Spin Reorientation Transition Temperature Research Articles

Mechanochemically Processed Nd−Fe−Co−Cr−B Nanoparticles with High Coercivity and Reduced Spin Reorientation Transition Temperature

Nd-Fe-B magnets, possessing the highest energy product, are extensively used in cutting-edge applications, including electrical machines and electrical vehicles. An environmentally benign and cost effective synthesis method of Cr alloyed Nd2 (Fe,Co)14 B magnetic nanoparticles using a dry mechanochemical process is reported. The method is solvent free, facile, energy efficient and scalable. The reduction of mixed oxides of Nd, Fe, Co, B and Cr is performed by using Ca. The coercivity (HC ) of the nanoparticles is found to depend on the dispersant content, with the highest value obtained for Nd2 (Fe11.25 Co2 Cr0.75 )B with 40 % CaO dispersant. The HC of isolated Nd2 (Fe11.25 Co2 Cr0.75 )B nanoparticles and nanoparticles embedded in a CaO matrix is found to be 11.5 kOe and 14.4 kOe, respectively, largest values for heavy rare earth free Nd-Fe-B nanoparticles with reasonable saturation and remanent magnetization, regardless of synthesis route. Considering the density of Nd2 Fe14 B, an energy product of 14.2 MGOe is obtained for the nanoparticles. The thermal coefficient of remanence and thermal coefficient of coercivity for aligned samples are -0.06 % and -0.29 %, respectively, in the temperature range between 100 K and 400 K. The spin reorientation temperature is found to be ∼30 K less than that of bulk Nd2 Fe14 B magnets.

Магнитные и магнитодиэлектрические свойства Ho-=SUB=-0.5-=/SUB=-Nd-=SUB=-0.5-=/SUB=-Fe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

AbstractThe magnetic and magnetodielectric properties of Ho_0.5Nd_0.5Fe_3(BO_3)_4 ferroborate with the competing Ho–Fe and Nd–Fe exchange couplings have been experimentally and theoretically investigated. Step anomalies in the magnetization curves at the spin-reorientation transition induced by the magnetic field B ║ c have been found. The spontaneous spin-reorientation transition temperature T _SR ≈ 8 K has been refined. The measured magnetic properties and observed features are interpreted using a single theoretical approach based on the molecular field approximation and calculations within the crystal field model of the rare-earth ion. Interpretation of the experimental data includes determination of the crystal field parameters for Ho^3+ and Nd^3+ ions in Ho_0.5Nd_0.5Fe_3(BO_3)_4 and parameters of the Ho–Fe and Nd–Fe exchange couplings.

Influence of particle size on spin switching properties and magnetoelectric coupling in SmFeO3

Controlling the magnetic properties of a material is of great importance for spintronics and magnetoelastic devices. We studied effect of reduced particle size on structural, dielectric and magnetic properties of SmFeO3 nanoparticles prepared by co-precipitation method (SFO-C) and by combustion (SFO-S). Reduced particle size modified interesting magnetic features of SmFeO3. Temperature dependent magnetic study reveal significant enhancement in magnetization reversal temperature and drop in spin reorientation transition temperature. The signature of spin reorientation transition for SFO-C (~ 300 nm) is marked at ~ 450 K, while this temperature drops down to ~ 400 K for SFO-C (~ 50 nm). The magnetization reversal temperature is achieved at 30.5 K for SFO-C, much higher than 4 K, reported for the single crystal and bulk SmFeO3. The presence significant anomalies in the temperature dependent dielectric behavior of SmFeO3 samples across spin reorientation transition temperature indicate magneto electrical coupling. Strong exchange–bias effect is observed at low temperature for both the samples. The lowering of spin reorientation/switching transition temperature due to reduction in particle size and the signature of magnetoelectric coupling at this temperature are useful for room temperature devices. The observed experimental results establish that the spin switching properties of SmFeO3 can be modified for practical applications in devices.

