6 Search Results

Conventionally, the modulation of the intrinsic Weyl nodes in Weyl semimetals is challenging, due to topological protection. Here we report the structural dependence of the Weyl nodes in a Co2⁢MnGa Heusler thin film via a temperature-dependent tetragonal distortion. The ability to manipulate these Weyl nodes allows for the control of the intrinsic electromagnetic properties. Temperature-dependent x-ray diffraction (XRD) measurements identify a compressive tetragonal distortion with decreasing temperature from 300 to 20 K. The calculated Weyl properties can be directly compared with experimental parameters through the temperature-dependent XRD measurements which show the intrinsic correlation between Weyl properties and important magnetic parameters.more » Further, the microscopic momentum space properties of Weyl nodes such as the distance (d_W), solid angle (Ω_W), tilt (φ_W), and nodal point energy (E_W) directly affect the macroscopic observable properties such as exchange stiffness (A), magnetization (M), and effective anisotropy field $$H^{eff}_{K}$$, as shown via structure-dependent density functional theory calculations. These predictions are experimentally observed as large variations in the bulk magnetization and effective anisotropy field as a function of temperature. These results highlight a unique degree of freedom in the control of macroscopic magnetic properties via the modulation of the intrinsic properties of Weyl nodes through structural distortions.« less

We report on the effects of annealing temperatures ranging from 225 °C to 325 °C on the magnetic properties of high aspect ratio iron oxide nanorods consisting of a ferrimagnetic Fe₃O₄ phase and an antiferromagnetic α-Fe₂O₃ phase in an as-prepared state. Annealing at the aforementioned temperatures under a constant flow of O₂ for 3 h leads to an increment of the volume fraction of the antiferromagnetic α-Fe₂O₃ phase and concomitant enhancement of the crystallinity of the ferrimagnetic Fe₃O₄ phase. These opposing effects compete with each other, resulting in a decrease in global magnetization with increasing the annealing temperature. The desirablemore » magnetic properties are achieved for the sample annealed at 250 °C. For all samples investigated, we observed an increase in low field magnetization at low temperatures after the sample is field cooled in the presence of a 1T magnetic field, which we attribute to the ordering of macro-spins of the weakly ordered antiferromagnetic α-Fe₂O₃ phase in the presence of the cooling field. Our study will pave the way for determining the optimal conditions to enhance the magnetic characteristics in iron oxide nanorods, which will enable its use in spintronics and biomedical applications.« less

Heusler alloy-based spin gapless semiconductors (SGSs) with very high Curie temperatures $\left(T_C\right)$ have recently gained enormous attention because of their unconventional electronic structures. They exhibit a nonzero band gap in one of the spin channels and a zero band gap in the other spin channel, making them an important class of materials for tunable spin transport. Here, we report the experimental observation of anomalous Nernst effect (ANE) in ${\mathrm{Co}}_{1+x}{\mathrm{Fe}}_{1-x}\mathrm{CrGa}$ ( $more »$ x = 0 , 0.2, 0.4, and 0.5), which are the emerging quaternary Heusler alloy-based SGSs. While the electron-electron elastic scattering and the disorder-mediated weak localization effect play the major roles in electrical transport for all the samples at low temperatures, the magnon-drag effect was found to dominate the longitudinal thermoelectric transport. The ANE coefficient at room temperature increases from $\approx 0.018\mu \mathrm{V}{\mathrm{K}}^{-1}$ for $x=0$ to $\approx 0.063\mu \mathrm{V}{\mathrm{K}}^{-1}$ for $x=0.5$, which is higher than that for ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ and compressively strained $\mathrm{SrRu}{\mathrm{O}}_3$ films. Our analysis indicates that the observed ANE in these samples originates from asymmetric skew scattering of charge carriers.« less

We report on the magnetic properties of biphase iron oxide nanorods (NRs) consisting of ferrimagnetic Fe₃O₄ and antiferromagnetic α-Fe₂O₃ phases. Annealing as-prepared NRs at 250 °C for 5h, significantly improved the crystallinity of the Fe₃O₄ phase and enhanced the volume fraction of the α-Fe₂O₃ phase. Magnetometry data consistently reveal these two magnetically distinct phases, which are not in proximity to each other but separated by a region of disordered spins giving rise to enhanced magnetization at low temperatures when the sample was cooled down from 300 K in the presence of a 1T field to 10 K. This phenomenon which is alsomore » known as the pinning effect is much more pronounced in the annealed sample, resulting from the increased volume fraction of the α-Fe₂O₃ phase which could strengthen the interfacial spin frustration between these two phases and enhance the density of disordered spins at the interface.« less

Here, we explore the change in effective magnetic anisotropy of the ferrimagnetic (FM) insulator nickel ferrite (NFO) thin film due to the inclusion of monolayer graphene (MLG) grown on top of the NFO layer. This was done by performing radio frequency (RF) transverse susceptibility (TS) measurements on bare NFO and NFO/MLG bilayer samples for both in-plane (IP) and out-of-plane (OOP) configurations utilizing a tunnel diode oscillator technique. Our magnetometry measurements indicated an enhancement in the overall saturation magnetization of the NFO/MLG bilayer with respect to the bare NFO film. The TS measurements reveal that the inclusion of MLG reduces themore » effective magnetic anisotropy for both IP and OOP configurations drastically, by up to a factor of 2 over the temperature range 40 K ≤ T ≤ 280 K. Since NFO is a magnetic substrate, it is possible that NFO could induce magnetic ordering in MLG at the NFO/MLG interface via the magnetic proximity effect. Furthermore, since NFO is insulating and MLG is a semimetal, there likely exists a large conductivity difference at the interface, making charge transfer plausible. These two effects could modify the interfacial magnetism leading to a change in the effective magnetic anisotropy. These results highlight the importance of understanding the interfacial magnetism of FM/MLG heterostructures.« less

Here, we report a comprehensive study of the temperature evolution of in-plane (IP) and out-of-plane (OOP) effective magnetic anisotropies in compensated ferrimagnetic Fe_100–xGd_x alloy films by employing direct current magnetometry and radiofrequency (RF) transverse susceptibility (TS) measurements. We suggest that our Fe_100–xGd_x system is chemically inhomogeneous and phase segregates into Fe- and Gd-enriched regions. Our IP and OOP magnetometry results indicate that the system undergoes a temperature-driven transformation from an IP-spin-configuration-dominated state to an OOP-spin-configuration-dominated state below a certain temperature (spin reorientation temperature). A two-step reversal behavior emerges in the OOP $$\textit{M(H)}$$ loop near compensation, which we attribute to themore » sequential magnetization reversals of Fe- and Gd-enriched domains. Field-induced spin-flop transitions were also observed near the compensation. Our RF TS measurements indicate that the effective magnetic anisotropy for the OOP configuration dominates over that for the IP configuration below a certain spin reorientation temperature. Both IP and OOP anisotropy fields determined from our TS measurement exhibit a minimum around the compensation temperature, which has been explained in the framework of the Stoner-Wohlfarth model.« less