The critical properties and the nature of the ferromagnetic-paramagnetic phase transition in the 2D organic-inorganic hybrid (CH₃NH₃)₂CuCl₄ single crystal have been investigated by dc magnetization in the vicinity of the magnetic transition. Different techniques were used to estimate the critical exponents near the ferromagnetic-paramagnetic phase transition such as modified Arrott plots, the Kouvel-Fisher method, and the scaling hypothesis. Values of β=0.22, γ=0.82, and δ=4.4 were obtained. These critical exponents are in line with their corresponding values confirmed through the scaling hypothesis as well as the Widom scaling relation, supporting their reliability. It is concluded that this 2D hybrid compound possesses strong ferromagnetic intra-layer exchange interaction as well as weak interlayer ferromagnetic coupling that causes a crossover from 2D to 3D long-range interaction.

We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic (AFM) material PrPd_0.82Bi₂. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at T_N～7 K. A large Sommerfeld coefficient of 329.23 mJ·mol^-1·K^-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k=(0 0 0) is formed below T_N. The Pr³⁺ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μ_B at 4 K, which is smaller than the effective moment of the free Pr³⁺ ion of 3.58 μ_B. PrPd_0.82Bi₂ can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.

In quasi-one-dimensional (q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic (AFM) compound YbAlO₃, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations, and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave (LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.

Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by post-growth thermal annealing. Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films. Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature . The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals. The results may be useful for room temperature spintronic applications based on group IV semiconductors.

We use quantum Monte Carlo simulations to study an S=1/2 spin model with competing multi-spin interactions. We find a quantum phase transition between a columnar valence-bond solid (cVBS) and a Néel antiferromagnet (AFM), as in the scenario of deconfined quantum-critical points, as well as a transition between the AFM and a staggered valence-bond solid (sVBS). By continuously varying a parameter, the sVBS-AFM and AFM-cVBS boundaries merge into a direct sVBS-cVBS transition. Unlike previous models with putative deconfined AFM-cVBS transitions, e.g., the standard J-Q model, in our extended J-Q model with competing cVBS and sVBS inducing terms the transition can be tuned from continuous to first-order. We find the expected emergent U(1) symmetry of the microscopically Z₄ symmetric cVBS order parameter when the transition is continuous. In contrast, when the transition changes to first-order, the clock-like Z₄ fluctuations are absent and there is no emergent higher symmetry. We argue that the confined spinons in the sVBS phase are fracton-like. We also present results for an SU(3) symmetric model with a similar phase diagram. The new family of models can serve as a useful tool for further investigating open questions related to deconfined quantum criticality and its associated emergent symmetries.

The cubic pyrochlore Dy₂Pt₂O₇ was synthesized under 4 GPa and 1000℃ and its magnetic and thermodynamic properties were characterized by DC and AC magnetic susceptibility and specific heat down to 0.1 K. We found that Dy₂Pt₂O₇ does not form long-range magnetic order, but displays characteristics of canonical spin ice such as Dy₂Ti₂O₇, including (1) a large effective moment 9.64 μ_B close to the theoretical value and a small positive Curie-Weiss temperature θ_CW=+0.77 K signaling a dominant ferromagnetic interaction among the Ising spins; (2) a saturation moment ～4.5 μ_B being half of the total moment due to the local <111> Ising anisotropy; (3) thermally activated spin relaxation behaviors in the low (～1 K) and high (～20 K) temperature regions with different energy barriers and characteristic relaxation time; and most importantly, (4) the presence of a residual entropy close to Pauling's estimation for water ice.

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.

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.

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.

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.

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 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.

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.