Temperature Dependence Of Magnetization Research Articles

Effects of K excess in microstructure of (Ba0.6K0.4)Fe2As2 superconducting powders

Abstract Iron-based superconductors (IBSs) are promising for high-field applications due to their exceptional characteristics, like ultrahigh upper critical field and minimal electromagnetic anisotropy. Creating multifilamentary superconducting wires with elevated transport critical current density is essential for practical use. The Powder in Tube (PIT) technique is commonly used for this purpose, but achieving optimal results requires careful exploration of powder microstructural properties. This is particularly crucial for superconductors like (Ba,K)122, the IBS most promising from an applicative point of view, where factors such as reactivity, volatility, and toxicity of constituent elements affect phase formation. Potassium volatility often leads to nonstoichiometric conditions, introducing excess potassium in the formulation. This study focuses on the impact of potassium excess δ on the microstructural properties of the ‘optimally doped’ (Ba0.6K0.4+δ )Fe2As2 phase (0 ⩽ δ ⩽ 0.08). Using techniques like Scanning Electron Microscopy, x-ray diffraction, and temperature-dependent magnetization measurements, we demonstrate the ability to produce nearly pure powders of the superconducting phase with controlled grain size. Our findings are relevant for PIT wire fabrication, where grain size strongly affects mechanical deformation. Grain size also influences transport properties, as observed in previous studies, where reducing grain size enhanced current-carrying capability at high magnetic fields.

Magnetic Hardening: Unveiling Magnetization Dynamics in Soft Magnetic Fe-Ni-B-Nb Thin Films at Cryogenic Temperatures.

Recent advancements in amorphous materials have opened new avenues for exploring unusual magnetic phenomena at the sub-nanometer scale. We investigate the phenomenon of low-temperature "magnetic hardening" in heterogeneous amorphous Fe-Ni-B-Nb thin films, revealing a complex interplay between microstructure and magnetism. Magnetization hysteresis measurements at cryogenic temperatures show a significant increase in coercivity (HC) below 25 K, challenging the conventional Random Anisotropy Model (RAM) in predicting magnetic responses at cryogenic temperatures. Heterogeneous films demonstrate a distinct behavior in field-cooled and zero-field-cooled temperature-dependent magnetizations at low temperatures, characterized by strong irreversibility. This suggests spin-glass-like features at low temperatures, which are attributed to exchange frustration in disordered interfacial regions. These regions hinder direct exchange coupling between magnetic entities, leading to magnetic hardening. This study enhances the understanding of how microstructural intricacies impact magnetic dynamics in heterogeneous amorphous thin films at cryogenic temperatures.

The B-site ordering in RFe0.5Cr0.5O3 ceramics and its effect on magnetic properties

Abstract To insight into the B-site ordering in RFe0.5Cr0.5O3 ceramics, a series of RFe0.5Cr0.5O3 ceramics (R = La, Y, Lu) were synthesized by the sol-gel method, and the structural and magnetic properties were systemically investigated. By using the Rietveld refinement of all samples, it is found that the structural distortion is increased as the R ionic radius decreases, leading to the weakened interactions between Fe/Cr ions. Besides, the Fe and Cr are arranged in disorder in LaFe0.5Cr0.5O3, but partially ordered in YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3, showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius. Through fitting the temperature-dependent magnetizations, it is identified that the magnetization reversal (MR) in disorder LaFe0.5Cr0.5O3 is resulted from the competition between the moments of Cr and Fe sublattices. In the partially ordered YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3 ceramics, because of the presence of Fe-O-Cr networks in the ordered domains whose moment is antiparallel to that of Fe-O-Fe and Cr-O-Cr in the disordered domains, the compensation temperature Tcomp of MR is increased by nearly 50 K. These results suggest that the changing of R-site ions could be used very effectively to modify the Fe-O-Cr ordering, apart from the structural distortion, which has a direct effect on the magnetic exchange interactions in RFe0.5Cr0.5O3 ceramics. Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion, one can expect a higher transition temperature Tcomp, providing a different view for adjustment of the magnetic properties of RFe0.5Cr0.5O3 ceramics for practical applications.

