Ferromagnetic suppression

In the preceding section, the magnetic field was mainly used to determine the saturation magnetization of ferromagnets. However, it is now well established that many actinide compounds have complex magnetic behaviour and the application of an external field may change or suppress antiferromagnetic structures. 

NpAs2 is antiferromagnetic below T = 52 K and becomes ferromagnetic below Tc = 18 K . Under field, the Curie point rises rapidly, until the antiferromagnetic phase is suppressed by 30 KOe (Fig. 8). 

Similarly, the c-axis cone phase was observed to be suppressed in Ho/Y (Jehan et al. 1993), while ferromagnetic order existed below 30 K in Ho/Lu superlattices with less than 20 Ho-atomic planes (Swaddling et al. 1992). 

Kadomtseva et al. (2000) measured thermal expansion and longitudinal and transverse magnetostriction in pulsed magnetic fields up to 25 T in Lai - Sr MnOj single crystals (x = 0.1,0.125 and 0.15). The results were ascribed to a suppression of the O phase and field-induced transitions to a new orbital-ordered ferromagnetic state. 

Mukhin et al. (2000) found that increasing Sr doping in Lai- Sr MnOs does suppress the (quasi-)ferromagnetic resonance frequency, whereas the (quasi-)AF resonance frequency is only slightly decreased (20%). This behaviour corresponds to a canted magnetic structure and its evolution with increasing x. 

Multilayered superconductor/ferromagnet S/F) structures are under an intensive study now (for a recent review see e.g. [1]). The interest in such systems originates from a possibility to find new physical phenomena as well from the hope to construct new devices based on these structures. Although a ferromagnet F attached to a superconductor S is expected to suppress the order parameter in S, under certain conditions superconductivity and ferromagnetism may coexist and exhibit interesting phenomena. In most papers on S/F structures the case of collinear (parallel or antiparallel) orientations... 

Fig. 1. Local diffusivity D E,tD) = E t) — E(t + tD)) )/tD of a random walk sampling a flat histogram in energy space for the two-dimensional ferromagnetic Ising model. The local diffusivity strongly depends on the energy with a strong suppression below the critical energy Ec — lAl N...

Figure 2 shows the optimized histogram for the two-dimensional ferromagnetic Ising model. The optimized histogram is no longer flat, but a peak evolves at the critical region around E —1.41 N of the transition. The feedback of the local diffusivity reallocates resources towards the bottlenecks of the simulation which have been identified by a suppressed local diffusivity. 

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