Observation of magnetization reversal and magnetocaloric effect in manganese modified EuCrO3 orthochromites

We report here an investigation on the structural, magnetic and magnetocaloric properties of Mn doped EuCr0.85Mn0.15O3 (ECMO) chromites synthesized via ceramic route. The compound crystallized into distorted orthorhombic structure with Pnma space group similar to that of its parent EuCrO3 compound, as revealed from the refined of x-ray powder diffraction pattern, but with an increase in the lattice volume. Neel temperature, noticed at 162K from the temperature variation of magnetization, smaller than that reported for pristine EuCrO3; indicated the influence of Mn3+ substitution in decreasing the antiferromagnetic ordering. Magnetization reversal evolved in the studied compound under lower field while such feature was absent in the undoped EuCrO3. Magnetocaloric effect was measured through the magnetic entropy change and relative cooling power. Near the spin reorientation transition temperature ~ 40K, the magnetic entropy change was equal to 3.788Jkg−1K−1 under 90kOe field with 215.22Jkg−1relative cooling power. The results have been understood in terms of the competition between Cr-rich clusters, Mn-rich clusters and local Mn-Cr ordered clusters and their different temperature dependency.

Magnetocaloric effect in Gd1−xNdxZn2

The magnetization of Gd1-xNdxZn2(0<x⩽1) was measured to study the effect of Nd substitution in GdZn2 with a Curie temperature of 85K and a spin-reorientation transition temperature of 58K on the magnetocaloric effect. The Nd counterpart NdZn2 shows antiferromagnetic order at 23K. Samples of Gd1-xNdxZn2 (0<x⩽1) were prepared by the melt-growth method. In Nd-substituted systems, the anomaly due to spin-reorientation disappeared. For x⩾0.6, field-induced metamagnetic transitions were observed, indicating an antiferromagnetic ground state. This complex magnetism may originate from competition between ferromagnetic and antiferromagnetic interactions. Magnetic entropy change ΔSm was calculated based on the magnetization measurements. ΔSm was suppressed by Nd substitution for x values up to 0.6. For x=1 (NdZn2), the maximum value of ΔSm was −9J/K kg, which is almost the same as those of other Nd-based magnetocaloric materials.

Study of Mn doped multiferroic DyFeO3 ceramics

Structural, Raman, room temperature and temperature dependent leakage current density, dielectric, magnetization and room temperature Mossbauer studies of Mn doped DyFeO3 (i.e., DyFe1−xMnxO3; x=0 to 0.5) polycrystalline materials prepared through sol-gel route are reported in this paper. From Rietveld refinement of x-ray diffraction (XRD) patterns it is found that all the samples are formed in single phase without any detectable impurity. The Raman modes with doping are consistent with literature of such doped orthoferrites. From the room temperature (RT) leakage current density (J-E) measurements, it is observed that leakage current density increases with Mn doping concentration, which is explained in terms of microstructure. The leakage current density is found to decrease with the decrease of temperature in each sample as observed from low temperature leakage current density (J-E) measurements. Further, activation energy is calculated from the temperature dependent J-E data. The dielectric loss data is observed to exhibit frequency dependence and the activation energy obtained indicate the contribution from space charges. From temperature dependent magnetization data, it is found that with the increase of Mn content, the spin reorientation (SR) transition temperature (TSR) moves towards higher temperature. From M-H curves at 10K and 300K with different Mn doping concentrations, it is found that saturation Magnetization (MS) decreases with increase of Mn doping. Room temperature Mossbauer data shows the presence of Fe3+ state and the gradual decrease of internal hyperfine filed with increase of Mn content.

Magnetic and hyperfine interactions in HoFe1−xCrxO3 (0≤x≤1) compounds

We report on the magnetic and Mössbauer properties of polycrystalline HoFe1-xCrxO3 (0≤x≤1) compounds. Magnetization data reveals the continuous tailoring of magnetic transition due to weakening of Ho3+-Fe3+ and Fe3+-Fe3+ interactions in the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The observed decrease in Néel temperature (TN) and increase in spin re-orientation transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed to the weakening of Fe(Cr)-O-Fe(Cr) antiferromagnetic exchange interaction. In addition, we also attribute such a change in TN to the enhancement of ferromagnetic interaction of adjacent Cr3+ moments through t-e hybridization as a result of the structural distortion. The decrease in isomer shift (IS) suggests enhancement of the interaction between nuclear charge with the 3s electrons as a result of decrease in radial part of 3d wave function with Cr addition. In this paper we also discuss about the variation of quadrupole splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3 (0≤x≤1) compounds.

