Magnetic properties and peculiarity of magnetic states in dilute antiferromagnets Mn_{1−x}Zn_{x}F_{2}
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The dependence of magnetic moment and susceptibility on temperature, magnetic field and frequency of some single crystals Mn_{1−x}Zn_{x}F_{2} (x≈x_{e}=0.75—percolation limit) were experimentally investigated. Our experiments show that (Bazhan and Petrov 1984; Cowleyet al 1984; Villain 1984) in these crystals the nonequilibrium magnetic state of spinglass type with finite correlation length appears as temperature decreasesT<T in weak magnetic fields. This state is determined by fluctuation magnetic moments √nμ (wheren is the number of magnetic ions, corresponding to finite correlation length andμ the magnetic moment Mn^{+1}).
In the experiments in low magnetic fields and frequencies there are no peculiarities in the magnetic susceptibility temperature dependence atT≠T_{f}. At temperaturesT>T_{f} andT<T_{f} magnetic susceptibility is determined by$$\chi \left( {T > T_f } \right) = \frac{{N\left\langle \mu \right\rangle ^2 }}{{3k\left( {T + \theta } \right)}} = \frac{N}{n}\frac{{\left\langle {\sqrt n \mu } \right\rangle ^2 }}{{3k\left( {T + \theta } \right)}} = \chi \left( {T< T_f } \right)$$. In strong magnetic fields and large frequencies there are peculiarities in thex(T) dependence atT=T_{f}. AtT<T_{f} and strong magnetic fieldsX(T)=x_{0} andT<T_{f} and at large frequenciesx(T)=x_{0}+α/T.
The dependences of magnetic susceptibility on the frequency are determined by the magnetic system relaxation. Calculations and comparison with experiments show that the relaxation of the investigated magnetic systems atT<T_{f} follows the relaxation lawM(t)=M(0) exp[−(t/τ)^{r}], suggested in Palmeret al (1984) for spin-glasses relaxation taking into account the time relaxation distributionτ_{0}....τ_{max} in the system and its ‘hierarchically’ dynamics.
A N Bazhan^{1} S V Petrov^{1}
Volume 97, 2023
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