Magnetic Transition Behavior Research Articles

Effect of Fe on the microstructure and magnetic transition of Mn-Fe-P-Si Microwires

This work systematically investigated the effect of Fe content on the microstructure and magnetic transition behaviors of melt-extracting Mn-Fe-P-Si microwires. It was shown that the Fe content does not change the main phase of the samples, i.e. Fe2P compound, which decreased with the increasement of Fe content. The transition temperature (Ttran) decreased from 311 to 245.5 K while the thermal hysteresis (Thys) increased from 9.5 to 22.5 K increasing Fe from 0.90 to 1.05. The samples realized the first order magnetic transition at x = 1.00 and 1.05, correspondingly the samples demonstrated large magnetic hysteresis losses (Wy,) and isothermal magnetic entropy change (−∆Sisopeak) at 5 T, 59.1 J kg−1 and 14.5 J kg−1 K−1 for the sample x =1.00, 58.4 J kg−1 and 15.8 J kg−1 K−1 for the sample x = 1.05. In contrast, the samples at x = 0.90 and 0.95 indicated second order transition character, and the Wy and −∆Sisopeak were much smaller, i.e. 14.8 J kg−1 and 10.3 J kg−1 K−1, 9.7 J kg−1 and 10.7 J kg−1 K−1 respectively for the samples x = 0.90 and 0.95. The largest effective refrigerant capacity (RCE, 293.7 J kg−1, 5 T) is found at x = 0.90. The reduced hysteresis and maintained competitive isothermal magnetic entropy change make the melt-extracting Mn-Fe-P-Si microwires with optimized Fe content as a promising magnetocaloric material family applied in real magnetic refrigeration applications.

Anomalous Hall effect and magnetic transition in the kagome material YbMn6Sn6

We investigate the magnetic and transport properties of a kagome magnet YbMn6Sn6. We have grown YbMn6Sn6 single crystals having a HfFe6Ge6 type structure with ordered Yb and Sn atoms, which is different from the distorted structure previously reported. The single crystal undergoes a ferromagnetic phase transition around 300 K and a ferrimagnetic transition at approximately 30 K, and the magnetic transition at low temperature may be correlated to the ordered Yb sublattice. Negative magnetoresistance has been observed at high temperatures, while the positive magnetoresistance appears at 5 K when the current is oriented out of kagome plane. We observe a large anisotropic anomalous Hall effect with the intrinsic Hall contribution of 141 Ω−1cm−1 for σzxint and 32 Ω−1cm−1 for σxyint , respectively. These values are similar to those in YMn6Sn6 with the same anisotropy. The magnetic transition and anomalous Hall behavior in YbMn6Sn6 highlights the influence of the ordered Yb atoms and rare earth elements on its magnetic and transport properties.

Effect of Al doping on magnetocaloric effect and mechanical properties of La(FeSi)13-based alloys

La(Fe,Si)13 is a candidate room temperature magnetic refrigeration material owing to its large magnetocaloric effect and an adjustable Curie temperature. The structure, magnetocaloric effect, and mechanical properties of La(Fe,Si)13 strongly depend on its microscopic atomic environment. Proportional doping of magnetic or ductile elements can improve its magnetocaloric and mechanical properties. Here, magnetocaloric effect, and mechanical properties of Al-doped La(Fe,Si)13 alloys were studied through density functional theory calculations and experiments. The experimental results show that the doping of Al can increase the Curie temperature of the alloy, broaden the full width at half maximum (FWHM) and improve the mechanical properties of the alloy. The density functional theory describes the magnetic transition and mechanical behavior of the alloy, which is consistent with the experimental results. Therefore, the appropriate doping of Al in La(FeSi)13 alloy can obtain good integrated refrigeration capacity, which is helpful to realize multi-stage refrigeration application in a wide temperature range.

Weak magnetic doping effect on the magnetic transition, magnetocaloric properties, and super-invar behavior in TbCo2Vx system