Crystal growth of Sm0.3Tb0.7FeO3 and spin reorientation transition in Sm1−xTbxFeO3 orthoferrite

In this work, Sm0.3Tb0.7FeO3 single crystal was successfully grown by optical floating zone method. Sm0.3Tb0.7FeO3 samples with a-, b-, and c-orientation were manufactured by means of Laue photograph. Magnetic properties of Sm0.3Tb0.7FeO3 single crystals are studied over a wide temperature range from 2 to 400K. Spin reorientation transition from Γ2 to Γ4 are observed by means of the temperature dependence of magnetization It indicated the reorientation transition temperature of Sm1−xTbxFeO3 single crystals is lowered with the contents of Tb contents rising based on this work and our previous works, thus the spin reorientation transition temperature can be adjusted through changing the compound in orthoferrites materials, which means that we can get orthoferrites single crystals with high magnetism property in various temperature through material design.

Effect of Mn doping on magnetic and dielectric properties of YFeO3

We report the magnetic and dielectric properties of single phase samples of orthorhombic YFe1−xMnxO3 (x=0.0–0.3). The Néel temperature is found to decrease from 646K for x=0–428K for x=0.3 due to the weakening of superexchange interaction upon Mn3+ substitution. In addition, Mn substitution induces spin re-orientation transition and the spin re-orientation transition temperature is found to increase from 81 K for x=0.1–295K for x=0.3. It is explained in terms of significant magnetic anisotropy introduced by the substituted Mn3+ ions. From the analysis of magnetization data exchange field, Dzyaloshinskii-Moriya field and canting angle were estimated and their temperature dependence in the vicinity of spin re-orientation transition temperature is studied. Study of complex impedance spectrum, dielectric constant and ac electrical conductivity in a wide range of frequency (102–106Hz) across the Néel temperature elucidates the role played by both grains and grain boundaries in shaping the dielectric relaxation. The depressed/asymmetric semicircular shape of Nyquist plots depicts the presence of non-Debye type dielectric relaxation, which is attributed to the short-range movement of oxygen vacancies. The observed increase in dielectric constant and its loss component with increase in Mn concentration is attributed to the leakage current due to hopping of charge carriers between Fe2+ and Fe3+ sites as well as due to the movement of oxygen vacancies. An anomaly in the dielectric constant is observed for all samples in the vicinity of Néel temperature and it is attributed to the disappearance of spin canting induced improper ferroelectric order at the onset of magnetic ordering. The analysis of ac electrical conductivity spectra in terms of Jonscher’s power law suggests that the charge carriers undergo quantum mechanical tunneling between asymmetric double well potential.

Competition of single-ion anisotropy of Sm and Dy ions during the spin-reorientation transition in (Nd1–x–y Sm x Dy y )(FeCo)B supermagnets

It has been found that an increase in the Sm concentration in the range x = 0.05–0.18 in (Nd1‒x‒ySmxDyy)(FeCo)B supermagnets leads to a shift in the spin-reorientation transition temperature to higher values, whereas a Dy addition results in a decrease in the transition temperature. Single-ion anisotropy of Sm and Dy ions has different symmetry, making contributions of opposite signs to the resulting magnetic anisotropy of the lattice. Therefore, the threshold temperature TS of the spin-reorientation transition, which is determined by the balance of magnetic anisotropies of sublattices, can be controlled using ions with different symmetries.

Spin reorientations and crystal field modification in Ho1−y GdyAl2 compounds

We have performed an experimental and theoretical investigation on the spin reorientation transitions Ho1−y GdyAl2 compounds. Crystallographic, magnetic and calorimetric measurements have been performed for five selected samples in the Ho1−y GdyAl2 series (y = 0, 0.25, 0.5, 0.75 and 1.0). From the results, a linear increase in the lattice parameter as a function of Gd-content (y) is observed. Magnetization measurements show that all samples present collinear ferromagnetism. Specific heat measurements were performed in order to detail the first-order spin reorientation transition (FOSRT) that appears for HoAl2 around 20 K. Furthermore, we investigated how the increase in Gd content affects the character of such phase transition. Our results show a slightly modification in the spin reorientation transition temperature, which moves to lower temperatures as Gd is increased in HoAl2, whereas for the selected concentrations up to x = 0.75 the first-order character of the transition is maintained. The theoretical analysis by means of a model Hamiltonian that includes crystal field, exchange and Zeeman interactions reveals a modification in the crystal-field acting on Ho ions as Gd-content is increased.

