66 research outputs found
Polar domain walls trigger magnetoelectric coupling
Interface physics in oxide heterostructures is pivotal in material's science.
Domain walls (DWs) in ferroic systems are examples of naturally occurring
interfaces, where order parameter of neighboring domains is modified and
emerging properties may develop. Here we show that electric tuning of
ferroelastic domain walls in SrTiO3 leads to dramatic changes of the magnetic
domain structure of a neighboring magnetic layer (La1/2Sr1/2MnO3) epitaxially
clamped on a SrTiO3 substrate. We show that by exploiting the resposiveness of
DWs nanoregions to external stimuli, even in absence of any domain
contribution, prominent and adjustable macroscopic reactions of neighboring
layers can be obtained. We conclude that polar DWs, known to exist in other
materials, can be used to trigger tunable responses and may lead to new ways
for manipulation of interfacial emerging properties
High temperature magnetic stabilization of cobalt nanoparticles by an antiferromagnetic proximity effect
Thermal activation tends to destroy the magnetic stability of small magnetic
nanoparticles, with crucial implications in ultra-high density recording among
other applications. Here we demonstrate that low blocking temperature
ferromagnetic (FM) Co nanoparticles (TB<70 K) become magnetically stable above
400 K when embedded in a high N\'eel temperature antiferromagnetic (AFM) NiO
matrix. The origin of this remarkable TB enhancement is due to a magnetic
proximity effect between a thin CoO shell (with low N\'eel temperature, TN; and
high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix
(with high TN but low KAFM). This proximity effect yields an effective AFM with
an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to
NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations
via core-shell exchange-bias coupling, leading to the observed TB increase.
Mean-field calculations provide a semi-quantitative understanding of this
magnetic- proximity stabilization mechanism
Magnetoelastic coupling in La2/3Sr1/3MnO3 thin films on SrTiO3
Clamping of epitaxial La2/3Sr1/3MnO3 (LSMO) magnetic thin films on SrTiO3 (STO) substrates is shown to promote a clear modification of their magnetic properties at the STO cubic-tetragonal transition. Two distinct mechanisms triggered by the STO transition, namely magnetic domain pattern reconstruction and creation of regions within the magnetically soft LSMO with enhanced magnetic anisotropy, are proposed to be behind the observed anomalous magnetic responses at low ac-magnetic field and at high dc-field, respectively. The persistence of these anomalies in LSMO films as thick as 220 nm shines new light into the magnetoelastic coupling mechanisms across interfaces
CoFe2O4/buffer layer ultrathin heterostructures on Si(001)
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Epitaxial films of ferromagnetic CoFe2O4 (CFO) were grown by pulsed laser deposition on Si(001) buffered with ultrathin yttria-stabilized zirconia (YSZ) layers in a single process. Reflection high-energy electron diffraction was used to monitor in real time the crystallization of YSZ, allowing the fabrication of epitaxial YSZ buffers with thickness of about 2 nm. CFO films, with thicknesses in the 2-50 nm range were subsequently deposited. The magnetization of the CFO films is close to the bulk value. The ultrathin CFO/YSZ heterostructures have very flat morphology (0.1 nm roughness) and thin interfacial SiOx layer (about 2 nm thick) making them suitable for integration in tunnel (e.g., spin injection) devices
Magnetoelectric effect and phase transitions in CuO in external magnetic fields
Apart from being so far the only known binary multiferroic compound, CuO has
a much higher transition temperature into the multiferroic state, 230 K, than
any other known material in which the electric polarization is induced by
spontaneous magnetic order, typically lower than 100 K. Although the
magnetically induced ferroelectricity of CuO is firmly established, no
magnetoelectric effect has been observed so far as direct crosstalk between
bulk magnetization and electric polarization counterparts. Here we demonstrate
that high magnetic fields of about 50 T are able to suppress the helical
modulation of the spins in the multiferroic phase and dramatically affect the
