Spin Reorientation Transition Temperature Research Articles

Spin reorientation, spin switching, and magnetic compensation in Er1−xSmxFeO3 single crystals

We investigated spin reorientation, magnetic compensation and spin switching transitions in a series of high-quality single crystals of Er1−xSmxFeO3 (x = 0, 0.2, 0.4, 0.6, 0.8) prepared using the optical floating zone method. Structural and other preliminary characterizations confirmed the quality and phase purity of the crystals. Rietveld refinement of powder XRD data indicates that lattice parameters a and c increase linearly with increasing Sm concentration, whereas b remained constant. Field-cooled cooling (FCC) measurements revealed a temperature-induced spin reorientation transition (SRT) from Γ4 (Gx, Ay, Fz) to Γ2 (Fx, Cy, Gz) for all the samples. SRT temperature increased with Sm concentration and spread widely above and below room temperature. Moreover, magnetic compensation is common to all the compositions but decreases as Sm doping increases. We also observe type-I spin switching in samples with x = 0, 0.2, and 0.4 at an applied field of 60 Oe under FCC protocol, with a reduction in spin switching temperature as Sm content increased. For Sm-rich samples (x = 0.6, 0.8), spin switching was absent at 60 Oe.

Room-temperature spin reorientation transition and low-temperature significant magnetothermal effect in Mn-doped DyFeO3 single crystals

Rare-earth orthoferrites (RFeO3) promise in spin storage and spin sensing, but the majority of the magnetic phase transition and intriguing properties occur at low temperatures. Searching for higher-temperature or even room-temperature spintronics devices has been a critical challenge in the development of spintronics. We doped Mn ions into Fe sites of DyFeO3 in 10%–50 % ratios to coexist antiferromagnetic and ferromagnetic coupling in the ab plane and elevate their spin reorientation transition (SRT) temperatures. The structural, magnetic, and magnetothermal properties of the Mn-doped DyFeO3 single-crystal system are investigated. With increasing doping ratio, the Néel temperature progressively falls, while the SRT temperature (TSR) continuously rises to the room temperature of 307 K with a 40 % doping ratio, making it promising for room-temperature spin storage devices. When the ratio reaches 50 % (half doping), the magnetic configuration of Dy sublattices changes and a significant magnetothermal effect is observed. Because of low-field metamagnetic phase transition, the magnetic entropy change along the c-axis approaches 10.41 J/kg·K for the half doping crystal at 5 K (0 J/kg·K for DyFeO3, 0.93 J/kg·K for orthorhombic DyMnO3). The large adiabatic temperature change contributed by magnon indicates the exceptional refrigeration efficiency in a direct way. Therefore, it is possible to convert DyFeO3 into a room-temperature spin storage device material or a magnetic refrigeration contender at low temperatures.

Crystal structure, magnetic and Mössbauer studies of DyFexMn1-xO3 multiferroic manganites

The influence of iron replacement on the structural and magnetic properties of Dysprosium manganites was studied using the series of DyFexMn1-xO3 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) compounds. All samples were fabricated by means of the modified auto-combustion sol-gel method, followed by the ball milling technique. Orthorhombic structure (Pnma space group) with high phase purity and crystallinity featured all samples, according to X-ray diffraction analysis. The temperature dependence of magnetization curves indicated antiferromagnetic (AFM) to paramagnetic (PM) transition with the increase in temperature. The Néel temperature (TN) was observed to shift to higher temperatures, whereas the spin reorientation transition temperature (TSR) reduced as Fe3+ content increased. Cusps in the zero-field-cooled (ZFC) curves were detected at low temperatures (around 4 K) as an indication of the ordering of the Dy spin. 57Fe Mӧssbauer spectra in samples with low iron content were dominated by a high spin (Fe3+) paramagnetic doublet at both 295 K and 78 K, while the distribution in the hyperfine magnetic field accounted for the appearance of the broadening magnetic peaks. High iron samples revealed a magnetic sextet with fit-resolved patterns that indicated a strong AFM coupling of Fe3+ ions. The hyperfine magnetic field (Bhf) magnitude demonstrated a linear increase with the increase in iron doping.

Exploration of low field magnetic states in NdCe x CrO3

We report the structural and magnetic properties of NdCe x CrO3 () single-phase samples to classify the influence of Ce substitution on the Nd-site. The electron density profile indicates the possible covalent nature of Cr–O bonds. The x-ray photoelectron spectroscopy confirms a mixed Ce valency with a constant ratio of Ce3+/Ce4+ ions in all substituted compounds and the charge neutralization through the oxygen vacancies. The magnetization measurements reveal an increase in antiferromagnetic ordering temperature () and spin-reorientation transition temperature () and unfold soft spin-reorientation attributed to diluted superexchange interactions upon Ce incorporation. The presence of mixed Ce ions induces the merging of the hysteresis loop with a significant exchange bias (EB) field. We demonstrate for the first time that the magnitude of the magnetization is different for the same applied field in positive and negative directions, indicating the existence of two different magnetic states. The difference between these two magnetic states possibly arises from the pinning of Cr3+ spins, which requires an additional Zeeman energy for it to rotate. This maximum Zeeman energy from the normalized magnetic susceptibility vs. temperature curves correlates with the maximum EB field, validating unusual EB in these compounds.

