The magnetic domain structure on the (0 0 1) plane of an Fe
 16.1
Ga
 83.9
 single crystal grown by the Czochralski method was observed by magneto-optic Kerr effect microscopy. In zero magnetic field, four different domain phases appeared, with magnetization in four kinds of '1 0 0 magnetic easy directions on the (0 0 1) plane. That is, the magnetic domain structure in zero field was composed of straight 90° domain walls and stair-like 180° domain walls. When a magnetic field was applied in the [0 1 0] direction, primarily 180° domain walls moved, whereas 90° domain walls did not. A striped domain structure composed of 90° domain walls was formed at a field of about 560 Oe, 180° domain walls having almost disappeared. A single domain structure was obtained by applying a field of about 1980 Oe. Magnetostriction in the [0 1 0] direction on the (0 0 1) plane was only about 10 ppm in a field of about 560 Oe and reached a saturation value of about 153 ppm at a field of about 1980 Oe. This magnetostrictive behavior contributes to the evolution of the magnetic domain structure.

Magnetic domain structure and magnetostriction of Fe-Ga single crystal grown by the czochralski method

We have investigated exchange-spring magnets made from powders prepared by high-energy milling Nd2Fe14B mixed with 10%wt. Fe, milled for 6 h in a planetary mill, varying the rotation velocity and the starting grain refinement of the soft phase. The samples were characterized by X-ray diffraction, magnetization techniques and 57Fe Mossbauer spectroscopy. The diffractometric and Mossbauer analyses revealed that the Nd2Fe14B compound was partially decomposed in the milling process, increasing the amount of free iron and reducing the grain size of both. Indicative for the Fe2B and Nd1-eFe4B4 phase separation was also found. The magnetization versus applied magnetic field curves showed that both the remanence and coercive field for the 500 rpm milled samples reached values higher than those earlier obtained for un-milled or similarly milled single Nd2Fe14B. However, milling with 600 rpm showed to be deleterious to the same magnetic parameters. It was also demonstrated that milling using iron with less refined grains is more effective to improve the magnetic properties of the composite system.

Structural and magnetic characterization of the Nd 2 Fe 14 B + 10%wt.Fe system subjected to high-energy milling

Remenance and coercivity in Nd2Fe14B materials are strongly dependent on the microstructural aspects like phases morphology and grain size. The coercivity (Hc) of a magnetic material varies inversely with the grain size (D) and there is a critical size below which Hc∝D6. Domain wall pinning by grain boundaries and foreign phases is the important mechanism in explaining the improvement in coercivity and remenance. Nd2Fe14B intermetallic compound with stochiometric composition was prepared from pure elements (Nd ‐99.5%, Fe—99.95%, B ‐99.99%) by arc melting in argon atmosphere. Magnetic Force Microscope (MFM) gives high‐resolution magnetic domain structural information of ferromagnetic samples. DI‐3100 Scanning Probe Microscope with MESP probes was used For MFM characterization of the samples. Magnetic domains observed in cast ingots were very long (up to 40 μm were observed) and approximately 1–5 μm wide due to high anisotropy of the compounds. Magnetic domains have displayed different image contrast and mo...

Magnetic Force Microscopy Investigation of Magnetic Domains in Nd2Fe14B

The effect of ball milling on the structural and magnetic properties of Nd2Fe14B intermetallic compound was studied by X-ray diffraction (XRD) and magnetisation measurements. The average crystallite size calculated from the XRD patterns on the powders ball milled (BM) for 40 h is seen to lie in the range of 25–50 nm, whereas the particle size estimated using atomic force microscopy imaging is in the range of 40–100 nm. Magnetisation and anisotropy of BM Nd2Fe14B were found to decrease with increasing milling time. This was explained based on the increased defect density with milling and reduction in particle size. Using a differential scanning calorimeter, recovery and recrystallisation of the BM samples were studied during heating. The Curie temperature was found to decrease with increasing milling time. The BM samples were annealed at 1173 K for 15 min, and XRD and magnetisation studies were conducted. Mechanisms of α-Fe separation and change in intrinsic properties during milling and annealing ...

K. Prasad Rao

Papers

Magnetic Force Microscopy Investigation of Magnetic Domains in Nd2Fe14B

Studies on structural and magnetic properties of ball milled Nd2Fe14B intermetallic powders