Journal of Magnetism and Magnetic Materials 248 (2002) 101–111 Anomaly in cluster glass behaviour of Co 0.2 Zn 0.8 Fe 2 O 4 spinel oxide R.N. Bhowmik*, R. Ranganathan Saha Institute of Nuclear Physics, Experimental condensed matter Physics division, Low temperature Physics division 1/AF, Bidhannagar, Calcutta-700064, India Received 25 October 2001 Abstract We report cluster glass behaviour mixed with short-range ferrimagnetic ordering in Co 0.2 Zn 0.8 Fe 2 O 4 spinel oxide. The AC susceptibility data show a maximum at T f 1 E110 K and a shoulder at T f 2 E212 K: The DC magnetization data also show a maximum at T m1 E110 K and a shoulder at T m2 E260 K: The frequency dependence of AC susceptibility and field dependence of DC magnetization data suggest a cluster spin-glass freezing at T f 1 E110 K: The appearance of shoulder in AC susceptibility data at T f 2 E212 K can be explained in terms of freezing of larger size clusters associated with anisotropy distribution. This is a pseudo-phase transition related to cluster size effect, rather than spin-glass-like freezing. The AC susceptibility, DC magnetization and room temperature M . ossbauer spectroscopy measurements suggest that above 260 K the magnetic phase is dominated by short-range interacting clusters in paramagnetic state, called cluster-paramagnetic phase and at 110 KoT p260 K short-range ferrimagnetic phase coexist with cluster spin- glass phase, called mixed magnetic phase, in the present system. r 2002 Elsevier Science B.V. All rights reserved. PACS: 75.50.Gg; 75.50.Lk; 75.40.Gb; 75.50.y Keywords: Cluster glass; Ferrimagnetism; Local spin canting; Coercivity; Spinel oxide 1. Introduction Over the past 30 years, ferrite spinel oxide has been the subject of research interest because of its potential application and physics point of view [1–3]. Particularly, frustrated magnetic systems with antiferromagnetic exchange interaction shows interesting magnetic properties which distinguish them from both antiferromagnets and conven- tional structurally disordered spin glasses [1]. CoFe 2 O 4 is a spinel oxide with ferrimagnetic ordering temperature at 860 K. If Co 2+ is replaced by Zn 2+ ion, the system ZnFe 2 O 4 becomes an antiferromagnet with ordering temperature at 9 K [4]. Extensive works have been performed on the solid solution of Co 1x Zn x Fe 2 O 4 , x ranging from 0 to 1. But the exact nature of magnetic ordering for all the compositions are not very clear. Petitt et al. [4] performed M . ossbauer spectroscopy on Co 1x Zn x Fe 2 O 4 (x ¼ 021). The M . ossbauer data show a decrease of magnetization for xX0:6; because of localized spin canting in B sublattice. *Corresponding author. E-mail addresses: rnb@cmp.saha.ernet.in (R.N. Bhowmik), ranga@cmp.saha.ernet.in (R. Ranganathan). 0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0304-8853(02)00190-7