In this work, the V-doped effect on the magnetic transition and magnetocaloric properties have been studied systematically for TbCo2Vx (0 ≤ x ≤ 0.2) series. All samples were characterized by powder X-ray diffraction (XRD) as cubic structures (Fd-3 m) at room temperature. The Curie temperatures TC of TbCo2Vx decrease monotonically from 234 K (x = 0) to 214 K (x = 0.2) corresponding to a monotonically increasing value of lattice a. The slightly diminished magnetic saturation moment MS from 6.35 μB/f.u to 6.12 μB/f.u with the x value increasing indicates weak magnetic doping in this system, which can also be reflected in the slight decrease of the maximum values of magnetic entropy change (-ΔSM) from 6.23 J kg-1K−1 to 5.27 J kg-1K−1 (0–5 T). X-ray photoelectron spectrum (XPS) measurements confirm that the weak magnetic doping originates from the multivalences of V2+ and V4+, compared with other normally nonmagnetic V-doped cases reported before. Both the Banerjee criteria and rescaled magnetic entropy change lines deny the first-order transition in parent compound TbCo2 as reported recently. Almost zero thermal expansion near TC in TbCo2 with thermal expansion coefficient αl = -1.43 × 10-6 K−1 indicates weak magnetostriction, which is another experimental hint for second-order transition. The deviation of the critical exponents to Mean-field theory in TbCo2 implies some crystal defects and inhomogeneous polycrystalline distribution inside, which should also be a key point for the divergence of first-order and second-order transition in different samples of TbCo2 as reported before. Super-invar behavior with αl = 4.4 × 10-7 K−1 was found in the x = 0.2 component by macro-thermal expansion measurement.

Successive magnetic transitions and magnetocaloric effects in intermetallic compounds RE5Pt3 (RE = Dy, Ho)

The structure, low-temperature magnetic transition behaviors, and magnetocaloric properties of rare-earth-based binary compounds RE5Pt3 (RE = Dy, Ho) were studied. Both of the compounds crystallize in the Mn5Si3 hexagonal structure with a P63/mcm space group. With the decrease of temperature, the compounds undergo a phase transition from the paramagnetic (PM) state to the ferromagnetic (FM) state, followed by a spin reorientation. In the paramagnetic region, the reciprocal magnetic susceptibilities of RE5Pt3 obey the Curie-Weiss law. The effective paramagnetic magnetic moment values were determined to be 10.59 μB/Dy3+ and 10.40 μB/Ho3+, respectively, with the corresponding paramagnetic Curie temperatures of 30.0 K and 16.4 K. The maximum magnetic entropy changes (-ΔSM) of RE5Pt3 (RE = Dy, Ho) were calculated to be 8.2 J/kg K and 9.1 J/kg K for a field change of 0–5 T. In addition, it is confirmed that the successive magnetic phase transition enlarges the magnetic entropy change and the working temperature region by Lorentz bimodal fitting. Evidently, the RE5Pt3 (RE = Dy, Ho) compounds with reversible MC effect are expected to have effective applications in the low-temperature range.

Spin glass behavior and dielectric properties of Sm2CuMnO6 perovskites

Monoclinic Sm2CuMnO6 is a fascinating material that exhibits intriguing magnetic and dielectric properties. In this study, we investigated the magnetic transition, conduction mechanism, and dielectric behavior of the material. Mott's variable range hopping of polarons is proposed as a satisfactory explanation for the conduction process, shedding light on the underlying charge transport mechanism. Furthermore, the material displays a spin glass transition at a freezing temperature of Tf = 18 K, suggesting the presence of competing magnetic interactions. Dielectric measurements reveal intriguing temperature and frequency dependence of the dielectric constant (ε) in Monoclinic Sm2CuMnO6. Below 100 K, the dielectric constant remains unchanged with variations in both temperature and frequency, indicating a stable dielectric response. However, above 100 K, ε exhibits an increasing trend with rising temperature and also displays frequency dependence. This behavior suggests the contribution of both deformational and relaxation polarizations, emphasizing the complex nature of the dielectric response.

Synthesis and Characterization of a One-Dimensional Malleable Spin-Crossover Polymer Complex Modified by Methoxy Polyethylene Glycol.

A novel one-dimensional malleable spin-crossover (SCO) complex {[Fe(MPEG-trz)3](BF4)2} has been successfully synthesized by molecular self-assembly between 4-amino-1,2,4-triazoles (MPEG-trz) grafted with a long flexible chain methoxy polyethylene glycol (MPEG) and metallic complex Fe(BF4)2•6H2O. The detailed structure information was illustrated by using FT-IR and 1H NMR measurements, while the physical behaviors of the malleable SCO complexes were systematically investigated by using magnetic susceptibility measurements using superconductivity quantum interference device (SQUID) and differential scanning calorimetry (DSC). This new metallopolymer exhibits a remarkable spin crossover transition behavior, between two spin quantum states (Fe2+ ions): high spin (HS) state (quintet state) and low spin (LS) state (singlet state), at a specific critical temperature with a slender hysteresis loop of 1 K. DFT computations revealed the partial rules of HOMO-LUMO energy levels and spin density distributions of different four-position substituted [Fe(1,2,4-triazole)3]2+ derivatives with different length of repeat units in polymer complexes. This can go a step further to depict the spin and magnetic transition behaviors of SCO polymer complexes. Furthermore, the coordination polymers possess an excellent processability due to an outstanding malleability, which can be easily shaped into a polymer film with spin magnetic switching properties.

