Antiferromagnetic-ferromagnetic Transition Research Articles

Structural and critical properties of Pr0.5Sr0.5MnO3 nanoparticle

In this work, a sample of Pr0.5Sr0.5MnO3 nanoparticles with an average crystalline size of <D> = 58 ± 2 nm was prepared by a combination of reactive milling method for 6 h at room temperature and heat treatment at the 1100 °C for 0.5 h. The x-ray diffraction analysis revealed the existence of a Pr0.5Sr0.5MnO3 single phase with the tetragonal structure (I4/mcm space group). Temperature and magnetic field dependences of magnetisation measurements indicated a coexistence of two magnetic phase transitions. One is the antiferromagnetic-ferromagnetic transition at T N = 150 K. The other is the second-order ferromagnetic-paramagnetic phase transition at T C = 273.5 K. Using the modified Arrott plots and the Kouvel-Fisher methods, the critical isotherm analysis, and the scaling relation, the magnetic order in Pr0.5Sr0.5MnO3 nanoparticle sample has been pointed out. Accordingly, the critical exponents were found to be β = 0.486, γ = 1.181, and δ = 3.249. These values are quite close to the allowable exponents of the mean field model, suggesting an existence of the long-range ferromagnetic order. A slight deviation from the mean field model has been explained by the formation of the core/shell structure in Pr0.5Sr0.5MnO3 nanoparticle.

First-principles design of ferromagnetic monolayer MnO2 at the complex interface

Rapidly increasing interest in low-dimensional materials is driven by the emerging requirement to develop nanoscale solid-state devices with novel functional properties that are not available in three-dimensional bulk phases. Among the well-known low-dimensional systems, complex transition metal oxide interface holds promise for broad applications in electronic and spintronics devices. Herein, intriguing metal-insulator and ferromagnetic-antiferromagnetic transitions are achieved in monolayer MnO2 that is sandwiched into SrTiO3-based heterointerface systems through interface engineering. By using first-principles calculations, we modeled three types of SrTiO3-based heterointerface systems with different interface terminations and performed a comparative study on the spin-dependent magnetic and electronic properties that are established in the confined MnO2 monolayer. First-principles study predicts that metal-insulator transition and magnetic transition in the monolayer MnO2 are independent on the thickness of capping layers. Moreover, 100% spin-polarized two-dimensional electron gases accompanied by robust room temperature magnetism are uncovered in the monolayer MnO2. Not only is the buried MnO2 monolayer a new interface phase of fundamental physical interest, but it is also a promising candidate material for nanoscale spintronics applications. Our study suggests interface engineering at complex oxide interfaces is an alternative approach to designing high-performance two-dimensional materials.

Electron doping induced stable ferromagnetism in two-dimensional GdI3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM–FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d–4f hybridization. Moreover, the shortened Gd–Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.

Insight into tunable electronic and magnetic properties in 2D ferromagnetic/antiferromagnetic van der Waals heterostructure

Two dimensional (2D) van der Waals (vdW) heterostructures have recently emerged as attractive candidates in spintronic devices. Here, a field-effect spin filter based on the 2D antiferromagnetic (AFM)/ferromagnetic (FM) vdW heterostructure, MnPS3/MnCl3, is proposed. The ground state of the MnPS3/MnCl3 heterostructure is predicted to be a type-I AFM semiconductor with AFM Néel ordering in MnPS3 and MnCl3 monolayers. Interestingly, an AFM–FM transition is found for the MnPS3/MnCl3 heterostructure when reducing the interlayer distance to the range of d &amp;lt; 2.0 Å. Moreover, the MnPS3/MnCl3 heterostructure undergoes semiconductor, metal, and half-metal transitions with the interlayer distance decreasing. Moreover, a semiconductor–half-metal transition can also be observed for MnPS3/MnCl3 by applying an external electric field. Our study offers a potential way to design spintronic devices by 2D layered magnetic vdW heterostructure.

Room temperature giant magnetocaloric effect in Pd doped FeRh and the effect of martensitic transition

FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (Tt) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude.

