Magnetization Process of Ising Spin Chains at the Domain Boundaries in CoCl₂2H₂O

Abstract

Small magnetization jumps in CoCl₂2H₂O recently observed by Kuramitsu et al. are explained by considering the flopping of Ising spin chains at the domain boundaries of ferrimagnetic CoCl₂2H₂O. The mechanism of these transitions is essentially same as that described by Ono et al., but detailed discussions of domain boundaries in this paper gives direct image of manner in which the irregular spin sites arise and leads to a prediction of the similar phenomena in the antiferromagnetic state. It is also proved that the numbers of the extraordinary critical fields are limited to two and five in the ferri- and antiferromagnetic states, respectively. The obtained additional critical fields are H_c3=4H₁−2H₂=36.6 kOe and H_c4=4H₁=41.2 kOe in the ferrimagnetic state, which are same as H_c′ and H_c″ described by One et al. and are in good agreement with the experimental results, and H_c5=0, H_c6=2H₂=4.6 kOe, H_c7=2H₁=20.6 kOe, H_c8=2H₁−2H₂=16.0 kOe and H_c9=2H₁+2H₂=25.5 kOe in the antiferromagnetic state, of which H_c6 and H_c7 were observed by this author. The size of the domain is estimated as 0.3 μm using a simple model. Possibility of spin-cluster resonance at the domain boundaries is also discussed.