Insights into crystal structure, temperature-dependent magnetization and dielectric relaxation mechanism in Bi substituted samarium iron garnet

The single phase Sm3−xBixFe5O12 with x=0.0,0.2,0.4 and 0.6 samples are synthesized by solid-state reaction method. We have systematically studied the structural, morphological, temperature dependent magnetic and electric properties. All the samples crystallize in simple cubic crystal structure and belongs to Ia3‾d space group. The lattice constant and bond angle between Fe(a)−O−Fe(d) network is enhanced with Bi substitution. As a result, the ferrimagnetic transition temperature is also enhanced from 565K to 569K. We have examined the applicability of Bloch's and Cojocaru's laws to our temperature-dependent magnetization data and find that Bloch's T3/2 law is not suitable due to geometrical asymmetry, long wavelength excitation, and local atomic disorders. However, Cojocaru's law which accounts for the geometrical aspects, provides a better fit to our magnetization data. Further, the impedance plots at room temperature exhibit no relaxation which is attributed to the limited mobility of charge carriers. On the other hand, the high temperature impedance data represents dielectric relaxation at a particular frequency. This frequency is used to determine the relaxation time which is fitted to Arrhenius law and activation energy is evaluated. The activation energy lies in between 0.24−0.32eV which corresponds to the singly ionized oxygen vacancies. The conduction mechanism is analyzed with Variable range hopping model and the average hopping length and hopping energies are also determined for these garnet samples.

Exploring the structural, magnetic and shielding performance of Mn doped Yb2O3 and Eu2O3 nanostructures

Re2-xMnxO3 (ReYb or Eu, x = 0.0, 0.05, 0.1, 0.15) nanostructures were produced utilizing the sol-gel procedure. The crystal structure and microstructure of all samples were analyzed based on XRD measurements using the Rietveld profile approach. The lattice parameter, cation distribution of different cations between different crystallographic sites, bond lengths of different polyhedrons, crystallite size, micro-strain and distortion index of the different polyhedrons of the formed sample were determined. Mn cations were found to prefer the 8b sites of the cubic bixbyite structure. The average crystallite size decreased following doping, while the microstrain experienced a significant increase. The low temperature dependent magnetizations for Yb1.85Mn0.15O3 and Eu1.85M0.15O3 nanostructures under a magnetic field of 200 Oe were investigated. Curie–Weiss law was employed to determine the magnetic configuration of the samples. The values of the effective magnetic moments μeff are 4.89 μB and 3.77 μB for Yb1.85Mn0.15O3 and Eu1.85M0.15O3, whereas the calculated values are 4.531 μB and 3.535 μB, respectively. The shielding properties of Re2-xMnxO3 (ReYb or Eu) nanostructures were studied using the Phy-X/PSD simulation program. The linear attenuation coefficients (LAC) and mass attenuation coefficients (MAC) values of the Yb2-xMnxO3 samples are greater than those of the Eu2-xMnxO3 samples. The half value length (HVL) and tenth value length (TVL) values increased as Mn was added to Re1.85Mn0.15O3 nanostructures. Yb1.85Mn0.05O3 and Eu1.85Mn0.05O3 nanostructures have the highest mean free path (MFP) values of 3 cm and 4 cm, respectively, at an energy of 5 MeV. The exposure build-up factor (EBF), and energy absorption build-up factor (EABF) values affected by the host rare earth oxide and the amount of Mn doping. The Re1.85Mn0.15O3 nanostructures exhibit a greater capacity to absorb photons with lower energy rather than higher energy. Yb1.85Mn0.15O3 nanostructure demonstrates exceptional neutron shielding capacities.

Exploring magnetic transitions in the FeIn2xCr2-2xS4 semiconductor system through Electron spin resonance

Electron spin resonance (ESR) was employed to investigate the effects of composition and temperature on the FeIn2xCr2-2xS4 semiconductor system. The samples were synthesized using Chemical Vapor Transport (CVT), and their structural characteristics were analyzed through X-ray diffraction and Scanning Electron Microscopy (SEM). For magnetic characterization, magnetization curves M(H) and temperature-dependent magnetization curves M(T) were obtained under both zero-field and field cooling conditions. A paramagnetic behavior was observed for all samples above 180 K, transitioning to a potential long-range spin-glass-like behavior below this temperature. By comparing the results with those presented in the literature, we suggest a reentrant spin glass behavior for the samples with higher Cr concentration. The Electron spin resonance (ESR) spectra revealed asymmetric signals indicative of strong magnetic anisotropies. The inverse of the normalized area in the ESR spectra revealed three distinct regions above the Néel temperature; this observation is consistent with the sensitivity of the lattice parameters of indite. The study elucidates the intricate magnetic behaviors influenced by composition and temperature in the FeIn2xCr2-2xS4 semiconductor system, contributing to a deeper understanding of the material’s properties. This comprehensive investigation, utilizing a range of analytical techniques, advances our knowledge of the system’s magnetic characteristics and provides valuable insights for future research in related semiconductor materials.

