Magnetic Phase Transition Temperature Research Articles

Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe3: Experiment and Calculation.

This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe3. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe3 was solved in the space group Cmcm (a = 4.3086(3) Å, b = 14.3093(9) Å, and c = 11.1957(7) Å) with the KZrCuS3 structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe6]9-) form two-dimensional layers (Er(Te1)2/2e(Te2)4/2k-)∞2, while distorted tetrahedra ([CuTe4]7-) form one-dimensionally connected substructures (Cu(Te1)2/2e(Te2)2/1t5-∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers (CuErTe32-∞2) between which Eu2+ ions are located in a trigonal-prismatic coordination environment (EuTe610-). The trigonal prisms are connected by faces, forming chains (Eu(Te1)2/2(Te2)4/22-∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh3 with Ch = S, Se, and Te) and tellurides (EuLnCuTe3 with Ln = Gd, Er, and Lu). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe3 were performed. The types and wavenumbers of fundamental modes were determined, and the involvement of ions in the IR and Raman modes was assessed. The experimental Raman spectra were interpreted. The telluride EuErCuTe3 at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh3 with Ch = S and Se). Its experimental magnetic characteristics were close to the calculated ones. The decrease in the magnetic phase transition temperature in the series of the erbium chalcogenides was discovered.

Geometrically frustrated Gd2Ti2O7 oxide: A comprehensive exploration of structural, magnetic, and magnetocaloric properties for cryogenic magnetic cooling applications

The magnetocaloric effect (MCE) has been extensively studied in various magnetic solids, aiming to both facilitate practical applications in magnetic cooling and deepen our understanding these materials’ intrinsic properties. This study presents a systematic investigation of Gd2Ti2O7 oxide, characterized by a geometrically frustrated magnetic structure, focusing on its structural and magnetic characteristics through experimental analysis and theoretical calculations. Emphasis is placed on its magnetic phase transition (MPT) and magnetocaloric properties, scrutinizing temperatures as low as 0.4 K and magnetic fields up to 16 T. The results reveal that Gd2Ti2O7 oxide possesses a crystalline cubic pyrochlore-type structure with an antiferromagnetic (AFM) semiconductor ground state. The material undergoes a first-order MPT in low field and low-temperature regimes, transitioning to a second-order MPT above 2 K up to 16 T. Evaluation of magnetocaloric parameters, including maximum magnetic entropy change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, indicates moderate values under low magnetic field changes, while significantly large values are achievable under high magnetic field changes. This finding suggests that potential cryogenic magnetocaloric materials (MCMs) with optimal performance should exhibit low MPT temperatures induced by magnetic frustration and possess a ground state with a sufficiently large magnetic moment induced by low magnetic fields, thus avoiding excessively strong AFM coupling. This study lays the groundwork for future cryogenic MCM design and provides valuable insights into the intrinsic properties of geometrically frustrated magnetic materials.

The varying nature of the martensitic phase transition and associated entropy changes in a Co and Cr doped pseudo-ternary Heusler alloy system

We have investigated the magnetostructural phase transitions and the associated entropy changes in a system of three Heusler alloys, namely: Ni2Mn0.55Cr0.45Ga, Ni2Mn0.55Co0.10Cr0.35Ga, and Ni2.15Mn0.75Cr0.1Ga. All three alloys exhibited first-order martensitic phase transition. An inter-martensitic phase transition raised the magnetic and structural phase transition temperatures, and partially decoupled the said transitions. Furthermore, field magnetization measurements demonstrated that a significant reduction in magnetic hysteresis is achieved in the Ni2Mn0.55Co0.10Cr0.35Ga compound, resulting in improved effective refrigerant capacity values. The largest magnetic entropy change of −23.5 J/kg K and refrigeration capacity of 97.7 J/kg were observed in Ni2.15Mn0.75Cr0.1Ga. This observation of mitigated deficiencies in materials experiencing a first-order phase transition is relevant towards their application in magnetic refrigeration.

Mutual control of electric and magnetic orders near room temperature in Al doped Y-type hexaferrite single crystals

Realizing robust magnetoelectric (ME) coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices. Here we report a systematic study on the magnetic, dielectric, and ME coupling properties of Y-type hexaferrite Ba0.5Sr1.5Co2Fe12–xAlxO22 (x = 0.0, 0.5, 1.0) single crystals. The Al doping can induce the shifting of the alternating longitudinal conical (ALC)-proper screw (PS) magnetic phase transition temperature from 200 K for x = 0.0 to 365 K for x = 1.0. The most interesting feature is that the Ba0.5Sr1.5Co2Fe11AlO22 single crystal displays a direct and converse ME coupling coefficient with ∼ 3,100 ps/m and ∼ 3,900 ps/m at 250 K, respectively, due to the Al-doped enhanced stability of ALC phase. Moreover, the exchange bias also verifies the strong coupling of electric and magnetic orders. These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.

