The structural, magnetic properties, and electronic structures of hexagonal FeCoSn compounds with as-annealed bulk and ribbon states were investigated by x-ray powder diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscope (TEM), scanning electron microscope (SEM), magnetic measurements, and first-principles calculations. Results indicate that both states of FeCoSn show an Ni₂In-type hexagonal structure with a small amount of FeCo-rich secondary phase. The Curie temperatures are located at 257 K and 229 K, respectively. The corresponding magnetizations are 2.57 μ_B/f.u. and 2.94 μ_B/f.u. at 5 K with a field of 50 kOe (1 Oe=79.5775 A·m^-1). The orbital hybridizations between 3d elements are analyzed from the distribution of density of states (DOS), showing that Fe atoms carry the main magnetic moments and determine the electronic structure around Fermi level. A peak of DOS at Fermi level accounts for the presence of the FeCo-rich secondary phase. The Ni₂In-type hexagonal FeCoSn compound can be used during the isostructural alloying for tuning phase transitions.

Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi₂Se₃ thin film on a single-crystalline LaCoO₃ thin film on SrTiO₃ substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi₂Se₃ films with highest quality on LaCoO₃ favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi₂Se₃/LaCoO₃ heterostructures, which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.

We present a study of magnetocaloric effect of the quasi-two-dimensional (2D) ferromagnet (CH₃NH₃)₂CuCl₄ in ab plane (easy-plane). From the measurements of magnetic field dependence of magnetization at various temperatures, we have discovered a large magnetic entropy change associated with the ferromagnetic-paramagnetic transition. The heat capacity measurements reveal an abnormal adiabatic change below the Curie temperature T_c~8.9 K, which is caused by the nature of quasi-2D layered crystal structure. These results suggest that perovskite organic-inorganic hybrids with a layered structure are suitable candidates as working substances in magnetic refrigeration technology.

The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents (σ_sc), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe₂₀Ni₈₀ (Py) than that of Ni is obtained from the nonlocal voltage measurements.

The multiferroicity in the RMn₂O₅ family remains unclear, and less attention has been paid to its dependence on high-temperature (high-T) polarized configuration. Moreover, no consensus on the high-T space group symmetry has been reached so far. In view of this consideration, one may argue that the multiferroicity of RMn₂O₅ in the low-T range depends on the poling sequence starting far above the multiferroic ordering temperature. In this work, we investigate in detail the variation of magnetically induced electric polarization in GdMn₂O₅ and its dependence on electric field poling routine in the high-T range. It is revealed that the multiferroicity does exhibit qualitatively different behaviors if the high-T poling routine changes, indicating the close correlation with the possible high-T polarized state. These emergent phenomena may be qualitatively explained by the co-existence of two low-T polarization components, a scenario that was proposed earlier. One is the component associated with the Mn³⁺-Mn⁴⁺-Mn³⁺ exchange striction that seems to be tightly clamped by the high-T polarized state, and the other is the component associated with the Gd³⁺-Mn⁴⁺-Gd³⁺ exchange striction that is free of the clamping. The present findings may offer a different scheme for the electric control of the multiferroicity in RMn₂O₅.

We report a strong antiferromagnetic (AFM) interlayer coupling in ferromagnetic La_0.67Sr_0.33MnO₃/SrRuO₃ (LSMO/SRO) superlattices grown on (111)-oriented SrTiO₃ substrate. Unlike the (001) superlattices for which the spin alignment between LSMO and SRO is antiparallel in the in-plane direction and parallel in the out-of-plane direction, the antiparallel alignment is observed along both the in-plane and out-of-plane directions in the present sample. The low temperature hysteresis loop demonstrates two-step magnetic processes, indicating the coexistence of magnetically soft and hard components. Moreover, an inverted hysteresis loop was observed. Exchange bias tuned by the temperature and cooling field was also investigated, and positive as well as negative exchange bias was observed at the same temperature with the variation of the cooling field. A very large exchange field (H_EB) was observed and both magnitude and sign of the H_EB depend on the cooling field, which can be attributed to an interplay of Zeeman energy and AFM coupling energy at the interfaces. The present work shows the great potential of tuning a spin texture through interfacial engineering for the complex oxides whose spin state is jointly determined by strongly competing mechanisms.

Single-grain models with different cerium contents or structural parameters have been introduced to investigate the reversal magnetization behaviors in cerium-containing magnets. All the micromagnetic simulations are carried out via the object oriented micromagnetic framework (OOMMF). As for single (Nd,Ce)₂Fe₁₄B type grain, the coercivity decreases monotonously with the increase of the cerium content. Four types of grain structure have been compared:single (Nd,Ce)₂Fe₁₄B type, core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type with 2 nm thick shell, core (Ce₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type, and core (Nd₂Fe₁₄B)-shell (Ce₂Fe₁₄B) type. It is found that core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type grain with 2 nm thick shell always presents the largest coercivity under the same total cerium content. Furthermore, the relationship between the coercivity and the shell thickness t in core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type grain has been studied. When the total cerium content is kept at 20.51 at.%, the analyzed results show that as t varies from 1 nm to 7 nm, the coercivity gradually ascends at the beginning, then quickly descends after reaching the maximum value when t=5 nm. From the perspective of the positions of nucleation points, the reasons why t affects the coercivity are discussed in detail.

