Magnetic anisotropy of R2T14B (R=rare earth and T=transition metals such as Fe and Co) and partly substituted derivatives thereof are studied over a range of temperatures. The salient features are axial anisotropy for Y2Fe14B versus planar anisotropy for Y2Co14B. Only R with negative second-order Stevens’ factor (such as Nd) will show axial anisotropy contributions near room temperature. However, even in this case nonaxial contributions compete at cryogenic temperature, leading to a spin reorientation for R=Nd and Ho with TRs=140 and 62 K, respectively, for the Fe-based compounds. The symbol R is used to amplify the point that the spin reorientation is primarily triggered by an internal competition of R in question. The origin of this anisotropy competition is further illuminated by studies on partly R substituted materials, such as (Nd1−xRx)2Fe14B. Several contributions to the complex situation are considered including: (a) different site contributions (4f, 4g), (b) different order crystal-field terms, such as V02, V22, and V04 on 4f and 4g, (c) relative magnitude of exchange and crystal field, and (d) the trend for smaller R to preferentially occupy the 4f site. Another type of spin reorientation is observed when R and T sublattice anisotropies compete. An example is Er2Fe14B with TR-Ts=326 K. More complex mixed cases are either observed or predicted.

Trends in structural and magnetic parameters are presented and discussed for Nd2Fe14−xTxB with T=Cr, Mn, Co, Ni, Al. Some data are also included on the Y analog systems. Partial Al substitution strongly increases c/a. We show that this has to do with preferential occupation of the larger atom (Al) in the σFe layer. Co and Ni substitutions increase Curie temperature (TC) while all others decrease it. Anisotropy constants K for 300 K decrease in all cases investigated compared to Nd2Fe14B. Some discussion is given to the general mode of preferential substitution and the concomitant effects on magnetic anisotropy.

NdDyFe14B shows a spin reorientation around TS =92 K which is lower than that obtained for Nd2Fe14B (150 K). Neutron diffraction on powder specimen indicates a preferential occupation for Dy atoms of the 4 f sites, but does not reveal the spin reorientation.

A spin reorientation occurs in Nd2Fe14B starting around Ts= 150 K. We present data on tendencies in spin reorientations in systems (Nd1−xRx)2Fe14B and Nd2Fe14−xAxB where R=different rare earths and A=Co, Al. The insensitivity of Ts to some of these substitutions appears to indicate that Nd alone is responsible for the transition. We discuss a model according to which this transition may be triggered primarily by a competition amongst the anisotropies of the two Nd sites. According to a crystal field analysis the Nd 4f site should be more susceptible to plane preference while the Nd 4g site should have axial anisotropy. At lower temperatures the 4f site gains in relative importance and triggers the spin reorientation. The absence of a similar spin reorientation in analogous systems however indicates a complex situation.

AbstractKDE‐Verbindungen vom CeCmB‐Struktur‐Typ wurden durch Induktionsschmelzen hergestellt und als Modellverbindungen zur Untersuchung der inneren magnetischen Härte im Hinblick auf die Permanentmagnetentwicklung analysiert (R ‐ Y, Pr, Sm, Gd, Lu; T. ‐ C04, Co2Fe2, Co3Fe, Fe2Ni2, FeNi3, Co3Ni, Fe.).

The structural and magnetic behavior is presented for selected metalloid (B,C) containing hexagonal and tetragonal rare earth-transition metal compounds and compound series. Focus is on materials with high Fe content and resulting high magnetizations. The unusual axial ratios and features of the sheet type structures of these materials have pronounced consequences on such properties as magnetic anisotropy and magnetic hardness. Individual site anisotropy contributions are studied by temperature dependence of magnetization along easy and hard magnetic axes. As an example it is found that tetragonal Nd2Fe14B has axial anisotropy with HA = 76 kOe at 300 K but shows tendencies for a spin reorientation around 150 K. Y2Fe14B has axial anisotropy with HA = 25 kOe but does not exhibit a similar spin reorientation. This indicates that the two crystallographic Nd sites (4f and 4g) have axis and plane preference respectively, with different temperature dependencies. Axial Nd anisotropy is a consequence of the lack of Nd coordination along the z axis due to intervening thick Fe layers. Both extrinsic (fine particle) and intrinsic magnetic hardness is observed. Crystallographically disordered materials show intrinsic hardness based on domain wall pinning by local fluctuations of magnetic parameters. Strong nucleation phenomena are characteristic for ordered materials in bulk and powder form. The unusually high achievable ratios of extrinsic coercivities to anisotropy fields in the metalloid stabilized materials are related to their chemically relatively inert layer structure. This appears to lead to less corrugated surface structures and is so responsible for the characteristic domain wall nucleation processes.