Field-cooled Curves Research Articles

Synthesis and characterization of a two-dimensional antiferromagnet KNiB4O6F3 with triangular spin lattice

We prepared a layered antiferromagnet KNiB4O6F31 by hydrothermal synthesis, and characterized its structure and physical properties by X-ray diffraction, magnetization and specific heat measurements as well as thermal stability, FTIR and UV–vis–NIR measurements. 1 consists of layers of composition [NiB4O6F3]- separated by layers of K+ cations. And Ni2+ ions are arranged in slightly distorted triangular pattern in each [NiB4O6F3]- layer. The magnetic susceptibility measurements indicate no divergence between the zero-field-cooled and field-cooled curves down to 7.9 K, below which a long-range order takes place as verified by specific heat measurements. The M(H) curve linearly increases when the field is weak (below ∼2 T), confirming that the ground state of 1 is antiferromagnetic. At 7 T, the magnetization of 1 is 1.67 μB which is lower than the saturation magnetization.

Anomalous magnetic behavior in MnFePSi glass-coated microwires

We studied the MnFePSi glass-coated microwires (GCMWS) prepared by using Taylor–Ulitovsky technique at low magnetic fields and low temperatures. While regular ferromagnetic behavior has been observed at room temperature, anomalous magnetic behavior is observed for the glass-coated microwires samples. Notable metamagnetic phase transition is observed for bulk alloy sample from the magnetic hysteresis loops measured at 5 K. Meanwhile, extraordinary metamagnetic phase transition is seen at hysteresis loops measured at temperature below 100 K. In addition, M-H loops show harder magnetic properties compared to the bulk sample, where the coercivity, Hc, of glass-coated microwire is about 64 times higher than the one reported in bulk alloy. Additionally, the hysteresis loops of glass-coated microwires measured at temperature lower than 100 K show multistep magnetic behaviour. Zero Field Cooling (ZFC), Field Cooling (FC) and Field Heating (FH) curves of bulk samples show totally different magnetic behaviour compared to the microwire sample measured at the same conditions due to the different microstructure phases for the bulk and microwires samples. The present findings demonstrate the significant impact of drawing, quenching and stresses induced by glass-coating on the microstructure and magnetic characteristics of MnFePSi-metallic alloys as compared to their bulk form. Furthermore, we confirmed that, in contrast to the bulk form constraint, the Taylor-Ulitovsky process for metallic glass-coating microwires may alter the physical characteristics and extend the applications of MnFePSi alloys.

Revealing magnetic and physical properties of TbFe4.4Al7.6: experiment and theory

We report on the magnetic, electrical transport, caloric and electronic structure properties of TbFe4.4Al7.6 polycrystalline alloy using experiment and theory. The alloy crystallizes in tetragonal structure with I4/mmm space group with lattice parameters a = b = 8.7234(5) Å and c = 5.0387(6) Å. It is ferrimagnetic with a compensation temperature of Tcmp∼ 151 K, Curie–Weiss temperature θCW∼ 172.11 K and an effective magnetic moment μeff = (2.37±0.07) μB /f.u with Z = 2. At low temperatures, kinetic arrest-like first-order phase transition is realized through the thermal hysteresis between field-cooled cooling and field-cooled warming curves of M(T) and virgin curves of M(H) and ρ(H) which are outside the hysteresis loops with metamagnetic transition. The high magnetic field suppression of multiple transitions and reduced coercive field Hcoer and remnant magnetization Mrem with increasing temperature are reported. Hcoer and Mrem cease to exist above the compensation temperature Tcmp . A correlation between the isothermal magnetization and resistivity is discussed. Specific heat C(T) analysis reveals a Sommerfeld parameter of γ = 0.098 J⋅mol−1⋅K−2 and a Debye temperature of θD∼351.2 K. The sample is metallic as inferred from the ρ(T) behavior and Sommerfeld parameter. The magnetoresistance of the alloy is low and negative which indicates the suppression of weak spin-fluctuations. This alloy avoids the tricritical point despite first-to-second order phase transition. The electronic and magnetic structure calculations, by making use of full potential linearized augmented plane wave method, suggest metallic ferrimagnetic ground state of TbFe4.4Al7.6 with Tb atoms contributing ferromagnetically (5.87 μB ) and Fe atoms with antiferromagnetic contribution (2.67 μB ), in close agreement with the experimental observation.

