Mössbauer study ofNi0.25Zn0.75

S. C. Bhargava

¹

,

N. Zeman

²

Abstract

A Mossbauer study of Ni025Zn{) 75Fe204 has been made in the temperature range from 4.2 to 300 K, in the presence of longitudinal fields up to 80 kG. It is possible to distinguish between the effects of ionic spin relaxation and superparamagnetism on the shape of a Mossbauer spectrum using an external magnetic field, and effects of ionic spin relaxation are found to dominate the spectra of the ferrite. The Neel temperature is found to be higher than 350 K, although the collapse of the magnetic splitting in the absence of an external field occurs at -250 K. Ionic spin relaxation cannot give rise to the collapse of the magnetic splitting below T&. This is concluded to be due to superparamagnetism.

The magnetic behaviour of the magnetically diluted spinel compound Fe0.6Mg1.6Ni0.1Ti0.7O4 studied by Mössbauer spectroscopy

“…This observation might explain why for many magnetically diluted spinel systems superparamagnetic clusters have been reported. For instance, Bhargava and Zeman [6] mentioned the presence of cluster superparamagnetism at higher temperatures (T4200 K) in the compound Ni 0.25 Zn 0.75 Fe 2 O 4 , whereas at low temperatures a localised-canting is proposed for the same compound [14]. This discrepancy can most likely be attributed to the sample preparation.…”

“…All these features have to some extent been observed in the external-field spectra of magnetically diluted spinels such as Ni-Zn ferrites [6], Mg-Ti ferrites [8], Li-Ti ferrites [24], and Mg-Al ferrites [10]. In some of mentioned spinel systems, the A-and B-site Fe could not be separated in their MS spectra.…”

“…This can lead to an ordered non-collinear spin structure as has been demonstrated by Yafet and Kittel [3]. However, when one sublattice is magnetically diluted there is no longer a long-range ordering and localised spin canting states (LCS) [4][5][6][7] or spin-glass (SG) behaviour [7][8][9][10][11] may appear. In this respect, the canting of the spins originating from the antiferromagnetic J BB (or J AA )4J AB interactions, leads to canted configurations or to frustration which together with disorder prevent magnetic ordering even though the magnetic interaction may be strong.…”

“…However, in the case of Ni-Zn ferrite A-and B-site subspectra were well resolved showing also merely a B-site canting. In this particular system, the behaviour of the B-site canting has been interpreted by a two-state Yafet-Kittel model for which the canting disappears at higher temperatures, resulting in a collinear ferrimagnetic ordering [6]. A-and B-site ferric components were also well resolved for the Li-Ti ferrites and canting in both sublattices could be concluded.…”

“…SPM in mixed ferrites has been explained by the existence of magnetic clusters, i.e., diamagnetic isolation of ferrimagnetic areas in the crystals, as initially proposed by Ishikawa (1962) for Zn-Ni ferrites [12] and later by Pekoshevski et al [13]. Otherwise, Bhargava et al [10,14] showed from external-field Mö ssbauer measurements that in Ni-Zn ferrite SPM effects only play a role at high temperatures (4250 K), whereas at low temperatures LCS are dominant. A superparamagnetic cluster behaviour was also reported for the spinel solid solution Mg 1+x Fe 2(1Àx) Ti x O 4 by De Grave et al [15,16] and later in some particular compounds by Fayek et al [17].…”