Neutron-scattering study of incommensurate magnetic order in the heavy-fermion superconductor UNi{sub 2}Al{sub 3}

Journal Article · Sat Nov 01 04:00:00 EST 1997 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.56.11749· OSTI ID:544937

Lussier, J G; Mao, M; Schroeder, A; Garrett, J D; Gaulin, B D ^[1]; Shapiro, S M ^[2]; Buyers, W J ^[3]

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1. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1 (CANADA)
2. Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)
3. National Research Council, Neutron Program for Materials Research, Chalk River Laboratories, Chalk River, Ontario, K0J 1J0 (CANADA)

Elastic neutron scattering from a single-crystal sample of the heavy-fermion superconductor UNi{sub 2}Al{sub 3} has revealed the onset of long-range magnetic order below T{sub N}=4.6 K. This order is characterized by an incommensurate (IC) ordering wave vector given by ( (1) /(2) {plus_minus}{tau},0, (1) /(2) ) with {tau}=0.11{plus_minus}0.003. The intensity of several magnetic satellite Bragg peaks within the (h,0,l) plane is well described by a model in which the spins lie within the basal plane and are modulated in amplitude from site to site. By applying a magnetic field to select from all the possible domains, we find that the moment is polarized along the {bold a} direction, with a maximum amplitude of 0.21{plus_minus}0.1{mu}{sub B} per uranium atom. The order-parameter exponent {beta} associated with this transition is 0.34{plus_minus}.03, which is typical of three-dimensional ordering transitions. Measurements down to {approximately}0.3 K show that the magnetic order coexists with superconductivity below T{sub C}{approximately}1.2 K, and that these states are coupled as shown by anomalous behavior of the magnetic order parameter around T{sub C}. Measurements were also made in magnetic fields of up to 8 T applied perpendicular to the (h,0,l) plane, along ({minus}1,1,0), a near-neighbor direction within the hexagonal basal plane. While the field does not influence T{sub N}, it does increase the intensity of the magnetic Bragg peaks by a factor of {approximately}1.5, as well as increase the IC part of the ordering wave vector at low temperatures. {copyright} {ital 1997} {ital The American Physical Society}

• OSTI ID: 544937
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 18 Vol. 56; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
AMPLITUDES
MAGNETIC FIELDS
MAGNETIC PROPERTIES
NEUTRON DIFFRACTION
NICKEL ALLOYS
ORDER PARAMETERS
ORDER-DISORDER TRANSFORMATIONS
POLARIZATION
URANIUM ALLOYS