electric polarization. Furthermore, just below the spontaneous transition from
commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213
K, even modest magnetic fields induce a transition into the incommensurate
structure and then suppress it at higher field. Thus, remarkable hidden
magnetoelectric features are uncovered, establishing CuO as prototype
multiferroic with abundance of competitive magnetic interactions.Comment: 26 pages, 5 figure
Why the iron magnetization in Gd2Fe14B and the spontaneous magnetization of Y2Fe14B depend on temperature differently
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.It is demonstrated that the temperature dependence of the iron sublattice magnetization in Gd2Fe14B is affected significantly by the Gd-Fe exchange interaction. This is at variance with the common perception that MFe(T) in iron-rich rare-earth intermetallics is determined predominantly by the Fe-Fe exchange. This phenomenon is discussed by considering the modification of the low-energy spin-wave spectrum of Gd2Fe14B, as compared to that of Y2Fe14B, under the influence of the Gd-Fe interaction. The result is of particular significance for evaluating the temperature dependence of the magnetocrystalline anisotropy of iron or cobalt compounds with anisotropic rare earths (e.g., Nd2Fe14B) and in turn, of the hard magnetic properties of such compounds
Microstructural characterization of L10 FePt/MgO nanoparticles with perpendicular anisotropy
L10 FePt nanoparticles with perpendicular magnetic anisotropy were fabricated on a heated MgO substrate by using an atomic deposition technique. The microstructure of the FePt nanoparticles was studied by transmission electron microscopy and high resolution transmission electron microcopy. The as-made L10 FePt nanoparticles are isolated and have a faceted morphology with a bimodal distribution of particle size as small as 2.5 nm. A semicoherent atomic interface between the FePt nanoparticles and the MgO substrate is observed. The room temperature coercivity of these FePt nanoparticles was measured via both superconducting quantum interference device and magneto-optical Kerr effect techniques and found to be as high as 6.7 kOe
Conical antiferromagnetic order in the ferroelectric phase of Mn0.8Co0.2WO4 resulting from the competition between collinear and cycloidal structures
Evolution of competing commensurate collinear (AF4) and incommensurate cycloidal (AF2) magnetic structures in Mn0.8Co0.2WO4 multiferroic was studied by neutron diffraction, magnetic, and pyroelectric characterization measurements. In contrast to pure and slightly Co doped MnWO4, the antiferromagnetic AF4 collinear phase [k1=(1/2,0,0)] inherent to the pure CoWO4 was observed below Néel temperature TN≈20 K in Mn0.8Co0.2WO4. This collinear order survives down to the lowest temperature reached in the experiments (2 K) even after the appearance of the second (cycloidal AF2) spin order below TFE≈8.5 K [k2=(−0.211,1/2,0.452)]. Ferroelectric polarization along b axis was revealed below TFE in the low temperature conical phase resulting from the superposition of the AF4 and AF2 spin structures. The arrangement of the spins after the two successive magnetic transitions are thoroughly described. In particular, we found that spins in the AF4 phase are aligned along the easy direction in the ac plane (∼142∘ with respect to the c* axis), while the cycloidal AF2 spin order is developed in the magnetically hard directions, perpendicular to the easy one, and consequently the TFE decreases compared to the pure MnWO4
Electric field control of exchange bias in multiferroic epitaxial heterostructures
The magnetic exchange bias between epitaxial thin films of the multiferroic
(antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft
ferromagnetic (FM) layer is used to couple the magnetic response of the
ferromagnetic layer to the magnetic state of the antiferromagnetic one. We will
show that biasing the ferroelectric YMnO3 layer by an appropriate electric
field allows modifying and controlling the magnetic exchange bias and
subsequently the magnetotransport properties of the FM layer. This finding may
contribute to pave the way towards a new generation of electric-field
controlled spintronics devices.Comment: 15 pages, 5 figures, submitte
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