We report a comprehensive Raman scattering study on layered MPS₃ (M=Mn, Fe, Ni), a two-dimensional magnetic compound with weak van der Waals interlayer coupling. The observed Raman phonon modes have been well assigned by the combination of first-principles calculations and the polarization-resolved spectra. Careful symmetry analysis on the angle-dependent spectra demonstrates that the crystal symmetry is strictly described by C_2h but can be simplified to D_3d with good accuracy. Interestingly, the three compounds share exactly the same lattice structure but show distinct magnetic structures. This provides us with a unique opportunity to study the effect of different magnetic orders on lattice dynamics in MPS₃. Our results reveal that the in-plane Néel antiferromagnetic (AF) order in MnPS₃ favors a spin-phonon coupling compared to the in-plane zig-zag AF in NiPS₃ and FePS₃. We have discussed the mechanism in terms of the folding of magnetic Brillouin zones. Our results provide insights into the relation between lattice dynamics and magnetism in the layered MPX₃ (M=transition metal, X=S, Se) family and shed light on the magnetism of monolayer MPX₃ materials.

Chemical pressure induced by iso-valent doping has been widely employed to tune physical properties of materials. In this work, we report effects of chemical pressure by substitution of Sb or P into As on a recently discovered diluted magnetic semiconductor (Ba,K)(Zn,Mn)₂As₂, which has the record of reliable Curie temperature of 230 K due to independent charge and spin doping. Sb and P are substituted into As-site to produce negative and positive chemical pressures, respectively. X-ray diffraction results demonstrate the successful chemical solution of dopants. Magnetic properties of both K-under-doped and K-optimal-doped samples are effectively tuned by Sb- and P-doping. The Hall effect measurements do not show decrease in carrier concentrations upon Sb- and P-doping. Impressively, magnetoresistance is significantly improved from 7% to 27% by only 10% P-doping, successfully extending potential application of (Ba,K)(Zn,Mn)₂As₂.

The magnetic properties of inverse ferrite (Fe³⁺) [Fe³⁺Co²⁺]O₄^2-,(Fe³⁺) [Fe³⁺Cu²⁺]O₄^2-,(Fe³⁺) [Fe³⁺Fe²⁺]O₄^2-, and (Fe³⁺) [Fe³⁺Ni²⁺]O₄^2- spinels have been studied using Monte Carlo simulation. We have also calculated the critical and Curie Weiss temperatures from the thermal magnetizations and inverse of magnetic susceptibilities for each system. Magnetic hysteresis cycles have been found for the four systems. Finally, we found the critical exponents associated with magnetization, magnetic susceptibility, and external magnetic field. Our results of critical and Curie Weiss temperatures are similar to those obtained by experiment results. The critical exponents are similar to those of known 3D-Ising model.

The magnetization-direction-dependent inverse spin Hall effect (ISHE) has been observed in NiFe film during spin Seebeck measurement in IrMn/NiFe/Cu/yttrium iron garnet (YIG) multilayer structure, where the YIG and NiFe layers act as the spin injector and spin current detector, respectively. By using the NiFe/IrMn exchange bias structure, the magnetization direction of YIG (M_YIG) can be rotated with respect to that of NiFe (M_NiFe) with a small magnetic field, thus allowing us to observe the magnetization-direction-dependent inverse spin Hall effect voltage in NiFe layer. Compared with the situation that polarization direction of spin current (σ_s) is perpendicular to M_NiFe, the spin Seebeck voltage is about 30% larger than that when σ_s and M_NiFe are parallel to each other. This phenomenon may originate from either or both of stronger interface or bulk scattering to spin current when σ_s and M_NiFe are perpendicular to each other. Our work provides a way to control the voltage induced by ISHE in ferromagnets.

We present an overview in the understanding of spin-transfer torque (STT) induced magnetization dynamics in spin-torque nano-oscillator (STNO) devices. The STNO contains an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized spin polarizing layer. After a brief introduction, we first use mesoscopic micromagnetic simulations, which are based on the Landau-Lifshitz-Gilbert equation including the STT effect, to specify how a spin-torque term may tune the magnetization precession orbits of the free layer, showing that the oscillator frequency is proportional to the current density and the z-component of the free layer magnetization. Next, we propose a pendulum-like model within the macrospin approximation to describe the dynamic properties in such type of STNOs. After that, we further show the procession dynamics of the STNOs excited by IP and OP dual spin-polarizers. Both the numerical simulations and analytical theory indicate that the precession frequency is linearly proportional to the spin-torque of the OP polarizer only and is irrelevant to the spin-torque of the IP polarizer. Finally, a promising approach of coordinate transformation from the laboratory frame to the rotation frame is introduced, by which the nonstationary OP magnetization precession process is therefore transformed into the stationary process in the rotation frame. Through this method, a promising digital frequency shift-key modulation technique is presented, in which the magnetization precession can be well controlled at a given orbit as well as its precession frequency can be tuned with the co-action of spin polarized current and magnetic field (or electric field) pulses.