Fe-induced modifications in the magnetic and dielectric response of EuTiO3: Unraveling the linkage to oxygen vacancies

EuTi1−xFexO3 (x = 0.0–0.5) is studied to analyze the effect of Fe substitution on structural, dielectric and magnetic properties. We found that Fe substitution in place of Ti increases the barrier for charge carrier hopping therefore, suppresses the electrical conduction in the material. It has also been observed that characteristic G-type antiferromagnetic ordering of pure EuTiO3 can be significantly modified with Fe doping. Interestingly, formation of oxygen vacancies due to Fe substitution allows next nearest neighbor Eu ion interaction and generates ferromagnetic response in the magnetic hysteresis loops. Magnetic phase transition temperature also shifts to the higher temperature side with the increase in Fe concentration till x = 0.3 which implies strengthening of magnetic interaction. Schematic models based on the crystal and electronic structure are presented to explain the observed dielectric and magnetic response and it is concluded that both features can be tuned by the Fe substitution.

Electric, Dielectric, and Phonon Properties of Cu2OCl2

Investigating the multiferroic properties of , their temperature and magnetic‐field dependencies around the magnetic and ferroelectric phase transition temperatures and are analyzed using a microscopic model and Green's function technique. Near the Neel temperature , a kink in the specific heat and also in the phonon energy and damping due to strong anharmonic spin–phonon interaction is observed. The kink in disappears with increasing magnetic field h. The polarization shows also a small anomaly at and decreases with increasing magnetic field h. This behavior strongly suggests that exhibits multiferroic characteristics. A kink at can be seen in the real part of the dielectric constant , too. It should be noted that demonstrates a significant increase with increasing field strength h below , which is a pronounced magneto‐dielectric effect. These findings qualitatively agree with the experimental data.

Magnetic properties and large cryogenic magnetocaloric effects in the RE2SiO5 (RE = Gd, Dy, Ho, and Er) silicates

We herein investigated four rare earth (RE)-based oxides, the RE2SiO5 (RE = Gd, Dy, Ho, and Er) silicates, regarding their structural and cryogenic magnetic properties. All the RE2SiO5 silicates are found to crystallized in a monoclinic structure. X-ray photoemission spectroscopy spectra illustrate that RE, Si and O elements in RE2SiO5 silicates are present as RE3+, Si4+, and O2−, respectively. The Dy2SiO5 reveals a first-order magnetic transition around 4.5 K. The magnetic phase transition temperatures are probably below 2 K for the RE2SiO5 (RE = Gd, Ho, and Er) silicates. Large cryogenic magnetocaloric effects (MCE) and good magnetocaloric performances were observed in the RE2SiO5 silicates. The MCE parameters in terms of the maximum magnetic entropy changes, the temperature-averaged entropy change (5 K-lift) and refrigerant capacity under a magnetic field change of 0–5 T are determined to be 35.5, 30.4 J/kgK, and 215.7 J/kg for Gd2SiO5, to be 13.3, 12.9 J/kgK, and 190.5 J/kg for Dy2SiO5, to be 15.3, 15.1 J/kgK, and 274.1 J/kg for Ho2SiO5 and to be 17.9, 16.5 J/kgK, and 181.14 J/kg for Er2SiO5, respectively. These derived values of MCE parameters of the RE2SiO5 silicates, especially for Gd2SiO5, are at similarly high level with or better than those of the updated candidate materials, making them also of potential for practical magnetic refrigeration applications.