Analysis of negative magnetization and dielectric studies in holmium substituted samarium iron garnet

We have used solid-state reaction approach for the preparation of polycrystalline samples of (Sm1-xHox)3Fe5O12(x=0.0 to 1.0) and the phase formation is verified by the refinement of X-ray diffraction patterns using Ia3‾d space group. The lattice constant is found to be decreased while the average grain size increases with Ho doping. The transition temperature (TC) for ferrimagnetic to paramagnetic state decreases from 561 K to 541 K for x=0.0 to x=1.0. Also, M−T plots demonstrate that every sample exhibit spin reorientation transition and with Ho doping the spin reorientation transition temperature (TSR) is reducing from 65K(x=0.0) to 20K(x=1.0). Interestingly, negative magnetization is observed for x=0.4 sample and is confirmed by applying different magnetic fields. Moreover, magnetic compensation is also observed in samples with x≥0.4. The Nyquist plots extracted from complex impedance spectra show the deviation from the ideal Debye type relaxation. It is observed that the dielectric constant has increased from 104 to 106 in the lower frequency zone with x varying from 0.0 to 1.0 making them a promising material for microwave applications.

Spin switching in room temperature spin reorientation transition process of Sm0.8Yb0.2FeO3 single crystal

We report that the introduction of a certain proportion of Yb ions into SmFeO3 single crystal can modulate the reduction of the spin reorientation (SR) transition temperature down to the room temperature region. Simultaneously, it maintains the spin configuration change between Γ2 (Cy, Gz, Fx) and Γ4 (Gx, Ay, Fz) and raises the magnetization compensation temperature of the single crystal. Both Zero-Field-Cooling (ZFC) and Field-Cooled-Cooling (FCC) modes along the a-axis are present with two type-I spin switching effects, which can be effectively regulated by the applied magnetic field. Interestingly, the type-II spin switching effect is observable along the c-axis in the ZFC mode under lower magnetic fields during the SR transition process at room temperature, an interesting magnetization phenomenon that is suppressed when the magnetic field is greater than 38 Oe. This type of spin switching effect arises from a partial flip of the moments of Sm3+. Additionally, the sharp spin switching induced by the magnetic field is also observed along the a- and c-axes with the variation of the magnetization with the applied magnetic field (M-H). This work is valuable for providing an insight into the magnetic coupling and competition between the two sublattices in the RFeO3 system and for facilitating the practical application of relevant spin switching materials.

Topological Hall effect associated with spin reorientation transition in tetragonal Mn1.9Co0.1Sb ferrimagnet

Ferrimagnetic Mn2Sb-based compounds with the tetragonal structure have been of interest due to multiple magneto-functional properties. But very few investigations about the topological transport properties have been reported in these alloys yet, especially those around the spin reorientation transition (SRT). In this work, a large topological Hall resistivity up to 0.42 μΩ cm is observed at 260 K, ~24 K higher than SRT temperature TSR, in tetragonal Mn1.9Co0.1Sb alloy. What’s more, large topological Hall effect occurs in a relatively wide temperature interval of 100 K from 220 to 320 K, which would mainly originate from the formation of noncoplanar magnetic structure due to magnetic domain rotation when the magnetic moment located at Mn sites rotates from the direction paralleling to c axis to (a, b) plane around the SRT with reducing temperature. The microstructure observation bears this out. The present study implies that Mn2Sb-based alloys should be the promising candidates for technological applications in spintronic devices.

Nanoscale magnetic bubbles in Nd2Fe14B at room temperature

The increasing demand for computer data storage with a higher recording density can be addressed by using smaller magnetic objects, such as bubble domains. Small bubbles predominantly require a strong saturation magnetization combined with a large magnetocrystalline anisotropy to resist self-demagnetization. These conditions are well satisfied for highly anisotropic materials. Here, we study the domain structure of thin ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ lamellae. Magnetic bubbles with a minimum diameter of 74 nm were observed at room temperature, approaching even the range of magnetic skyrmions. The stripe domain width and the bubble size are both thickness dependent. Furthermore, a kind of bubble was observed below the spin-reorientation transition temperature that combine bubbles with opposite helicity. In this paper, we reveal ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ to be a good candidate for a high-density magnetic bubble-based memory.