Exploration of Griffiths phase, spin glass behaviour and memory effect in a frustrated Al2MnCoO7 pyrochlore compound

Al2MnCoO7 pyrochlore compound has been synthesized following the multistep solid-state ceramics route. The compound exhibits a monoclinic structure, which was confirmed through the X-ray diffraction pattern analysis. The magnetization measurements in both zero-field-cooled (ZFC) and field-cooled (FC) modes indicate that the compound undergoes a phase transition from paramagnetic (PM) to antiferromagnetic (AFM) state at the Néel transition temperature TN ∼31 K. Notably, below TN, there is a substantial discrepancy between the ZFC and FC curves, which can be ascribed to the existence of competing ferromagnetic (FM) and AFM interactions, resulting in a glassy behaviour. Additionally, the compound demonstrates a Griffiths phase above TN, signifying the presence of ferromagnetic clusters within the PM region of the material. The spin-glass behaviour is confirmed by the shift of maxima towards higher temperatures with increasing frequency in the ac susceptibility measurement. The memory effect also confirms the spin-glass nature of the compound. The Arrott's plots confirmed that the magnetic phase transition in the material to be a second-order type. Additionally, the material exhibited a maximum magnetic entropy change (−ΔS) value of 1.08 J/kg.K and a relative cooling power of 36.60 J/kg under an applied magnetic field of 5 T.

Study on the structure, Mössbauer and magnetic properties of polycrystalline Mn-doped SmFeO3

SmFe1−xMnxO3 (x = 0.0, 0.1, 0.3) polycrystalline powder samples were prepared by sol-gel method, and the obtained samples were all orthorhombic structures with Pbnm space group. Mössbauer spectroscopy at room temperature confirmed the +3 oxidation state of iron. All samples were fitted by sextet spectra, indicating that the samples are magnetically ordered at room temperature. The zero-field-cooled and field-cooled curves of SmFe0.9Mn0.1O3 sample show a reverse crossover trend at 5 K，and the magnetization is significantly enhanced after reaching the spin-switching transition temperature (Tssw∼285 K). SmFe0.7Mn0.3O3 sample exhibits a second-order spin-reorientation transition in the temperature range of 236–281 K. Rare-earth Sm ions underwent a spin-ordered transition from a paramagnetic state to an antiferromagnetic state at around 8 K. Due to the Dzyaloshinskii-Moriya antisymmetric interaction, the M − H curves of the sample at 5 K and 300 K both exhibit weak ferromagnetism.

Observation of itinerant ferromagnetic behaviour in equiatomic medium entropy AlNiCo alloy

A medium entropy AlNiCo alloy has been synthesized by vacuum arc melting, which shows single phase B2 structure. Atom probe tomography analysis showed that the elements are homogeneously and randomly distributed in AlNiCo alloy without any clustering tendency. A detailed analysis of temperature and field dependent magnetization data suggests an itinerant ferromagnetic ground state of AlNiCo alloy. The magneto crystalline anisotropy is evaluated to be 1.03 × 105 ergs/cm3 at 5 K. A broad maximum at low temperature in zero-field-cooled (ZFC) magnetization, as well as irreversibility of ZFC and field-cooled (FC) curves indicated a glassy behavior. This observation is supported by the memory effects observed at low temperature. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions. To the best of our knowledge, this is the first report on microstructure and magnetic properties of an equiatomic ternary AlNiCo alloy.

Evidence for suppression of collective magnetism in Fe-Ag granular multilayers

Evidence for the suppression of collective magnetic behavior of dipolarly interacting Fe nanoparticles is found in Fe-Ag granular multilayers. Interaction of Fe particles separated by an Ag layer is studied as a function of the nominal thickness of the Ag layer. The surprisingly increasing interaction with increasing Ag-layer thickness, verified by memory-effect measurements, is explained by the formation of pinholes in the Ag layer at small Ag thicknesses, allowing direct ferromagnetic coupling between the Fe particles. This coupling may hinder the frustration of superspins favored by dipolar interactions. At larger Ag thicknesses, the Ag layer is continuous without pinholes and frustration leads to the appearance of the superspin-glass state. The effect of increasing interactions correlates well with the growing deviation at low temperatures of the measured field-cooled (FC) magnetization from the interaction-free FC curve calculated by a model based on the relaxation of two-level systems. Similar phenomenon is reported in a recently published paper (Sánchez et al., Small2022, 18, 2106762) where a dense nanoparticle system is studied. Here the collective magnetic behavior of the particles due to dipolar interactions is suppressed when the anisotropy energy of the individual particles exceeds a certain threshold.

