Spin effects in defect reactions

The objective of this investigation is to evaluate the effect of weak magnetic fields on the defect structure of a wide range of nonmagnetic crystals. The available experimental data are interpreted within the framework of the phenomenological scheme of magnetic field-assisted defect reactions in solids within a concept of defect-induced lattice magnetism. We elucidate the principal difference between the defect reactions in solids and chemical reactions of radical pairs in liquids, emphasizing the role of the media in the spin-dependent effects. The defect reactions may be induced by both pulsed magnetic fields and microwaves, as well as by a constant magnetic field. A macroscopic manifestation of the quantum phenomenon is a long-time dramatic change in the defect structure and some physical and chemical properties of crystalline materials. One can use the magnetic field treatment for a control modification of the defect structure of crystals. We predict the effect of temperature windows inside which magnetic fields can determine the defect structure.

Figure 1

(Color online) Planar distribution of elements (by EPMA data) in the surface layer $\sim 1\mathrm{\mu m}$ of the $\mathrm{In}\mathrm{As}$ (top panel) and the ${\mathrm{Sb}}_{0.8}{\mathrm{As}}_{0.2}$ crystals (bottom panel): (a) before PMF treatment; (b) – (e) 5, 10, 20, and 100 days after the PMF treatment ($H_0=3\mathrm{kOe}$, $t=4\times {10}^{-5}\sec$, $N=1500$ pulses, $f=50\mathrm{Hz}$, $T=300\mathrm{K}$). Colors of the $\mathrm{In}\mathrm{As}$ (${\mathrm{Sb}}_{0.8}{\mathrm{As}}_{0.2}$), $\mathrm{In}\left(\mathrm{Sb}\right)$, and $\mathrm{As}$ phases are gray, black, and white (yellow, red, and green in the color online version), respectively. The size of image is $500\times 500\mathrm{\mu m}$.

Figure 2

Time dependence of the inhomogeneity parameter $\delta \left(t\right)$ of component distribution in the surface layer of the $\mathrm{In}\mathrm{As}$ crystal after the PMF treatment. The samples are as follows: 1 is a control sample; 2 – 5 are PMF samples treated at $H_0=1,2,3,\text{and}5\mathrm{kOe}$, respectively. Other treatment parameters are the same as defined in Fig. 1.

Figure 3

Energy dependences $E\left(r\right)$ of singlet (ground state) and triplet (excited state) terms of two electrons of a radical pair as a function of distance $r$ between the radicals (a). Vibrational (bold lines) and magnon (thin lines) structure of an adiabatic electron term $E\left(Q\right)$ of the ground state of defect in solid state, shown schematically depending only on the configuration coordinate $Q$ (b).

Figure 4

Configuration diagram: (a) crossing of electron terms with spin ban on transitions between the DC and RP terms; (b) anticrossing of the terms in the case of diffusion behavior of $\text{DC}\leftrightarrow \text{RP}$ transitions.

Figure 5

Structure of spin wave functions (a) and Zeeman splitting (b) of the ground and the first excited levels of the $i$-configuration.