Efficient manipulation of antiferromagnetically coupled materials that are integration-friendly and have strong perpendicular magnetic anisotropy (PMA) is of great interest for low-power, fast, dense magnetic storage and computing. Here, we report a distinct, giant bulk damping-like spin–orbit torque in strong-PMA ferrimagnetic Fe 100− x Tb x single layers that are integration-friendly (composition-uniform, amorphous, and sputter-deposited). For sufficiently thick layers, this bulk torque is constant in the efficiency per unit layer thickness, [Formula: see text]/ t, with a record-high value of 0.036 ± 0.008 nm −1 , and the damping-like torque efficiency [Formula: see text] achieves very large values for thick layers, up to 300% for 90 nm layers. This giant bulk torque by itself switches tens of nm thick Fe 100− x Tb x layers that have very strong PMA and high coercivity at current densities as low as a few MA/cm 2 . Surprisingly, for a given layer thickness, [Formula: see text] shows strong composition dependence and becomes negative for composition where the total angular momentum is oriented parallel to the magnetization rather than antiparallel. Our findings of giant bulk spin torque efficiency and intriguing torque-compensation correlation will stimulate study of such unique spin–orbit phenomena in a variety of ferrimagnetic hosts. This work paves a promising avenue for developing ultralow-power, fast, dense ferrimagnetic storage and computing devices.
more »
« less
Engineering large perpendicular magnetic anisotropy in amorphous ferrimagnetic gadolinium cobalt alloys
Amorphous magnetic alloys with large perpendicular magnetic anisotropy (PMA) have emerged as a suitable material choice for spintronic memory and high-frequency non-reciprocal devices on-chip. Unlike ferromagnets, ferrimagnets offer faster switching dynamics, lower net saturation magnetization, minimal stray field and a lower net angular momentum. Ferrimagnetic thin films of Gd x Co 1− x sputter deposited as heterostructures of Ta/Pt/Gd x Co 1− x (t)/Pt on Si/SiO 2 have bulk-like PMA for thicknesses of 5–12 nm and room-temperature magnetic compensation for x = 28–32%. Preferential oxygenation of GdCo has been found to increase the effective anisotropy energy density by an order of magnitude and produce near-ideal remanence ratios. X-ray photoelectron spectroscopy accurately quantifies the metal-oxidation ratio, which shows that an oxygen-rich and Co-deficient stoichiometry (Gd 21 Co 28 O 51 ) likely weakens the ferromagnetic exchange interaction between Co–Co and contributes additional antiferromagnetic exchange through superexchange-like interactions between Gd and Co via O, resulting in a stronger out-of-plane magnetization. Even greater PMA and giant-anisotropy field of 11 kOe are achieved in super-lattices of the Gd 21 Co 28 O 51 heterostructure. The combination of ferrimagnetic ordering in amorphous Gd x Co 1− x and its affordance of pathways for engineering large PMA will enable the design of integrated high-frequency devices beyond 30 GHz and ultrafast energy efficient memory devices with switching speeds down to tens of picoseconds.
more »
« less
- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10411529
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 11
- Issue:
- 14
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 4820 to 4829
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Magnetic insulators, such as the rare‐earth iron garnets, are promising materials for energy‐efficient spintronic memory and logic devices, and their anisotropy, magnetization, and other properties can be tuned over a wide range through selection of the rare‐earth ion. Films are typically grown as epitaxial single crystals on garnet substrates, but integration of these materials with conventional electronic devices requires growth on Si. The growth, magnetic, and spin transport properties of polycrystalline films of dysprosium iron garnet (DyIG) with perpendicular magnetic anisotropy (PMA) on Si substrates and as single crystal films on garnet substrates are reported. PMA originates from magnetoelastic anisotropy and is obtained by controlling the strain state of the film through lattice mismatch or thermal expansion mismatch with the substrates. DyIG/Si exhibits large grain sizes and bulk‐like magnetization and compensation temperature. Polarized neutron reflectometry demonstrates a small interfacial nonmagnetic region near the substrate. Spin Hall magnetoresistance measurements conducted on a Pt/DyIG/Si heterostructure demonstrate a large interfacial spin mixing conductance between the Pt and DyIG comparable to other garnet/Pt heterostructures.
