High-entropy enhanced room-temperature ferroelectricity in rare-earth orthoferrites

Single-phase multiferroic materials of rare-earth orthoferrites with magnetism and ferroelectricity are of great technological importance in storage devices.However,the polarization(P)of these materials is generally weak(0.01μC-cm^(-2)),and the ferroelectricity is reported to exist below room temperature(25℃).Here,(Bi_(0.2)La_(0.2)Y_(0.2)Dy_(0.2)Tb_(0.2))FeO_(3)(BLYDTFO)high-entropy oxides that exhibit a saturation P of 5.3μC.cm^(-2)at the electric field(E)of 45 kV·cm^(-1)at room temperature was designed and fabricated by the conventional solid-phase method.The results show that configurational entropy introduces atomic disorder and a larger tilt of BO6 octahedron,which facilitates noncentrosymmetric distortion and ferroelectricity at room temperature compared with other single components(LaFeO_(3),YFeO_(3),DyFeO_(3),and TbFeO_(3)).This high-entropy approach expands the compositional window of the rare-earth orthoferrites to enhance the ferroelectricity in multiferroic applications.

Terahertz spin dynamics in rare-earth orthoferrites

Recent interest in developing fast spintronic devices and laser-controllable magnetic solids has sparked tremendous experimental and theoretical efforts to understand and manipulate ultrafast dynamics in materials.Studies of spin dynamics in the terahertz(THz)frequency range are particularly important for elucidating microscopic pathways toward novel device functionalities.Here,we review THz phenomena related to spin dynamics in rare-earth orthoferrites,a class of materials promising for antiferromagnetic spintronics.We expand this topic into a description of four key elements.(1)We start by describing THz spectroscopy of spin excitations for probing magnetic phase transitions in thermal equilibrium.While acoustic magnons are useful indicators of spin reorientation transitions,electromagnons that arise from dynamic magnetoelectric couplings serve as a signature of inversion-symmetry-breaking phases at low temperatures.(2)We then review the strong laser driving scenario,where the system is excited far from equilibrium and thereby subject to modifications to the free-energy landscape.Microscopic pathways for ultrafast laser manipulation of magnetic order are discussed.(3)Furthermore,we review a variety of protocols to manipulate coherent THz magnons in time and space,which are useful capabilities for antiferromagnetic spintronic applications.(4)Finally,new insights into the connection between dynamic magnetic coupling in condensed matter and the Dicke superradiant phase transition in quantum optics are provided.By presenting a review on an array of THz spin phenomena occurring in a single class of materials,we hope to trigger interdisciplinary efforts that actively seek connections between subfields of spintronics,which will facilitate the invention of new protocols of active spin control and quantum phase engineering.

Sonocatalytic activity of LuFeO_3 crystallites synthesized via a hydrothermal route

LuFeO3 crystallites of different sizes and morphologies were synthesized via a hydrothermal route. The sonocatalytic properties of the as-synthesized samples were investigated by degrading various organic dyes, including acid orange 7 （AOT）, rhodamine B （RhB）, methyl orange （MO）, and methylene blue （MB）, under ultrasonic irradiation, revealing that they exhibit excellent sonocatalytic activity toward the degradation of these dyes. Particularly, the synthesized bar-like particles with lengths of-3 μm and widths of-1μm have the highest sonocatalytic activity, and the degradation percentage of AO7 reaches 89% after 30 min of sonocatalysis. The effects of inorganic anions such as CI-, NO3-, SO42-, PO43-, and HCO3- on the sonocatalysis efficiency were investigated. Hydroxyl radicals （·OH） detected by fiuorimetry using terephthalic acid as a probe molecule were found to be produced over the ultrasonic-irradiated LuFeO3 particles. The addition of ethanol, which acts as a· OH scavenger, leads to quenching of ＂OH radicals and a simultaneous decrease in the dye degrada- tion. This suggests that ＂OH is the dominant active species responsible for the dye degradation.

Magneto-elastic waves in the orthoferrite plates induced by solitary domain wall

Dynamics of domain walls(DWs) was studied in transparent thin orthoferrite samples with weak ferromagnetic ordering at subsonic and supersonic speeds.Direct measurements were made of flexural vibration amplitude in the samples studied,which were induced by a solitary DW with periodic actions of a driving magnetic field.The values of the amplitude reached 7 nm at a resonance.The formation of magnetoelastic solitons was observed and their dynamics was studied at a resonance between an elastic and a spin subsystems.Solitons lag behind the DW at the moment when the DW surpasses the sound barrier and are ahead of it at the subsonic motion.

Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd_(0.5)Pr_(0.5)FeO_(3)single crystal

The single crystals of Nd_(0.5)Pr_(0.5)FeO_(3)were successfully grown by optical floating zone method.Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal.The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure.At high temperatures(T>66 K),it shows the typical characteristics ofΓ_(4)(G_(x),A_(y),F_(z))state.With the decrease of the temperature,it undergoes a first-order spin reorientation transition fromΓ_(4)(G_(x),A_(y),F_(z))toΓ_(2)(F_(x),C_(y),G_(z))state in the temperature window of 45-66 K under an applied magnetic field of 0.01 T.As the temperature drops to~17 K,a new magnetic interaction mechanism works,which results in a further enhancement of magnetization.The T-H phase diagram of Nd_(0.5)Pr_(0.5)FeO_(3)single crystal was finally constructed.

