Magnetization anomalies in melt-spun Ni–Mn–Ga ribbons

Superparamagnetism and superspin glass behaviors in multiferroic NiMn‐based magnetic shape memory alloys

“…Bhatti et al and Pérez‐Landazábal et al confirmed the superparamagnetic behavior of martensite in the Ni 44 Co 6 Mn 40 Sn 10 and Ni 45 Mn 36.7 In 13.3 Co 5 alloys, respectively. Chernenko et al and Perekos et al found superparamagnetic behavior in Ni–Mn–Ga melt‐spun ribbons and powders , respectively. Superparamagnetic state of martensite was also evidenced in a Cu–Mn–Al melt‐spun ribbon by Konoplyuk et al .…”

“…Srivastava et al estimated the diameter of the magnetic clusters from the magnetization data for the Ni 57 Mn 21 Al 22 alloy, which is about 4.5–5 nm. The diameter of the magnetic clusters in the Ni 50.3 Mn 30 Ga 19.7 spark‐eroded powders and Ni 45.7 Mn 37.2 Ga 17.1 ribbon was estimated, from the magnetization data as well, to be ∼9 nm and ∼3 nm , respectively. It is inferred from the above investigations that the magnetic clusters that are responsible for the superparamagnetic and superspin glass behaviors of martensite are at the nanoscale level.…”

“…Besides this possibility, other chemical and/or structural inhomogeneities could also be the origin of the magnetic clusters. The chemical inhomogeneities may result from local fluctuations in composition and formation of secondary phases/precipitates in a solid solution . As the NiMn‐based magnetic shape memory alloys are usually found in the Mn‐rich composition region, formation of Mn clusters or Mn‐rich precipitates was considered to be possible origin of magnetic clusters in some references .…”

“…The chemical inhomogeneities may result from local fluctuations in composition and formation of secondary phases/precipitates in a solid solution . As the NiMn‐based magnetic shape memory alloys are usually found in the Mn‐rich composition region, formation of Mn clusters or Mn‐rich precipitates was considered to be possible origin of magnetic clusters in some references . On the other hand, as the excess Mn atoms occupy some of the Z sites in the Ni–(Co)–Mn–Z (Z = In, Sn, Sb) alloys, the Mn‐poor regions were suggested to tend to form magnetic clusters in some other references because in the Mn‐poor regions the Mn–Mn distance is larger which can easily lead to ferromagnetic exchange interactions.…”

Microstructure and properties of Ni–Mn–Ga alloys produced by rapid solidification and pulsed electric current sintering

“…Melt-spinning is used commercially to produce nanocrystalline Nd-Fe-B powders for permanent magnets [11,12]. Rapidly quenched Ni-Mn-Ga ribbons have been used for the thin film applications and composite structures and their structural and magnetic behavior has been studied quite intensively [13][14][15][16][17][18][19][20]. However, the size of the melt-spun ribbon as such does not meet the demands of the large-dimensional applications.…”