallography,magnetism together with cryogenic magnetocaloric effects were systematically investigated.The crystallographic results demonstrate the cubic perovskite structure for all the compounds,with the space group of Pm3m.Two magnetic phase transitions are observed in these second-order phase transition(SOPT) materials.The joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO compounds.As the Mn content increases,gradually widened-ΔS_(M)-T curves are obtained,and two peaks with a broad shoulder are observed in the-ΔS_(M)-T curves for Δμ_(0)H≤0-1 T.Under a field change of 0-5 T,the values of maximum magnetic entropy change(-ΔS_(M)^(max)) and refrigeration capacity(RC) are evaluated to be 34.7 J/(kg·K) and 364.9 J/kg for EuTi_(0.8625)Nb_(0.0625)Mn_(0.075)O_(3), 27.8 J/(kg·K) and367.6 J/kg for EuTi_(0.8375)Nb_(0.0625)Mn_(0.1)O_(3),23.2 J/(kg·K) and 369.2 J/kg for EuTi_(0.8125)Nb_(0.0625)Mn_(0.125)O_(3),17.1 J/(kg·K) and 357.6 J/kg for EuTi_(0.7875)Nb_(0.0625)Mn_(0.15)O_(3),respectively.The co nsiderable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.

Enhanced low-field magnetocaloric effect in Dy-doped hexagonal GdBO_(3) compounds

Borates have attained increasing attention attributed to their excellent thermal stability,distinctive thermodynamic property,and high mechanical strength in recent years.A series of polycrystalline Dydoped GdBO_(3) compounds was prepared,their crystal structures,magnetic properties,and cryogenic magnetocaloric effects were comprehensively investigated.The compounds crystallize in hexagonal structure(space group P6_(3)/mmc),the lattice constant decreases with the increase of Dy content.Dydoping in GdBO_(3) significantly reduces critical magnetic field and enhances low-field magnetocaloric effect.The maximum magnetic entropy changes for the Gd_(1-x)Dy_(x)BO_(3)(x=0.6,0.8,and 1)compounds in a field change of 2 T surpass 17.3 J/(kg·K)at 2.5 K,enhanced by nearly 120%compared to GdBO_(3)(8.0 J/(kg·K)).Besides,the corresponding refrigeration capacity increases from 33.9 to 62.2,57.2,and 72.5 J/kg,respectively,with an enhancement of 70%-110%.The considerable maximum magnetic entropy change,refrigerating capacity,and temperature averaged entropy change make them competitive candidates for cryogenic magnetic refrigeration.

Enhanced low-field magnetocaloric effect in Nb and Al co-substituted EuTiO_(3)compounds

The magnetic ground state switching between antiferromagnetic(AFM)and ferromagnetic(FM)states in EuTiO_(3)provides the feasibility of regulating its magnetic properties and magnetocaloric effect.First-principles calculations demonstrate that the magnetic ground states for EuTi_(0.875)Nb_(0.0625)Al_(0.0625)O_(3),EuTi_(0.8125)Nb_(0.125)Al_(0.)0_(625)O_(3),and EuTi_(0.75)Nb_(0.125)Al_(0.125)O_(3)are FM coupling.Experimental results also exhibit the FM coupling domination in these compounds,accompanied by a significantly enhanced low magnetic field magnetocaloric effect.The maximum magnetic entropy change of all the samples surpasses15 J kg^(-1)K^(-1)with a field change of 1 T.which is 1.4 times as large as that of bulk EuTiO_(3).Especially,the maximum refrigerating capacity for EuTi_(0.8125)Nb_(0.125)Al_(0.0625)O_(3)compound is evaluated to be 88.1 J kg^(-1),more than three times of that of EuTiO_(3).The remarkable magnetocaloric performances prove Nb and Al co-substituted EuTiO_(3)compounds to be competitive candidates for magnetic refrigeration in the liquid helium temperature regime.