Study of magnetocaloric properties of small Bi-doped Pr0.55Ca0.05Ba0.40Mn1−xBixO3 manganites

Here, we investigated the magnetic and magnetocaloric (MC) properties of manganites labeled PrCaBaMnO and PrCaBaMnBiO, with compositions Pr0.55Ca0.05Ba0.40Mn1−xBixO3 (x = 0 and 0.02), respectively. The solid-state reaction method was used for sample preparation, and the structural properties were checked using X-ray diffraction (XRD). Temperature dependence of magnetization (M(T)) measurements was carried out in the range of 5–300 K under 100 Oe field to determine the transition temperature of the manganites. Magnetic entropy change (-ΔSM\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{\ ext{M}}$$\\end{document}) values were computed from field-dependent magnetization (M(H)) measurements. For the 2 T magnetic field values, the -ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {{S}_{ }}_{\ ext{M}}^{\ ext{max}}$$\\end{document} values for the PrCaBaMnO and PrCaBaMnBiO manganites are 3.15 and 2.86 Jkg-1K-1, respectively. Relative Cooling Power (RCP) values were calculated from the temperature dependence of -ΔSM\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{\ ext{M}}$$\\end{document} (T) curves, resulting in 82.4 and 88.6 Jkg-1 for PrCaBaMnO and PrCaBaMnBiO, respectively. Banerjee’s criterion and Franco’s universal master curve confirmed that the transition type for the studied manganites is second order.

Infrared spectroscopic study on Nb-ion-irradiated MgB2 thin films

Magnesium diboride (MgB2) is a two-band superconductor with a high superconducting critical temperature (Tc) of approximately 39 K. Owing to the lack of vortex pinning centers, MgB2 exhibits an abrupt decline in the critical current density (Jc) in an applied magnetic field. Here, we prepared 1 MeV Nb ion-irradiated MgB2 thin-film samples with doses of 3×1013, 7×1013, and 9×1013 ions/cm2. Temperature-dependent magnetization and x-ray diffraction (XRD) measurements were performed to determine the Tc and c-axis lattice constant of each sample. Furthermore, a Fourier transform infrared (FTIR) spectroscopy was performed to obtain the infrared properties of the Nb-ion-irradiated MgB2 thin-film samples. The optical conductivity of each sample in the low-energy region was fitted with two (narrow and broad) Drude modes. We found that the spectral weight redistribution from the low-to high-frequency regions and the broadening of the narrow Drude mode caused by irradiation are closely related to the reduction in Tc.

Effects of Mg Substitution on the Structural with Rietveld Analysis, Magnetic and Magnetocaloric Properties of Ni-Cu-Cd Bulk Ceramics

Bulk ceramics with optimized density are highly prioritized over ferrite nanoparticles to fabricate devices for their optimal magnetic saturation, lower coercivity, and anisotropy, enhanced resistance, etc. To achieve such bulk specimen using Ni0.5-yMgyCu0.2Cd0.3Fe2O4 disc samples are sintered at 1423 K keeping the heating and cooling rate at 10 K and 5 K respectively. In due course, structural as well as theoretical Rietveld analysis, optical, and magnetic properties have been analyzed using these bulk samples. XRD has explored structural properties and after that these values have analyzed with the Rietveld refinement procedure and obtained goodness of χ2 (1–2) value and other parameters such as lattice parameters, crystal structures, cation distribution, and maximum entropy mapping. Surface morphology and grain size have examined from the as-grown surface without further polishing and annealing by electron microscopy and revealed a decreasing trend of grain size 6.1 µm to 4.2 µm. UV–Vis spectroscopy characterization ensured optical properties for bulk as well as nanopowders and the band gap has been found in the range of 1.4 to 1.6 eV and is increasing with Mg content. Magnetic hysteresis loop exhibits a less decreasing nature up to y = 0.3 of magnetic saturation along with the Law of Approach to saturation which compiles magnetic anisotropy. The temperature-dependent magnetization curves exhibit a sharp decreasing value (i.e. dM/dT maximum) at Curie point, decreasing from 630 K to 505 K with increasing Mg content. At.3 T magnetic field the changes in relative cooling power value have been found in the range 53.82Jkg-1 to 37.79Jkg-1 which could be considered as potential for magnetocaloric refrigeration.

