Formation process of MnBi thin films

Abstract

Williams has found that when Mn and Bi are successively evaporated on a glass substrate, followed by prolonged annealing around 300 "C, a ferromagnetic MnBi thin film can be obtained with its c-axis perpendicular to the film plane. I n order to elucidate the formation process of the film, Rutherford backscattering (RBS) experiment, X-ray diffractometry, electron microscope study, and magnetic measurement are carried out. It is found that a t the first stage of annealing up to 250°C a non-magnetic transitional compound Mnl.2Bi is formed, and during the subsequent annealing at 250 "C, the final MnBi crystals with the aligned c-axes nucleate, and grow at the expense of the transitional phase. It seems likely that at the last stage of reaction, a few Bi crystals remaining in the transitional phase may serve as the nuclei.Williams hat gefunden, daB durch sukzessives Aufdampfen von Mn und Bi auf ein Glassubstrat sowie nachfolgender ausgedehnter Temperung bei 300 "C eine ferromagnetische MnBi-Schicht erhalten wird, deren c-Achse senkrecht zur Schichtebene ist. Um den Bildungsprozel) der Schicht aufzudecken, werden Rutherford-Ruckstreu-Experimente (RBS), Rontgendiffraktometrie, Elektronenmikroskopieanalysen und magnetische Messungen durchgefiihrt. Es wird gefunden, daB bei der ersten Ausheilstufe bis 250 "C eine nichtmagnetische Vbergangsverbindung Mn1,zBi gebildet wird und wiihrend der nachfolgenden Temperung bei 250 "C die endgiiltigen MhBi-Kristalle mit ausgerichteter c-Achse gebildet werden und auf Kosten der Vbergangsphase wachsen. Es scheint wahrscheinlich, daB bei den letzten Reaktionsstufen einige Bi-Kristalle, die in der ubergangsphase zuriickbleiben, als Keime wirken konnen.

Magnetic, optical, and magneto-optical properties of MnX(X=As, Sb, or Bi) from full-potential calculations

“…68 ͑2͒ The optical constants for MnBi are sensitive not only to the film composition ratio of Mn/Bi, 69,70 but also the surface states of the films since there is always excess Mn or Bi on the film surface. 71 Further, the reported experimental measurements are made on thin films, whereas our theoretical spectra are valid for ideal single crystals.…”

Formation process of MnBi thin films

“…In this stage, on the other hand, the Bi spectrum of plateau shape gradually decreases in height but increases in width. These results obviously show that Mn diffuses so fast into the Bi layer as to complete the mutual diffusion up to 250 "C. Such a situation seems rather similar to that in Chen's method [3]. X-ray diffractometry was made on the same specimens to examine the phase constituents involved.…”

“…When the double layer film is annealed at 300 "C, we can obtain a well-orientated MnBi film in a very short period of time. Iwama et al [3] have investigated the formation process by Chen's method, to elucidate that the Bi film firstly evaporated has a texture in which its trigonal c-axis perpendicular to the substrate, and during annealing up to 300 "C, Mn atoms preferentially diffuse into the Bi layer to form MnBi crystals with their c-axes aligned. In Williams' method, however, the Bi layer deposited on the Mn layer has no texture, though the method enables one to prepare a similar well-textured MnBi thin film.…”

Synthesis of Hard Magnetic α-MnBi Phase by High Pressure Torsion and Field Assisted Annealing

“…Furthermore, the dissolution o already existing α-MnBi phases could be driven by an increased Mn diusion to the sample surace. At least or thin lms, a high migration o Mn atoms in Bi is already reported [47]. On the other hand, in case o O diusion the pronounced oxygen sensitivity o the α-MnBi phase is already described by Cui et al [48].…”