Hartmut Nagel

Coercivity and microstructure of Sm(Co0.87Cu0.13)7.8

The magnetic hardness of Sm(Co0.87Cu0.13)7.3 in bulk form is caused by pinning of the domain walls at precipitates which are of the Sm(Co,Cu)5 type. The hard magnetic properties of both the 2 : 17 matrix and the 1 : 5 precipitate phase have been investigated in the temperature range between 77 and 800 K. The domain‐wall energies have been determined from the surface domain patterns observed by means of the magneto‐optical Kerr effect. It is shown that the coercivity mechanism in Sm(Co0.87Cu0.13)7.8 cannot be explained by the difference of the magnetic crystal anisotropy constants K1 of matrix and precipitate phase only. However, the coercivity may be described by the decrease in the domain‐wall energy γ at the precipitates. γ of the 2 : 17 matrix was found to be five times that of the 1 : 5 precipitate phase (38 and 7.5 erg cm−2, respectively) resulting in an attractive interaction between the precipitates and the domain wall. The magnetic field necessary to overcome this attractive interaction has been e...

Hard‐magnetic properties and microstructure of Sm(Co,Cu)z compounds

Magnetic measurements and metallographic investigations are reported on Sm(Co,Cu)z alloys. The compositions lie between the rare‐earth (RE) to transition‐metal (TM) ratios of 1 : 5 and 2 : 17 with a content of copper of up to 35% of the TM fraction. The materials were analyzed both in the as‐cast and heat‐treatment conditions. The remanence BR scales with composition. The coercivity IHc showed a maximum along a tieline from the off‐stochiometric Sm(Co0.65Cu0.35)5.6 to the Sm2Co17 phase. In the as‐cast state the hysteresis loops are not square. High‐temperature homogenization yields ideal demagnetization curves. Subsequent annealing at lower temperatures T resulted in two coercivity peaks as a function of T. The peak temperatures decrease with increasing Cu concentration, e.g., for 35% Cu of TM 450 and 650 °C and for 20% Cu of TM 650 and 850 °C were found. Alloys near the 2 : 17 phase boundary contain 2 : 17 as a massive primary phase in a 1 : 5 matrix. The squareness of the hysteresis loops implies that t...

An electron microscope study of Sm‐Co‐Cu–based magnetic materials with the Sm2Co17 structure

In an electron microscope study of aged Sm‐Co‐Cu–based magnetic materials with the Sm2Co17 structure, it is shown that the previously reported coercivities of these materials are a consequence of the presence of very fine precipitates of the Cu‐containing SmCo5 phase which act as pinning centers. In comparing the microstructures of alloys with different Sm/Co,Cu ratios, and with some Co replaced by Fe, a marked difference is observed both in the precipitate morphology and the fault density of the matrix phase. Possible reasons for this are discussed, and it is shown that the lattice misfit has a marked effect on the morphology.

Mischmetal‐cobalt as a permanent magnetic material

Permanent magnets based on MMCo5(MM=mischmetal) were produced by powder metallurgical means with a coercivity IHc=9 kOe, a remanence Br=7.8 kG, and an energy product of (BH)max=14.5 MG Oe. These values could be increased by substituting some MM by Sm and Nd. The influence of MM composition on both the primary magnetic properties, as measured on single crystals, and the secondary magnetic properties and their temperature dependences was studied. The saturation magnetization Ms, the remanence Br, and the anisotropy field Ha vary almost linearly with composition. In contrast, IHc showed a more complex compositional dependence; it increases with increasing La content, decreases with Ce and Pr content, and passes through a maximum with increasing Nd content. The temperature dependence of IHc reflects the temperature dependence of Ha from the different compositions. A two‐step postsintering heat treatment was developed which results in good hard magnetic properties. The first step of 1 h at 1250 K is a homogeni...

Hard magnetic properties of Sm-Co-Cu-Fe single phase 2-17 bulk samples

Sm(Co 0.08 Cu 0.13 ) z alloys were prepared with 7.2 \leq z . Homogenization heat-treatment yielded single phase 2-17 material for z > 7.2 . For z = 7.8 some of the Co was substituted by Fe. The alloys remained single phase for up to 15 % Co substituted. With further increasing Fe content a Co-Fe phase appears accompanied by a strong decrease of the hard magnetic properties. The compounds were hard magnetic in bulk form with ideal rectangular hysteresis loops. The coercivity could be increased by a factor > 2 with a low temperature heat-treatment. B R values > 11 kG together with I H c values of about 4 kOe were achieved on single crystal samples. The coercivity mechanism in these materials is pinning of Bloch walls.

Magnetic properties of R(Co1−yCuy)z compounds

The hard magnetic characteristies of compounds having composition Sm(Co1−yCuy)z and lying within the phase space 5⋅0?z?8⋅5, 0?y?1⋅0, are strongly influenced by the nature of their metallurgical microstructure. However, by measurement of the anisotropy field, domain size, and angular dependence of the coercivity, and in conjunction with data obtained from transmission electron microscopy, as well as the implications of a theoretical model for the coercivity in these materials, and simple arguments concerning the diluting effect of copper upon the primary magnetic properties of the constituent phases, the principal features of this group of materials may be clarified.