The crystallographic and magnetic properties are presented for van der Waals antiferromagnetic FePS₃. High-quality single crystals of millimeter size have been successfully synthesized through the chemical vapor transport method. The layered structure and cleavability of the compound are apparent, which are beneficial for a potential exploration of the interesting low dimensional magnetism, as well as for incorporation of FePS₃ into van der Waals heterostructures. For the sake of completeness, we have measured both direct current (dc) and alternating current (ac) magnetic susceptibility. The paramagnetic to antiferromagnetic transition occurs at approximately T_N~115 K. The effective moment is larger than the spin-only effective moment, suggesting that an orbital contribution to the total angular momentum of the Fe²⁺ could be present. The ac susceptibility is independent of frequency, which means that the spin freezing effect is excluded. Strong anisotropy of out-of-plane and in-plane susceptibility has been shown, demonstrating the Ising-type magnetic order in FePS₃ system.

We investigate the critical exponents and magnetocaloric effect of Co_2-xZrSn polycrystal. The Co_2-xZrSn undergoes a second-order ferromagnetism phase transition around the Curie temperature of T_c~280 K. The critical behavior in the vicinity of the magnetic phase transition has been investigated by using modified Arrott plot and Kouvel-Fisher methods. The obtained critical exponents, β, γ, and δ can be well described by the scaling theory. The determined exponents of Co_2-xZrSn obey the mean-field model with a long-range magnetic interaction. In addition, the maximum magnetic entropy change -ΔS_M^max of Co_2-xZrSn is about 0.57 J·kg^-1·K^-1 and the relative cooling power (RCP) is 14.68 J·kg^-1 at 50 kOe (1 Oe=79.5775 A·m^-1).

A single-phase iron oxide Ba_0.8Sr_0.2FeO_3-δ with a simple cubic perovskite structure in Pm-3m symmetry is successfully synthesized by a solid-state reaction method in O₂ flow. The oxygen content is determined to be about 2.81, indicating the formation of mixed Fe³⁺ and Fe⁴⁺ charge states with a disorder fashion. As a result, the compound shows small-polaron conductivity behavior, as well as spin glassy features arising from the competition between the ferromagnetic interaction and the antiferromagnetic interaction. Moreover, the competing interactions also give rise to a remarkable exchange bias effect in Ba_0.8Sr_0.2FeO_2.81, providing an opportunity to use it in spin devices.

CrI₃ in two-dimensional (2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale. The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides. Here we studied the CrI₃ nanoribbon (NR) and nanotube (NT) systematically to seek the possible size and edge control of the electronic and magnetic properties. We find that ferromagnetic ordering is stable in all the NR and NT structures of interest. An enhancement of the Curie temperature T_C can be expected when the structure goes to NR or NT from its 2D counterpart. The energy difference between the FM and AFM states can be even improved by up to 3-4 times in a zigzag nanoribbon (ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at E_F. In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.

Electrical spin, which is the key element of spintronics, has been regarded as a powerful substitute for the electrical charge in the next generation of information technology, in which spin plays the role of the carrier of information and/or energy in a similar way to the electrical charge in electronics. Spin-transport phenomena in different materials are central topics of spintronics. Unlike electrical charge, spin transport does not depend on electron motion, particularly spin can be transported in insulators without accompanying Joule heating. Therefore, insulators are considered to be ideal materials for spin conductors, in which magnetic insulators are the most compelling systems. Recently, we experimentally studied and theoretically discussed spin transport in various antiferromagnetic systems and identified spin susceptibility and the Néel vector as the most important factors for spin transport in antiferromagnetic systems. Herein, we summarize our experimental results, physical nature, and puzzles unknown. Further challenges and potential applications are also discussed.

We reported a study of tunnel magnetoresistance (TMR) effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging. TMR value up to 290% has been observed in single (La_1-yPr_y)_1-xCa_xMnO₃ nanowires with varying width. We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions. Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.

We present the experiment observation of a giant topological Hall effect (THE) in a frustrated kagome bilayer magnet Fe₃Sn₂. The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K. Its maximum absolute value reaches ~2.01 μΩ·cm at 300 K and 0.76 T. The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration, possibly related to the magnetic frustration interaction in Fe₃Sn₂.

We report the detailed physical properties of quaternary compound Ba₂BiFeS₅ with the key structural ingredient of isolated FeS₄ tetrahedra. Magnetization and heat capacity measurements clearly indicate that Ba₂BiFeS₅ has a paramagnetic to antiferromagnetic transition at about 30 K. The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe³⁺ ion with S=5/2, implying the possible short-range antiferromagnetic fluctuation in Ba₂BiFeS₅.