Influence of high pressure on the remarkable itinerant electron behavior in Y0.7Er0.3Fe2D4.2 compound

A monoclinic Y0.7Er0.3Fe2D4.2 compound exhibits unusual magnetic properties with different field induced magnetic transitions. The deuteride is ferrimagnetic at low temperature, and the Er and Fe sublattices present magnetic transitions at different temperatures. The Er moments are ordered below TEr = 55 K, whereas the Fe moments remain ferromagnetically coupled up to TM0 = 66 K. At TM0, the Fe moments display a sharp ferromagnetic–antiferromagnetic transition (FM–AFM) through itinerant electron metamagnetic behavior very sensitive to any volume change. Y0.7Er0.3Fe2D4.2 becomes paramagnetic above TN = 125 K. The pressure dependence of TEr and TM0 has been extracted from magnetic measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures decrease linearly upon applied pressure with dTEr/dP = −126 and dTM0/dP = −140 K GPa−1 for a field of B = 0.03 T. Both magnetic Er and ferromagnetic Fe orders disappear at P = 0.44(4) GPa. However, under a larger applied field B = 5 T, dTM0/dP = −156 K GPa−1, whereas dTEr/dP = −134 K GPa−1 showing weaker sensitivity to pressure and magnetic field. At 2 K, the decrease of the saturation magnetization under pressure can be attributed to a reduction of the mean Er moment due to canting and/or a crystal field effect. Above TM0, the magnetization curves display metamagnetic behavior from an AFM to FM state, which is also very sensitive to the applied pressure. The transition field Btrans, which increases linearly upon heating, is shifted to a lower temperature upon applied pressure with ΔT = −17 K between 0 and 0.11 GPa. These results show strong decoupling of the Er and Fe magnetic sublattices vs temperature, applied field, and pressure.

Magnetic phase diagram mapping in Fe1−xRhx composition-spread thin films

We have fabricated high-quality polycrystalline Fe1−xRhx composition-spread thin films by cosputtering Fe and Rh, and investigated their structural and magnetic transformations as a systematic function of composition. With increasing Rh concentration, Fe1−xRhx thin film undergoes from an α׳ phase to a disordered γ phase and also shows a magnetic transition from a ferromagnetic phase to a paramagnetic phase. Vibrating-sample magnetometry and x-ray magnetic circular dichroism measurements show an antiferromagnetic-ferromagnetic transition in the range of 0.52 &amp;lt; x &amp;lt; 0.58 in the Fe1−xRhx composition gradient at room temperature. Based on our structural and magnetic property mapping, we construct a thin-film phase diagram of Fe1-xRhx. Compared to reported results in bulk alloys, the antiferromagnetic-ferromagnetic transition in the Fe1−xRhx thin films was found to occur at slightly higher Rh concentrations, while the boundary between the pure γ phase and the α׳/γ mixed phase region is shifted to the lower concentration Rh.

Antiferromagnet-Ferromagnet Transition in Fe1-xCuxNbO4.

Iron niobates, pure and substituted with copper (Fe1-xCuxNbO4 with x = 0-0.15), were prepared by the solid-state method and characterized by X-ray diffraction, Raman spectroscopy, and magnetic measurements. The results of the structural characterizations revealed the high solubility of Cu ions in the structure and better structural stability compared to the pure sample. The analysis of the magnetic properties showed that the antiferromagnetic-ferromagnetic transition was caused by the insertion of Cu2+ ions into the FeNbO4 structure. The pure FeNbO4 structure presented an antiferromagnetic ordering state, with a Néel temperature of approximately 36.81K. The increase in substitution promoted a change in the magnetic ordering, with the state passing to a weak ferromagnetic order with a transition temperature (Tc) higher than the ambient temperature. The origin of the ferromagnetic ordering could be attributed to the increase in super-exchange interactions between Fe/Cu ions in the Cu2+-O-Fe3+ chains and the formation of bound magnetic polarons in the oxygen vacancies.