Transport characterization of magnetic phase transition in Mn<sub>3</sub>Sn thin films

In recent years, topological antiferromagnetic material with hexagonal Kagome structure has attracted great research interest due to its unique properties. Although its net magnetic moment is close to zero, the topological antiferromagnet exhibits the strong magnetoelectric, the magneto-optical, and the magnetothermal effect, with a strength comparable to that of ferromagnetic material, which makes it highly valuable for various applications. After several years of extensive studies, it has been realized that most of the unique properties of topological antiferromagnet are actually closely related to its magnetic structure. However, it has been found that the magnetic structure of the material is highly sensitive to its chemical composition and growth condition. Therefore, it is crucial to develop a universal and simple method of measuring the magnetic structure and determining the magnetic phase transition of hexagonal Kagome topological antiferromagnetic material, which can severe as a good supplement for the current high-energy neutron diffraction approach that is not accessible for ordinary laboratories. In this study, we have successfully prepared high-quality (<inline-formula><tex-math id="M3">\begin{document}$ 11\bar{2}0 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M3.png"/></alternatives></inline-formula>)-oriented hexagonal Kagome antiferromagnetic Mn<sub>3</sub>Sn thin films on (<inline-formula><tex-math id="M4">\begin{document}$1 \bar{1} 02$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M4.png"/></alternatives></inline-formula>)-oriented Al<sub>2</sub>O<sub>3</sub> single crystal substrates by using the pulsed laser deposition method. After systematically measuring how the magnetic and transport properties of the Mn<sub>3</sub>Sn thin film change with temperature, it is found that its magnetization curve, Hall resistivity curve, and magnetoresistance curve exhibit certain anomalous features at some or all of its three magnetic phase transition temperatures. These features can serve as good evidences of magnetic phase transitions in this hexagonal Kagome antiferromagnetic Mn<sub>3</sub>Sn thin film, or even could be used to measure the temperatures of these magnetic phase transitions. Our work contributes to the further advancement of the application of hexagonal Kagome topological antiferromagnetic materials to spin electronic devices.

Two-dimensional ferromagnetism induced by Jahn-Teller distortion and orbital order

As the dimension of the system decreases, the quantum confinement effect and electronic correlation interaction inside the material will be correspondingly enhanced, often resulting in some novel physical properties. Recently, the freestanding perovskite oxide films down to the monolayer limit have been successfully prepared and can be transferred to any desired substrate, providing a great opportunity to explore the functional properties of two-dimensional perovskites. In perovskite materials, Jahn-Teller distortion and orbital order often cause a variety of correlated electronic behaviors. However, unlike van der Waals materials that retain their structural and chemical bonding characteristics when reduced to the monolayer limit, perovskite materials may undergo structural reconstruction when reduced to two dimensions. Therefore, whether Jahn-Teller distortion and related effects exist in the perovskite monolayer limit, and whether two-dimensional perovskite can exhibit some new properties different from its bulk phase, have become urgent issues to be solved. In this work, perovskite fluoride KCuF<sub>3</sub> and its monolayer have been comparatively studied by means of first-principles calculation, symmetry analysis, and Monte Carlo simulation methods, to reveal the change in lattice dynamics, structural, electronic, and magnetic properties caused by dimensionality reduction in perovskites. The results show that the cooperative Jahn-Teller distortion and the in-plane staggered orbital order occurring in the KCuF<sub>3</sub> bulk can be retained to the monolayer limit. However, unlike the bulk phase, the Jahn-Teller distortion mode appears as a soft mode of the prototype phase in the monolayer, and the insulating property of the monolayer does not rely on the emergence of the Jahn-Teller distortion, but is related to the enhancement of the electronic correlation effect. The staggered orbital order causes the nearest-neighbor exchange interaction to be ferromagnetic, resulting in the monolayer being a two-dimensional ferromagnetic insulator, different from the antiferromagnetic phase in the bulk. Monte Carlo simulations predict that the Curie temperature of the monolayer is about 5 K, which is much lower than the Néel temperature of the bulk phase, indicating that the disappearance of interlayer coupling leads to a significant reduction in the magnetic phase transition temperature. This work provides guidance and reference for the study of two-dimensional perovskite materials and the design of perovskite-based two-dimensional ferromagnets.

Enhanced magnetoelectric coupling effect in Mg-doped Y-type hexaferrite BaSrCo2-xMgxFe11.1Al0.9O22 ceramics

The influences of Mg doping on the magnetic order structure and magnetoelectric (ME) effect were investigated in Y-type hexaferrite BaSrCo2-xMgxFe11.1Al0.9O22 (x = 0.00, 0.25, 0.50, 0.75, 1.00) ceramics. The results revealed that the Mg doping could increase the magnetic phase transition temperature. The optimal magnetic-driven electric polarization could be obtained at x = 0.25 ceramic, exhibiting a maximum electric polarization of 16.22 μC/m2 and a ME coefficient of 203 ps/m at 100 K. The stability of reversible electric polarization was demonstrated via the measurement of continuous magnetic field cycles. Moreover, the ME phase diagram was established by measuring the magnetic dielectric properties. Finally, a possible Mg-tune magnetic structure was proposed to explain the enhanced ME effect.

