B. J. Kirby

NIST Center for Neutron Research

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J. A. Borchers

NIST Center for Neutron Research

Alexander J. Grutter

NIST Center for Neutron Research

Brian B. Maranville

National Institute of Standards and Technology

M. R. Fitzsimmons

Oak Ridge National Laboratory

Elke Arenholz

Institute of Electrical and Electronics Engineers

Dustin A. Gilbert

University of Tennessee at Knoxville

Kai Liu

Georgetown University

J. K. Furdyna

University of Notre Dame

S. G. E. te Velthuis

Argonne National Laboratory

C. F. Majkrzak

National Institute of Standards and Technology

Cooperative Institutions

Chinese Academy of Sciences

Argonne National Laboratory

Oak Ridge National Laboratory

National Institute of Standards and Technology

Lawrence Berkeley National Laboratory

University of Minnesota

Stanford University

University of California, Berkeley

Massachusetts Institute of Technology

NIST Center for Neutron Research

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Correlating magnetic structure and magnetotransport in semimetal thin films of Eu1−xSmxTiO3

Physical Review Materials (2020)

Zach Porter Ryan F. Need Kaveh Ahadi Yang Zhao Zhijun Xu

We report on the evolution of the average and depth-dependent magnetic order in thin-film samples of biaxially stressed and electron-doped EuTiO3 for samples across a doping range < 0.1 to 7.8 × 1020 cm-3. Under an applied in-plane magnetic field, the G-type antiferromagnetic ground state undergoes a continuous spin-flop phase transition into in-plane, field-polarized ferromagnetism. The critical field for ferromagnetism slightly decreases with an increasing number of free carriers, yet the field evolution of the spin-flop transition is qualitatively similar across the doping range. Unexpectedly, we observe interfacial ferromagnetism with saturated Eu2+ moments at the substrate interface at low fields preceding ferromagnetic saturation throughout the bulk of the degenerate semiconductor film. We discuss the implications of these findings for the unusual magnetotransport properties of this compound.

Magnetic semiconductor

Saturation (graph theory)

10.1103/physrevmaterials.4.054411

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Citations (4)

Spin excitations in [La1−xCaxMnO3] in the mixed-phase region

Journal of Applied Physics (2002)

L. Stumpe B. J. Kirby H. Kaiser J. J. Rhyne J. F. Mitchell

The magnetic excitations and the ferromagnetic order parameter have been studied by neutron scattering in a series of the manganese-based CMR perovskites [La1−xCaxMnO3] (x=0.46, 0.48, 0.50) near the metallic ferromagnetic to insulating antiferromagnetic phase. Well-defined ferromagnetic spin waves were detected for the x=0.46 and x=0.48 compositions. From the measurements of the order parameter, only the x=0.48 sample showed conclusive evidence of a coexistence of an antiferromagnetic phase with the ferromagnetic phase. For this composition, hysteresis was observed in the spin wave intensity but not in the spin stiffness parameter. This effect indicates that the ferromagnetic exchange is not perturbed by the antiferromagnetic ordering. No measurable ferromagnetic magnetization was found in the x=0.50 sample; thus no spin waves could be detected. The results indicate that the onset of the antiferromagnetism upon hole doping for the series occurs in a narrow region of x below the x=0.50 phase boundary.

Spin wave

Phase boundary

10.1063/1.1448307

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Citations (2)

Impact of Interfacial Magnetism on Magnetocaloric Properties of Thin Film Heterostructures | NIST

Applied Physics Letters (2011)

B. J. Kirby June W. Lau D. V. Williams C. A. Bauer Casey W. Miller

Magnetism

NIST

Magnetic refrigeration

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Magnetic compound refractive lens for focusing and polarizing cold neutron beams

Review of Scientific Instruments (2007)

Kenneth C. Littrell S. G. E. te Velthuis G. P. Felcher Sungkyun Park B. J. Kirby

Biconcave cylindrical lenses are used to focus beams of x rays or neutrons using the refractive properties of matter. In the case of neutrons, the refractive properties of magnetic induction can similarly focus and simultaneously polarize the neutron beam without the concomitant attenuation of matter. This concept of a magnetic refractive lens was tested using a compound lens consisting of 99 pairs of cylindrical permanent magnets. The assembly successfully focused the intensity of a white beam of cold neutrons of one spin state at the detector, while defocusing the other. This experiment confirmed that a lens of this nature may boost the intensity locally by almost an order of magnitude and create a polarized beam. An estimate of the performance of a more practically dimensioned device suitable for incorporation in reflectometers and slit-geometry small angle scattering instruments is given.

