The study of the microscopic magnetic structure of bulk single crystal Islands of neodymium have shown that in them there is a new type of self-generated spin glass. This glass is no structural disorder and magnetic disorder occurs due to various interactions between the individual spins having opposite signs. The work, published in the journal Science, researchers showed a link between magnetic and crystal structure of islets, and examined the characteristic of spin glass aging effect.
In ordinary glass the atoms are arranged randomly, it is an amorphous substance. The term “spin glass” appeared by analogy with the ordinary glass to describe substances with an amorphous arrangement of the magnetic moments. Spin glass is a substance with such a magnetic structure in which magnetic moments of individual atoms are randomly oriented in space. In contrast to ferromagnets and antiferromagnets (which may be called magnetic crystals) in spin glasses there is no ordering of magnetic moments (strictly speaking — there is no long-range order).
The structure of the spin glass occurs due to the presence of indirect exchange interaction between magnetic ions RKKY-exchange interaction, which is the General conduction electrons. It is changing depending on the distance sign, in contrast to the magnetic interaction, which minimizes the energy when antiparallel orientation of spins. The presence of two competing interactions when adding structural disorder leads to a disordered and complex magnetic structure.
Spin glass is formed below a certain characteristic temperature. The structure of the magnetic moments it is almost stable, however, there is a small change (drift) of the magnetic moment with time. This phenomenon is called magnetic viscosity (magnetic or aging) and is somewhat like the slow flow of glass.
A typical spin glass is an alloy with the inclusion of magnetic impurities in large enough concentrations, from 0.1 to 10 percent. The magnetic ions occupy random positions in the lattice of the alloy, while for spin glasses the disorder. However, in 2016 theorists have described (1,2) the alternative situation in which the spin glass can be formed in the anisotropic crystal without any impurities in the presence of the same competing interactions — that is, in the absence of disorder in the arrangement of atoms. The substance became known as self-organizing spin glass.
To create a self-organizing spin glass researchers from the University of Nijmegen (the Netherlands) under the leadership of Alexander Cagetories (Alexander Khajetoorians) drew attention to the neodymium — a very interesting metal. On the one hand, it is known that neodymium is a ferromagnetic with a Neel temperature of about 20 Kelvin. On the other hand, the structure of the magnetization of neodymium is still uncertain. There is evidence in favor of the additional phase transition below the Neel temperature, magnetostructural other studies showed the presence of domains with complex frequency structure that may be a sign of self-organization for spin glass.