We report the properties of a new class of high‐performance permanent magnets prepared from Nd‐Fe‐B and Pr‐Fe‐B alloys Magnetic hardening is achieved by rapid solidification Energy products of these isotropic materials can exceed 14 MGOe with intrinsic coercivities of ∼15 kOe X‐ray and microstructural analyses indicate that the alloys exhibiting optimum characteristics are comprised of roughly spherical crystallites, strongly suggesting that the coercivity mechanism is of the single‐domain particle type The crystallites are composed of an equilibrium R‐Fe‐B intermetallic phase having tetragonal symmetry, and the stability of this phase with respect to other rare earths and other metalloids has been investigated

Pr‐Fe and Nd‐Fe‐based materials: A new class of high‐performance permanent magnets (invited)

Microwave ferrites are ubiquitous in systems that send, receive, and manipulate electromagnetic signals across very high frequency to quasi-optical frequency bands. In this paper, modern microwave ferrites are reviewed including spinel, garnet, and hexaferrite systems as thin and thick films, powders and compacts, and metamaterials. Their fundamental properties and utility are examined in the context of high frequency applications ranging from the VHF to millimeter-wave bands. Perspective and outlook of advances in theory, processing, and devices occurring in the science and engineering communities since the year 2000 are presented and discussed.

Modern Microwave Ferrites

A review is given of the formation, the crystal structure and the magnetic properties of several classes of rare earth based intermetallic compounds that lend themselves as starting materials of permanent magnets. These compounds include R2Fe14B, R2Fe14C and R2Co14B and the large class of ternary rare earth compounds having the tetragonal ThMn12 structure. Special emphasis is given to the changes in magnetic properties of R2Fe17 compounds observed after interstitial solution of C or N atoms. The magnetic properties of all these compounds are discussed in terms of current models based on intersublattice and intrasublattice exchange and the interplay between the rare earth sublattice anisotropy and 3D sublattice anisotropy. A substantial portion of the review is devoted to manufacturing routes of permanent magnets and a description of the coercivity mechanisms operative in the magnets. A comparison is made of the performance and economic costs of various types of magnets and novel applications are briefly discussed.

https://iopscience.iop.org/article/10.1088/0034-4885/54/9/001/pdf

New developments in hard magnetic materials

We have explored the hard magnetic properties of melt‐spun Nd‐Fe‐B alloys. A maximum energy product of 14.1 MG Oe has been observed, the highest value ever reported for a light rare earth‐iron material. X‐ray analyses indicate that the alloys exhibiting optimum characteristics are comprised of roughly spherical crystallites of an equilibrium Nd‐Fe‐B intermetallic phase. The observed grain sizes are in or near the estimated single‐domain range, suggesting that the coercivity arises principally from the formation of single‐domain particles.

High‐energy product Nd‐Fe‐B permanent magnets

A review is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and non-magnetic metals, with emphasis on the magnetic properties. Included are the properties of compounds in which the non-rare-earth component is a 4d or 5d transition element. Special consideration is given to the properties of pseudo-binary compounds. Results of magnetisation measurements, neutron diffraction and neutron scattering are discussed together with results derived from NMR, ESR and Mossbauer effect spectroscopy. An evaluation is given of the relevance of the experimental results with respect to different types of exchange interactions in this class of intermetallics. Special consideration is also given to the influence of crystal field effects on the magnetic properties and, furthermore, to the occurrence of intermediate valences in several of the compounds of Ce, Sm, Eu and Yb.

https://iopscience.iop.org/article/10.1088/0034-4885/42/8/003/pdf

Intermetallic compounds of rare earths and non-magnetic metals

Giant magnetostriction materials

Mössbauer evidence of spin reorientation in single crystal Nd2Fe14B

Abstract: A new class of melt quenched amorphous magnetic alloys

Magnetization of (Y0.9R0.1)2Fe14B single crystals

Torque measurements have been performed on single crystal HoAl2 compound in order to examine the origin of the 20 K specific heat anomaly that occurs in polycrystalline HoAl2. The experimental results indicate the anomaly is due to a spin reorientation between the [110] and [100] in the (100) plane as the temperature is increased. Crystal field calculations suggest the transition should be of the first order; however, torque measurements show that the transition takes place continuously over a finite temperature range.

B. N. Das

Papers

Giant magnetostriction materials

Mössbauer evidence of spin reorientation in single crystal Nd2Fe14B

Abstract: A new class of melt quenched amorphous magnetic alloys

Magnetization of (Y0.9R0.1)2Fe14B single crystals

Spin reorientations in single crystal HoAl2