Correlation between Magnetocaloric Properties and Magnetic Exchange Interaction in Gd54Fe36B10-xSix Amorphous Alloys.

Gd54Fe36B10-xSix (x = 0, 2, 5, 8, 10) amorphous ribbons were fabricated by melt-spinning technique. Based on the molecular field theory, the magnetic exchange interaction was analyzed by constructing the two-sublattice model and deriving the exchange constants JGdGd, JGdFe and JFeFe. It was revealed that appropriate substitution content of Si for B can improve the thermal stability, maximum magnetic entropy change and widened table-like magnetocaloric effect of the alloys, while excessive Si will lead to the split of the crystallization exothermal peak, inflection-like magnetic transition and deterioration of magnetocaloric properties. These phenomena are probably correlated to the stronger atomic interaction of Fe-Si than that of Fe-B, which induced the compositional fluctuation or localized heterogeneity and then caused the different way of electron transfer and nonlinear variation in magnetic exchange constants, magnetic transition behavior and magnetocaloric performance. This work analyzes the effect of exchange interaction on magnetocaloric properties of Gd-TM amorphous alloys in detail.

Thickness-Dependent Oscillation Behavior of Magnetic Phase Transitions in Pt Ultrathin Films with Small Orbital Moment

Ferromagnetism in nano-Pt films originates from the quantum-confinement effect that depends on film thickness. Studies of the electronic states of nano-Pt will aid in developing methods for efficiently utilizing its large spin-orbit coupling.

Magnetic behaviors and magnetocaloric effects in rare earth high-entropy amorphous/nanocrystalline alloys

Rare earth high-entropy alloys (RE–HEAs) exhibit great potential to be applied as refrigerants due to their good comprehensive magnetocaloric properties. In this work, octary GdTbDyHoErTmCoAl and GdTbDyHoErTmCoNi RE–HEAs with amorphous/nanocrystalline structure exhibiting comparable magnetocaloric effect were synthesized. Both RE–HEAs show a second-order magnetic phase transition in the temperature range of hydrogen liquefaction. Due to the complex magnetic interactions, a spin glass-like behavior at low temperatures is observed in the RE–HEAs. A superior magnetocaloric effect is obtained in the nanocrystalline GdTbDyHoErTmCoNi high-entropy alloy that is multiphase attributed to a stronger magnetic exchange interaction when compared with the other that exhibits single amorphous structure. Despite heterogeneous microstructure, homogeneous chemical distributions are observed in the partially crystallized high-entropy alloy. In addition, the magnetocaloric effect and magnetic transition behavior of rare earth medium- and high-entropy alloys, including the RE–HEAs in this study, are summarized and discussed. The results in this work provide a helpful guide for the design of RE–HEAs for hydrogen liquefaction applications with excellent magnetocaloric effects.

Magneto-Structural Transition and Refrigeration Property in All-D-Metal Heusler Alloys: A Critical Review

Abstract: All-d-metal Heusler alloys has attracted much attention due to its unique magnetic properties, martensite transformation behavior and related solid-state refrigeration performance. These unique type alloys are recently discovered in 2015 and have been widely studied; however, systematic reviews on their magneto-structural transition and refrigeration property are rare. In this review, we first summarize the preparation techniques and microstructure of the bulk alloys and ribbons. Then the magnetic transition and martensite transformation behavior are reviewed, focusing on the correlation between magneto-structural transition and refrigeration properties. The effects of element doping, external magnetic and mechanical fields on the martensite transformation and corresponding magnetic entropy change are summarized. We end this review by proposing the further development prospective in the field of all-d-metal Heusler alloys.

