Magnetic Mechanism Of The Fe-Nd-Al Amorphous Alloys

The development and production of rare earth permanent magnets start earlier inour country which are rich in rare earth resources, and the total output of our countryis leading in the world. In1996, the preparation of the Nd-Fe-Al bulk amorphousalloys successfully opened up a new field for the application of rare earth based bulkamorphous alloys in the hard magnetic materials due to its hard magnetic propertiesat room temperature and good glass forming ability. The development of this alloyhas important economic benefits to convert China’s rare earth resources advantagesinto industrial advantages. However, the hard magnetic mechanism of the Nd-Fe-Albulk amorphous alloys is still unclear to date.In this dissertation, vibrating sample magnetometer (VSM), differential scanningcalorimeter (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM),focused ion beam (FIB) and high resolution transmission electron microscopy(HRTEM) have been employed. The magnetic property, phase composition andmicrostructure of the Fe53Nd37Al10and Nd60Fe30Al10alloys with different coolingrates were investigated at different temperatures. The hard magnetic mechanism ofthe Fe-Nd-Al amorphous alloy is discussed in the reference with the typicalmagnetic model, and the results are summarized as follows:(1) All the samples of the Nd60Fe30Al10alloy show hard magnetic properties. Thecoercivity of the Nd60Fe30Al10alloy with thickness of1mm is highest. Thecoercivity of the ribbons is lower and decreases gradually with the increasingcooling rate. There are small steps in the hysteresis loops of the ribbons with5m/sand20m/s wheel speed.(2) The Fe53Nd37Al10alloy with thickness of1mm almost has soft magneticproperty at room temperature, with a small step in the hysteresis loop. There is noexchange coupling interaction in the as cast alloy. The5m/s-ribbon of theFe53Nd37Al10alloy shows the highest coercivity, with a step in the hysteresis loop.The exchange coupling interaction exists verified by the M Hcurve with twopositive peaks. The M Hcurve of the20m/s-ribbon has only one smallpositive peak. All the Fe53Nd37Al10ribbons show hard magnetic properties, and theircoercivity decrease gradually with the increasing cooling rate.(3) The coercivity of the1mm-thick Fe53Nd37Al10alloy almost remain constantwhile that of the ribbons increase obviously at low temperatures. All theFe53Nd37Al10ribbons exhibit exchange coupling interaction at low temperature, andthe peak value in the M Hcurve decreases with the increasing cooling rate.The5m/s-ribbon of the Fe53Nd37Al10alloy partially matches the pinning model, andthe step of the hysteresis loop is larger at lower temperature. Both the20m/s-and60m/s-ribbon of the Fe53Nd37Al10alloy match the pinning model, and their hysteresisloops show steps at low temperature. The ZFC and FC curves bifurcate at a certain low temperature, and the applied field essentially equals the sample’s coercivity atextremum temperature of the ZFC curve.(4) There are many lath-shaped Nd2Fe17crystals with different size embedding inthe amorphous matrix of the1mm-thick Fe53Nd37Al10alloy. A few of Nd crystalphases are apt to appear between two adjacent Nd2Fe17crystals. In the5m/s-ribbon,there are plenty of Nd2Fe17phases with5μm in size and clusters of5nm in diameterin the amorphous matrix. A lot of clusters of5nm in diameter are found in the20m/s-ribbon, while a few clusters of2nm in diameter exsit in the60m/s-ribbon.