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Nanocrystalline Eu-doped PrB 6 ultrafine powders have been successfully fabricated through solid-state chemical reaction of Eu 2 O 3 , PrCl 3 and NaBH 4 as raw materials. The optical absorption properties of the synthesized samples were investigated by experimental measurement and theoretical calculation. As a result, a strong red-shift of transmittance wavelength of nanocrystalline PrB 6 is achieved via altering the Eu doping. Theoretically, the doping of divalent Eu into trivalent PrB 6 reduces the plasma frequency excitation energy and increases the corresponding transmittance wavelength. Additionally, the synchrotron radiation absorption shows that Pr and Eu atoms exist in the form of Pr3+ in PrB 6 and Eu2+ in EuB 6 , and X-ray photoelectron spectroscopy results also indicate that Eu exists in the state of Eu2+ in the nanocrystalline Pr 0.4 Eu 0.6 B 6 , which confirms that the Eu doping reduces the number of conduction electrons in PrB 6 and decreases the plasma frequency excitation energy. [ABSTRACT FROM AUTHOR]

Recent studies have pointed out that first-order magnetic transitions can be affected by defects. It however remains unclear which precise microstructural features are involved and how to pragmatically control their formation. Here, we show that a genuine technical parameter such as the compaction pressure employed prior to the sintering can induce subtle differences on magnetization data and yet correspond to a large evolution of the magnetocaloric performances in MnFe 0.95 P 0.575 Si 0.36 B 0.065 compounds prepared by powder metallurgy, resulting in an enhancement of the isothermal entropy change (Δ S) in 1 T up to ∼40 %. This outcome is unexpected as Δ S normalized per mass should not be affected by what is at first glance a matter of compaction or density. Our detailed structural and microstructural investigations indicate that the sharpening of the transition for the highest compaction pressures originate from different distributions of the secondary phase at the grain boundaries. This work not only bring into light an interesting fundamental question how microstructural details can affect the development of a magnetic transition, it has also important practical consequences to ensure a reproducibility of large magnetocaloric or thermomagnetic effects in MnFe(P,Si,B) materials for possible applications. [Display omitted] • Magnetocaloric performances of MnFe(P,Si,B) increase with higher green compaction. • Final density not affected by green pressure with common 24 h high temperature sintering. • Increase in ΔS is not related to secondary phase content but rather to its distribution. [ABSTRACT FROM AUTHOR]

In view of the interest that (Fe,Co) 2 (P,Si) compounds have as potential permanent magnets, their structural and magnetic phase diagrams are explored focusing on establishing the range where the hexagonal Fe 2 P-type structure is observed. In Fe 1.93- x Co x P 1- y Si y , the highest Si content prior entering a mixed phase domain is y ≈ 0.5. At high Si content but low Co for Fe substitutions, a structural distortion leading to a body-centered orthorhombic structure occurs. At high Co contents, when the Fe 2 P unit cell reaches a critical volume of about 102.4 Å3, the samples crystallize in a Co 2 P-type orthorhombic structure. Within the Fe 2 P-type structural range, the evolution of the unit-cell volume appears to follow the Vegard's law, but this hides strongly anisotropic changes. Simultaneous Co for Fe and Si for P substitutions increase the range where the hexagonal structure is observed in comparison to ternary Fe 2 (P,Si) and (Fe,Co) 2 P. The samples are ferromagnetic, but with Curie temperatures showing an unusual evolution, uncorrelated to the c/a ratio of the lattice parameters. At low Si content, T C increases with Co for Fe substitutions. For y = 0.2, the evolution is not significant, while at high Si content T C systematically decreases with the increase in Co. Large Si and Co substitutions lead to a swift weakening of the magnetocrystalline anisotropy until the easy axis anisotropy turns from the c axis toward the a-b plane. This study guides future investigations by restricting the range where desirable properties for permanent magnetic applications can be expected to 0.1 ≲ x ≲ 0.3 and 0.1 ≲ y ≲ 0.3. [Display omitted] • Structural and magnetic phase diagrams of (Fe,Co) 1.93 (P,Si) compounds are built. • Relationships between the three crystal structure types are established. • Ferromagnetic ordering temperature surprisingly not correlated to the c/a structural ratio. • Composition range desirable for permanent magnetic properties is determined. [ABSTRACT FROM AUTHOR]

