Domain structure of aNd60Al10Fe20

Abstract

Magnetic domain structure of Nd 60 Al 10 Fe 20 Co 10 bulk metallic glass ͑BMG͒ has been studied by using magnetic-force microscopy. In the magnetic-force images it is shown that the exchange-interaction-type magnetic domains with a period of about 360 nm do exist in the BMG, which is believed to be associated with the appearance of hard-magnetic properties in this system. The existence of the large-scale domains demonstrates that the magnetic moments of a great deal of short-scale ordered atomic clusters in the BMG have been aligned by exchange coupling. Annealing at 715 K leads to partial crystallization of the BMG. However, the exchange coupling is stronger in the annealed sample, which is considered to arise from the increase of transition-metal concentration in the amorphous phase due to the precipitation of Nd crystalline phase.Nd-Fe-Al-based bulk metallic glasses ͑BMG͒ with a diameter up to 12 cm have been recently prepared. 1 This BMG system has evoked an extensive attention due to its hard magnetic properties at room temperature. 2-8 The high coercivity of these amorphous alloys is striking because no structural anisotropy exists in the disordered packing solid. It is supposed that the BMG is an ensemble of short-scale ordered magnetic atomic clusters in uniform distribution. These clusters consist of Nd and transition elements and possess large random anisotropy. It is the magnetic-exchange coupling among them that causes the high coercivity of this magnetic system. Most of the consequent results supported this model. 7-9 However, no direct experimental evidence for the existence of exchange-coupling interaction in this system has been presented so far. Therefore, it is of a special interest to study the magnetic domain structure of the BMG. In this paper, the magnetic domain structure of Nd 60 Al 10 Fe 20 Co 10 was investigated by magnetic-force microscopy ͑MFM͒.Ingots with compositions of Nd 60 Al 10 Fe 20 Co 10 were prepared by arc melting from elemental Nd, Fe, Al, and Co with a purity of 99.9% in a titanium-gettered argon atmosphere. Cylindrical specimens of around 3 mm in diameter and 50 mm in length were prepared from the ingots by die casting into a copper mold under argon atmosphere. The details of preparation can be seen in Ref. 5. The structure of the as-cast cylinder was characterized by x-ray diffraction ͑XRD͒. 5 Magnetic measurements were performed using a vibrating sample magnetometer with a maximum applied field of 1592 kA m Ϫ1 . The study of domain structure was carried out by using Digital Instruments NanoScope IIIa D-3000 MFM. It allows the topographic and magnetic-force images to be collected separately and simultaneously in the same area of the sample by using Tapping/Lift modes. The magnetic tips used were microfabricated Si cantilevers with a pyramidal tip coated with magnetic Co-Cr thin film of 40 nm thickness and a coercivity of about 32 kA m Ϫ1 . For the mode of dynamic detection, the cantilever is vibrated and its resonant frequency f 0 and phase will be modulated by the magnet...

Magnetic properties and magnetic domain structure of bulk glass forming Nd60Al10Fe20Co10 alloy

“…The dark area indicates that the magnetization direction in this area is nearly parallel to the upward tip magnetization, and the bright area indicates the opposite. This kind of magnetic contrast is similar to our previous results on Ndbased BMG but the magnetic force contrast in the ribbon is lower than that in a cast bulk sample [13]. The average periodicity (L) of the domain pattern and the average contrast between dark and bright areas were measured by means of section analysis, revealing L ≈ 360 nm, the maximum phase shift ∆φ max (represents the magnetic force) is 3.54 degrees, and the root mean square (RMS) of the magnetic force is 0.226 degrees.…”

“…TEM and HRTEM results also prove the presence of some unknown nano-scale phases in the ribbons and BMG of similar systems [2,13,25]. The magnetic properties of the present thick ribbons and bulk samples [13] are indeed similar to Nd-Fe binary alloys [17][18][19][20][21][22][23][24]. Consequently, we suggest that the presence of a SRO structure, which has a similar local structure as the A1 phase in Nd -Fe binary alloys, is responsible for the hard magnetic properties in samples subjected to relatively low quenching rates (ribbons melt-spun at 3 or 6 m/s in the present work).…”

“…High coercivity is revealed for the thick ribbons (exceeding 100 µm), with a value lower than that in bulk samples of the same composition, whereas thin ribbons are magnetically soft [13]. The MFM images show particles with a size of about 5 nm in the ribbon melt-spun at 3 m/s.…”

“…Further details regarding the MFM experiments are given in Ref. [13]. The ribbons were studied on their non-contact side without any pre-treatment.…”

Effect of Fe content on the thermal stability and dynamic mechanical behavior of NdAlNiCu bulk metallic glasses

“…In other words, by increasing Fe content in the present system, amorphous phases with different chemical composition form during cooling in the high Fe content alloys, in addition to the decrease of total amorphous fraction. The amorphous phase separation was also indicated by others in the high Fe content Nd-based BMG through low temperature magnetic measurements [26]. The glass transition and crystallization processes take place gradually, but has little thermal effect, as each amorphous phase has a quite small volume fraction.…”