I n ZnFe,O, irradiated by fast neutrons a superparamagnetic state (an ensemble of ferrimagnetic regions with equally probable distribution of cations over Aand B-sites in paramagnetic matrix) is achieved. The properties of superparamagnetic state allow to make conclusions about the character of replacement cascades in ferrites with spinel structure.Some parameters of the replacement cascade are given. It is shown experimentally how the irradiation temperature influence the size of the disordered regions.In ZnFqO,, das mit schnellen Nentronen bestrahlt wurde, wird ein superparamagnetischer Zustand erhalten (ein Ensemble von ferrimagnetischen Bereichen mit einer Wahrscheinlichkeitsgleichverteilung der Kationen iiber die Aund B-Pliitze in einer paramagnetischen Matrix). Die Eigemchaften des superparamagnetischen Zustands erlauben Schliisse iiber den Charakter der Verlagerungskaskaden in Ferriten mit Spinellstruktur. Einige Parameter der Verlagerungskaskade werden angegeben. Es wird experimentell gezeigt, wie die Bestrahlungstemperatur die GroDe der fehlgeordneten Bereiche beeinflul3t.
3+ 3+-FeIt is known that intersublattice (A -B) exchange Fe interaction in many types of ferrites with spinel structure causes in the main the ferrimagnetic order.However, the presence, as a rule, of two (or more) types of magnetic ions in ferrites makes this important interaction difficult to study.The zinc and magnesium monoferrites belong to the not numerous class of compounds with one type of magnetic cations. But their magnetic properties in the equilibrium state essentially differ on account of the different cation distribution.Zinc ferrite has the structure of a normal spinel and therefore there exist in it weak negative iron-iron interactions in the B-sublattice that cause antiferromagnetic ordering of magnetic moments at low temperatures (1). OF the contrary, magnesium ferrite turns out to be a typical ferrimagnet due to a structure similar to the inversed ond (2).It is natural that ferrites of similar structure and with sufficient number of magnetoactive cations in A-and B-sublattices should be the most convenient ones for studying the intersublattice exchange Fe -Fe interactions. 3+ 3+As it was shown in (3) such isostructural (with equally probable distribution of cations over A-and B-sites) state in such class of ferrites might be achieved by the influence of fast neutrons upon them.The study of the suggested cation distribution and of the character of exchange interactions in irradiated zinc and magnesium ferrites has been carried out by the method of powder neutronography. The separation of nuclear and magnetic scatterings in the neutron diffraction pattern has been achieved with a magnetic field being applied along the scattering vector during the measuring process. The details of the experimental methods a r e given in (3).
The influence of neutron radiation on the value of an average molecular magnetic moment nB, the Curie temperature TC, and the structural parameters of mixed Mn‐Zn and NiZn ferrites was studied. It is shown by methods of structural neutronography and small‐angle diffuse magnetic neutron scattering that essentially irreversible changes of all quantities measured experimentally observed at irradiation doses higher than 1018 cm−2 are caused mainly by the creation of disordered phase microregions during irradiation. The appearence of such regions is assumed to be caused by the so‐called “displacement spikes”.
The cations in ferrites with spinel structure of the Me Fe (hlexFe2-x)04 type 1-x x (Me two-valent cations, x degree of inversion) may occupy two different types of sitesthe tetrahedral (a) and the octahedral ones (b), formed by the close packing of oxygen anions. It i s well-known (1, 2) that the equilibrium cation distribution at a temperature T i s determined by the mass action law) change of the internal energy of a where k Boltzmann constant, E b ferrite molecule connected with the cation pair exchange, E. preference energy of cations of type i (i: Me, Fe) to the site b. b = Enile -EFe 0 1 From equation (1) it follows that the immediate determination of E from meas-0 urements of the temperature dependence of the degree of inversion o r from different properties, caused by the degree of inversion, is possible only for ferrites with low values of E b i (for example, Me = Mg , Cu) .In this paper a method of experimental determination of high values of the preference energy is proposed with zinc ferrite a s an example (it possesses the structure of the normal spinel under the usual conditions). The essence of the method is the following.-2By irradiation with fast neutrons of D ,lo2' cm dose on ferrites an irreversible non-equilibrium cation distribution i s achieved at T = 320 K close to the statistical one x = 2/3 (3). This is accompanied by an increase of the ferrite internal energy with a value proportional to E . During the annealing this stored energy transfers into the specimen thermal energy and it allows to determine E . 0 0
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.