Replacement of Dy and substitution of Nd in NdFeB‐based permanent magnets by Ce, the most abundant and lowest cost rare earth element, is important because Dy and Nd are costly and critical rare ...earth elements. The Ce, Co co‐doped alloys have excellent high‐temperature magnetic properties with an intrinsic coercivity being the highest known for T ≥ 453 K.
Magnetic properties of Ce and Co co-doped (Nd1-xCex)2Fe14-yCoyB compounds have been investigated both in bulk polycrystalline and rapidly solidified nanostructured ribbon forms. For certain Ce ...concentrations the materials exhibit spin re-orientation transitions below 140 K. The Curie temperatures, saturation magnetizations, and other magnetic properties relevant for applications as permanent magnets are controlled by Ce and Co substitutions for Nd and Fe, respectively. Most importantly, the results show that Ce, Co co-doped compounds are excellent replacements for several Dy-based high performance permanent magnets (dysprosium is one of the critical elements and is, therefore, in short supply). The high temperature (>375 K) magnetic properties for Nd–Ce–Fe–Co–B based alloys show promise not only as a replacement for Dy-doped Nd2Fe14B permanent magnets, but the new alloys also require significantly lower amounts of Nd, which too is the critical element that can be replaced by a more abundant Ce.
Transmission electron microscopy (TEM) micrographs of the free side (a), the wheel side (b) of (Nd0.8Ce0.2)2Fe14B melt spun ribbon. (c) Maximum energy product, (BH)max, as functions of temperature for melt spun ribbons of Nd2Fe14B, (Nd0.8Ce0.2)2Fe14B and (Nd0.8Ce0.2)2Fe14Co2B. Display omitted
Magnetocaloric refrigeration is a solid-state cooling approach that promises high energy efficiency and low environmental impact. It remains uncompetitive with conventional vapor-compression ...technologies due to lack of high-performing materials that exhibit large magnetocaloric effects in low magnetic fields. Here we report a game-changing enhancement of the magnetocaloric response in a transition-metal-based Ni–Co–Mn–Ti. Mechanically and chemically stable rapidly solidified ribbons exhibit magnetic entropy changes as high as ∼27 J⋅kg−1K−1 for a moderate field change of 2 T, comparable to or larger than the best known materials for near-room temperature applications. The ribbons can be easily manufactured in large quantities and the transition temperature can be adjusted by varying Co concentration.
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Long-range magnetic ordering of two-dimensional crystals can be sensitive to interlayer coupling, enabling the effective control of interlayer magnetism towards voltage switching, spin filtering and ...transistor applications. With the discovery of two-dimensional atomically thin magnets, a good platform provides us to manipulate interlayer magnetism for the control of magnetic orders. However, a less-known family of two-dimensional magnets possesses a bottom-up assembled molecular lattice and metal-to-ligand intermolecular contacts, which lead to a combination of large magnetic anisotropy and spin-delocalization. Here, we report the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning with a coercivity coefficient up to 4 kOe/GPa, while pressure-controlled interlayer magnetism also presents a strong dependence on alkali metal stoichiometry and composition. Two-dimensional molecular interlayers provide a pathway towards pressure-controlled peculiar magnetism through charge redistribution and structural transformation.
The influence of transition metal oxide (MO) on the structural, magnetic, and magnetocaloric properties for La 0.45 Nd 0.25 Sr 0.3 MnO 3 (LSMO)/<inline-formula> <tex-math notation="LaTeX">x ...</tex-math></inline-formula>-wt.% MO (MO = CuO, CoO and NiO) nanocomposite samples has been investigated using X-ray powder diffraction (XRD) and magnetic measurements. Pure phase nanocomposites were prepared via the one-pot autocombustion method. The XRD patterns of the composite reveal the presence of a distinct pure phase of LSMO and MOs. Temperature-dependent field-cooled magnetization curve exhibits second-order phase transition near room temperature. The isothermal magnetic entropy change (<inline-formula> <tex-math notation="LaTeX">\Delta S_{M} </tex-math></inline-formula>) is calculated from magnetic isotherms. LSMO-2.5 wt.% CuO composite-display <inline-formula> <tex-math notation="LaTeX">\Delta S_{M}\sim -3.95 </tex-math></inline-formula> J/kg<inline-formula> <tex-math notation="LaTeX">\cdot \text{K} </tex-math></inline-formula>, highest among studied composites, which is 110% higher than LSMO. While the relative cooling power (RCP) values were observed to be maximum for 5 wt.% CoO composite.
•The effects of Bi substitution on the magnetic properties of La2-xBixNiMnO6 double perovskite series were explored.•The Bi3+ substitution increased the saturation magnetization by ∼15%.•Curie ...temperature, TC was also found to increase with Bi3+ substitution.•The critical behavior of La2-xBixNiMnO6 was investigated.
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The influence of A-site Bi substitution on B-site cation ordering, crystal structure, and magnetic properties of La2-xBixNiMnO6 double perovskites has been studied. Compounds with and without Bi substitution adopt monoclinic crystal structure with the P21/n space group as determined from the Rietveld refinement of x-ray diffraction data. X-ray photoelectron spectroscopy indicated an increase in Mn4+/Mn3+ and Ni2+/Ni3+ ratios in Bi substituted sample, and hence emphasized improved Ni and Mn ordering. This has been well supported by bond length analysis which suggested a compression in<Mn–O>and elongation in<Ni–O>bond lengths. The Bi substituted compound showed a relatively larger moment as compared to the parent sample, which was attributed to the suppression of antisite disorder i.e., enhanced Ni-Mn cation ordering due to Bi substitution. The temperature-dependent dc magnetization studies reveal a ferromagnetic to paramagnetic phase transition, and the Curie temperature has been observed to increases with Bi substitution. The critical exponent analysis around phase transition also confirmed the increase in the critical temperature for the Bi substituted compound. A detailed analysis of the critical behavior has been performed using different models, which suggested a long-range ferromagnetic ordering for both pure and Bi substituted samples.
