THE COMPUTATION OF MAGNETIC FORCES OF NEW TYPE HARD MAGNETIC MATERIALS AND THE STUDY ON THE TEST SYSTEM FOR THE MECHANICAL PARAMETERS

This paper presents theoretical computations of magnetic force bearings made of new type hard magnetic materials neodymium iron boron. A set of devices capable of simultaneously measuring magnetic eccentricity, crosswise stiffness and magnetic pulling force is designed.

Formation of L1_(0)-FeNi hard magnetic material from FeNi-based amorphous alloys

L1_(0)-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe_(42)Ni_(41.3)Si_8 B_(4)P_(4)Cu_(0.7)amorphous alloy,and the L1_(0)-FeNi formation mechanism has been studied.It is found the L1_(0)-FeNi in annealed samples at 400℃mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 600 C lower than the measured onset temperature of the second stage with a50 C/min heating rate.Annealing at 4000 C after fully crystallization still caused a slight increase of coercivity,which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1_(0)phase,or the removal of B from L1_(0)lattice and improvement of the ordering quality of L1_(0)phase due to the reduced temperature from520℃to 400℃.The first stage of crystallization has hardly direct contribution to L1_(0)-FeNi formation.Ab initio simulations show that the addition of Si or Co in L1_(0)-FeNi has the effect of enhancing the thermal stability of L1_(0)phase without seriously deteriorating its magnetic hardness.The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects.The approaches of synthesizing L1_(0)-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.

Microstructure and magnetic properties of Fe-Co-Nd-Y-B alloys obtained by suction casting method

The phase composition, magnetic properties i.e. coercivity and the magnetic polarization at room temperature for the bulk Fe67Co5Nd3Y6B19 and Fe64Co5Nd6Y6B19 alloys were studied. The bulk amorphous Fe67CosNd3Y6B19 alloy, inhomogeneous in the as-quenched state, crystallized after annealing at 948 K for 0.5 h and consisted of Nd2Fe14B-type, Fe2B and paramagnetic phases. The rapidly solidified Fe64Co5Nd6Y6B19 alloy contained the Nd2Fel4B-type and paramagnetic phases. The annealing of the bulk Fe67CosNd3Y6B19 alloy at 948 K for 0.5 h led to hard magnetic properties. However, the bulk Fe64Co5Nd6Y6B19 alloy exhibited good hard magnetic properties directly after preparation.

Systematic study of the dependence of magnetic and structural properties of Nd2Fe14B powders on the average particle size

A systematic study of the magnetic and structural properties dependence on the particle size was realized.For this,commercial NdFeB powder was separated into five different mean particle sizes using sieves.Besides,from the original powder,eleven samples were also produced by mechanical milling assisted by surfactant,using various milling times.A total of sixteen samples were studied by scanning electron microscopy(SEM),X-ray diffraction(XRD),vibrating sample magnetometry(VSM),and Mdssbauer spectrometry(MS).The particle sizes of the samples vary from the micrometer to the nanometer scale.The crystallite size decreases with decreasing particle size.XRD result indicates that the Nd2Fe14B phase is found in all the samples,and the presence of this phase is also corroborated by MS using six sextets for fitting their spectra,with an additional singlet corresponding to the Nd1.1Fe4B4 phase.The mean hyperfine magnetic field increases with increasing particle size because the magnetic dipolar interaction between the magnetic moment of the particles increases with particle size.From the VSM measurements the magnetic energy density(BH)max values were calculated for different particle sizes,and their maximum value of 34.45 MGOe is obtained for the sample with the particle size of 60μm.

Controlled synthesis and excellent magnetism of ferrimagnetic NiFe_(2)Se_4 nanostructures

3d transition metal chalcogenides have attracted much attention due to their unique magnetic properties.Although various Cr,V,and Fe-based chalcogenides have been fabricated recently,the limited Curie temperature(T_C)still hinders their practical application.Based on the structural and magnetic advantages of MFe_(2)O_(4)and Fe_(3)Se_(4),we developed a one-pot solution synthesis method for the fabrication of NiFe_(2)Se_(4)nanostructures with structural continuity,to facilitate the investigation of their magnetic properties.Notably,the morphology of Ni Fe_(2)Se_(4)can be controlled from nano-rods to nano-platelets by controlling the growth direction.The coercivity(H_(C))of NiFe_(2)Se_(4)with nano-cactus structure exhibits a maximum of 12.77kOe at 5 K.The coercivity of ferrimagnetic NiFe_(2)Se_(4)nano-platelets can be further adjusted to 1.52 kOe at room temperature.These results show that the magnetic properties of NiFe_(2)Se_(4)can be significantly modified by controlling their morphologies.We also extend the method to the synthesis of Co Fe_(2)Se_(4)nano-cactus with an ultrahigh coercivity of 17.85 k Oe at 5 K.Obviously,the synthesis strategy and their excellent magnetic properties of MFe_(2)Se_(4)have sparked interest in ternary transition metal selenides as potential hard magnetic materials.