Nucleation fields in an exchange spring hard magnet

Abstract

A detailed study of magnetization processes has been carried out on a new type of hard magnetic material. The material Nd3.8Fe73.3V3.9B18.0Si1.0 is unique among hard magnets due to the exchange coupling of two ferromagnetic materials, one of which is soft and the other hard. The combination of the two materials gives a composite material, with a high magnetic saturation and coercivity. The irreversible components of magnetization for the material were examined using the demagnetizing remanence curve (DCD) and the isothermal remanence curve (IRM) for the magnetizing case. The nature of the interactions in the material were also studied using the delta M plot obtained via the DCD and IRM remanence curves. The reversible components were obtained from the M-H loop data, Mrev=Mtot-Mirr. Measurements of magnetic time dependence have also been carried out to provide fluctuation field data, Hf, from which activation volumes of reversal, v, for various fields have been obtained. The mean activation field Ha, obtained by extrapolating the linear portion of the fluctuation field data to zero, is the same as the mean nucleation field Hn obtained from the reversible components, Mrev of the demagnetizing remanence curve. Assuming spherical volumes of reversal, the dimensions of the soft and hard phases, obtained from the mean volume of activation, v(Hn) are close to the critical dimensions of the soft and hard phases.

Annealing dependence of magnetic interactions in YCo5(70%wt) + Y2Co17(30%wt) nanocomposite powders

“…This is not the case for the sample annealed for 5.5 min: as the inset in Fig. 3 shows, the demagnetization curve for this nanocomposite exhibits a "knee" which is common behavior for spring-magnets with a microstructure that does not favor exchange coupling (e.g., the grain size in one or both phases is too large) [9,10]. Thus, the DC-magnetization results above are in agreement with the annealing-induced increase of the grain size of the soft magnetic phase.…”

A simple approach to the First Order Reversal Curves (FORC) of two-phase magnetic systems

“…More quantitatively, since the error will be proportional to the neglected switching field overlap, the overlap between the switching field distributions [7] can give an estimate of the error. This could be simply estimated by differentiating the remanence curves [21]. For instance, for the examples presented in Ref.…”

Magnetic Properties Hard-Soft SmCo<sub>5</sub>-FeNi and SmCo<sub>5</sub>-FeCo Composites Prepared by Electroless Coating Technique

“…For materials with high H C values (H C > 2M s ), the theoretical limit for the energy product is limited only by M s and is given by (BH) max  (2M s ) 2 . Methods to overcome this limitation have focused on developing high anisotropy materials with high M s and Curie temperatures (T C ), materials which are based on rare-earth (RE)-transition metal (TM) intermetallics such as SmCo 5 [1][2][3]. In spite of the considerable improvement in the magnetocrystal line anisotropy, these materials still exhibit lower M s than Co, Fe or Fe 65 Co 35 , which have 4M s values of 18, 21, and 24 kG, respectively [1].…”

“…The soft phase, rich in transition metal, enhances satura tion magnetization, while the hard phase provides the required magnetic anisotropy and stabilizes the exchange coupled soft phase from demagnetization. Most of the reported literature on spring magnets is based on Nd 2 Fe 14 B or Sm 2 Fe 17 (hard)-α-Fe or Fe 3 B (soft) [5][6][7]. Insufficient temperature stability and poor corrosion re sistance are main factors limiting applications of Nd 2 Fe 14 B-based magnets.…”

“…Insufficient temperature stability and poor corrosion re sistance are main factors limiting applications of Nd 2 Fe 14 B-based magnets. However, the family of sa marium based alloys such as SmCo 5 and Sm 2 Fe 17 N x could be an attractive candidate material since it can be used as the hard phase due to its high magnetization (SmCo 5 , M s ~ 0.84 MAm ) [8]. The exchange-spring magnets have been fabricated by melt-spinning, hot-compaction [9], mechanical alloying [10,11], however these techniques yields nanocomposites with random dispersion and orientation of hard magnetic phase and often having no control on the growth of softphase [6,12].…”