Magnetic phase transition and magnetocaloric effect of RE2RuIn (RE = Dy, Ho, Er, Tm)

In this work, we provide an experimental investigation on the magnetic phase transition (MPT) and magnetocaloric (MCE) properties of the RE2RuIn (RE = Dy, Ho, Er, Tm) samples with a bcc superstructure. The indides RE2RuIn order magnetically at low temperature and exhibit large cryogenic reversible MCEs around their MPT temperatures. The magnetocaloric parameters including the peak value of magnetic entropy change, temperature-averaged entropy changes with 5 K-lift, and refrigerant capacity under magnetic field change of 0–7 T are determined to be 18.6 J/kgK, 18.2 J/kgK, and 372.2 J/kg around 15.6 K for Dy2RuIn, to be 22.6 J/kgK, 22.0 J/kgK, and 415.6 J/kg around 3.0 K for Ho2RuIn, to be 21.1 J/kgK, 19.8 J/kgK, and 346.3 J/kg around 6.4 K for Er2RuIn, to be 21.3 J/kgK, 20.7 J/kgK, and 347.8 J/kg around 3.2 K for Tm2RuIn, respectively.

Rare‐Earth‐Free Mn30Fe20−xCuxAl50 Magnetocaloric Materials with Stable Cubic CsCl‐Type Structure for Room‐Temperature Refrigeration

AbstractMagnetic refrigeration technology based on the magnetocaloric effect (MCE) of magnetic substances has been considered a prominent, energy‐efficient, and environmentally benign cooling method. Exploring suitable magnetic substances is a prerequisite for practical applications. A family of rare‐earth‐free magnetocaloric materials called Mn30Fe20−xCuxAl50 alloys is identified room‐temperature refrigeration, which are derived from the well‐known MnAl‐based permanent magnets. As expected from experimental and theoretical investigations, all of the Mn30Fe20−xCuxAl50 alloys are crystallized in a stable cubic CsCl‐type crystal structure, revealing a single second‐order type magnetic phase transition (MPT) with tunable MPT temperature. They also exhibit a large reversible MCE and good magnetocaloric performances in a wide temperature range. Crucially, these Mn30Fe20−xCuxAl50 alloys represent a rare case of magnetic materials belonging to a large family that can be fabricated from low‐price, earth‐abundant, and non‐toxic elements. They could provide new choices for practical room‐temperature magnetic refrigeration applications.

Quantum geometric spin frustration of antiferromagnetic CuFeO2 enables photocatalytic applications

Photocatalysis, containing a potential solution to the global crises of energy shortage and the greenhouse effect, has been studied extensively in recent years. The CuFeO2 (abbreviated as CFO) is a material with a Delafossite structure, and has also been widely studied because of its triangular lattice antiferromagnets. The triangular lattice composed of Fe3+ ions, along with strong antiferromagnetic spin coupling between the Fe3+ ions, leads to a geometric spin frustration. Furthermore, CFO is also a potential candidate for the photocatalytic material due to its narrow band gap of 1.1–1.6 eV, electrochemical stability in an aqueous environment, high charge carrier mobility, flat-band potential positioned at ∼ 1 eV, and contains an abundance of raw materials in the earth. In this study, we successfully grew the size and highly-quality CFO single crystals using the optical floating-zone technique. Powder x-ray diffraction (XRD) and Rietveld refinement indicate that the CFO is a rhombohedral structure with a space group of R3̅m, consisting of edge-shared FeO6 octahedron to form the FeO2 layer, and the Cu cations occupied between the two FeO2 layers. The core-level electron energy loss (EEL) spectra found the valence of Fe and Cu in CFO is +3 and +1, respectively. The low-loss EEL spectrum observed two volume plasmons at ∼5 eV and ∼23 eV contributed from the collective oscillation of Cu-O antibonding states σCu−O* and mixed nonbonding Cu 3dxy, σCu−O bonding states, and Fe-O, respectively, based on the density function theory calculation. The optical absorption spectrum measured the energy bandgap for CFO is about 1.5 eV. The Raman spectrum shows significant Eg and A1 g vibration modes corresponding to the in-plane Fe-O and out-of-plane Cu-O vibrations, respectively. Both magnetic susceptibility, χ(T), with the applied magnetic field along the c-axis and specific heat capacity reveal the two magnetic phase transition temperatures at low temperatures: TN1 = 13.5 K when transition from paramagnetic (PM) phase to partially disordered antiferromagnetic, and TN2 = 10.5 K when complete transition from partially disordered antiferromagnetic to antiferromagnetic phase. The additional calculation of magnetic entropy change is 0.15, which is roughly close to 0.2, meaning that only 1/5 of the Fe3+ spins are disordered when transforming from PM states to partially disordered at T < TN1 in this study. The presence of instantaneous ferromagnetic spin arrangement (↑↑↓) extends the residence time of H2O on the surface of CFO, facilitating electron exchange with CFO and promoting photocatalytic water splitting reactions.