Half-metallic transition for ZGNRs adsorbing porphine molecules under an in-plane external electric field

The controlling of magnetic transition behavior by changing the coupling between molecule and nanoribbon has attracted a new topic. Here we study a zigzag graphene nanoribbon (ZGNR) absorbing the porphine molecules with different manners under an in-plane external electric field. These structureless systems may exhibit sensitive magnetic response. By employing the first-principles calculations, we find that the sensitivity of magnetic response for the asymmetry structure model is superior to the symmetry one. In general a series of the magnetic phase transitions for the asymmetry models can be induced by an in-plane external electric filed. Particularly, asymmetrical model of ZGNR absorbing porphine molecule at one side can transfer the half-metallic state from spin-up sub-band to spin-down one. Our analysis demonstrate that the phase transition is manipulated by the direction changing of the interior electric field. Interestingly, the models of structural asymmetry can exhibit spin-polarized electron band structures with the spin-polarization rate reaching up to 100%. The findings may provide an approach for the design of new devices to realize logic operation within spintronics.

Magnetic transition behavior and electromagnetic properties of Zr substituted Bi0.5Y1.5−xCa1+xZrxV0.5Fe4.5−xO12 garnets

Magnetic transition behavior and electromagnetic properties of Zr substituted Bi0.5Y1.5−xCa1+xZrxV0.5Fe4.5−xO12 garnets

Influence of Covalent Element B and Si Addition on Magnetocaloric Properties of Gd-Co-Fe-(B,Si) Amorphous Alloys

The effect of covalent element addition on the magnetic and magnetocaloric properties of ferrimagnetic Gd60Co20Fe20 amorphous alloy was studied. Particularly, the co-doping of B and Si promoted the magnetocaloric performance (with a larger magnetic entropy change |ΔSM| at higher working temperature) of the initial Gd60Co20Fe20 amorphous alloy. This is possibly ascribed to the modified magnetic transition behavior. Additionally, the broadened magnetocaloric effect with |ΔSM| of 2.25 J kg−1 K−1 at 222.5 K under a magnetic field change of 0–2 T and high relative cooling power of 396.0 J kg−1 were obtained for (Gd0.6Co0.2Fe0.2)95B2Si3. These properties reveal that the material could be a good candidate as a magnetic refrigerant suitable for active magnetic refrigerators.

Octagonal-siloxane based transparent and robust crack-healing surface for optical-scar recovery

Siloxane derivatives are a class of emerging hybrid materials that provide optical transparency and mechanically flexible characteristics owing to the low rotational barrier of the framework. To devise a robust and flexible self-healing platform, we designed an octagonal-siloxane derivative with four furan units and applied bifunctional maleimides as dienophiles to implement the reversible Diels–Alder (DA) reaction for crack healing. The feasibility of the DA reaction was confirmed by both the appearance of a cyclohexyl moiety in 1H-nuclear magnetic resonance spectra and heat transition behaviors during heating-cooling cycles in differential scanning calorimetry. The crack-healing efficiency of the designed octagonal-siloxane was sensitively affected by the heat-treatment temperature, and the crack recovery rate reached over 95% within 60 s upon heating at 100 °C. In addition, the crack recovery tendency was almost intact during repetitive heating-cooling cycles. The devised crack-healing film exhibited greater than 95% transparency in the entire visible region, and the effective modulus reached 7.8 GPa. In particular, when CdSe/ZnS quantum dots (QDs) were embedded into the octagonal-siloxane based film, it was confirmed that optical scars exhibiting luminescence defects were effectively recovered, and the emission characteristics of the QDs were not critically compromised even under solvent-exposed circumstances.

Optimization of microstructure and magnetocaloric effect by heat treatment process in LaFe11.7Si1.3 microwire

A large magnetocaloric effect and significantly shortened annealing process were obtained simultaneously in melt-extracted LaFe11.7Si1.3 microwires. Large amounts of La(Fe,Si)13 phases were formed within 5 min when annealed at 1353 K via a rapid peritectic reaction, because the nanoscale dendrites and a small amount of nanoscale La(Fe,Si)13 phases discovered inside grains could provide a lot of nucleation sites. Thereby, the main phase in LaFe11.7Si1.3 microwire after annealed at 1353 K for 5 min was La(Fe,Si)13 phase, although a small quantity of α-Fe and La-rich phases still remained in the microstructure. The annealed LaFe11.7Si1.3 microwires exhibited a first-order magnetic transition behavior and a large maximum magnetic entropy change of 7.7 J/kg K under a magnetic field of 1.4 T with negligible magnetic hysteresis. However, the strength of the first-order transition became weakened with the extension of annealing time. Finally, the working temperature range of LaFe11.7Si1.3 microwires was elevated to room temperature by hydrogenation, which expanded the application of LaFe11.7Si1.3 microwires in active magnetic regenerator.

