T.H. Jacobs

Bio: T.H. Jacobs is an academic researcher from Philips. The author has contributed to research in topics: Magnetization & Magnetic anisotropy. The author has an hindex of 21, co-authored 43 publications receiving 1475 citations. Previous affiliations of T.H. Jacobs include Leiden University.

Nitrogen atom location in rhombohedral and hexagonal RE2Fe17Nx compounds

Abstract: High resolution neutron powder diffraction studies were performed on Nd2Fe17Nx and Y2Fe17Nx. A strong preferential site occupation of the N atoms on the 9e position of the rhombohedral compound Nd2Fe17Nx was observed. In the hexagonal compound Y2Fe17Nx the N atoms occupy primarily the 6h sites (82%) and only a small fraction goes into the 12i site (12%). The refined nitrogen occupation numbers correspond to the formula compositions Nd2Fe17N2.6 and Y2Fe17N2.9.

New developments in hard magnetic materials

Abstract: 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.

Negative thermal expansion in functional materials: controllable thermal expansion by chemical modifications

Abstract: Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a “perfect” NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.