Unusual Lattice‐Magnetism Connections in MnBi Nanorods

Abstract

Lattice parameter, particle size, and thermal expansion results obtained from high‐temperature synchrotron transmission X‐ray diffraction are reported for magnetostructual NiAs‐type MnBi nanorods embedded in a Bi matrix. The structural data are consistent with elevated‐temperature magnetic measurements that indicate a first‐order nanorod Curie transition at 520 K, significantly depressed from the bulk MnBi Curie temperature of 633 K. The data suggest that the unit cell volume dependence of the magnetic behavior—also known as the volume exchange striction—of the MnBi compound is the determining factor underlying this phenomenon. The results imply that materials with magnetostructural transitions of technological interest may be altered by strain effects to tailor the interatomic distances towards the critical transition values.

Size Dependence of Magnetostructural Transition in MnBi Nanorods

“…Recently, Kang et al synthesize isolated FLTP MnBi nanorods with average diameter and length of 10 and 30 nm. ,, Due to the longer length, the third confinement dimension in MnBi nanorods becomes fully relaxed so that the nanorods acquire the two-dimension confinement of nanowires, namely, D 0 = 4 h with d = 1 in this case. It is evident that A C = 2π( D /2) 2 + π DL and V C = π( D /2) 2 L for nanorods where L denotes the length of nanorods.…”

“…[2][3][4][5][6] At room temperature MnBi is ferromagnetic with the hexagonal NiAs structure (low-temperature phase or "FLTP"), and it undergoes a bulk first-order magnetostructural transition at T t ) 633 K to the paramagnetic "stuffed" Ni 2 In structure (hightemperature phase or "PHTP"). [7][8][9][10] Magnetostructural transitions comprise simultaneous magnetic and structural phase changes of an abrupt and hysteretic nature, which are different from the canonical ferromagnetic transition of second-order thermodynamic character.…”

“…Because of its high uniaxial magnetic anisotropy (∼2 × 10 7 erg/cm 3 at 500 K) along its c axis and record magneto-optical Kerr rotation of 1.25° at room temperature, MnBi has been considered for potential applications in high-temperature permanent magnets, data storage, and magneto-optical media. − At room temperature MnBi is ferromagnetic with the hexagonal NiAs structure (low-temperature phase or “FLTP”), and it undergoes a bulk first-order magnetostructural transition at T t = 633 K to the paramagnetic “stuffed” Ni 2 In structure (high-temperature phase or “PHTP”). − Magnetostructural transitions comprise simultaneous magnetic and structural phase changes of an abrupt and hysteretic nature, which are different from the canonical ferromagnetic transition of second-order thermodynamic character.…”

Study of the Magnetic Properties of the Compound Mn Bi Using the Monte Carlo Simulations

“…In fact, M B is a ferromagnetic inter-metallic structure with hexagonal structure of N A type. M B has been interesting due to the exceptionally high magnetic anisotropy of the low-temperature phase [4] and the favorable magneto-optical properties of the high-temperature phase [5]. It is remarkable that the coercivity of the low temperature phase increases with temperature and is much greater than that of the N -F -B magnets at higher temperatures.…”

Wafer-Scale Synthesis of Monodisperse Synthetic Magnetic Multilayer Nanorods

“…Anisotropic nanoparticles − can have very special properties, different from their spherical counterparts. As one example, nanorod synthesis using various chemical methods − has received much recent attention and, consequently, major progress in controlling nanorod shapes has been made.…”