Carbon-Doped Co2MnSi Heusler Alloy Microwires with Improved Thermal Characteristics of Magnetization for Multifunctional Applications.

In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.

Impact of vanadium substitution on structural, magnetic, microwave absorption features and hyperfine interactions of SrCo hexaferrites

The Co-V co-substituted nano Sr-hexaferrite, Sr0.5Co0.5VxFe12−xO19 (0.00 ≤ x ≤ 0.08) (V→SrCo (0.00 ≤ x ≤ 0.08) NHFs), were manufactured by citrate combustion route. The microstructure, morphology, magnetic features, hyperfine interactions and oxidation state and chemical composition of products explained by XRD, SEM with EDX, HR-TEM, VSM, Mossbauer spectrometry, and XPS, respectively. The DXRD (Average crystallite size) of products were assessed via Scherrer formula as within the range of 37 and 83 nm. The hexagonal morphology and chemical composition of the products was presented by TEM, HR-TEM, SEM and EDX analyses. The XPS analysis provided both the composition and oxidation states of prepared NHFs. Mossbauer spectra showed that the s electron density around Fe3+ ions of all sites except 12k influenced V3+ content. The coercivity data indicates that all samples denote a magnetically hard material at both low and high temperatures. Ms, Mr and nB fluctuate with respect to dopant concentration and attain their highest magnitudes for the V→SrCo (x = 0.04) NHFs. A SQR of around 0.5 is achieved at each temperature, reflecting a relatively high large anisotropy field. The field-cooling (FC) curves of all samples yield a drop in magnetization with increasing temperature. Their irreversibility temperature is detected to be beyond 325 K. Both M-H and M-T imply the ferrimagnetic behavior of different samples. Microwave properties were measured between 2 and 18 GHz as S11-S21 parameters. It demonstrated non-linear behavior of the microwave properties vs. V concentration. The origin of the reflection losses in NHVs can be explained by the dipole polarization processes.

Manipulation of the Martensitic Transformation and Exchange Bias Effect in the Ni45Co5Mn37In13 Ferromagnetic Shape Memory Alloy Films

The martensitic phase transition and exchange bias effect of the Ni-Mn-based ferromagnetic shape memory alloys (FSMAs) Ni45Co5Mn37In13 (Ni-Co-Mn-In) films are investigated in this paper. The martensitic transformation properties of the Ni-Co-Mn-In alloy target material are manipulated by the process of electric arc melting, melt-fast quenching, and high-temperature thermal pressure. The Ni-Co-Mn-In alloy films with martensite phase transition characteristics are obtained by adjusting deposition parameters on the (001) MgO substrate, which shows a significant exchange bias (EB) effect at different temperatures. With increasing sputtering power and time, the film thickness increases, resulting in a gradual relaxation of the constraints at the interface between the film and the substrate (the interfacial strain decreases as the increase of thin film thickness), which promotes the martensite phase transition. Between zero-field cooling (ZFC) and field-cooled (FC) curve obvious division zone, the decrease of exchange bias field (HEB) and coercive force field (Hc) with an increase in test temperature is due to ferromagnetic (FM) interaction begins to dominate, resulting in a reduction of antiferromagnetic (AFM) anisotropy at the interface. The maximal HEB and Hc reach ~465.7 Oe and ~306.9 Oe at 5 K, respectively. The manipulation of the martensitic transformation and EB effect of the Ni-Co-Mn-In alloy films demonstrates potential application in the field of information and spintronics.