Dynamics of electron density, spin-phonon coupling, and dielectric properties ofSmFeO3nanoparticles at the spin-reorientation temperature: Role of exchange striction

Samarium orthoferrite $(\mathrm{SmFe}{\mathrm{O}}_{3})$ has been the subject of debate on the existence or nonexistence of ferroelectric properties. It has a high spin-reorientation transition temperature ${T}_{\mathrm{SR}}$ (480 K). Detailed synchrotron x-ray diffraction and Raman spectroscopy dielectric investigations in the 300 to 600 K temperature range of $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles $(\ensuremath{\sim}65\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ have been performed. Raman spectroscopy established the existence of strong spin-phonon coupling and magnetostriction in the system. Magnetic measurements showed a spin-reorientation transition region from 480 to 450 K similar to that of a single crystal. The dielectric constant confirmed a clear anomaly around ${T}_{\mathrm{SR}}$. The signature of unusual relaxor ferroelectric behavior in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles from 380 to 480 K was observed in the dielectric properties. The electron density plots obtained using Rietveld refinement of the synchrotron x-ray diffraction data showed the displacement of the Sm and Fe ions, which can play a key role in the anomalous behavior at ${T}_{\mathrm{SR}}$. The analysis indicated the presence of magnetoelectric coupling due to the exchange interaction between Sm and Fe spins in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles.

High-resolution spectroscopy of HoFe3(BO3)4 crystal: a study of phase transitions

The transmission spectra of HoFe3(BO3) multiferroic single crystals are studied by optical Fourier-transform spectroscopy at temperatures of 1.7–423 K in polarized light in the spectral range 500–10 000 cm–1 with a resolution up to 0.1 cm–1. A new first-order structural phase transition close to the second-order transition is recorded at Tc = 360 K by the appearance of a new phonon mode at 976 cm–1. The reasons for considerable differences in Tc for different samples of holmium ferroborate are discussed. By temperature variations in the spectra of the f–f transitions in the Ho3+ ion, we studied two magnetic phase transitions, namely, magnetic ordering into an easy-plane structure as a second-order phase transition at TN = 39 K and spin reorientation from the ab plane to the c axis as a first-order phase transition at TSR = 4.7 ± 0.2 K. It is shown that erbium impurity in a concentration of 1 at % decreases the spin-reorientation transition temperature to TSR = 4.0 K.

Enhanced spin – Reorientation temperature and origin of magnetocapacitance in HoFeO3

We report on the increase in the spin reorientation temperature in HoFe0.5Cr0.5O3 compound by isovalent substitution (Cr3+) at the Fe-site and the magnetocapacitance in the HoFeO3 compound. Spin reorientation transition is evident around 50K and 150K for the x=0 and x=0.5 compounds respectively. The increase in the spin reorientation transition temperature in case of x=0.5 compound can be attributed to the domination of the Ho3+–Fe3+ interaction over the Fe3+–Fe3+ interaction. Decrease in Néel temperature from 643K (x=0) to 273K (x=0.5) can be ascribed to the decrease in the interaction between antiferromagnetically aligned Fe3+ moments as a result of the dilution of the Fe3+ moments with the Cr3+ addition. From the magnetization M vs. magnetic field H variation it is evident that the coercivity, HC decreases for x=0.5 compound, hinting the magnetic softening of the HoFeO3 compound. Observed magnetocapacitance could be due to lossy dielectric mechanism in the present compound. Indeed, present results would be helpful in understanding the physics behind rare-earth orthoferrites.

Zero-field cooled exchange bias effect in LaxSm1−xCrO3 (x=0–0.9) ceramics

The zero-field cooled exchange bias (ZEB) and conventional field cooled exchange bias (CEB) effects are investigated in single phase bulk SmCrO3 ceramics below the spin reorientation transition temperature. The ZEB field is found to be ~5.065kOe at 20K, revealing a large value compared with other ZEB systems. Nonmagnetic La3+ as a dopant is introduced into the system to confirm the influence of Sm3+ on the ZEB effect. A schematic diagram based on the coupling between the internal magnetic sublattices of Sm3+ and Cr3+ is used to understand the ZEB effect.

Elliptic NdCrO3 microplate by a simple one‐step hydrothermal synthesis route and its characterization and magnetic properties

Elliptic NdCrO3 microplates were synthesized by a simple and facile one‐step hydrothermal method of processing temperature 280 °C for 3 days. The products prepared in this paper have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), X‐ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR) and field‐emission scanning electron microscopy (FESEM). The magnetic properties of the final sample are also studied. The XRD pattern indicates the pure orthorhombic phase for NdCrO3 particles, the XPS, XRF and FTIR results further demonstrate the composition and purity of the final product. A possible growth mechanism for elliptic NdCrO3 microplates is proposed. Through the investigation of magnetic properties, it can be generally concluded that the orthorhombic elliptic NdCrO3 microplates exhibit typical behaviors of magnetic transition, spin reorientation transition and magnetic exchange bias. The Néel temperature is 218 K and the spin reorientation transition temperature is 46 K. The hysteresis loop under 5 K shows that the value of exchange bias field (Hex) is 12 Oe and the shift of remanent magnetization (ΔM) is 0.008 emu/g, respectively.

