Amorphization of Neutron-Irradiated Yttrium Iron Garnet

Abstract

Polyerystalline samples of yttrium iron garnet (VIG) irradiated by different fluences of fast neutrons (0 to 1.6 × 1024m−2) are investigated by X‐ray and magnetic methods. It is found that fast neutron irradiation leads to partial amorpliization of YIG. Moreover, at irradiation by high fluences (≈︁ 1024 m−2) one can obtain practically a complete amorphous state. The magnetic state of the amorphous samples is the “spin glass” one, the freezing temperature is about 70 K. Possible reasons resulting in the amorphization of YIG under neutron irradiation are analysed.

Displacement Defect Formation in Complex Oxide Crystals under Irradiation

“…At such fluences an increase of the crystal lattice parameter as well as a decrease of the saturation magnetization and Curie temperature take place. In a number of papers [35,38,39,41] it was shown convincingly that a disordering process is responsible for these changes that occur as losing of long-range order in microareas that have been affected by the atom±atom displacement cascades. The rest bulk remains of the garnet structure.…”

Effect of alloying by gadolinium on the magnetic properties of irradiation-amorphized oxides of the Y3 − x Gd x Fe5O12 system

“…A brilliant example is the amorphization of the widely used in practice yttrium iron garnet Y 3 Fe 5 O 12 and related compounds [1][2][3][4][5][6]. In the crystalline state, the yttrium iron garnet exhibits a long range ferrimagnetic order, and its resultant magnetic moment is due to the non equivalence of the sublattices in which there are located Fe 3+ ions connected with each other by a neg ative indirect exchange interaction.…”

“…The amorphous state of oxide with a garnet structure was obtained in [1][2][3][4][5][6] via irradiation by fast neutrons. This method makes it possible to consequently trace the change in the magnetic state in the course of the amor phization of the crystalline structure of the garnet.…”

Materials Degradation and Detection (MD2): Deep Dive Final Report

“…18 /cm 2 dose, cations redistribute into disordered nanoregions (1.2-3.5 nm), T c increases, max magnetization (low T) decreases; at highest fluence, Ni-Zn conductivity changes from p-type to n-type (Chukalkin et al 1974 (Chukalkin et al 1983) Fast neutrons E>1 MeV in reactor Amorphization of YIG at highest fluences; sample becomes a spin glass with Tf ~70 K and shows bifurcation in FC/ZFC magnetization; summary discussion on spinels and hexaferrite crystal structures not changes by high fluences but garnets changed due to large ion size difference between rare earths and transition metals resulting in frozen disorder. ), and shortwave absorption edge broadens; data are explained by assuming disordered nanoregions of 6-8nm created from displacement cascades and resulting in amorphous areas which spread out the energy of transitions at the optical edge.…”

“…Neutron damage studies of magnetic sensor materials are few and far between (see Appendix for an incomplete summary), and results indicate a wide range of behaviors, including amorphization (Chukalkin et al 1983), cation site mixing (Chukalkin et al 1975), superparamagnetism (Parkhomenko et al 1976), anisotropy change (Chukalkin et al 1981), loss of remnance (Anderson et al 2005), or complete loss of magnetization due to radiation-induced thermal spikes (Liu et al 2007). In addition to their use in magnetostrictive transducers, magnetic materials are integral to the operation of linear variable differential transformers (LVDTs), which will also find future use as in-pile diagnostic instruments ).…”