Magnetic transition behavior and large topological Hall effect in hexagonal Mn2−xFe1+xSn (x = 0.1) magnet

The magnetic transition, transport properties, and magnetic domain structures of the polycrystalline Mn1.9Fe1.1Sn compound with a hexagonal structure have been investigated. The result shows that ferromagnetic and antiferromagnetic phases coexist in this compound. A large topological Hall effect up to 3.5 μΩ·cm at 50 K has been found due to the formation of noncoplanar spin structures when the competition occurs among magnetocrystalline anisotropy, antiferromagnetic coupling, and ferromagnetic interaction at low temperature. The result of in situ Lorentz transmission electron microscopy cooling experiment at zero field indicates two shapes of domain walls containing vortexes coexisting simultaneously in the compound.

Successive magnetic transitions and magnetocaloric effects in intermetallic compounds RE7Rh3 (RE = Nd, Ho)

In this work, the structure, cryogenic magnetic transition behaviors and magnetocaloric properties in the intermetallic compounds RE7Rh3 (RE = Nd, Ho) have been investigated. Powder X-ray diffraction confirmed the formation of RE7Rh3 (RE = Nd, Ho) with hexagonal Th7Fe3-type crystal structure (space group P63mc). For the Nd7Rh3 compound, it exhibits two successive magnetic phase transitions with increasing temperature, that is, a first-order ferromagnetic-antiferromagnetic transition at Tt = 11.3 K and a second-order antiferromagnetic-paramagnetic transition at TN = 33 K. The reciprocal magnetic susceptibility of the Nd7Rh3 compound obeys the Curie-Weiss law in the paramagnetic region. According to Curie constant, the values of the effective magnetic moment (μeff) and the corresponding paramagnetic Curie temperature (θP) are determined to be 3.39 μB/Nd3+ and 38.6 K, respectively. While for Ho7Rh3, it undergoes paramagnetic to antiferromagnetic transition at TN = 33.5 K followed by the other two magnetic transitions states at Tt = 23.5 K and TSR = 7.2 K with decreasing temperature. The effective magnetic moment of Ho7Rh3 is evaluated to be 10.2 μB/Ho3+, and the negative value of paramagnetic Curie temperature (−10 K) indicates the dominant antiferromagnetic interaction in the Ho7Rh3 compound. For a magnetic field change of 5 T, the maximum magnetic entropy changes of Nd7Rh3 and Ho7Rh3 are calculated to be 6.40 J/kg K and 3.06 J/kg K with the corresponding refrigerant capacity values of 164 J/kg and 85 J/kg, respectively.

Effect of B-site vanadium (V) doping on the structural, magnetic and magnetocaloric properties of Ba2FeMo1-xVxO6 perovskite

The effects of B-site Vanadium (V) doping on the structural, magnetic and magnetocaloric properties of double perovskite compound Ba2FeMoO6 were investigated. The Ba2FeMo1-xVxO6 (0.0 ≤ x ≤ 0.4) samples were synthesized using the conventional solid state reaction method and were observed to crystallize in the cubic phase with space group Fm-3m using the X-ray diffraction pattern of the material. The temperature dependent as well as the isothermal magnetization data confirmed the ferromagnetic behavior of the samples. The second order magnetic phase transition of all the samples were established using the Arrott plots analysis. The highest spontaneous magnetization was found to be 34.76 emu/g at 100 K with a sharp magnetic transition behavior near transition temperature (TC) = 315 K for pristine Ba2FeMoO6 (BFMO) sample. TC approached near room temperature (≈300 K) followed by a reduction in the spontaneous magnetization values on the partial substitution of Mo with V. Our findings in this work suggest that the magnetic and magnetocaloric behavior of the double perovskite Ba2FeMoO6 can be tailored through the controlled partial substitution at B-site. The B-site doping in these perovskite compounds can effectively tune the physical properties and the technological potential in numerous fields can be foreseen.

Experimental demonstration of two-photon magnetic resonances in a single-spin system of a solid

While the manipulation of quantum systems is significantly developed so far, achieving a single-source multi-use system for quantum-information processing and networks is still challenging. A virtual state, a so-called ``dressed state," is a potential host for quantum hybridizations of quantum physical systems with various operational ranges. We present an experimental demonstration of a dressed state generated by two-photon magnetic resonances using a single spin in a single nitrogen-vacancy center in diamond. The two-photon magnetic resonances occur under the application of microwave and radio-frequency fields, with different operational ranges. The experimental results reveal the behavior of two-photon magnetic transitions in a single defect spin in a solid, thus presenting new potential quantum and semi-classical hybrid systems with different operational ranges using superconductivity and spintronics devices.