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr1−xGaxO3 perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO3 and BiCr0.9Ga0.1O3 crystallize in a monoclinic (m) C2/c structure. The Néel temperature (TN) decreases from 111 K in BiCrO3 to 98 K in BiCr0.9Ga0.1O3, and spin-reorientation transition temperature increases from 72 K in BiCrO3 to 83 K in BiCr0.9Ga0.1O3. o-BiCr0.9Ga0.1O3 with a PbZrO3-type orthorhombic structure is obtained by heating m-BiCr0.9Ga0.1O3 up to 573 K in air; it shows similar magnetic properties with those of m-BiCr0.9Ga0.1O3. TN of BiCr0.8Ga0.2O3 is 81 K, and TN of BiCr0.7Ga0.3O3 is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below TN = 56 K in BiCr0.6Ga0.4O3, TN = 36 K in BiCr0.5Ga0.5O3 and TN = 18 K in BiCr0.4Ga0.6O3. BiCr0.3Ga0.7O3 shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.

Spin reorientation transition in dysprosium-samarium orthoferrite single crystals

We report the control of spin reorientation (SR) transition in perovskite $\mathrm{D}{\mathrm{y}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{m}}_{x}\mathrm{Fe}{\mathrm{O}}_{3}$, a whole family of single crystals grown by an optical floating zone method from $x=0$ to 1 with an interval of 0.1. Powder x-ray diffractions and Rietveld refinements indicate that lattice parameters $a$ and $c$ increase linearly with Sm doping concentration, whereas $b$ keeps a constant. Temperature dependence of the magnetizations under zero-field-cooling (ZFC) and field-cooling (FC) processes are studied in detail. We have found a remarkable linear change of SR transition temperature in Sm-rich samples for $x&gt;0.2$, which covers an extremely wide temperature range including room temperature. The $a$-axis magnetization curves under the FC during cooling (FCC) process bifurcate from and then jump back to that of the ZFC and FC warming process in single crystals when $x=0.5\ensuremath{-}0.9$, suggesting complicated $4f\ensuremath{-}3d$ electron interactions among $\mathrm{D}{\mathrm{y}}^{3+}\text{\ensuremath{-}}\mathrm{S}{\mathrm{m}}^{3+},\mathrm{D}{\mathrm{y}}^{3+}\text{\ensuremath{-}}\mathrm{F}{\mathrm{e}}^{3+}$, and $\mathrm{S}{\mathrm{m}}^{3+}\text{\ensuremath{-}}\mathrm{F}{\mathrm{e}}^{3+}$ sublattices of diverse magnetic configurations. The magnetic properties from the doping effect on SR transition temperature in these single crystals might be useful in the material physics and device design applications.

Anomalies in magnetoelastic properties of DyFe11.2Nb0.8 compound

The structural and magnetic properties of DyFe11.2Nb0.8 compound have been investigated by high intensity, high resolution synchrotron x-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements as well as Mössbauer spectroscopy (5–300 K). The easy magnetization direction at room temperature is along the c-axis. With decreasing temperature, the magnetocrystalline anisotropy changes from easy-axis to easy-cone at Tsr2 (∼202 K), then to easy plane at Tsr1 (∼94 K). The thermal expansion coefficient obtained from the synchrotron x-ray study exhibits clear anomalies around both of the spin reorientation transition temperatures. The 57Fe hyperfine interaction parameters and magnetic moments values have been determined for the 8i, 8j, and 8f sites from the Mössbauer spectra.

Anomalous magnetization dynamics near the spin-reorientation transition temperature in ε-In0.24Fe1.76O3 nanowires

It is found that increasing the frequency of an alternating magnetic field leads to an anomalous shift in the temperature maximum of the dynamic magnetic susceptibility in ε-In0.24Fe1.76O3 nanowires in a direction opposite to theoretical predictions for thermally activated processes. This unusual effect can be explained in terms of a redistribution of the contributions to the dynamic magnetic susceptibility from the high- and low-temperature phases, each of which is described by a cluster glass model. The contributions of these phases to the electron spin resonance spectra are identified.