EXPLORING THE INFLUENCE OF B-SITE DOPANTS ON STRUCTURAL AND MAGNETIC PROPERIES IN La0.8Ag0.2Mn1-XCoxO3 (x: 0 and 0.1) COMPOUNDS

This study examines the structural, electrical, magnetic, and magnetocaloric properties of La0.8Ag0.2Mn0.9A0.1O3 (A: Mn, and Co) compounds under doping in the B-site. XRD results show that the compound containing Co ions directly replaced Mn ions in the B-site without forming a secondary phase containing higher metallic Ag impurities. The data obtained using Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), the temperature dependence of magnetization (M-T), the magnetic field dependence of magnetization (M-H), and the magnetic entropy change (SM) analysis reveal the effect of the doped element on the magnetic properties of the compounds due to the changes they create in the structural and Mn3+/Mn4+ ratio. It has been determined that the paramagnetic to ferromagnetic transition temperature (Curie temperature, TC) of the La0.8Ag0.2Mn0.9Co0.1O3 (LAMO-Co) is quite lower than the LAMO.

Crystal growth of the [formula omitted]PdSi3 ([formula omitted] rare earth) materials using the optical floating zone technique

The rare-earth palladium silicides host an array of complex magnetic phases. In this paper, we report the growth of large single crystals of the R2PdSi3 family, (where R= Ce, Nd, Gd, Tb, Ho and Er) by the floating zone technique using a high-power xenon arc-lamp furnace. The crystal boules obtained have been examined for their quality using x-ray diffraction techniques, elemental analysis, and their magnetic properties have been investigated through temperature dependent magnetisation measurements.

Fine tuning of Mn/Co vacancies for optimized magnetocaloric performance in MnCoGe alloys

As a family of rare-earth-free magnetocaloric materials, MnCoGe-based alloys have attracted intensive attention in the past few years. In this study, we reveal that the deficiency of either Mn or Co reduces the valence electron concentration of MnCoGe system, thereby lowering its structural transition temperature (Ttr) by pushing the Fermi level away from the Mn-Mn antibonding electronic states. Moreover, Ttr is found to be more sensitive to Co content. By systematically analyzing the temperature dependent magnetization plots and Arrott curves, it is proven that the magnetic and structural degrees of freedom are coupled in the Mn0.97CoGe alloy, resulting in a first-order magnetic phase transition. On the contrary, MnCo0.98Ge undergoes a second-order transition. As a consequence, the Mn0.97CoGe alloy exhibits a maximum magnetic entropy change of 27.6 J kg−1K−1 under a magnetic field of 5 T near the Curie temperature of 265 K, corresponding to a refrigeration capacity of 212.1 J kg−1. Our work demonstrates Mn/Co vacant MnCoGe alloy as a robust candidate of magnetic substance for room temperature magnetocaloric refrigeration.

Reduced internal stress of quasi-single crystalline Na4Fe3(PO4)2P2O7 electrode enhancing sodium-ion kinetics

A NASICON-type quasi-single crystalline Na4Fe3(PO4)2P2O7 (SC) cathode material was successfully synthesized via a freeze-drying method. The as-optimized SC sample displays both outstanding rate performance (107.9 and 88.5 mAhg−1 at 0.1C and 5C, respectively) and excellent cycling stability (88.1 % of capacity retention after 1000 cycles at 1C). Reduced sodium ion migration path of as-prepared SC cathode material effectively enhanced the kinetics of Na+ upon cycling. More importantly, the SC structure could suppress nearly 50 % of internal strain, prodigiously reducing the local stress accumulation accompanied by the inhomogeneous sodium concentration gradient during the charging/discharging processes. The smaller the stress accumulation, the more stable the crystal structure would be obtained, which maintained a more superb mechanical stability of the SC cathode material. At the same time, a high-spin state of Fe in the SC sample was confirmed by both of electron paramagnetic resonance and temperature-dependent magnetization susceptibility, indicating that the eg orbital occupation of Fe2+ could be regulated to optimize the bond strength between the reduction and oxidation processes. As a consequence, the band gap of SC material has decreased from 1.66 to 1.45 eV, and the electronic conductivity has increased from 6.0 to 32.4 μS/cm. It is believed that the SC cathode material could be a competitive candidate material for sodium ion batteries.