A solid solution of (1-x) BaTiO3–(x)LaFeO3 (x=0, 0.007, 0.015, 0.031, 0.062) has been investigated for room temperature multiferroicity and magnetodielectric effect. The incorporation of La and Fe ...ions in ferroelectric BaTiO3 leads to increased lattice disorder and generation of oxygen vacancies that induces magnetism. A detailed correlated study using XRD, XPS and Raman spectroscopy is being reported. A typical ferromagnetic and ferroelectric nature of each sample are confirmed by M − H and P–E hysteresis loops, respectively at room temperature. Temperature dependent dielectric studies reveal the decrease of transition temperature from 137 0C for undoped to room temperature for increasing substitution. The changes in the dielectric property with applied magnetic field shows the indications of magnetodielectric effect. For x = 0.015, existence of both proper ferroelectric without lossy properties and ferromagnetic properties in a single tetragonal phase makes it a perfect room temperature multiferroic material. For this sample, the magnetodielectric coupling is the strongest with Magnetocapacitance of ~2.7% and Magneto loss of ~0.8% at 10kHz and 1T. The multiferroicity and the magnetodielectric effect exhibited by this material has been correlated to the structural properties, electric and magnetic properties, changes in valence states, and oxygen vacancy (Ov).
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•Room temperature multiferroicity•Magnetodielectric effect•Correlation of structural and valence state studies•Structure correlated dielectric properties•Influence of oxygen vacancies and cationic valence state on magnetism•Bound magnetic polarons
We have synthesized a series of Co-doped Mn0.5Fe0.5Ni1−xCoxSi0.94Al0.06 (0.025 ≤ x ≤ 0.05) alloys by arc melting followed by a rapidly quenched vacuum suction casting technique and studied the ...magnetic and magnetocaloric properties of the system. All measurements were performed on the as-cast and annealed samples. X-ray diffraction data indicated that the samples exhibited a hexagonal phase at room temperature. Magnetization data showed that the annealed samples exhibited significantly larger transition temperatures than the as-cast samples. All samples showed the first-order phase transition with a thermomagnetic hysteresis of more than 20 K. The phase transitions were accompanied by isothermal entropy changes of as large as −16.4 J kg−1 K−1 and −42.4 J kg−1 K−1 for field changes of 20 and 50 kOe, respectively. Large refrigeration capacities and temperature averaged entropy changes of up to 201 J/kg and 34.05 J kg−1 K−1, respectively, were observed for a field change of 50 kOe.
Aluminum-doped ErCr1-xAlxO3 orthochromites prepared via autocombustion technique were investigated for their magnetic and magnetocaloric properties. X-ray diffraction confirmed that samples were ...orthorhombic phases with the Pbnm space group without a trace of any impurity. As analyzed via Rietveld refinement of XRD data, structural parameters such as lattice parameters, volume, bond angle, and bond lengths were affected by doping nonmagnetic Al3+ in the compound. ErCrO3 possesses the long-range antiferromagnetic ordering with a weak display ferromagnetism at TN =133 K. Low-temperature high-field magnetic study shows a decrease in Neel temperature (TN ∼ 114 K for x = 0.5), suggesting magnetic ordering suppression due to Al3+ doping. The asymptotic paramagnetic Curie temperature Tcw = −25 K suggests the predominance of antiferromagnetic interactions in ErCrO3 orthochromites, which was observed to increase with Al3+ doping. Isothermal magnetization data show changes in magnetic entropy (−ΔSMmax) and relative cooling power (RCP). The magnetic entropy change, −ΔSMmax, for ErCrO3 estimated from magnetization measurements show 11.60 J kg−1 K−1 at 11 K and a relative cooling power (RCP) of 209.4 J kg−1 at 5 T applied field. While ErCr0.75Al0.25O3 show a maximum magnetic entropy of 11.52 J kg−1 K−1 at 11 K with a 5 T applied field and RCP of 186.66 J kg−1, whereas ErCr0.5Al0.5O3 displayed −ΔSMmax of 11.63 J kg−1 K−1 at 5 K with a 5 T applied field and RCP value of 160.78 J kg−1. The results show that nonmagnetic doping, such as Al3+, could maintain the compound’s magnetocaloric property to an extent.
The first-order phase transition and associated magnetocaloric properties of Mn0.5Fe0.5Ni0.95Cr0.05Si0.95Al0.05 have been studied by x-ray diffraction and dc magnetization measurements. The ...diffraction data for the sample showed that both the orthorhombic and hexagonal crystalline phases coexisted at room temperature. The temperature dependence of magnetization was measured at a constant field of 0.2 T. The first-order phase transition was observed at 325 K during heating and at 306 K during cooling, showing a thermomagnetic hysteresis of 19 K. For magnetic field change of 5 T, the entropy changes evaluated from the isothermal magnetization data peaked at 322 K during warming and at 313 K during cooling, showing a thermomagnetic hysteresis of 9 K. This difference in the magnitude of the thermomagnetic hysteresis was attributed to the virgin effect due to stress and crack formation during the first cooling from hexagonal to orthorhombic phase. Peak entropy changes of −16 J kg−1 K−1 and −42 J kg−1 K−1 were observed on heating for field changes of 2 and 5 T, respectively. The related refrigeration capacities were 74 J/kg (2 T) and 194 J/kg (5 T).
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