Magnetic lens

Neutron radiation

10.1063/1.2709844

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Citations (10)

Magnetization reversal of Ga1−xMnxAs layers separated by a nonmagnetic spacer

Journal of Applied Physics (2008)

B. J. Kirby J. A. Borchers X. Liu Z. Ge Y. J. Cho

We have used polarized neutron reflectometry to individually examine the magnetization reversals of ferromagnetic Ga1−xMnxAs layers separated by a nonmagnetic GaAs spacer layer of varying thickness. For each of the samples studied, the top Ga1−xMnxAs layer is adjacent to a Be-doped Al0.25Ga0.75As capping layer on one side and the GaAs spacer on the other, while the bottom Ga1−xMnxAs layer is surrounded by GaAs on either side. For samples with spacer thicknesses of 12 and 6nm, antiparallel alignment of the two Ga1−xMnxAs layer magnetizations was observed at multiple fields, implying that hole doping from the capping layer strongly affects the coercivity of the top Ga1−xMnxAs layer but has a weaker effect on the coercivity of the bottom Ga1−xMnxAs layer. However, for a spacer thickness of 3nm, both top and bottom Ga1−xMnxAs layers appear to be equally influenced by the capping layer, as virtually identical coercivities were observed. This behavior is evidence of coupling between the Ga1−xMnxAs layers across the 3nm GaAs spacer.

Neutron reflectometry

Magnetic semiconductor

10.1063/1.2838236

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Citations (6)

Tunable Noncollinear Antiferromagnetic Resistive Memory through Oxide Superlattice Design

Physical Review Applied (2018)

Jason Hoffman Stephen M. Wu B. J. Kirby Anand Bhattacharya

A central challenge in the burgeoning field of antiferromagnetic spintronics is to find materials with an antiferromagnetic state that can be both controlled and read out. To address this challenge, the authors create artificial La${}_{0.67}$Sr${}_{0.33}$MnO${}_{3}$/LaNiO${}_{3}$ superlattices that are $n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}y$ antiferromagnetic, featuring a state that can be controlled with a small external magnetic field and read out via resistance measurements. This approach introduces ferromagnetlike controllability in an antiferromagnetic system, in a tunable manner, without sacrificing the advantageous properties (such as low stray fields) of antiferromagnetism.

Resistive touchscreen

Lanio

10.1103/physrevapplied.9.044041

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Citations (19)

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

npj Quantum Materials (2018)

Ryan F. Need Patrick Marshall Eric Kenney A. Suter T. Prokscha

Abstract High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO 3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO 3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d 0 band insulator SrTiO 3 when embedded within a d 1 Mott SmTiO 3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T * . The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

Pseudogap

Mott insulator

10.1038/s41535-018-0081-8

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Citations (9)

The use of symmetry to correct Larmor phase aberrations in spin echo scattering angle measurement

Review of Scientific Instruments (2008)

R. Pynn W. T. Lee Paul Stonaha Vaishali Shah A. L. Washington

Spin echo scattering angle measurement (SESAME) is a sensitive interference technique for measuring neutron diffraction. The method uses waveplates or birefringent prisms to produce a phase separation (the Larmor phase) between the "up" and "down" spin components of a neutron wavefunction that is initially prepared in a state that is a linear combination of in-phase up and down components. For neutrons, uniformly birefringent optical elements can be constructed from closed solenoids with appropriately shaped cross sections. Such elements are inconvenient in practice, however, both because of the precision they demand in the control of magnetic fields outside the elements and because of the amount of material required in the neutron beam. In this paper, we explore a different option in which triangular-cross-section solenoids used to create magnetic fields for SESAME have gaps in one face, allowing the lines of magnetic flux to "leak out" of the solenoid. Although the resulting field inhomogeneity produces aberrations in the Larmor phase, the symmetry of the solenoid gaps causes the aberrations produced by neighboring pairs of triangular solenoids to cancel to a significant extent. The overall symmetry of the SESAME apparatus leads to further cancellations of aberrations, providing an architecture that is easy to construct and robust in performance.

Larmor precession

Solenoid

Neutron spin echo

10.1063/1.2927251

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Citations (12)

Impact of interfacial magnetism on magnetocaloric properties of thin film heterostructures

Journal of Applied Physics (2011)

B. J. Kirby June W. Lau D. V. Williams C. A. Bauer Casey W. Miller

Polarized neutron reflectometry was used to determine the depth profile of the magnetic moment per Gd atom, mGd, in a Gd(30 nm)/W(5 nm) multilayer. Despite sharp interfaces observed by transmission electron microscopy, mGd is systematically suppressed near the Gd-W interfaces. Because the peak magnetic entropy change is proportional to mGd2/3, this results in a reduction of the maximum achievable magnetocaloric effect in Gd-W heterostructures. By extension, our results suggest that creating materials with Gd-ferromagnet interfaces may increase the mGd relative to the bulk, leading to enhanced magnetocaloric properties.

Magnetic refrigeration

Magnetism

Neutron reflectometry

Reflectometry

10.1063/1.3555101

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Citations (24)

Controllable magnetic phase front in a vertically graded Ni$_{x}$Cu$_{1-x}$ alloy film

Bulletin of the American Physical Society (2015)

B. J. Kirby H. Belliveau Dustin D. Belyea Tatiana Eggers Paul Kienzle

Magnetic alloy

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