Optimizing the curie temperature of La0.67Sr0.33MnO3–based composite materials around room temperature through the addition of Mo, Mn, and Ni metallic elements

Our study sheds light on the role of secondary phases in optimizing the magnetic properties of LSMO, offering valuable insights into the relationship between impurity phases, Curie temperature (TC), and magnetic entropy change. To achieve this goal, the Mn, Ni, and Mo elements were individually incorporated into the LSMO matrix to the formation of secondary phases. The solid-state reaction method was employed to create composite materials of (0.8)La0.67Sr0.33MnO3 + (0.2)A (A=Mn, Ni, and Mo). XRD and SEM results confirmed the successful formation of impurity phases within the main LSMO phase. From temperature-dependent magnetization (M(T)) measurements, it was determined that the TC of the samples approach towards room temperature with the existence of impurity phases. Additionally, the relationship between electron bandwidth (W) and TC was examined. The lowest TC value was observed for the lowest value of W. Besides these, the effect of the formation of impurity phases on the maximum magnetic entropy change (-ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{M}^{max}$$\\end{document}) value is examined, and it is seen that impurity phases cause a decrease in the (-ΔSMmax)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(-\\Delta {S}_{M}^{max})$$\\end{document} values.

Strong influence of magnetic field and non-uniform stress on elastic modulus and transition temperatures of twinned Ni–Fe(Co)–Ga alloy

The magnetization value and electric resistivity of the single-crystalline sample of Ni50Fe19Co4Ga27 shape memory alloy were measured. The elastic modulus was determined by the Dynamic Mechanical Analysis (DMA). The characteristic temperatures of martensitic transformation (MT) of the alloy were estimated from the temperature dependences of magnetization, electric resistivity and elastic modulus. A significant disparity between MT temperatures resulting from DMA and those estimated from magnetic and resistivity measurements was discovered. It was argued that the discrepancy is caused by the non-uniform mechanical stressing of twinned single crystal by the DMA analyzer. Moreover, the DMA measurements revealed a significant decrease of the elastic modulus of twinned martensite under the applied magnetic field of 1.5 kOe. To explain this effect, the temperature-dependent Young’s modulus of twinned crystal lattice was computed. The computations showed that the experimentally observed field-induced change of the elastic modulus is caused by the stress-assisted detwinning of the crystal lattice by the applied magnetic field.

Borides Mn3-x{Rh,Ir}5B2 with Ti3Co5B2-type: X-ray single crystal and TEM data, physical properties

A cursory investigation of the phase relations in the Mn-{Rh,Ir}-B systems prompted for each system a ternary compound, Mn3-x{Rh,Ir}5B2, the crystal structure of them was determined from X-ray single crystal data to be isotypic with the Ti3Co5B2-type (space group P4/mbm, No. 127). In both cases the Mn-site in 2a at the origin of the unit cell exhibits a significant defect (or Mn/B substitution). Transmission electron microscopy studies confirm the absence of a superstructure related to these defects/disorder. The two phases, Mn3-xRh5B2 (x∼0.34) and Mn3-xIr5B2 (x∼0.85) at 950 °C show rather limited homogeneity regions pointing towards higher Mn-contents. Whereas temperature dependent magnetization and specific heat measurements of Mn2.15Ir5B2 do not reveal any indication for a magnetic phase transition in the temperature range from 3 to 300 K, a broad specific heat anomaly at around 200 K and a tilde shape of the temperature dependent magnetization of Mn2.66Rh5B2 appears indicative of an antiferromagnetic phase transition. The latter is also reflected by an anomaly of the electrical resistivity (ρ; 4–300 K) of Mn2.66Rh5B2 which displays a non-monotonous temperature dependence, whereas ρ(T) of Mn2.15Ir5B2 displays a simple metallic-like behavior dominated by scattering from defects. Elastic moduli and Poisson's ratio were determined at room temperature from Resonant Ultrasonic Spectroscopy (RUS) data yielding Young's moduli of E ∼ 170 GPa for Mn2.66Rh5B2 and E ∼ 210 GPa for Mn2.15Ir5B2. Vickers hardness HV is lower for Mn2.66Rh5B2 (HV = 590 ≅ 5.79 GPa) than for Mn2.15Ir5B2 (HV = 655 ≅ 6.42 GPa). The indentation fracture toughness for Mn2.15Ir5B2 was IKC = 0.71 ± 0.5 MPa m1/2.

