Transcript スライド 1 - Binghamton University

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 intercluster 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
Susceptibility
Tcl
Tcu
Anomalous memory
phenomena(*)
Nonlinear magnetic
response
Ceramic like lattice
structure is verified
experimentally
Neutron scattering
Tcl
Tcu
Schematic show of
intermediate glassy state
PpP
Present experimental results
Aging time dependence of
zerofield cooled magnetization MZFC (↓)
SZFC (t)
=(1/H)・
(dMZFC/dlnt
)
(→)
T-dependence of
Stretched Exp
Relaxation time
S2
S1
Schematic show of
a speculated two-subsystempicture in the intermediate
glassy phase (**)
Conclusion
In the intermediate state between Tcl and Tcu, the system is composed of two sub-systems. One subsystem
S1 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 system S2 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 S2 consisting 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.