Effects of magnetic field and hydrostatic pressure on the antiferromagnetic–ferromagnetic transition and magneto-functional properties in Hf1-xTaxFe2 alloys

Effects of magnetic field and hydrostatic pressure on the antiferromagnetic–ferromagnetic transition and magneto-functional properties in Hf1-xTaxFe2 alloys

Magnetic, structural and magnetocaloric properties of Y0.9Gd0.1Fe2Hx hydrides

At 300 K, Y$_{0.9}$Gd$_{0.1}$Fe$_{2}$H$_{x}$ hydrides crystallize sequentially with increasing H concentration in various structures related to a lowering of the cubic MgCu$_{2}$ type structure of the parent alloy: cubic C1, monoclinic M1, cubic C2, monoclinic M2, cubic C3, orthorhombic O. Above 300 K, they undergo a first-order transition at a T$_{O-D}$ temperature driven by order-disorder of hydrogen atoms into interstitial sites. Their magnetic, structural and magnetocaloric properties have been investigated through magnetic measurements, and high-resolution synchrotron diffraction experiments. The magnetization at 5 K decreases slightly from 4 to 3.8 ${\mu}_{B}$ for x = 3 to 3.9 H f.u., then with a larger slope for higher H content. A discontinuous decrease of the magnetic transition temperature is observed: M1 and C2 hydrides are ferrimagnetic with T$_{C}$ near 300 K, M2 hydride displays a sharp ferromagnetic-antiferromagnetic transition at T$_{FM-AFM}$ =144 K, whereas C3 and O hydrides present only a sharp increase of the magnetization below 15 K and a weak magnetization up to RT. Negative magnetic entropy variations (${\Delta}$S$_{M}$) are measured near T$_{C}$ for the M1 and C2 phases, near T$_{FM-AFM}$ for the M2 phase, whereas positive ${\Delta}$S$_{M}$ peaks due to inverse MCE effect are found near T$_{O-D}$. A structural and magnetic phase diagram is proposed.

Magnetism, spin-phonon coupling and Kitaev interaction in Mott insulator La2ZnIrO6 single crystal oxide

Due to the coexistence of spin-orbital coupling (SOC) and electron correlation interactions, double perovskite iridates are considered ideal material to investigate the Mott insulating states and Kitaev interactions. In this work, we studied the spin-orbital coupling (SOC), spin-phonon coupling (SPC), and Kitaev magnetism in antiferromagnetic La2ZnIrO6 single crystal by magnetometer and Raman scattering spectroscopy measurements. Based on the temperature dependence of the magnetization under different magnetic fields, we found that all the initial temperatures of the paramagnetic-ferromagnetic transition were basically concentrated around 8.8 K, while the temperature of ferromagnetic-antiferromagnetic transition continued to decrease from 7 K to 2 K. Anomalous modes of frequency softening at magnetic-order temperature were detected from the polarized Raman scattering spectra, indicating the presence of strong spin-phonon coupling and Kitaev interaction in La2ZnIrO6.

Enhanced Performance of ΔTad upon Frequent Alternating Magnetic Fields in FeRh Alloys by Introducing Second Phases.

The cyclability and frequency dependence of the adiabatic temperature change (ΔTad) under an alternating magnetic field (AMF) are significantly important from the viewpoint of refrigeration application. Our studies demonstrated, by direct measurements, that the cyclability and low-magnetic-field performance of ΔTad in FeRh alloys can be largely enhanced by introducing second phases. The ΔTad under a 1.8 T, 0.13 Hz AMF is reduced by 14%, which is much better than that (40-50%) of monophase FeRh previously reported. More importantly, the introduction of second phases enables the antiferromagnetic-ferromagnetic phase transition to be driven by a lower magnetic field. Thus, ΔTad is significantly enhanced under a 0.62 T, 1 Hz AMF, and its value is 70% larger than that of monophase FeRh previously reported. Although frequency dependence of ΔTad occurs, the specific cooling power largely increases by 11 times from 0.17 to 1.9 W/g, as the frequency increases from 1 to 18.4 Hz under an AMF of 0.62 T. Our analysis of the phase transition dynamics based on magnetic relaxation measurements indicates that the activation energy barrier is lowered owing to the existence of second phases in FeRh alloys, which should be responsible for the reduction of the driving field. This work provides an effective way to enhance the cyclability and low-magnetic-field performance of ΔTad under an AMF in FeRh alloys by introducing second phases.

