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Abstract

Magnetic Ordering of CoCl 2 -GIC: a Spin Ceramic -Hierarchical Successive Transitions and the Intermediate Glassy Phase- by *)M. Suzuki, I.S. Suzuki and **)M. Matsuura *)Dept ≈ . Phys., SUNY Binghamton and **)Fukui Univ. Tech. Abstract

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Abstract

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  1. Magnetic Ordering of CoCl2-GIC: a Spin Ceramic-Hierarchical Successive Transitions and the Intermediate Glassy Phase- by *)M. Suzuki, I.S. Suzuki and **)M. Matsuura *)Dept≈. Phys., SUNY Binghamton and **)Fukui Univ. Tech. Abstract Stage-2 CoCl2-GIC is a spin ceramic and shows hierarchical successive transitions at Tcu (≈ 9 K) and Tcl (≈ 7 K) from the paramagnetic phase into an intra-cluster (two-dimensional ferromagnetic) order with inter-cluster disorder and then to an inter-cluster (three-dimensional antiferromagnetic like) order over the whole system. The nature of the inter-cluster disorder was suggested to be of spin glass by nonlinear magnetic response analyses around Tcu and by studies on dynamical aspects of ordering between Tcu and Tcl. Here, we present a series of time dependence of zero-field cooled magnetization MZFC after the aging protocol below Tcu. The time dependence of the relaxation rates SZFC(t) =(1/H)dMZFC/d(lnt) dramatically changes from the curves of normal spin glass aging effect below Tcl to those of two peaks above Tcl. The characteristic relaxation behavior apparently indicates that there coexist two different kinds of glassy correlated regions below Tcu. Previously established Experimental results PpP Susceptibility Anomalous memory phenomena(*) Nonlinear magnetic response Tcl Tcu Ceramic like lattice structure is verified experimentally Neutron scattering Tcl Tcu Schematic show of intermediate glassy state Present experimental results T-dependence of Stretched Exp Relaxation time Aging time dependence of zerofield cooled magneti- zation MZFC (↓) SZFC (t) =(1/H)・ (dMZFC/dlnt) (→) S2 S1 Schematic show of a speculated two-subsystem-picture in the intermediate glassy phase (**) Conclusion In the intermediate state between Tcl and Tcu, the system is composed of two sub-systems.One subsystemS1 enters into a spin glass-like ordered state at Tcu. The relaxation rate SZFC is described by a SER of long relaxation timeτ1, the value of which increases with decreasing T. The system is speculated to remain in the same state below Tcl, say a frozen state. The other systemS2 enters into a similar glassy state below Tcu but of much shorter relaxation time τ2 than the former. The ordered feature apparently changes across Tcl into another one with aging behavior in the normal spin glass. From these facts, the transition at Tcl is taken as that of S2consisting probably of ferromagnetic clusters under a random field produced by almost frozen S1, consisting probably of the spins in the boundary region of ferromagnetic clusters (cf.above Figure(**)). Such a description could describe the anomalous memory phenomena (cf.above Figure(*)) of thermoremanent magnetization Mr which have long remained unsolved as a puzzling problem.

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