Effects of Pr3+ ion doping on magnetic features of Ni–Co nanospinel ferrites synthesized via sonochemical approach

The praseodymium ion (Pr3+) substituted Ni0.5Co0.5Fe2O4 nanospinel ferrites, (Co0.5Ni0.5PrxFe2-xO4 (Pr → CoNi) (x ≤ 0.10) NSFs), were synthesized via sonochemical route. XRD confirmed the single cubic structure of all samples with the crystallite size within the range of 9–11 nm.The morphology of (Pr → CoNi) (x ≤ 0.10) NSFs) particles was analyzed by SEM and TEM and showed the spherical shape. Mossbauer study showed that the larger Pr3+ ions prefer the B site. According to the magnetic study, the superparamagnetic character increased with increase of Pr3+ions. The magnetic characteristics are elucidated through both hysteresis curves and temperature (T) dependence of magnetization (M). Magnetization (M) vs external field (H) hysteresis curves were performed at both 300 (RT) and 10 K. It is revealed that Pr → CoNi NSFs exhibit superparamagnetic (SPM) nature performed at RT. Saturation magnetization (Ms), magnetic moment (nB), squareness ratio (SQR), remanence (Mr), and coercivity (Hc) were determined. The Hc of Pr → CoNi (x ≤ 0.10) NSFs was found to be larger than that of the host material. On the other hand, at both temperatures, the magnetization data demonstrates the crucial impact of Pr3+ ions which diminish the Ms, Mr and nB of the host material. The magnetic parameters for Pr → CoNi (x ≤ 0.10) NSFs barely fluctuate and depend on the cation distribution. At 10 K, the SQR of all samples is calculated to be ∼ 0.5 which reflects the uniaxial symmetry and a single-domain structure formation. For Pr → CoNi (x ≤ 0.10) NSFs, much lower SQR values are attained at room temperature (RT), indicating a decrease in the exchange interaction, and suggesting a multi-domain wall structure. For Pr → CoNi (x ≤ 0.10) NSFs, the M values through field-cooling (FC) curves exhibit a slight decrease with increasing T. Their zero field-cooling (ZFC) curves display a nonmonotonic decrease with the decreasing T and result in a low magnetization at low Ts. ZFC and FC curves of Pr → CoNi (x ≤ 0.10) NSFs indicate a large irreversibility.

Single-Molecule Magnets Based on Heteroleptic Terbium(III) Trisphthalocyaninate in Solvent-Free and Solvent-Containing Forms

Binuclear heteroleptic triple-decker terbium(III) phthalocyaninate (Pc)Tb[(15C5)4Pc]Tb(Pc), where Pc2− is phthalocyaninate dianion and 15C5 is a 15-crown-5 moiety, has been synthesized as a solvent-free powder (1) and a well-defined crystal solvate with o-dichlorobenzene (Pc)Tb[(15C5)4Pc]Tb(Pc)⋅6C6H4Cl2 (2). In the crystal structure of 2, the Tb-N(Pc) distances to the nitrogen atoms in the outer and inner decks are 2.350–2.367(4) and 2.583–2.598(4) Å, respectively, and the Tb–Tb distance is 3.4667(3) Å. The twist angle between the outer and the inner decks is 42.6°. The magnetic properties were studied for both 1 and 2. The χMT magnitude of 23.3 emu⋅K/mol at 300 K indicates a contribution of two TbIII centers with the 7F6 ground state. The χMT product increases with decreasing temperature to reach 38.5 emu⋅K/mol at 2 K. This is indicative of ferromagnetic coupling between TbIII spins in accordance with previous data for triple-decker lanthanide phthalocyaninates of a dipolar nature. Both forms show a single-molecule magnet (SMM) behavior manifesting the in-phase (χ′) and out-of-phase (χ″) AC susceptibility signals in an oscillating field of 3 Oe with estimated effective spin-reversal energy barriers (Ueff) of 222(9) and 93(7) cm−1 for 1 and 2, respectively. The compounds show narrow hysteresis loops in the −1 – +1 kOe range, and the splitting between the zero-field-cooling and field-cooling curves is observed below 6 K. Thus, in spite of similar static magnetic characteristics, each form of the Tb(III) complex shows a different dynamic SMM behavior.

