Zero magnetization curves

Ehrenfest s concept of the discontinuities at the transition point was that the discontinuities were finite, similar to the discontinuities in the entropy and volume for first-order transitions. Only one second-order transition, that of superconductors in zero magnetic field, has been found which is of this type. The others, such as the transition between liquid helium-I and liquid helium-II, the Curie point, the order-disorder transition in some alloys, and transition in certain crystals due to rotational phenomena all have discontinuities that are large and may be infinite. Such discontinuities are particularly evident in the behavior of the heat capacity at constant pressure in the region of the transition temperature. The curve of the heat capacity as a function of the temperature has the general form of the Greek letter lambda and, hence, the points are called lambda points. Except for liquid helium, the effect of pressure on the transition temperature is very small. The behavior of systems at these second-order transitions is not completely known, and further thermodynamic treatment must be based on molecular and statistical concepts. These concepts are beyond the scope of this book, and no further discussion of second-order transitions is given. 

Analysing the two constituents of this equation, one verifies that l/sec crosses zero not only at t = 0, 7/2, T,... as the primary field does (Fig. 10.9(b)(iv)), but also if d(B1 + B2)/dH is zero (Fig. 10.9(fc)(iii)). Since the latter occurs for t = 0, 7/2, 7,..., but also at t = 7/4, 37/4,..., Usec appears with twice the frequency of the primary current. Hence, one has to extract the second harmonics from the voltage signal l/sec in order to get a measure for the strength of H0. (There are also odd overtones due to the saturation effects in the magnetization curves and the antisymmetry of these curves with respect to H = 0, but these can be effectively discriminated against the desired second harmonics.)... 

It is impossible to calculate the total magnetization curve M(H) in a multisublattice model, since the molecular-field coefficients 7 are unknown. Nevertheless it is possible to show that most of them are about zero. The latter circumstance permits to describe the magnetization curve and the magnetic structures in the vicinity of the critical fields hi and /12. 

Understanding the magnetic properties of a collection of well-isolated clusters is of great interest for exploring FePt clusters as a media for EHDR beyond 1 Tera bit/in. Dilute FePt C cluster films were prepared by the multilayer method as described earlier. Thus Stoner-Wohlfarth-like behavior has been observed in a FePt C cluster film with FePt volume fraction of 5 %, [45], Figure 27 shows the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves for as-deposited and annealed FePt C cluster film with 5 vol. % FePt. 

Figure 23. (a) Zero-field cooled, FC, and REM magnetization curves for (Cp2Mn)[Ni(dmit)2]. (b)... 

The upper critical field value //, 2 has been determined from magnetization curves A/(7) taken by zero-field cooling to well below 7,., applying various fields in the range of 0.2 to 5 T, and recording values by warming the sample to well above T,. Typical magnetization curves for different fields are shown in the inset of Fig. 3(b). 

Figure 2. High-resolution temperature-dependent magnetization measurements obtained on Ks Cjo ( ) and Kj eo (O) samples highlighting the depression in for the isotopically sutetituted material. The samples were initially cooled in zero field to S K, and then the curves were recorded on warming in a field of 20 Oe. The curves were normalized to the Value of the magnetization at S K. The inset shows a full magnetization curve for a K3 C o sample.

Fig. 13 Correlation of the metamagnetomagnetism, metamagnetoelasticity, and colossal magnetoresistance in manganites. The vertical shifts of the magnetization curves are given for convenience only the curves of strain L and resistivity R are normalized by their values at zero field [30]...

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