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An enhancement of the Curie temperature, [T.sub.C], was deduced from ac-susceptibility measurements on the [R.sub.2][Fe.sub.14]B (R = Nd and Pr) phase for exchange coupled nanocrystalline magnets with respect to corresponding microcrystalline magnets.

We describe the construction of a thermomagnetic analyser that uses a microfurnace. The equipment can work in the temperature range of -30 [degrees] C up to 1000 [degrees] C, with heating/cooling rates as high as 50 [degrees] C/min. without temperature hysteresis. The design allows the use of excitation and pick-up coils with thousands of turns, working at room temperature. This gives a high sensitivity to the equipment as revealed by the measurement of magnetic transitions in thin films with masses in the order of 500 [[micro]gram]. The reproductibility of the measurements is very good, and there is only noticeable drift in the most sensitive range.

We studied the high temperature decomposition mechanism for the [Fe.sub.17][Sm.sub.2][N.sub.3] phase using several different experimental techniques, as thermomagnetic and thermogravimetric analyses. Our results show that the decomposition occurs in a two step scheme. In the first reaction we have the formation of SmN and a solid solution of nitrogen in iron. In the second step, this solid solution degases, and we observe the evolution of nitrogen over a broad temperature range.

The nitrogen diffusion patterns on several RE2Fe17 intermetallic compounds are studied. The nitriding process was done in both slabs and powder samples, which were characterized and analyzed thermomagnetically and metallographically. The diffusion process occurs by both mechanisms: shell-core model and along preferential paths. A broadening caused by stress or by dilution was detected in pure phase transition.

The effects of different contents of nitrogen in both Pr2Fe17 and Nd2Fe17 and of cobalt in both Nd2Fe17 and Nd2Fe17N2 center dot 2 are investigated by means of Mossbauer spectroscopy (MS) and thermal magnetic analysis (TMA). The results confirm that either nitrogen or cobalt increases the hyperfine field (Bhf) as well as the Curie temperature (Tc) of the material. The hyperfine parameters for nominal contents of nitrogen above y = 1.5 are the same as those observed in fully nitrided samples. Our data also reveal that the combination of both N and Co produces an additional increase of Tc. The same behaviour is observed in Bhf of Nd2(Fe1-xCox)17N2 center dot 2 in the range 0 < x < 0.1. After a restricted maximum at x approximately equal to 0.02-0.05, Bhf decreases with increasing x.

We describe the construction of a thermomagnetic analyser that uses a microfurnace. The equipment can work in the temperature range of -30/spl deg/C up to 1000/spl deg/C, with heating/cooling rates as high as 50/spl deg/C/min. without temperature hysteresis. The design allows the use of excitation and pick-up coils with thousands of turns, working at room temperature. This gives a high sensitivity to the equipment as revealed by the measurement of magnetic transitions in thin films with masses in the order of 500 /spl mu/g. The reproducibility of the measurements is very good, and there is only noticeable drift in the most sensitive range. [ABSTRACT FROM PUBLISHER]