Superconductivity and magnetism in a novel La0.85Ga0.15FeAsO compound

We report magnetization measurements on samples of La0.85Ga0.15FeAsO in the wide temperature range of 10 K-400 K, up to the field of 90 kOe having been prepared by solid-state reaction. This novel compound crystallizes with the tetragonal ZrCuSiAs-type structure. The crystal structure was determined by X-ray powder diffraction (P4/nmm: a = 4.032 Å, and c = 8.741 Å).Temperature dependence of magnetization for this compound is measured with zero-field cooling (ZFC) and field cooling (FC) with an application of H = 50 Oe. The large bifurcation between the ZFC and FC curves has been observed starting at around 370 K. At lower temperatures below Tscset−on∼37 K, superconductivity and magnetism coexist. Intermediate temperature range (37 K< T < 300 K), the sample is in a mixed state of the ferromagnetic clusters with paramagnetic moments, described well by the Modified Curie Weiss expression. At higher temperatures above 360 K, it is a pure paramagnetic, described perfectly by the simple Curie-Weiss expression.The natures of the superconducting flux-pinning centers are revealed based on analysis of the pinning force, Fpin at T = 10 K. The normalized pinning force, Fp/Fp, max versus H indicates the filamentary character owing to the pinning parameters, p = 0.5, q = 2. These results point out that, in the superconductivity, the dominance of grain boundary with single-vortex pinning (μ =1/7) mechanismThe Curie temperature, Tcurie was estimated using the modified Arrot plots. The critical exponents, β, ϒ, and δ were estimated, and their values are in close agreement with those predicted for a mean-field-like behavior at a magnetic phase transition.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO 3

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO ₃

Magnetic spin order in the honeycomb structured Pb6Co9(TeO6)5 compound

We present a comprehensive experimental and theoretical study of the structural, electronic, magnetic, and thermodynamic properties of a ${\mathrm{Pb}}_{6}{\mathrm{Co}}_{9}{({\mathrm{TeO}}_{6})}_{5}$ single crystal. The ${\mathrm{Pb}}_{6}{\mathrm{Co}}_{9}{({\mathrm{TeO}}_{6})}_{5}$ crystal has shown a unique type of magnetic spin-lattice coupling, in which the lattice structure consists of four different Co ions sites with distorted octahedral coordinations. The x-ray photoelectron spectroscopy (XPS) results confirmed the oxidation states of Pb, Co, Te, and O elements in the sample. Moreover, XPS spectra revealed the adsorbed oxygen in the defect/vacancy sites of the lattice structure. The dc magnetization measurements exhibited a complex magnetic behavior with ferrimagnetic (FIM) transition with Curie temperature ${T}_{C}$ at $\ensuremath{\sim}21$ K. At lower magnetic fields $H$, the zero-field-cooled and field-cooled curves showed a broad hump at $\ensuremath{\sim}10.8$ K and a shoulder peak at $\ensuremath{\sim}6.2$ K, which are suppressed at higher magnetic fields. The ac susceptibility data indicated spin-glass-like features. The heat capacity ${C}_{P}$ measurements confirmed the FIM transition at ${T}_{C}$ at $\ensuremath{\sim}21$ K, but without any trace of additional peaks at lower temperatures. The estimated Curie-Weiss constant ${\ensuremath{\theta}}_{\mathrm{CW}}$ showed a peculiar field-dependent behavior along the $H\ensuremath{\parallel}c$ direction of the single crystal, where ${\ensuremath{\theta}}_{\mathrm{CW}}$ is less field dependent for the $H\ensuremath{\perp}c$ direction. A large coercivity (13 kOe) is observed at 2 K for $H\ensuremath{\parallel}c$, whereas the magnetization curve of the single crystal is dominated by an antiferromagnetic feature for $H\ensuremath{\perp}c$. The behaviors indicate the anisotropy nature of the exchange interactions in the compound. The local spin density approximation $+ U$ total energy calculations were performed for various collinear spin configurations of a classical Heisenberg model in order to obtain the magnetic exchange interactions ${J}_{i}$ at different distances for different neighbors.

Memory effect in Fe-Ag granular multilayers

Magnetic memory effect was measured in Fe-Ag granular multilayers by employing the so-called stop-and-wait protocol in order to reveal super-spin glass (SSG) behavior and explore the role of intra- and interlayer interactions which can influence the superparamagnetic (SPM) behavior of Fe particles separated by Ag layers. Calculations based on the relaxation of two-level systems are made to obtain the evolution of the magnetization of interaction-free SPM particles as a function of temperature and time for arbitrary annealing procedures, e.g., zero-field-cooled (ZFC) and field-cooled (FC) susceptibility (low-field magnetization) or temperature-cycling measurements. In samples with a single Fe layer of different nominal thicknesses, both the observed memory effect and the low-temperature deviation of the measured FC magnetization from the calculated interaction-free FC curve are attributed to the effect of dipolar interactions. Estimates on the anisotropy energy suggest the importance of the surface anisotropy of the Fe particles in the magnetic behavior.

