Hard magnetization axis

Due to the in-plane surface anisotropy [23] the easy magnetization axis in thin iron films is the in-plane [110] direction being the hard magnetization axis of bulk Fe, switching at a critical thickness to the one of bulk crystals, i.e. the [001] direction. For cobalt films the anisotropy causes the easy magnetization axis to lie in-plane in contrast to bulk-hcp Co with its easy axis perpendicular to the basal plane. Thick rare earth metal films exhibit an easy axis within the surface plane. The shape anisotropy may also change the easy magnetization axis. 

Fig. 4.21, Mossbauer spectra of KjFeF at different temperatures with a field of 10 T applied along a hard magnetic axis. Ordering is indicated between 8.35 and 8.58 K. (Boersma et al, 1982.)...

EuIn2P2 magnetic susceptibility shows a clear magnetic transition at about 24 K. In Fig. 11.5 c, magnetic susceptibility as a function of the a, a-h, and c direction were obtained on a plate crystal. The a axis exhibits the largest susceptibility and is the easy magnetization direction. The c axis is the hard magnetization direction. 

Fig. 54 Magnetization curve for easy [0001 — c axis] and hard [1010] axis for cobalt showing large magnetocrystalline anisotropy (from Ref. 122).

The slightly reduced values of the room-temperature anisotropy fields when relatively small amounts of Fe in R2Fe14B are replaced by Co (see fig. 19) are not the only reason why Co substitution does not lead to improved hard magnetic properties. This is true for the temperature coefficient of the coercive force in particular. A probable reason for this is that not only JIA itself but also its temperature dependence becomes less favourable upon Co substitution. This may be inferred already from a comparison of the temperature dependences of HA in the pure ternaries Nd2Fe14B and Nd2Co17B shown in fig. 21, where it can be seen that the slope of the HA(T) curve for the latter compound around room temperature is much steeper than that of the former. In fact, the HA(T) curve in Nd2Co14B tends to approach the horizontal axis at a temperature of about 540 K, which is still far below the corresponding Curie temperature (Tc = 1007 K). The most obvious... 

Fig. 35. Comparision of the hard magnetic properties of two hard magnetic materials a and b. (Left) Flux density B (full lines) and magnetic polarization J (dashed lines) as a function of the demagnetizing field strength H. (Right) Product BH (horizontal axis) plotted versus B (vertical axis) for both materials a and b. The working point corresponding to (BFf)max is indicated on the B(H) curve (left point for material a and b) by a filled and open circle, respectively.

Fig. 4.22. The ratio of ordering temperatures with and without an applied field Tn(B)/7n(0) as a function of the applied field B for KjFeFj. The points A are for B applied along the easy magnetic axis and the points O and are for B applied along hard magnetic axes. (Boersma et al., 1982.)...

The mineral barium magnetoplumbite has the chemical formula BaFe Oig or BaO -bFeiOs and is perhaps the most important of the hexagonal ferrite since it is a hard magnet with the spins all aligned along the c-axis. This oxide is used in the magnetic stripe on credit cards. 

Jensen and Palmer (1979) studied the behavior of cge in the ferromagnetic phase of Tb under magnetization along the hard a-axis in the basal plane. Application of a... 

Substitution for Fe has a drastic effect on intrinsic magnetic properties. Partial substitution by or decreases J) without affecting seriously, resulting in larger and values. Substitution by Ti and Co causes a considerable decrease in K , the uniaxial anisotropy (if j > 0) may even change into planar anisotropy (if < 0). Intermediate magnetic stmctures are also possible. For example, preferred directions on a conical surface around the i -axis are observed for substitution (72). For a few substitutions the value is increased whereas the J) value is hardly affected, eg, substitution of Fe byRu (73) or by Fe compensated by at Ba-sites (65). 

The substrate was also found to influence the properties of the electrolessly deposited vertical media CoNiMnP, CoNiReMnP, and CoNiReP. The c-axis orientation had a larger degree of perpendicular orientation for films deposited on electroless NiP than for those deposited on Cu foil, presumably because of the smaller roughness of the former substrate [43]. The double-layer (magnetically soft interface, magnetically hard bulk) properties of CoNiReP deposited on a NiMoP underlayer [57] have already been discussed. 

The structures of electroplated hard alloys have been less extensively studied than those of similar electrolessly deposited materials. Sallo and co-workers [118-120] have investigated the relationship between the structure and the magnetic properties of CoP and CoNiP electrodeposits. The structures and domain patterns were different for deposits with different ranges of coercivity. The lower-f/c materials formed lamellar structures with the easy axis of magnetization in the plane of the film. The high-Hc deposits, on the other hand, had a rod-like structure, and shape anisotropy may have contributed to the high coercivity. The platelets and rods are presumed to be isolated by a thin layer of a nonmagnetic material. 

---