Abstract
Interstitial light elements play an important role in magnetic materials by improving the magnetic properties through changes of the unit cell volume or through orbital hybridization between the magnetic and interstitial atoms. In this review focusing on the effects of interstitial atoms in Mn-based compounds, which are not well researched, the studies of interstitial atoms in three kinds of magnetic materials (rare-earth Fe-, Mn-, and rare-earth-based compounds) are surveyed. The prominent features of Mn-based compounds are interstitial-atom-induced changes or additional formation of magnetism—either a change from antiferromagnetism (paramagnetism) to ferromagnetism or an additional formation of ferromagnetism. It is noted that in some cases, ferromagnetic coupling can be abruptly caused by a small number of interstitial atoms, which has been overlooked in previous research on rare-earth Fe-based compounds. We also present candidates of Mn compounds, which enable changes of the magnetic state. The Mn-based compounds are particularly important for the easy fabrication of highly functional magnetic devices, as they allow on-demand control of magnetism without causing a large lattice mismatch, among other advantages.
Highlights
Some crystal structures possess interstitial crystallographic sites, which light elements such as hydrogen, boron, carbon, nitrogen, and oxygen atoms can occupy
This review surveyed the studies of interstitial atoms in rare-earth Fe, Mn, rare-earth-based magnetic materials, especially focusing on the Mn-based compounds since the effect of interstitial atoms is not well investigated
The light elements would occupy the interstitial sites in the respective crystal structure, and change the unit cell volume, the degree of change depends on the strength of orbital hybridization between the magnetic and interstitial atoms
Summary
Some crystal structures possess interstitial crystallographic sites, which light elements such as hydrogen, boron, carbon, nitrogen, and oxygen atoms can occupy. Since the 1980s, interstitial atoms have attracted intense attention related to the improvement of magnetic properties of rare-earth Fe and Co-based permanent magnets [2,3,4,5,6]. Interstitial atoms have two major roles—influencing the stability of the crystal structure and in the modification or change in magnetic properties. In the former case, small amounts of interstitial light elements are required to stabilize the desired crystal structure; compounds without interstitial atoms would not exist in thermal equilibrium. The most well-studied platforms for interstitial atoms are rare-earth Fe-based permanent magnets. The larger ∆V/V for Sm2 Fe17 N3 is ascribed to the fact that Fe magnetic moments in the Th2 Zn17 -type structure are less itinerant
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