While rare-earth magnets exhibit unchallenged hard-magnetic properties, looking for alternatives based on inexpensive elements of non-critical supply remains of utmost interest. Here, we demonstrate that (Fe,Co) 2 (P,Si) single crystals combine a large magnetocrystalline anisotropy (K 1 ≈ 0.9 MJ m−3 at 300 K), high Curie temperatures (T C up to 560 K) and an appreciable saturation specific magnetization (101 A m2 kg−1) leading to a theoretical | BH | max ≈ 165 kJ m-3, making them promising candidate materials as rare-earth-free permanent magnets. Our comparison between (Fe,Co) 2 P and (Fe,Co) 2 (P,Si) single crystals highlights that Si substitution reduces the low-temperature magnetocrystalline anisotropy, but strongly enhances T C , making the latter quaternary alloys most favorable for room temperature applications. Submicron-sized particles of Fe 1.75 Co 0.20 P 0.75 Si 0.25 were prepared by a top-down ball-milling approach. While the energy products of bonded particles are to this point modest, they demonstrate that permanent magnetic properties can be achieved in (Fe,Co) 2 (P,Si) quaternary alloys. This work correlates the development of permanent magnetic properties to a control of the microstructure. It paves the way toward the realization of permanent magnetic properties in (Fe,Co) 2 (P,Si) alloys made of economically competitive Fe, P and Si elements, making these materials desirable for applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Ternary intermetallics deriving from ScFe 2 Laves phases can present a relatively unique case of ferro-ferromagnetic transition originating from an iron moment instability, which is potentially interesting for several applications. Yet, at the exception of (Sc,Ti)Fe 2 , their structural and magnetic phase diagrams remain scarcely explored. Here, we present a systematic investigation of the crystal structure and magnetic properties of Sc 1-x Nb x Fe 2 intermetallics. This series is found to mostly crystallize in the C14 hexagonal structure. But, in contrast to former studies, a C14/C15 hexagonal/cubic dimorphism is observed for the binary parent ScFe 2 , with the C15 structure that can be brought to the edge of stability depending on heat treatments. This led us to revisit the properties of ScFe 2 via first-principles calculations. The total energy difference between C14 (stable) and C15 structures is found small, and C15 ScFe 2 is predicted to be ferromagnetic with a saturation magnetization close to that of C14 ScFe 2 , which is fully compatible with experimental observations. Experimentally, Sc 1-x Nb x Fe 2 intermetallics with x ≤ 0.35 are ferromagnetic with Curie temperatures decreasing with increasing the Nb content; while such a long range ferromagnetic order with net magnetization is no longer observed for x > 0.6. A Néel transition is observed around 250 K in 0.6 ≤ x ≤ 0.9 alloys, this antiferromagnetic order is coexisting with a minor ferromagnetic phase, in line with former results from Mössbauer spectroscopy. For 0.2 ≤ x ≤ 0.3 samples, an ─unusual─ ferro.-ferromagnetic transition with a change in magnetization from ~1.2 μ B /Fe to ~0.9 μ B /Fe upon heating is found around 150 K in addition to the ferro-paramagnetic transition. This broad ferro.-ferromagnetic transition is isostructural as the C14 hexagonal crystal structure is preserved, but it leads to a virtually zero thermal expansion up to 250 K. [Display omitted] • Structural and magnetic phase diagrams of Sc 1-x Nb x Fe 2 are explored. • Sc 1-x Nb x Fe 2 with x < 0.25 are ferromagnets with high Curie temperatures. • Sc 1-x Nb x Fe 2 with x > 0.5 no longer show high moment ferromagnetic order. • For 0.25 = x ≤ 0.3, an unusual ferro.-ferromagnetic transition with zero thermal expansion is found. • ScFe 2 parent shows hexagonal C14/cubic C15 dimorphism depending on heat treatment. [ABSTRACT FROM AUTHOR]