-
more » « less
Abstract This report is on the observation and theory of electric field
E induced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite. Using microwave measurement techniques, it was found that a DC electric field along the hexagonal c-axis results in significant changes in the saturation magnetization and uniaxial magneto-crystalline anisotropy field and these changes are proportional to the square of the applied static electric field. The NLME effects were present with or without an external bias magnetic field. TheE -induced variation in magnetic order parameters is attributed to weakening of magnetic exchange and spin–orbit interactions since conduction electrons in the ferrite are effectively excluded from both interactions while being in transit from one Fe ion to another. We present a phenomenological theory which considers magneto-bielectric effects characterized by a quadratic term in electric fieldE in the free energy density. The coefficients for the NLME coupling terms have been calculated from experimental data and they do show variations with the Al substitution level and the largest rates of change of the saturation magnetization and anisotropy constant change with the applied power were observed for x = 0.4. It was also clear from the study that strength of the NLME effect does not depend on the amount Al substitution, but critically depends on the electrical conductivity of the sample with the highest NLME coefficients estimated for the sample with the highest conductivity. Results of this work are of importance for a new family of electric field tunable, miniature, high frequency ferrite devices. -
more » « less
Abstract The presence of multiple competing periodicities may result in a system to go through states with modulated periodicities, an example of which is the self-similar staircase-like structure called the Devil’s Staircase. Herein we report on a novel staircase structure of domain periodicity in an amorphous and centrosymmetric Fe/Gd magnetic thin film system wherein the reciprocal space wavevector
Q due to the ordered stripe domains does not evolve continuously, rather exhibits a staircase structure. Resonant X-ray scattering experiments show jumps in the periodicity of the stripe domains as a function of an external magnetic field. When resolved in components, the length-scale step change along Qx was found to be an integral multiple of a minimum step height of 7 nm, which resembles closely to the exchange length of the system. Modeling the magnetic texture in the Fe/Gd system as an achiral spin arrangement, we have been able to reproduce the steps in the magnetization using a Landau-Lifshitz spin dynamics calculation. Our results indicate that anisotropy and not the dipolar interaction is the dominant cause for the staircase pattern, thereby revealing the effect of achiral magnetism. -
SUMMARY Anisotropy of remanent magnetization and magnetic susceptibility are highly sensitive and important indicators of geological processes which are largely controlled by mineralogical parameters of the ferrimagnetic fraction in rocks. To provide new physical insight into the complex interaction between magnetization structure, shape, and crystallographic relations, we here analyse ‘slice-and-view’ focused-ion-beam (FIB) nano-tomography data with micromagnetic modelling and single crystal hysteresis measurements. The data sets consist of 68 magnetite inclusions in orthopyroxene (Mg60) and 234 magnetite inclusions in plagioclase (An63) were obtained on mineral separates from the Rustenburg Layered Suite of the Bushveld Intrusive Complex, South Africa. Electron backscatter diffraction was used to determine the orientation of the magnetite inclusions relative to the crystallographic directions of their silicate hosts. Hysteresis loops were calculated using the finite-element micromagnetics code MERRILL for each particle in 20 equidistributed field directions and compared with corresponding hysteresis loops measured using a vibrating sample magnetometer (VSM) on silicate mineral separates from the same samples. In plagioclase the ratio of remanent magnetization to saturation magnetization (Mrs/Ms) for both model and measurement agree within 1.0 per cent, whereas the coercivity (Hc) of the average modelled curve is 20 mT lower than the measured value of 60 mT indicating the presence of additional sources of high coercivity in the bulk sample. The VSM hysteresis measurements of the orthopyroxene were dominated by multidomain (MD) magnetite, whereas the FIB location was chosen to avoid MD particles and thus contains only particles with diameters <500 nm that are considered to be the most important carriers of palaeomagnetic remanence. To correct for this sampling bias, measured MD hysteresis loops from synthetic and natural magnetites were combined with the average hysteresis loop from the MERRILL models of the FIB region. The result shows that while the modelled small-particle fraction only explains 6 per cent of the best fit to the measured VSM hysteresis loop, it contributes 28 per cent of the remanent magnetization. The modelled direction of maximal Mrs/Ms in plagioclase is subparallel to [001]plag, whereas Hc does not show a strong orientation dependence. The easy axis of magnetic remanence is in the direction of the magnetite population normal to (150)plag and the maximum calculated susceptibility (χ*) is parallel to [010]plag. For orthopyroxene, the maximum Mrs/Ms, maximum χ* and the easy axis of remanence is strongly correlated to the elongation axes of magnetite in the [001]opx direction. The maximum Hc is oriented along [100]opx and parallel to the minimum χ*, which reflects larger vortex nucleation fields when the applied field direction approaches the short axis. The maximum Hc is therefore orthogonal to the maximum Mrs/Ms, controlled by axis-aligned metastable single-domain states at zero field. The results emphasize that the nature of anisotropy in natural magnetite does not just depend on the particle orientations, but on the presence of different stable and metastable domain states, and the mechanism of magnetic switching between them. Magnetic modelling of natural magnetic particles is therefore a vital method to extract and process anisotropic hysteresis parameters directly from the primary remanence carriers.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3TC00332A