Photo-induced antiferromagnetic-ferromagnetic and spin-state transition in a double-perovskite cobalt oxide thin film

Investigation of ultrafast dynamic behaviors can provide novel insights about the coupling mechanisms among multiple degrees of freedom in condensed matters, such as lattice, magnetism and electronic structure. Here we investigate both the ferromagnetic (FM) and antiferromagnetic (AFM) dynamics of a strongly correlated oxide system, GdBaCo2O5.5 thin film by time-resolved x-ray magnetic circular dichroism in reflectivity (XMCDR) and resonant magnetic x-ray diffraction (RMXD). A photo-induced AFM-FM transition characterized by an increase of the transient XMCDR (sensitive to FM order) beyond the unpumped value and a decay of RMXD (sensitive to AFM order) was observed. The photon-energy dependence of the transient XMCDR and reflectivity could be interpreted as a concomitant photo-induced spin-state transition (SST). The AFM-FM transition and SST couple with each other in the time domain, resulting in unusual dynamic behaviors of the magnetism.

Anomalous magnetic properties of GdCrTiO5 nanoparticles

In this report, the structural and magnetic properties of GdCrTiO5 nanoparticles were explored, which were synthesized through the sol-gel technique and subsequently calcined (at 800 °C). X-ray diffraction (XRD) studies revealed the orthorhombic crystal structure of synthesized GdCrTiO5 nanoparticles with space group Pbam. The transmission electron microscopy (TEM) images, with selected area electron diffraction (SAED) pattern, showed the particle size as 38.0 ± 0.4 nm and single crystalline nature of the sample. The temperature dependence of dc magnetization, M(T), was measured for GdCrTiO5 nanoparticles, and different magnetic transitions were confirmed, including the spin reorientation (TSR), Néel temperature (TN) and compensation temperatures (Tcomp1 and Tcomp2) in the material. Irreversibility appeared in field-cool-cooling (FCC), and field-cool-warming (FCW) curves at low temperatures, indicating a ferromagnetic-antiferromagnetic (FM-AFM) transition. Earlier, this FM-AFM transition and TSR, Tcomp was not observed in bulk GdCrTiO5. Both the FM nature and exchange bias (EB) effect are further established from the field-dependent magnetization measurements. Furthermore, a change in isothermal magnetic entropy (−ΔSm) of 22 ± 3 J.kg-1.K-1 is found below 10 K, for a 7 T difference in the field. The obtained magnetic properties in this report are discussed in terms of exchange frustration originating from the competing interactions of the magnetic sublattices of the Cr3+ and Gd3+ in the GdCrTiO5 nanoparticles.

Effect of substrate and Fe/Rh stoichiometry on first order antiferromagnetic–ferromagnetic transition in FeRh thin films

The effect of substrate induced strain and Fe/Rh stoichiometry on the antiferromagnetic (AFM)-ferromagnetic (FM) first order transition in sputter deposited FeRh thin films has been studied. Fe1−xRhx films of about 50 nm thickness and with x = 0.45, 0.50, 0.55 were deposited using magnetron sputtering on MgO (001), Al2O3 (0001) (AlO) and quartz (Qtz) substrates. These films were found to be epitaxial under compressive strain on MgO and polycrystalline under tensile strain on AlO. Films with x = 0.50 and 0.55 showed a first order AFM-FM transition near or above 300K. Our study shows that the transition temperature (Tt) is dictated by strain as it was found to vary linearly with out-of-plane strain for films on MgO and AlO. In the case of films on Qtz substrate, an open loop in isothermal magnetoresistance (MR) with a large negative MR was observed at room temperature.

Controlling the Metamagnetic Phase Transition in FeRh/MnRh Superlattices and Thin-Film Fe50-xMnxRh50 Alloys.

Equiatomic and chemically ordered FeRh and MnRh compounds feature a first-order metamagnetic phase transition between antiferromagnetic and ferromagnetic order in the vicinity of room temperature, exhibiting interconnected structural, magnetic, and electronic order parameters. We show that these two alloys can be combined to form hybrid metamagnets in the form of sputter-deposited superlattices and alloys on single-crystalline MgO substrates. Despite being structurally different, the magnetic behavior of the alloys with substantial Mn content resembles that of the FeRh/MnRh superlattices in the ultrathin individual layer limit. For FeRh/MnRh superlattices, dissimilar lattice distortions of the constituent FeRh and MnRh layers at the antiferromagnetic-ferromagnetic transition cause double-step transitions during cooling, while the magnetization during the heating branch shows a smooth, continuous trend. For Fe50-xMnxRh50 alloy films, the substitution of Mn at the Fe sites introduces an effective tensile in-plane strain and magnetic frustration in the highly ordered epitaxial films, largely influencing the phase transition temperature TM (by more than 150 K). In addition, Mn acts as a surfactant, enabling the growth of continuous thin films at higher temperatures. Thus, the introduction of hybrid FeRh-MnRh systems with adjustable parameters provides a pathway for the realization of tunable spintronic devices based on magnetic phase transitions.

