Spin freezing

Cooling by Liquids Shell-Freezing and Spin-Freezing... 

Shell-freezing a flask is placed in cold bath in such a way, that the neck of the flask is covered by the liquid. A motor turns the flask and the product freezes on the wall. 2. Spin-freezing one or more bottles are fixed to a jig and immersed in the bath. The jig turns the bottle(s) so fast around its (their) axle(s), that the liquid is distributed evenly on the wall(s). 3. Shell-freezing the bottles are placed on cylinders in the bath, the cylinders turn in the bath. The bottles are turned by the cylinders around their axes (Fig. 3 from [2.20]). 

Cooling by Liquids Shell-freezing and Spin-freezing... 

In the cooled bath the container can be rotated slowly (shell-freezing) or quickly (spin-freezing), as shown in Figure 2.1. The aim of both methods is to reduce the thickness of the liquid product before freezing, to e.g. 15-20 mm. For production purposes, this cannot be used since, first, the sterility of pharmaceutical products cannot be assured and the liquid must be removed from the surfaces before loading the vacuum plant. This can be done by hand for a limited number of containers, but not on a production scale. 

It shows a huge fhistration index of 150 with a spin freezing Tf = 3.4 K for a sample with 90% coverage of the pyrochlore slabs by Cr +. Several anomalous properties appear in the specific heat that are still not understood in detail bnt point to the possible involvement of spin singlets in the ground state... 

Coey and von Molnar (1978), by rf sputtering deposition, have studied a DyCu alloy with the following composition DyCU1.44Ar0.05O0.23- They observed a sharply defined spin-freezing temperature at 18K marked by a cusp in the low-field dc susceptibility (as for the Gd-Al system). They developed and discussed a... 

Fig. 24. Longitudinal field spectra for a Gaussian (left) and a Lorentzian (right) field distribution. The Gaussian case refers to spin freezing around 8.5 K in CePtSn, a concentrated spin system (Kalvius et al. 1995a) the Lorentzian case to a dilute Cu(Mn) spin glass below its glass transition temperature of 10.8K. The values of the longitudinal fields are (from top to bottom) 640, 320, 160, 80, 40 and OG (Uemuia et al. 1981). In both cases the set of spectra unambiguously proves that the spin systems are static.

Clearly, the study of CMR (GMR) systems containing rare earths has started and more work is to be expected in the near future. It has been demonstrated that nSR can provide important information on local aspects of the magnetic properties of these substances and in particular on the nature of phase transitions. The repeated appearance of spin freezing is noteworthy. Spin dynamical properties are another field of definite interest wich is open to p.SR It is generally believed that the transport properties of the manganese compounds are coupled to lattice and Mn spin dynamical effects. As of yet, it is not clear how well the findings of p.SR relate to the phenomenon of CMR (or GMR). 

Fig. 99. An example of inhamogeneous spin freezing, The sample is CeCuj Sij. (a) ZF xSR spectra, each consisting of a fast (static) and a slow (dynamic) relaxing signal. This distinction vanishes above 1K. (b) Relaxation rates vs. temperature, (c) Relative fractions of the spin-frozen (triangles) and the unfrozen (circles) parts. Tc is the superconducting transition temperature (see sect. 9.3.1.8) from Luke et al. (1994a).

In the paramagnetic regime (T > Tm), the spectra in a weak LF (needed to suppress the depolarization by Cu nuclear dipoles) for x > 0.08 were most easily fitted to a power exponential (exp[—(At) ]) relaxation. Hence the summary label relaxation rate in fig. 113 (left) refers to the static width Aeff (see eq. 74) for T dynamic rate A for r > Tu- The variation of power p was studied in some detail for the 10% sample. A decrease fromp w 1 at high temperatures top w 0.6 close to Tm was found. This is another indication that a disordered spin-glass-like state is approached and 7m might best be considered a spin freezing temperature. This spin-glass-like state, however,... 

Fig. 149. Left Signal amplitude (top) and relaxation rate (bottom) as a ftmction of temperature from ZF-p,SR data in U(Rho35Ru

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