Spin disorder

The simplest example of an order-disorder transformation in which only one element is involved is the ferro- to diamagnetic transformation of b.c.c. a-iron, when the magnetic properties change over a range of temperature, the completion of the transformation being at the Curie temperature. Since this transformation only requires a randomization of electron spins without atomic diffusion, the process is very rapid, and the degree of spin disorder closely follows the thermodynamic model as the temperature of the solid is brought up to the Curie temperature. 

Ulbrich and Waldbaum [14] pointed out that calorimetrically determined third law entropies for many geologically important minerals may be in error because site mixing among cations, magnetic spin disorder, and disorder among water molecules in the crystals is frozen in the samples used for calorimetric measurements. They have calculated corrections based on known crystallographic data for several minerals. 

Spin Disordered State (Quantum Spin Liquid State) Neighboring Superconductivity. .. 103... 

Tn = 52 K and above has a In T dependence, in contrast to the classical spin disorder theory, but again in agreement with the Kondo formulation (Eq. 21). 

The exchange integral J is found to be about 0.13 eV. A value J 0.23 eV was found using de Gennes spin disorder theory ... 

It is of course possible that a carrier in the conduction band or a hole in the valence band will form a spin polaron, giving considerable mass enhancement. The arguments of Chapter 3, Section 4 suggest that the effective mass of a spin polaron will depend little on whether the spins are ordered or disordered (as they are above the Neel temperature TN). This may perhaps be a clue to why the gap is little affected when T passes through TN. If the gap is U —%Bt -f B2 and Bt and B2 are small because of polaron formation and little affected by spin disorder, the insensitivity of the gap to spin disorder is to be expected. 

On the other hand, hopping conduction in antiferromagnetic insulators seems to be greatly affected by spin disorder, as shown by the work of Whall et al. (1987) on MnFe204, in which both dajdT and dS/dT show striking changes at the Neel temperatures (about 600 K). 

Another important issue requiring further studies is the role of carrier-carrier correlation. It is known that the effect of disorder on carrier-carrier interactions controls the localization and enhances the spin susceptibility (Altshuler and Aronov 1985), and thus the tendency towards ferromagnetism. However, spin-disorder scattering may limit the efficiency of this process (Altshuler and Aronov 1985). If this is the case, LSDA (Jungwirth et al. 1999 Lee et al. 2000) can provide a reasonable evaluation of the relevant Fermi-liquid parameter. 

However, the spin-disordered state of high 5spin can alternatively be achieved by adding heat to the spin system ... 

Hence, if the crystal is initially in a magnetically ordered state at (lattice) temperature T (hot lattice + cold spins), but is then demagnetized under adiabatic conditions (q = 0), the entropy of spin disordering must be drawn from the crystal lattice (because no heat can exchange with the surroundings), and the lattice temperature drops ... 

It should be noted here that the conclusion about s-wave nature of the SC order parameter is consistent with conclusion about s-wave symmetry of the SC order parameter in the bulk and d-wave symmetry at the surface of the sample of the cuprates [17]. It was noted in [17] that most conclusions about d-wave symmetry was obtained in experiments (e.g. ARPES ones) on the cuprates in which mainly surface phenomena have been used. In this sense, the resistive measurements on the cuprates (see, e.g. [4]) are essentially bulk in the nature. In addition, the electron scattering (in resistivity measurements) is sensitive to the spin disorder in the system (magnetic contribution in the electrical resistivity appears, see Sec.l). Moreover, the electron scattering permits probe not only static magnetic order but dynamical (short-lived) ones because of short characteristic times as compared e.g. with usual neutron scattering. 

These compounds are metallic conductors, and similar to YNiPb, the Bloch-Griineisen relation is also valid for Y2Ni2Pb. The magnetic ordering manifests in the temperature dependence of the resistivities through abrupt changes in the slopes (decrease of spin-disorder scattering). 

It was shown that the above procedure gave a satisfactory description of the experimentally observed variation of spin disorder resistivity with temperature in CeAl2... 

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