Investigation On The Formation Of Hard Magnetic Nd-based And Pr-based Bulk Amorphous Alloys And Their Physical Properties

A Nd₆0Al₁0Fe₂0Co₁0 and a series Pr-based BMGs are formed in this work. Glass forming, structure, thermal characters and crystallization are studied by XRD, DSC and DTA. And the physical properties such as the mechanical, thermal, electrical and magnetic properties are studied by ultrasonic, specific heat, resistance and magnetic properties' measurements.The Nd₆0Al₁0Fe₂0Co₁0 and a series Pr-based BMGs are prepared by cooper mold suction casting method. The almost amorphous structure is confirmed by XRD and DSC measurements, and it is found that the DSC trace of the Nd₆0Al₁0Fe₂0Co₁0 BMG has no glass transition region while the Pr55Al12Fe30Cu3 BMG has a wide glass transition about 75 K and the Tg is about 551 K with a heating rate of 30 K/min. Samples are annealed at difference temperatures that are determined by DSC results, and the structure is checked by XRD, and the crystallizing extents are measured by DSC. The melting temperature of the Pr55Al12Fe30Cu3 BMG is about 140 K higher than that of its corresponding crystallized alloy. All the as-prepared alloys have magnetic properties that have close relationship with GFA. The hard magnetic properties vanished when the alloys are crystallized. The magnetic properties at low temperature are measured and it is found that the properties change markedly with the decreasing temperature, the coercivity and the remanence increasing at first, and then decreasing at lower temperature while the saturation magnetiation is increasing continuously. AC magnetic susceptibility of the Nd₆0Al₁0Fe₂0Co₁0 alloys was measured, and it is found that the spin is frozen at about 18 K in the glassy alloy while there is no spin glass state in the crystallized alloy. The DC susceptibility of the Nd-based alloy is measured too, and the results indicate that when T >80 K, χglass>χcrystal while T < 80 K, χglass<χcrystal.Density and ultrasonic measurement for the Pr55Al12Fe30Cu3 BMG is performed, the velocity of the ultrasonic in the Pr55Al12Fe30Cu3 BMG is slower than that in the Nd₆0Al₁0Fe₂0Co₁0 BMG, and also, it is slower in the glassy Nd₆0Al₁0Fe₂0Co₁0 alloy than that in the crystallized alloy which accompany with the same relationship of the Young's modulus, shear modulus, density, bulk elasticity modulus and Debye' temperature.Low temperature specific heat on the Nd₆0Al₁0Fe₂0Co₁0 BMG and its corresponding crystallized alloy are investigated and found it changes at the temperaturewhere AC magnetic susceptibility is break. The data could be fitted by when T<20 K.Resistance and magnetoresistance measurement are performed for the Nd₆0Al₁0Fe₂0Co₁0, Pr55Al12Fe30Cu3 BMGs and their corresponding crystallized alloys, the results indicate that the two systems have positive coefficient of resistance both for their as-prepared and annealed alloys. Magnetoresistance for the Nd₆0Al₁0Fe₂0Co₁0 BMG and its corresponding crystallized alloy Increasing with the increasing magnetic field at low temperature. A max. of magnetoresistance is found for the Pr55Al12Fe30Cu3 BMG and its crystallized alloy at 5 K.