Temperature dependent interfacial-coupling and magnetization reversal of La2/3Sr1/3MnO3 film with inverted hysteresis features

Temperature-dependent magnetic anisotropy and interfacial coupling of La2/3Sr1/3MnO3 (LSMO) epitaxial films with inverted hysteresis (IHLs) features are investigated using a broadband ferromagnetic resonance (FMR) spectrometer. Through the dispersion relation obtained along [100], [110] and [010] axes, a simplified method is proposed to investigation in-plane magnetic anisotropy by broadband FMR in a cryostat. According to this method, the perpendicular uniaxial anisotropy, magneto-crystalline anisotropy, and interfacial coupling between the LSMO film and hard-magnetic interface layer are investigated as a whole. The measured value of interfacial coupling is −17.6 Oe at 300 K, close to the bias field found in minor loop, i.e., −18.4 Oe. The interfacial coupling is enhanced with the dropping of temperatures, and the value of interfacial coupling changed to −112 Oe at 10 K. A Stoner-Wohlfarth-like model is employed to calculate the hysteresis loops of the films based on the measured values of in-plane magnetic anisotropy and interfacial-coupling. The calculation reveals the mechanism of magnetization reversal and the origin of IHLs found in LSMO films.

Sperimagnetic states in amorphous Gd x (FeCo)1-x (0.2 ≤ x ≤ 0.3) alloys: insights from stochastic magnetic anisotropy analysis

Materials crucial for the advancement of magnetic recording technologies stand as pivotal elements in the development of a new generation of recording devices. Recent advancements in the manipulation of magnetization through laser pulses have underscored the significance of magnetic materials exhibiting robust magneto-optical properties. This study explores the manifestation of a sperimagnetic state in ferrimagnetic amorphous Gd x (FeCo)1−x alloys utilizing a stochastic magnetic anisotropy approach. Phase diagrams ‘magnetic field’-‘temperature’ and temperature dependencies of magnetization and compensation point were calculated using the mean-field approximation for temperature range from 50 to 700 K and different stoichiometry of the alloy, namely 0.2 ≤ x ≤ 0.3. Accounting for the stochastic anisotropy intrinsic to rare earth ions, a distribution of magnetic moments within the amorphous solid is discerned. Notably, this distribution predominantly manifests at the fringes of a canted phase, constituting the sperimagnetic structure. We demonstrate a direct correlation between an increased variance in normally distributed anisotropy constants of rare earth ions and a corresponding augmentation in the standard deviation of magnetization within the sperimagnetic structure. These findings not only contribute to a deeper understanding of the interplay between material composition and magnetic properties but also provide valuable insights for the advancement of magnetic recording technologies.

Trapped flux in a small crystal of CaKFe4As4 at ambient pressure and in a diamond anvil pressure cell

In an extension of our previous work, (Bud’ko et al 2023 Supercond. Sci. Technol. 36 115001) the measurements of temperature dependent magnetization associated with trapped magnetic flux in a small single crystal of CaKFe4As4, using zero—field—cooled and field—cooled protocols were performed, on the same crystal, at ambient pressure without a pressure cell and at 2.2 GPa in a commercial diamond anvil cell (DAC), showing comparable results. The data show that with a proper care and understanding, trapped flux measurements in superconductors indeed can be performed on samples in DACs under pressure, as was done on superhydrides (Minkov et al 2023 Nat. Phys. 19 1293).

Element-specific Curie temperatures and Heisenberg criticality in ferrimagnetic Gd6(Mn1−xFex)23 via Kouvel-Fisher analysis

Many large unit-cell rare-earth transition metal ternary alloys of the type Ra(M1−xM’x)b exhibit non-monotonic ferrimagnetic Curie temperatures (TC) coupled to monotonic composition-controlled magnetization. Its origin remains an important long-standing puzzle in the absence of studies probing their temperature-dependent element-specific magnetism. Here, in order to resolve this issue and identify design principles for new R-M-M’ permanent magnets, we carry out x-ray magnetic circular dichroism (XMCD) for the series Gd6(Mn1−xFex)23, x = 0.0 − 0.75. The results show that the net Mn-moment reduces and switches from parallel to antiparallel for x ≥ 0.2, while the Fe-moment is always antiparallel to the Gd-moment. Kouvel-Fisher analyses of XMCD data reveals distinct sublattice TC’s and 3D Heisenberg criticality. Band structure calculations show magnetic moments and density of states consistent with experiments. The magnetic phase diagram shows three regions characterized by (i) Mn-sublattice bulk-TC > Gd-sublattice TC, (ii) a reduced common-TC for all sublattices, and (iii) Fe-sublattice bulk-TC > Gd-sublattice TC. The Mn-moment switching and gradual increase of Fe-moment combine to cause non-monotonic TC’s with monotonic magnetization. The study indicates the importance of element-specific TC’s for tuning magnetic properties.