Antiferromagnetic elements

PROPERTIES OF MAGNETIC MATERIALS (continued) Ferro- and Antiferromagnetic Elements (continued)... 

The development of neutron diffraction by C G Shull and coworkers [30] led to the detennination of the existence, previously only a hypothesis, of antiferromagnetism and ferrimagnetism. More recently neutron diffraction, because of its sensitivity to light elements in the presence of heavy ones, played a cmcial role in demonstrating the importance of oxygen content m high-temperature superconductors. 

Although erbium is magnetic at very low temperatures, it is antiferromagnetic and becomes a superconductor at temperatures near absolute zero. It is insoluble in water but soluble in acids. Its salts range from pink to red. Erbium and some of the other rare-earth elements are considered to be impurities in the minerals in which they are found. Small quantities of erbium can also be separated from several other rare-earths. 

The substitution for Cu by a 3d metal produces drastic changes in the physical properties of the 90K phase, as shown in Figure 9a where the Tc s (as determined by ac-susceptibility measurements)are plotted as a function of x for the various series. Independent of the magnetic nature of the substituted element, for the trivalent ions (Fe, Co, and Al) Tc remains constant and equal to 90K up to the O-T transition and then decreases continuously to less than 4.2K at x-0.5. Upon increasing x further, the compounds become semiconductors and simultaneously antiferromagnetism associated with the Cu ions develops. In contrast to this behavior, for the divalent substituted Ni and Zn ions Tc decreases markedly, even at low x. 

Antiferromagnetism Positive Small X = constant Salts of transition elements (MnO)... 

In agreement with the overall behaviour of the / Ni2B2C compounds with heavy 4f elements R, shown in fig. g, this compound is the unique member of the / Ni2B2C series in which the onset of superconductivity takes place in an antiferromagnetically ordered state i.e. jTn — 11 K>7 C = 6.3K (also see table 7). It should be noted that in the ruthenocuprates discussed in subsection 1.3 also antiferromagnetic order (and even... 

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