Mechano-Synthesized Orthoferrite Starting from Wüstite Assisted by SPS

Stoichiometric mixtures of FeO and Y2O3 were milled and heat treated to obtain yttrium iron garnet, Y3Fe5O12. Two types of heating systems were used: one, a spark plasma sintering machine and the second, an electrical oven. The magnetic properties of the resulting specimens have been analyzed and discussed as a function of the grain size and the particles’ morphology. The partial formation of garnet and orthoferrite phases was revealed on the obtained powder through microstructural analyses after 9 h of ball milling. The milled powders were transformed into the orthoferrite phase after the SPS-treatment at 700°C and 900°C. Magnetic-saturation studies revealed magnetic responses up to 12.7 emu/g for specimens SPS-treated at 700°C, whereas 2.1 emu/g for samples SPS-treated at 900°C. Conventionally treated specimens at 700°C developed 0.36 emu/g of magnetization, while 0.93 emu/g was registered for those treated at 900°C.

Magnetic phase transition and continuous spin switching in a high-entropy orthoferrite single crystal

Rare-earth orthoferrite REFeO_(3)(where RE is a rare-earth ion)is gaining interest.We created a high-entropy orthoferrite(Tm_(0.2)Nd_(0.2)Dy_(0.2)Y_(0.2)Yb_(0.2))FeO_(3)(HEOR)by doping five RE ions in equimolar ratios and grew the single crystal by optical floating zone method.It strongly tends to form a single-phase structure stabilized by high configurational entropy.In the low-temperature region(11.6‒14.4 K),the spin reorientation transition(SRT)ofΓ_(2)(F_(x),C_(y),G_(z))‒Γ_(24)‒Γ_(4)(G_(x),A_(y),F_(z))occurs.The weak ferromagnetic(FM)moment,which comes from the Fe sublattices distortion,rotates from the a-to c-axis.The two-step dynamic processes(Γ_(2)‒Γ_(24)‒Γ_(4))are identified by AC susceptibility measurements.SRT in HEOR can be tuned in the range of 50‒60000 Oe,which is an order of magnitude larger than that of orthoferrites in the peer system,making it a candidate for high-field spin sensing.Typical spin-switching(SSW)and continuous spin-switching(CSSW)effects occur under low magnetic fields due to the strong interactions between RE‒Fe sublattices.The CSSW effect is tunable between 20‒50 Oe,and hence,HEOR potentially can be applied to spin modulation devices.Furthermore,because of the strong anisotropy of magnetic entropy change()and refrigeration capacity(RC)based on its high configurational entropy,HEOR is expected to provide a novel approach for refrigeration by altering the orientations of the crystallographic axes(anisotropic configurational entropy).

Yttrium-iron garnet and yttrium orthoferrite nanocrystals:Hydrothermal synthesis, magnetic property and phase transformation study

In this work,we present a new and fast method to obtain the single phase YFeO(YIG,cubic) and YFeO(YIP, orthorhombic) nanocrystals based on hydrothermal technique. The influence of initial Y/Fe mole ratio and calcination temperature on the nature, purity, phase structure, and morphology of the product was investigated by X-ray diffraction(XRD), Fourier-transform infrared(FT-IR) spectroscopy,energy-dispersive(EDX) X-ray spectroscopy, and field emission scanning electron microscopy(FESEM).The results show that the transformation of the as-synthesized YIG from amorphous to orthorhombic and finally to cubic phase occurs with the increase of annealing temperature. On this basis, the pure cubic phase YIG can be obtained by calcination(at 1100℃) of the precursor which is prepared using the hydrothermal treatment of mole ratio of Y:Fe = 1:1.5 exposure to an ammonia atmosphere. Also, the initial Y/Fe mole ratio of 1:1 and calcination temperature of 1000 ℃ are the optimal conditions to form single-phase nanocrystalline YIP. Further, vibrating sample magnetometry(VSM) measurements illustrate the average magnetic saturation, coercivity and remanence of 2.73 and 15.00 emu/g, 42.74 and40.02 Oe, and 1.65 and 4.30 emu/g for YIP and YIG nanocrystals, revealing their soft ferromagnetic character.

Preparation and characterization of perovskite REFeO_3 nanocrystalline powders

Combustion of nitrate-citrate gel was employed to prepare REFeO3(RE=Y,La and Gd) nanocrystalline powders.The samples were characterized with X-ray diffraction(XRD) analysis,thermal analysis(TG/DTA) and transmission electron microscopy(TEM).LaFeO3 crystallites were directly obtained by the sol-gel combustion process,and orthorhombic YFeO3 and GdFeO3 were formed when annealed at 800 oC.The investigation of magnetic properties showed that YFeO3 and LaFeO3 exhibited ferromagnetic behavior,while GdFeO3 presented...