Influence of non-magnetic Cu on structural, magnetic and magnetocaloric properties on NiMnIn bulk Heusler alloys

The structural, magnetic, and magnetocaloric characteristics of bulk Cu-doped Ni47Mn40-sCusIn13 Heusler alloys (s = 0 and 1) were investigated. Temperature-dependent magnetizations for Ni47Mn40-sCusIn13(s = 0 and 1) were performed under a magnetic field (H) 0.05 T. The substitution of Copper (Cu) for Manganese (Mn) reduces the structural as well as magnetic phase transition temperatures. At room temperature (RT), PXRD pattern of Ni47Mn40-sCusIn13 (s = 0 and 1) bulk Heusler alloys shows that both samples have a cubic structure. The copper substitution in the Mn-site shifts the martensitic transformation temperature to the low temperature side as valence electron concentrations (e/a) decrease [MS = 288 K for s = 0 and MS = 251 K for s = 1]. The isothermal magnetization [M(H)] curve in the vicinity of the martensitic transition for s = 1 alloy exhibits the typical metamagnetic behavior that is not present for s = 0 Heusler alloys. The alloys reveal positive magnetic entropy changes (ΔSM) for s = 0 and 1 respectively. A maximal ΔSM of 10 J.kg-1K−1 at a temperature of 248 K has been obtained in the s = 1 compare than ΔSM of 1.27 J.kg-1K−1 (s = 0) alloys for a field change of 0–5 T.

High-Performance Thermomagnetic Gd-Si-Ge Alloys.

Exploring low-grade waste heat energy harvesting is crucial to address increasing environmental concerns. Thermomagnetic materials are magnetic phase change materials that enable energy harvesting from low-temperature gradients. To achieve a high thermomagnetic conversion efficiency, there are three main material requirements: (i) magnetic phase transition near room temperature, (ii) substantial change in magnetization with temperature, and (iii) high thermal conductivity. Here, we demonstrate a high-performance Gd5Si2.4Ge1.6 thermomagnetic alloy that meets these three requirements. The magnetic phase transition temperature was successfully shifted to 306 K by introducing Ge doping in Gd5Si4, and a sharper and more symmetric magnetization behavior with saturation magnetization of Mmax = 70 emu/g at a 2 T magnetic field was achieved in the ferromagnetic state. The addition of SeS2, as a low-temperature sintering aid, to the Gd-Si-Ge alloy improved the material's density and thermal conductivity by ∼45 and ∼275%, respectively. Our results confirm that the (Gd5Si2.4Ge1.6)0.9(SeS2)0.1 alloy is a suitable composite material for low-grade waste heat recovery in thermomagnetic applications.

Magnetic and magnetocaloric properties of R55Co30Al10Si5 (R = Ho, Dy) metallic glass ribbons

Metallic glass alloys are suitable systems for the development of magnetocaloric refrigerated materials due to the stable physical properties and the adjustable magnetic phase transition temperature. Here, the glass formation ability (GFA), magnetic properties and magnetocaloric effects of R55Co30Al10Si5 (R = Ho, Dy) amorphous ribbons prepared by the melt-spinning technique were investigated. The X-ray diffraction and DSC measurement indicated that the metallic glass alloys have a completely amorphous structure and excellent glass formation ability. The amorphous ribbons were demonstrated to undergo a second-order magnetic phase transition (ferromagnetic to paramagnetic) around Tc ∼ 18 K for Ho55Co30Al10Si5, ∼34 K for Dy55Co30Al10Si5, respectively. The maximum magnetic entropy change (-ΔSMmax) and the corresponding refrigerant capacity (RC) values are 12.7 J/kg K, 343 J/kg for Ho55Co30Al10Si5, 9.1 J/kg K, 334 J/kg for Dy55Co30Al10Si5 under a field change ΔH= 5 T. The large -ΔSMmax and high RC suggest that R55Co30Al10Si5 (R = Ho, Dy) amorphous ribbons have potential applications in low temperature magnetic refrigeration.

