TY - JOUR
T1 - Nanoscale magnetic phase competition throughout the N i50-x C ox M n40 S n10 phase diagram
T2 - Insights from small-angle neutron scattering
AU - El-Khatib, S.
AU - Bhatti, Kanwal Preet
AU - Srivastava, Vijay
AU - James, R. D.
AU - Leighton, C.
N1 - Publisher Copyright:
©2019 American Physical Society.
PY - 2019/10/17
Y1 - 2019/10/17
N2 - The Ni2MnSn-derived Ni50-xCoxMn25+ySn25-y alloys are premier examples of a class of off-stoichiometric Heusler alloys recently discovered to exhibit attractive magnetic properties in tandem with extraordinarily reversible martensitic phase transformations. Multiferroicity, magnetic phase competition and separation, field-induced martensitic transformations, magnetic shape memory behavior, and sizable magneto-, elasto-, and barocaloric effects result, generating substantial interest and application potential. In this work we expand on a prior small-angle neutron scattering (SANS) study at a single composition (Ni44Co6Mn40Sn10) by exploring all three main regions of the recently established Ni50-xCoxMn40Sn10 phase diagram, i.e., at the representative y=15 composition. Wide temperature and scattering wave-vector range (20-500K, 0.004-0.2Å-1) SANS data on x=2, 6, and 14 polycrystals provide a detailed picture of the evolution in magnetic order and inhomogeneity. Consistent with recent studies with a variety of techniques, phase separation into short-range coexisting ferromagnetic and antiferromagnetic regions is deduced below the martensitic transformation at x=2 and 6, with average ferromagnetic cluster spacing of ∼13 nm. Remarkably, at x=14, where the martensitic transformation is suppressed and ferromagnetic austenite is stabilized to low temperatures, nanoscopic magnetic inhomogeneity nevertheless persists. Distinct ferromagnetic clusters (∼36-nm average spacing) in a ferromagnetic matrix are observed at intermediate temperatures, homogenizing into a uniform long-range ordered ferromagnet only at low temperatures. This unusual ferromagnet cluster/ferromagnet matrix inhomogeneity, as well as x-dependent subtleties of the superparamagnetic freezing of ferromagnetic clusters, are discussed in light of Mn55 nuclear magnetic resonance data, and the recent observation of annealing-induced core/shell nanoprecipitates. The origins of nanoscale magnetic inhomogeneity are discussed in terms of statistical variations in local composition and structure, tendency to chemical phase separation, and other forms of disorder.
AB - The Ni2MnSn-derived Ni50-xCoxMn25+ySn25-y alloys are premier examples of a class of off-stoichiometric Heusler alloys recently discovered to exhibit attractive magnetic properties in tandem with extraordinarily reversible martensitic phase transformations. Multiferroicity, magnetic phase competition and separation, field-induced martensitic transformations, magnetic shape memory behavior, and sizable magneto-, elasto-, and barocaloric effects result, generating substantial interest and application potential. In this work we expand on a prior small-angle neutron scattering (SANS) study at a single composition (Ni44Co6Mn40Sn10) by exploring all three main regions of the recently established Ni50-xCoxMn40Sn10 phase diagram, i.e., at the representative y=15 composition. Wide temperature and scattering wave-vector range (20-500K, 0.004-0.2Å-1) SANS data on x=2, 6, and 14 polycrystals provide a detailed picture of the evolution in magnetic order and inhomogeneity. Consistent with recent studies with a variety of techniques, phase separation into short-range coexisting ferromagnetic and antiferromagnetic regions is deduced below the martensitic transformation at x=2 and 6, with average ferromagnetic cluster spacing of ∼13 nm. Remarkably, at x=14, where the martensitic transformation is suppressed and ferromagnetic austenite is stabilized to low temperatures, nanoscopic magnetic inhomogeneity nevertheless persists. Distinct ferromagnetic clusters (∼36-nm average spacing) in a ferromagnetic matrix are observed at intermediate temperatures, homogenizing into a uniform long-range ordered ferromagnet only at low temperatures. This unusual ferromagnet cluster/ferromagnet matrix inhomogeneity, as well as x-dependent subtleties of the superparamagnetic freezing of ferromagnetic clusters, are discussed in light of Mn55 nuclear magnetic resonance data, and the recent observation of annealing-induced core/shell nanoprecipitates. The origins of nanoscale magnetic inhomogeneity are discussed in terms of statistical variations in local composition and structure, tendency to chemical phase separation, and other forms of disorder.
UR - http://www.scopus.com/inward/record.url?scp=85074390773&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85074390773&partnerID=8YFLogxK
U2 - 10.1103/PhysRevMaterials.3.104413
DO - 10.1103/PhysRevMaterials.3.104413
M3 - Article
AN - SCOPUS:85074390773
SN - 2475-9953
VL - 3
JO - Physical Review Materials
JF - Physical Review Materials
IS - 10
M1 - 104413
ER -