Annealing-time and annealing-temperature dependencies of the size of Ni-Mn-In shell-ferromagnetic nano-precipitates by Scherrer analysis

Abstract

Shell-ferromagnetic effects are observed in Ni-Mn-based off-stoichiometric Heuslers decomposed into ferromagnetic precipitates embedded in an antiferromagnetic matrix when the surface-to-volume ratio of the precipitates are sufficiently large. However, since the size of the precipitates have until now not been determined, it is not known which ratios are involved. Here we carry out a Scherrer analysis on decomposed specimens to determine the precipitate-size as a function of decomposition temperature and time.

Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk Ni50Mn45In5 Heusler alloys

“…The present SANS data reveal no characteristic signature indicative of such presumably small precipitates, which might indicate that their size is too small and their volume fraction is too low to give rise to a corresponding feature in the observed q region. This is consistent with our synchrotron x-ray data analysis and with the results reported in [5], where precipitate sizes of the order of 3-5 nm were found for samples of similar annealing conditions.…”

“…The histograms in Fig. 2(c suggest that the particle statistics have improved for the 700 K sample; that is, the vertical lines are more homogeneous, implying that the grain-size distribution has become less disperse after the heat treatment (in accordance with [5]). The presence of large crystals [large and intense spots in Fig.…”

“…A new functional property in the off-stoichiometric Ni 50 Mn 45 In 5 alloy was recently observed by Çakır et al [4]. The compound, when annealed at temperatures between about 650 and 750 K under a magnetic field as lit-* andreas.michels@uni.lu tle as 0.1 T [5], decomposes into nanosized Ni 50 Mn 25 In 25 precipitates which become embedded in a Ni 50 Mn 50 matrix. The precipitates have a Curie temperature of T C ∼ = 320 K and are FM at room temperature, whereas the matrix is AF.…”

“…Note that the experimental scatteringangle values ψ have been transformed into the corresponding values for Cu Kα radiation to ease the comparison with the data shown in [4]. In contrast to what was reported in [4,5] for powder samples (different from the bulk samples studied here), the transformation process of the initial-state sample in Fig. 2(a) (I4/mmm, a = 3.79 Å, c = 7.00 Å) into a NiMn tetragonal phase (I4/mmm, a = 3.75 Å, c = 7.00 Å) becomes only weakly visible at 700 K (appearance of a small hump at the position of the strongest NiMn tetragonal reflection).…”

Structure, Microstructure, and Magnetic Properties of Melt Spun Ni50Mn50−xInx Ribbons

“…It has been reported that the compound decomposes into FM nanoprecipitates embedded in a Ni 50 Mn 50 AF matrix at room temperature. Additionally, the negative shift of the magnetization in the Ni-Mn-In shell FM nano-precipitates has been attributed to the occurrence of the magnetic proximity effect, whereby the interfacial spins align along the field applied during segregation [31]. The spins at the interface with the NiMn matrix align with the annealing field during their growth and become strongly pinned in the field direction during annealing, forming the so-called shell ferromagnet.…”