Study On Magnetic Properties Of Bulk Amorphous Alloys Nd-R-Fe-Al(R=Dy, La Or Y)

Application and development of materials is the important milestoneto the progress of human being. As one of the important magnetic amorphousmaterials, RE-Fe( RE=Nd, Pr) metallic glasses with promising magneticproperties were developed by J. J. Croat and have been intensivelyinvestigated because of their great significance in material science and theirconsiderable technological promise. Nd-Fe-Al bulk metallic glasses (BMGs)have shown attractive glass-forming ability (GFA) and high coercivity atroom temperature. However, neither distinct glass transition nor supercooledliquid region has been observed in their diferential scanning calorimetry (DSC)traces, while the distinct glass transition and wide supercooled liquid regionare common features for other BMGs. And the high coercivity of the BMGs isanomalous because of their disordered structure。As a hard magnetic materialwith high coercive,it exploited likely one new area for bulk amorphousapplication. In this paper , amorphous ribbons were attained using melt-spuntechnology, and their magnetics performance have been investigated.Thereare great significance not only to the fundamental research but also to thepotential application.This paper consists of six chapters. The first and twice chapters mainlyintroduce the development of amorphous material and some measuring waysin this paper;auther's main research works are introduced from the thirdchapter to the sixth chapter . The main results are outlined as follows:1. The glass-forming ability and thermal stability of Na-R-Fe-Al wereinvestigated using XRD, SEM and DSC. The study indicated: it has neitherdistinct glass transition nor supercooled liquid region has been observed in thediferential scanning calorimetry (DSC) traces of Na-R-Fe-Al, and it did notconfirmed Tg point. It is found that addition of La reduce thermal stability ofNd-Fe-Al amorphous alloys, while addition of Y and Dy elements not onlypromote GFA of alloys,but also enhance its thermal stability.2.The magnetic of (Nd1-xDyx)60Fe30Al10 bulk amorphous alloys wasstudied. It is found that remanence Mr decreases with increasing content of Dy.Coercivity force increases rapidly when as Dy content is increased. Coercivityforce reach 6Koe at x=0.1.3. The coercivity of Nd-Fe-Al are decreased due to the addition ofnon-magnetic atom of La and Y. With increasing content of La, remanenceincrease, reaching a maximum as x=0.3, then begins to decrease. As forNdYFeAl amorphous alloys, Coercivity force decreases to 0 as x=0.4,bothremanence and magnetic energy level take on marked decrease trend along Ycontent increased.4. Magnetic characteristics are correlated closely with cooling rate. Itwas found that coercive force increased with the wheel speed, attains itsmaxinum at about 10m/s and 11m/s,then decrease with further increase thewheel speed,while cooling rate reach 20m/s , coercive force disappeared.5. According to the Henkel plot δm(H) curve, it can be conclude:theexchange coupling of atomic clusters has important influence on magnetperformance as the applied field was small;while magnetic dipole interactionhas important influence to magnet performance on the other hand. Becausethere are the great anisotropism for Dy,exchange coupling of atomic clusterscan be increased by substituting Dy for Nd. While addition of non-magnetismelement L(aor Y)results decreasing height of positive peakand increasing thatof negative peak, such phenomena became brilliance with increasing La(orY)contents. We knows that the exchange coupling can be improved for lowanisotropism,but direct exchange coupling of magnetic moments can bedecreased due to non-magnetism element La(or Y),and it can counteractincrease of exchange coupling ,then the exchange coupling of atomic clusterswill decrease and coercive force will also decrease.6. The coercivity indicates the ability of resisting the reversal field for apermanent magnets and the coercivity mechanism is key problem inpermanent magnetis.According to the initial magnetization curve of Nd base,dependence of reduced remanence and coercivity on magnetizing field andHenkel Plot,it is conclude that the coercivity mechanism is domain wallpinning. Investigation on reversible and irreversible behaviors inmagnetization and demagnetization curves of Nd-Dy-Fe-Al andNd-La(Y)-Fe-Al BMG , it shows that they have both similar change, and hardmagnetic properties originated from the magnetocrystalline anisotropic fieldof rare-earth element.