“…However, the C p / T vs T curves, shown in the top-left inset, reveal a broad downward hump at ∼18 K and another less wide upward at ∼5 K. The peak at ∼5 K (curve in 9 T) corresponds to the onset of AFM ordering of Gd 3+ magnetic moments, whereas at ∼18 K is attributed to the Schottky contribution that arises from crystal field transitions related mostly to the f -electrons of Gd 3+ . Similar behavior is commonly seen in other double perovskite compounds. − These anomalies are characteristic of disordered systems for which the competing magnetic interactions lead to short-range correlations . The lower right inset in Figure c shows the θ D as a function of temperature.…”
The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO 6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO 6 crystallizes in the orthorhombic phase (Pnma), with Gd 3+ /Sr 2+ and Co 2+/3+ /Fe 3+/4+ ions randomly distributed on the A-and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below T C ≈ 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe shortand long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel−Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO 6 , yielding the critical exponent β = 1.46(6)/1.45(6), γ = 1.48(5)/1.17(2), and δ = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (∼10 and ∼70 K), which match well with a Schottky anomaly (Gd-4f) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change ΔS M max ≈ 13 J kg −1 K −1 (at ∼8 K) under a field of 0−7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO 6 , making it a possible candidate for cryogenic applications.
“…However, the C p / T vs T curves, shown in the top-left inset, reveal a broad downward hump at ∼18 K and another less wide upward at ∼5 K. The peak at ∼5 K (curve in 9 T) corresponds to the onset of AFM ordering of Gd 3+ magnetic moments, whereas at ∼18 K is attributed to the Schottky contribution that arises from crystal field transitions related mostly to the f -electrons of Gd 3+ . Similar behavior is commonly seen in other double perovskite compounds. − These anomalies are characteristic of disordered systems for which the competing magnetic interactions lead to short-range correlations . The lower right inset in Figure c shows the θ D as a function of temperature.…”
The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO 6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO 6 crystallizes in the orthorhombic phase (Pnma), with Gd 3+ /Sr 2+ and Co 2+/3+ /Fe 3+/4+ ions randomly distributed on the A-and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below T C ≈ 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe shortand long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel−Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO 6 , yielding the critical exponent β = 1.46(6)/1.45(6), γ = 1.48(5)/1.17(2), and δ = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (∼10 and ∼70 K), which match well with a Schottky anomaly (Gd-4f) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change ΔS M max ≈ 13 J kg −1 K −1 (at ∼8 K) under a field of 0−7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO 6 , making it a possible candidate for cryogenic applications.
“…The oxygen octahedral cages are considerably distorted due to the comparatively small radius of the Gd 3+ ion. In a previous study, the polycrystalline form of GCMO revealed a large maximum entropy change of Δ S
M
≈ 24 J/kg·K 27 , attributed to the large magnetic moments of Gd 3+ ions.Figure 1Crystallographic structure of a GCMO crystal. ( a , b ) Views of the crystal structure of double perovskite GCMO crystal from the a- and c- axes, respectively.…”
The magnetocaloric effect (MCE) is described by the change in temperature of a material by magnetic field variation and is a crucial subject in magnetism; it is motivated by the desire to enhance energy-efficient magnetic refrigeration for clean technology. Despite the recent discovery of the giant cryogenic MCE in double perovskites, the role of magnetic anisotropy has not yet been clearly discussed, because of the averaging effect of polycrystalline samples. Here, we investigated the anisotropic MCE in the single-crystal double perovskite Gd2CoMnO6. In addition to the ferromagnetic order of the Co2+ and Mn4+ moments, the large Gd3+ moments align below T
Gd = 21 K, exhibiting an isotropic nature. Because of the intricate temperature development of magnetically hysteretic behaviour and metamagnetism, the change in magnetic entropy along the c-axis appears to be relatively small. On the contrary, the smaller but almost reversible magnetization perpendicular to the c-axis leads to a large MCE with a maximum entropy change of 25.4 J/kg·K. The anisotropic MCE generates a giant rotational MCE, estimated as 16.6 J/kg·K. Our results demonstrate the importance of magnetic anisotropy for understanding the MCE and reveal essential clues for exploring suitable magnetic refrigerant compounds aiming at magnetic functional applications.
“…The dotted line corresponds to the performances of GGG. (b) Comparisons of T ad with several top-performing magnetocaloric materials. − ,− Reproduced with permission from ref . Copyright 2022 Springer Nature.…”
Searching for working refrigerant materials is the key
element
in the design of magnetic cooling devices. Herein, we report on the
thermodynamic and magnetocaloric parameters of an X
1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements.
An overall correlation strength of |J|S
2 ≈ 3.4 K is derived via the mean-field estimate,
with antiferromagnetic correlations between the ferromagnetically
coupled Gd–Gd layers. The magnetic entropy change −ΔS
m is quite impressive, reaches 0.40 J K–1 cm–3 (58.5 J K–1 kg–1) at T = 2.7 K, with the
largest adiabatic temperature change T
ad = 23.2 K for a field change of 8.9 T. At T = 20
K, the lattice entropy S
L is small enough
compared to the magnetic entropy S
m, S
m/S
L = 21.3, which
warrants its potential in 2 −20 K cryocoolers with both the
Stirling and Carnot cycles. Though with relatively large exchange
interactions, the layered A-type spin arrangement ultimately enhances
the magnetocaloric coupling, raising the possibilities of designing
magnetic refrigerants with a high ratio of cooling capacity to volume.
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