TY - JOUR

T1 - Magnetic phase transition in disordered Fe-Ni alloys studied by means of small-angle neutron scattering and three-dimensional analysis of the neutron depolarization

AU - Grigoriev, S. V.

AU - Klimko, S. A.

AU - Kraan, W. H.

AU - Maleyev, S. V.

AU - Okorokov, A. I.

AU - Rekveldt, M. Th

AU - Runov, V. V.

PY - 2001/9/1

Y1 - 2001/9/1

N2 - The magnetic phase transition in iron-nickel fcc alloys Fe70Ni30 doped by carbon (0.7% at.) is investigated using the three-dimensional analysis of the neutron depolarization (ND) and small-angle neutron scattering (SANS). The coexistence and the growth of two different scale magnetic correlations are observed in a paramagnetic phase as temperature closes to TC. The usual critical fluctuations of a Lorentzian shape with size Rc<200 Å are found by the analysis of SANS intensity I(q). The ND analysis shows also presence of the large scale correlations (about 103-104 Å) with the "squared" Lorentzian shape. We attribute these large scale correlations to local variations of the Curie temperature TC. The local TC variations are described by the disorder parameters of the system: TC, a spread of TC variations ΔTC, and characteristic size of the local areas R0, where TC variations occur. The ratio between the depth of the TC variations (ΔTC/TC) and its characteristic correlation length R0/a (a is a lattice constant) determines a scenario of the transition: "percolative" or "homogeneous" ones. At R0/a≫ (ΔTC/TC)-2/3 locally ordered ferromagnetic regions appear in paramagnetic phase and form a large percolative cluster. In this case the connectivity length of the ordered regions dominates at the correlation length of thermal fluctuations. Therefore this transition goes in accordance with the "percolative" scenario. All three parameters of the transition are obtained from the data of the three dimension analysis of the ND. From the temperature dependence of the magnetization, we found TC=397±0.5 K and ΔTC=4.55±0.05 K. From ND data we estimated the temperature independent characteristic size R0 of the TC variations. It is equal to 104 Å.

AB - The magnetic phase transition in iron-nickel fcc alloys Fe70Ni30 doped by carbon (0.7% at.) is investigated using the three-dimensional analysis of the neutron depolarization (ND) and small-angle neutron scattering (SANS). The coexistence and the growth of two different scale magnetic correlations are observed in a paramagnetic phase as temperature closes to TC. The usual critical fluctuations of a Lorentzian shape with size Rc<200 Å are found by the analysis of SANS intensity I(q). The ND analysis shows also presence of the large scale correlations (about 103-104 Å) with the "squared" Lorentzian shape. We attribute these large scale correlations to local variations of the Curie temperature TC. The local TC variations are described by the disorder parameters of the system: TC, a spread of TC variations ΔTC, and characteristic size of the local areas R0, where TC variations occur. The ratio between the depth of the TC variations (ΔTC/TC) and its characteristic correlation length R0/a (a is a lattice constant) determines a scenario of the transition: "percolative" or "homogeneous" ones. At R0/a≫ (ΔTC/TC)-2/3 locally ordered ferromagnetic regions appear in paramagnetic phase and form a large percolative cluster. In this case the connectivity length of the ordered regions dominates at the correlation length of thermal fluctuations. Therefore this transition goes in accordance with the "percolative" scenario. All three parameters of the transition are obtained from the data of the three dimension analysis of the ND. From the temperature dependence of the magnetization, we found TC=397±0.5 K and ΔTC=4.55±0.05 K. From ND data we estimated the temperature independent characteristic size R0 of the TC variations. It is equal to 104 Å.

UR - http://www.scopus.com/inward/record.url?scp=4243225370&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.64.094426

DO - 10.1103/PhysRevB.64.094426

M3 - Article

AN - SCOPUS:4243225370

VL - 64

JO - Physical Review B-Condensed Matter

JF - Physical Review B-Condensed Matter

SN - 1098-0121

IS - 9

M1 - 094426

ER -