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Neodymium iron boron (NdFeB) magnets are sintered anisotropic materials. They were commercially introduced in the early 1980s, and since have been used in different applications owing to their superior properties. Herein, we investigated the influence of 0.5 to 8 h of milling time on the morphological, structural, and magnetic performance of Nd _9.6 Fe _80.3 Zr _3.7 B _6.4 powders produced using surfactant-assisted high-energy ball milling (SA-HEBM). The results revealed that the relationship between coercivity ( H _ci ) and milling time had a non-monotonous character reaching a maximum value of H _ci = 8.92 kOe after 1 h of milling. The effect of the volume ratio of various magnetic phases (Nd _2 Fe _14 B and α -Fe) on microstructure and magnetic properties was also reported. The highest specific saturation magnetization ( σ _s = 120 emu g ^−1 ) was attained after 8 h of milling for powders with volume fraction: Nd _2 Fe _14 B–81 ± 2% and α -Fe–12 ± 2%. The expected value of Nd _2 Fe _14 B specific saturation magnetization was estimated ( σ _N = 108 ± 2.5 emu g ^−1 ) using the experimental value of σ _s and magnetic phase volume fractions. The ratio of remanence to saturation magnetization of the Nd _2 Fe _14 B with milling time was also determined and analyzed.

Nanostructured alloy powders of SmCo5 + 10 wt% Fe obtained using recycled material were studied for the first time. The SmCo5 precursor was obtained from commercial magnets recycled by hydrogen decrepitation. The results were compared with identically processed samples obtained using virgin SmCo5 raw material. The samples were synthesized by dry high-energy ball-milling and subsequent heat treatment. Robust soft/hard exchange coupling was observed—with large coercivity, which is essential for commercial permanent magnets. The obtained energy products for the recycled material fall between 80% and 95% of those obtained when using virgin SmCo5, depending on milling and annealing times. These results further offer viability of recycling and sustainability in production. These powders and processes are therefore candidates for the next generation of specialized and nanostructured exchange-coupled bulk industrial magnets.

• Collective Curie temperature in Co 3 Gd 4 /Co 7 Gd 12 magnetic nanocomposites. • The variation of the magnetic entropy change has been investigated. • The interphase exchange coupling in the produced nanocomposites was investigated. The effect of interphase exchange coupling on the Curie temperature of mechanically milled Co 3 Gd 4 /Co 7 Gd 12 magnetic nanocomposites was studied. It was shown that the nanocomposites have a single critical temperature (195 K), approximately half way between those of the constituent alloys (160 K for Co 7 Gd 12 and 220 K for Co 3 Gd 4). The interphase exchange coupling within the nanocomposites was investigated, at 4 K, by the First Order Reversal Curve method. [ABSTRACT FROM AUTHOR]

(Nd,Dy) 2 Fe 14 B + x wt% Fe ( x = 10 and 22) nanocomposite magnetic powders are synthesized by mechanical milling and annealing. This paper resumes our studies on the influence of structure and microstructure on the magnetic properties of Nd 2 Fe 14 B/α-Fe exchange coupled hard/soft magnetic nanocomposites obtained by mechanical milling and annealing. Different microstructures are obtained by changing milling conditions. In order to recover the crystallinity of the hard magnetic phase and hinder the increase of the crystallite size of Fe, two types of annealing are performed after milling. The first one, a common heat treatment, is carried out at moderate temperatures between 450 and 650 °C for 1.5 h. The second one, short time annealing, is performed at much higher temperatures between 700 and 800 °C for up to 3 min. The structure and microstructure were studied by X-ray diffraction. The morphology and chemical homogeneity of the obtained powders are checked by Scanning Electron Microscopy and Energy Dispersive X-ray measurements. The magnetic behavior is checked from hysteresis curves and the field derivative of the magnetization curve ( dM/dH vs. H plots). [ABSTRACT FROM AUTHOR]

• Non-linear lattice expansion with the addition of Ga due to its monovalent state. • Structural transformation from L2 1 to HCP+intermetallic phase upon Ga substitution. • Increase in the paramagnetic fraction with sequential Ga substitution. • Weakening of magnetic exchange coupling with sequential Ga substitution. • The lattice parameter modelled using GPR shows non-linear trend upon Ga substitution. [Display omitted] The present study reports the evolution of microstructure and magnetic properties of Cu 2 MnAl 1−x Ga x Heusler alloys. The L2 1 phase, which remained stable up to a Ga substitution of x = 0.3, transformed into mixed phases, i.e., hexagonal close packed (HCP) and complex cubic structure (CCS) on further addition of Ga. The non-monotonic increase in the lattice constant indicates that some amount of Ga retains its monovalent state. The magnetic phase showed a transition from ferromagnetic to paramagnetic state with increasing Ga concentration. The re-entrant temperature (T R) decreased from 8.2 K to 5.2 K as Ga content increased from 5 at% to 10 at%. The strength of magnetic exchange-coupling also reduced with an increase in Ga content. Gaussian process regression (GPR) was used to estimate the lattice parameter using the ionic radii and Pauling electronegativity of the constituents. The modeling approach showed high accuracy and stability, providing new insights into future alloy development. [ABSTRACT FROM AUTHOR]

Nanostructured alloy powders of SmCo5 + 10 wt% Fe obtained using recycled material were studied for the first time. The SmCo5 precursor was obtained from commercial magnets recycled by hydrogen decrepitation. The results were compared with identically processed samples obtained using virgin SmCo5 raw material. The samples were synthesized by dry high-energy ball-milling and subsequent heat treatment. Robust soft/hard exchange coupling was observed—with large coercivity, which is essential for commercial permanent magnets. The obtained energy products for the recycled material fall between 80% and 95% of those obtained when using virgin SmCo5, depending on milling and annealing times. These results further offer viability of recycling and sustainability in production. These powders and processes are therefore candidates for the next generation of specialized and nanostructured exchange-coupled bulk industrial magnets. [ABSTRACT FROM AUTHOR]