Critical exponents and irreversibility lines of La$_{0.9}$Sr$_{0.1}$CoO$_3$ single crystal

Abstract

We have studied the dynamic and static critical behavior of spin glass transition in insulating La$_{0.9}$Sr$_{0.1}$CoO$_3$ single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature ($T_f$). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant $\tau_{0}$=1.6(9)$\times10^{-12}$ s, the dynamic critical exponent $z\nu$=9.5(2), and a frequency dependence factor $K$=$\Delta$$T_{f}/T_{f}$($\Delta$$log$$f$)=0.017, indicating that the sample enters into a canonical spin-glass phase below $T_{f}$=34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of $T_{f}$ through the static scaling hypothesis yields critical exponents $\beta$=0.89(1) and $\gamma$=2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement we have constructed the $H-T$ phase diagram which represents the field evolution of two characteristic temperatures: the upper one, $T_{w}(H)$, indicates the onset of spin freezing in a uniform external field $H$, while the lower one, $T_{s}(H)$, marks the onset of strong irreversibility of the frozen state. The low field $T_{s}(H)$ follows the critical line suggested by d'Almeida-Thouless model for canonical spin glass, whereas the $T_{w}(H)$ exhibits a reentrant behavior with a maximum in the $T_{w}(H)$ at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The re-entrant behavior of the GT line resembles that predicted theoretically for $n$-component vector spin glasses in the presence of a uniaxial anisotropy field.Comment: 11 pages, 7 figure