Thermal relaxation in a disordered one-dimensional array of interacting magnetic nanoparticles

We consider a system of single-domain magnetic nanoparticles placed along a linear chain and address the effect of the distance between them on the magnetic and thermal relaxation properties of the system. The nanoparticles interact with each other through the dipolar interaction and we introduce disorder into the system by allowing random sizes of the nanoparticles and random directions of their uniaxial anisotropy axes. In particular, the radius of the spherical nanoparticles are drawn from a log-normal distribution. The dynamical behavior of the magnetic moments of the system is studied through numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation, taking into account explicit temperature dependence of the saturation magnetization and uniaxial anisotropy energy density to describe the magnetic properties of perovskite manganite oxide nanoparticles. Hysteresis, zero-field-cooled and field-cooled curves are measured, from which we can find the coercive field and the blocking temperature as a function of the magnitude of the dipolar coupling, controlled by the distance between the particles. We show that both the coercive field and blocking temperature decrease as a function of the separation between the nanoparticles. The magnetic relaxation is measured as a function of both temperature and time, from which we estimate the effective energy barrier distribution of the system. We show that the peak of the energy barrier distribution moves to lower energies as the separation between neighboring particles increases, or equivalently, as the dipolar interaction is reduced.

Observation of large exchange bias field in Mn rich NiMnAl Heusler alloy thin film

In the present work exchange bias in Mn rich Ni-Mn-Al film has been studied. The film has been deposited by cosputtering from the targets of Ni, Mn and Al. It exhibits an antiferromagnetic B2 phase at room temperature. At low temperature, magnetization versus temperature (M-T) measurement shows a bifurcation among ZFC and FC curves. Hysteresis (M-H) loops measurements reveal the occurrence of exchange bias phenomenon at low temperature. Large HEB of 2.2 kOe for 20 kOe cooling field has been observed. There occurs a field induced ordering at temperature ~50 K reflected as coinciding ZFC (zero-field cooled) and FC (field-cooled) curves at large magnetic field. AC susceptibility measurement indicates the occurrence of cluster glass behaviour at low temperature. The exchange constant obtained from the best fit to the experimental data was found to be Ji ≈ −2 meV. The negative interface exchange constant indicates AFM coupling occurs among the coexisting phases. Exchange bias phenomenon may be associated to the coexistence of antiferromagnetic and ferromagnetic like ordering at low temperature. Cooling field dependence of HEB and coercive field HC indicate that an increase in anisotropy and growth of ferromagnetic clusters occurs at high magnetic field.

Distinct magnetic ground states of R2ZnIrO6 (R=La,Nd) determined by neutron powder diffraction

Double perovskite iridates $A_2$ZnIrO$_6$ ($A$ = alkaline or lanthanide) show complex magnetic behaviors ranging from weak ferromagnetism to successive antiferromagnetic transitions. Here we report the static ($dc$) and dynamic ($ac$) magnetic susceptibility, and neutron powder diffraction measurements for $A$ = La and Nd compounds to elucidate the magnetic ground state. Below 10~K, the $A$ = La compound is best described as canted iridium moments in an antiferromagnet arrangement with a propagation vector \textbf{k} = 0 and a net ferromagnetic component along the $c$-axis. On the other hand, Nd$_2$ZnIrO$_6$ is described well as an antiferromagnet with a propagation vector \textbf{k} = (1/2~1/2~0) below $T_\mathrm{N} \sim$ 17 K. Scattering from both the Nd and Ir magnetic sublattices were required to describe the data and both were found to lie almost completely within the $ab$-plane. $Dc$ susceptibility revealed a bifurcation between the zero-field-cooled and field-cooled curves below $\sim$13 K in Nd$_2$ZnIrO$_6$. A glassy state was ruled out by $ac$ susceptibility but detailed magnetic isotherms revealed the opening of the loop below 13~K. These results suggest a delicate balance exists between the Dzyaloshinskii-Moriya, crystal field schemes, and $d$-$f$ interaction in this series of compounds.