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This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

The fabrication method and magnetic properties of Sm12.5Co66.5Fe8Cu11Si2 alloy are presented in this article. The samples were produced by rapid quenching of the liquid alloy onto a rotating, copper wheel (the so-called ‘melt-spinning’ method) and they had a thin ribbon shape. The microstructure of the samples was investigated by measurements of diffraction patterns for powdered samples, in order to obtain data from the entire volume of the sample. It was found, that samples were composed of different amounts of Sm2Co17, SmCo5 and SmCo7 phases, depending on the linear velocity of the copper wheel used during the fabrication process. The magnetic measurements were performed using a vibrating sample magnetometer (LakeShore VSM) working with an external magnetic field of up to 2 T. It was found that the obtained ribbons displayed relatively good hard magnetic properties, such as remanence μ0MR, and high resistance to demagnetization fields JHC.

The aim of this paper is to present the results of crystallization studies for the bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025 Ti0.02W0.02B0.20)98Y2, Fe61Co10TixY6B20, Fe61Co10Ti2Y7B20 alloys. The crystallization of the alloys was studied by differential scanning calorimetry (DSC). The amorphicity of the investigated alloys in the as-quenched state was testified using Mossbauer spectroscopy, X-ray diffractometry and transmission electron microscopy. Moreover, X-ray diffractometry was applied to structure investigations of partially crystallized samples. The crystallization process in the investigated alloys occurs in one or two stages. Two peaks in the DSC curves can be overlapped or well separated indicating the complex crystallization processes. From X-ray diffraction we have stated that in both types of devitrification the crystalline phase can be ascribed to the α-FeCo. In the first stage the crystalline grains seem to grow from the nuclei frozen in the samples during the rapid quenching, whereas in the second one both the growth of the existed grains and creation of new ones during annealing may occur.

Modern Re-Fe-B hard magnetic materials, produced using rapid quenching technique, taking into account variations in chemical composition, can be divided into three groups i.e. of stoichiometric, Re2Fe14B composition, and with excess of rare earth or iron [1–3]. Materials, composed of Re-Fe-B compound with overstoichiometric rare earths, typically are characterized by worse glass transition ability, smallest Mr/Ms ratio and large coercivity. Their properties are shaped by exchange interactions between Re2Fe14B, which are weakened by an increased distance between the grains. Enlarged distance between grains is resulting from the presence of a thin boundary formed from an amorphous matrix of redundant rare earths. Additionally, the presence of such a boundary causes an increase in coercivity due to the strong bonding of domain walls at the grain boundaries [4]. The stoichiometric composition causes increase in glass transition ability, Mr/Ms ratio but also causes deterioration of coercivity. These changes are a result of a reduction in the distance between grains, by removing the paramagnetic amorphous matrix, and fi ner structure as a result of increase in glass transition ability [5]. The highest glass transition ability, fi ner structure and highest Mr/Ms ratio is met in Re-Fe-B compound with overstoichiometric iron. The signifi cantly higher value of the Mr/Ms ratio results from the presence of the strong exchange interactions, between particles that differ in magnetic hardness. The grains, of soft magnetic phase, have The microstructure and magnetic properties of Nd8.5Tb1.5Fe83Zr1B6 ribbons obtained at various cooling rates Marcin Dośpial, Jacek Olszewski, Marcin Nabialek, Pawel Pietrusiewicz, Tomasz Kaczmarzyk