Exploration of the rare-earth cobalt nickel-based magnetocaloric materials for hydrogen liquefaction

Magnetic refrigeration based on the magnetocaloric effect (MCE) of magnetic solids has been considered as an emerging technology for hydrogen liquefaction. However, the lack of high-performance materials has slowed the development of any practical applications. Here, we present a family of rare-earth cobalt nickel-based magnetocaloric materials, namely Dy1-xHoxCoNi and Ho1-xErxCoNi compounds, and systematically investigated their structural and magnetic properties as well as the MCE and magnetocaloric performance. All of these compounds crystallize in the C15-type Laves-phase structure and undergo typical second-order magnetic phase transition (MPT). The change in magnetism and the MPT temperature for the Dy1-xHoxCoNi and Ho1-xErxCoNi compounds originate from the exchange interactions between nearest-neighbor RE3+ ion pairs. No hysteresis magnetocaloric effect was achieved, and the MPT temperature of these compounds could be tuned from the liquefaction temperature of nitrogen (∼77 K) to hydrogen (∼20 K) by adjusting the ratio of rare-earth elements. This study's findings indicate that the Dy1-xHoxCoNi and Ho1-xErxCoNi compounds are of potential for practical magnetic refrigeration applications in the field of hydrogen liquefaction.

Large low-field reversible magnetocaloric effect in K3Gd(PO4)2 at sub-Kelvin temperature

We synthesized a potassium gadolinium phosphate K3Gd(PO4)2 with monoclinic structure (P21/m) by the high-temperature solid–state reaction method. Its lattice constants obtained by Rietveld refinements of XRD curve are a = 0.7411 nm, b = 0.5624 nm, and c = 0.9433 nm. Magnetic and magnetocaloric properties of K3Gd(PO4)2 were investigated in detail. The magnetic phase transition temperature of K3Gd(PO4)2 was determined by ultra-low temperature testing to be 0.58 K. K3Gd(PO4)2 exhibits large magnetic entropy changes (–ΔSM). The maximum –ΔSM are 20.2 and 29.4 J/(kg·K) in the magnetic field variation (ΔH) of 1 and 2 T, respectively, which are larger than that of the commercial Gd3Ga5O12 (GGG). The maximum adiabatic temperature change (ΔTad) reaches 5.91 K under a magnetic field change (ΔH) of 1 T. K3Gd(PO4)2 is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.

Synthesis and magnetic properties of ε-AlxFe2-xO3 nanoparticles

ε-AlxFe2-xO3 (x = 0, 0.125, 0.167, 0.222 and 0.4) nanoparticles were manufactured by a new kind of mesoporous template-compacted fumed silica. The effect of Al3+ composition on the purity and magnetic performances of the ε-AlxFe2-xO3 samples were investigated. The structural and magnetic performances of the samples were characterized by X-ray diffraction, transmission electron microscope and SQUID magnetometer. The results indicate that the doping of Al3+ can decrease the dimension of ε-Fe2O3 nanoparticles and effectively reduce the formation of α-Fe2O3 impurity in the samples. And the magnetic phase transition temperature of the ε-AlxFe2-xO3 samples decreases with the increase of Al3+. And the low temperature magnetic phase transition finally vanishes at x = 0.222. The ε-AlxFe2-xO3 samples exhibit large coercivity. With the increase of Al3+ content, the coercivity of ε-AlxFe2-xO3 increases firstly to a maximum and then decreases.

The Evolution of the Magnetic Properties&#x0D; of Iron Borate Single Crystals Doped with Gallium

Highly perfect FeBO3 and Fe0.91Ga0.09BO3 single crystals were studied in a wide temperature range using SQUID magnetometry. A theoretical model describing the temperature and field dependences of the magnetization of single crystals has been developed. It is found that even a small concentration of gallium,which is a diamagnetic impurity, substantially affects the magnetic properties of single FeBO3 crystals. In par-ticular, the Fe0.91Ga0.09BO3 crystal differs from the pure FeBO3 phase in by a lower magnetic phase transition temperature and a higher antiferromagnetic susceptibility at low temperatures.