Bias-dependent tunneling anisotropic magnetoresistance in antiferromagnetic Pd-doped FeRh-based junctions

We report the bias-dependent tunneling anisotropic magnetoresistance (TAMR) in antiferromagnetic α′-Fe(Rh0.98Pd0.02)/MgO/γ-Fe(Rh0.98Pd0.02) junctions. The TAMR effect is driven by the antiferromagnetic-ferromagnetic phase transition of α′-Fe(Rh0.98Pd0.02) and concomitantly large variation of the density of states (DOS) near the Fermi level. It exhibits polarity reversion behavior with increasing bias voltage, i.e., negative and positive polarities for low and high bias voltages, respectively. Such bias-dependent TAMR is comprehended by first-principle calculations, where a crossing point and subsequent magnitude-reversion emerge between the DOS of antiferromagnetic and ferromagnetic phases of α′-Fe(Rh0.98Pd0.02). Harnessing the tunneling behavior by a feasible bias voltage in an antiferromagnet-based junction is a frontier of great promise in antiferromagnet spintronics.

Electric-field manipulation of the magnetocaloric effect in a Fe49Rh51/PZT composite

By simultaneous measurements in a purpose-built setup, an electric-field manipulation of the magnetocaloric effect and strain in a Fe49Rh51/PZT composite with a sandwich-type connection was demonstrated. Using the strain measurements from two gauges attached to the opposite sides of the composite, as well as finite element modeling (FEM) simulations, it was shown that the deformation in the composite is of a bending type. Mechanical strain induced by the electric field does not exceed ∼500 ppm, which is four times smaller than the expansion of FeRh during the transition ∼2000 ppm. Applying an electric voltage to the PZT favors the transition, but the further expansion of FeRh is hindered and thus blocks the antiferromagnetic-ferromagnetic transition. Obtained experimental results and FEM simulations can be used in the design of new multicaloric composites with optimal ratio between PZT and multicaloric material.

Effects of Charge Transfer on the Critical Distance of the Interlayer Ferromagnetic Order Transition in SCrSe‐Based van der Waals Bilayers

Recently, the distance‐dependent interlayer magnetism transition from antiferromagnetic (AFM) to ferromagnetic (FM) has been predicted in many 2D FM bilayers. Effectively controlling critical distance is a key point for reversible AFM–FM transitions. Based on first‐principles calculations, it is found that the critical distance can be modulated by the charge transfer induced by elemental substitution of anionic sublayers in SCrSe‐based van der Waals (vdW) bilayer structures. The interlayer AFM–FM transition is dependent on the interlayer p z overlap, which is determined by the bonding strength (ΔE b) of the covalent‐like quasibonding (CLQB) from the coupling of interlayer p z orbitals. Large critical distance is achieved when the ΔE b is significant in the bilayers. The interlayer p z overlap is altered by inducing intralayer or interlayer charge transfer, modulating the critical distance of interlayer AFM–FM transition. This work contributes to the control of magnetic configurations in layered 2D FM materials.

Thermal Hysteresis Control in Fe49Rh51 Alloy through Annealing Process

We report the results of studies of the magnetic and transport properties of Fe49Rh51 alloy prepared by different sequences of quenching and the annealing process. The temperature dependences of the relative initial magnetic permeability and resistivity are analyzed. An optimal regime consisting of annealing at 1300 K for 440 min and quenching from 1300 K to 275 K is found to observe the desired narrow antiferromagnetic–ferromagnetic transition in Fe49Rh51 alloy under cyclic conditions. This has the potential to increase the efficiency of cooling devices based on the magnetocaloric effect of magnetic materials with a first-order field-induced phase transition.