Role of magnetocrystalline anisotropy on anisotropic magnetocaloric effect in single crystals

The role of magnetocrystalline anisotropy in single crystals played on the anisotropic magnetocaloric effect is studied based on Monte Carlo simulation. By taking into account the anisotropy, the spin reorientation transition (SRT) temperature (TSRT) may be higher than the Curie temperature and enhanced with larger anisotropy, and the magnetization behaviors at low temperatures below TSRT and under weak fields are highly sensitive to the anisotropy. The anisotropy of entropy change is the most significant when the magnetic field is parallel to the easy axis, while the maximum entropy change may increase or decrease with the anisotropy constant in a given direction depending on the magnetic field strength. Power-law fits have been conducted on the field dependence of the maximum entropy change and relative cooling power, which not only indicate a characteristic of the second-order phase transition but also demonstrate effect of anisotropy on magnetic order and dynamics during the SRT to contribute to the anisotropic magnetocaloric effect.

Structural, electronic and magnetocaloric properties of antiskyrmion hosting Heusler compounds: Mn2PtSn and Mn1.4PtSn

In this work, we have studied the structure, electronic and magnetic properties of Mn2PtSn and Mn1.4PtSn by using the ab initio calculations and Monte Carlo study. The ab initio calculations, based on the functional theory of density combined with the method of linear augmented plane waves at potential, are performed to investigate both electronic and magnetic properties of the two compounds. The total and partial densities of two systems have been calculated. Mn1.4PtSn, the first known Heusler tetragonal (Mn vacancy-induced) superstructure compound, opens a new direction of research for superstructure-related properties in a family containing multiple compounds. We have deduced the total magnetic moment of the two systems. We observe an anisotropic fractal magnetic pattern of zero-field closing domains above the spin-reorientation transition temperature, which transforms into a set of high-field bubble domains. Below the spin-reorientation transition temperature, the strong in-plane anisotropy as well as the zero-field fractal self-affinity is gradually lost, while the formation of high-field bubble domains remains robust. The magnetization, specific heat and magnetic entropy change have been obtained by using the Monte Carlo simulations. The relative cooling power has been obtained for different values of external magnetic field and temperatures.

Altering magnetic and optical features of rare earth orthoferrite LuFeO3 ceramics via substitution of Ir into Fe sites

LuFeO3 and LuFe1-xIrxO3 ceramics with x ​= ​0.05 and 0.10 have been obtained by solid-state reaction process. Scanning electron microscope (SEM) analyses have revealed the existence of both particle agglomeration and porosity of nature of the studied samples. The X-ray photoelectron spectroscopy (XPS) investigations have revealed that while Lu has 3+, Fe has mix valence states, 2+ and 3+. On the other hand, the Ir dopant has metallic and 4+ valence states in the study samples. The Raman investigations unveiled i) the Raman peak intensity reduces with Ir doping until ∼600 ​cm−1, ii) the peaks appearing between 200 ​cm−1 and 600 ​cm−1 wavenumbers shift toward the smaller values. Magnetic measurements, conducted by vibrating sample magnetometer (VSM), have shown the spin re-orientation (SR) transition temperature around 47 ​K for all the investigated samples. Furthermore, it is noticed the 5 ​mol % Ir doped sample has higher magnetization than other samples owing to existence of magnetic impurities such as Lu3Fe5O12. M ​− ​H loops have unveiled that Ir doping advances both Hc and Mr values compared to the undoped LFO sample. This increase in both Hc and Mr values could be due to 1) the variation of the canted angels of Fe3+ moments, 2) the advancement of energy of magnetocrystalline anisotropy, and 3) formation of secondary phases such as Lu3Fe5O12 and Fe3O4. Furthermore, the optical band gap examinations have revealed that the band gap of LFO reduces from 2.19 ​eV to 2.

Magnetothermal properties of [formula omitted] (x = 0, 0.05, 0.10, 0.15, 0.25 and 0.50) compounds

Magnetic and magnetocaloric properties of Ho1-xDyxAl2 compounds with x=0,0.05,0.10,0.15,0.25 and 0.50, modelled using a Hamiltonian that includes the exchange interactions between Ho-Dy, Ho-Ho and Dy-Dy ions in addition to the crystalline electric field and the Zeeman effects, have been compared with those determined experimentally. In order to reproduce experimentally observed global ferromagnetic ordering temperatures and spin reorientation transition temperatures as xDy varies, the exchange interactions between Ho-Dy and Ho-Ho were set as free parameters and adjusted to match the experimental results. We demonstrate that heat capacity of polycrystalline materials in non-zero magnetic fields can be satisfactory reproduced by using the average of multiple magnetic field directions with respect to the crystallographic coordinate system, while reasonably good agreement between experimentally determined and theoretically predicted magnetocaloric effects can be achieved considering an average of only three field directions.

Magneto-structural correlation across the spin reorientation transition temperature in pure and Sm substituted TmFeO3: A temperature dependent Raman and synchrotron X-ray diffraction study

This paper presents the magneto-structural study on orthoferrite TmFeO3 and Sm substituted TmFeO3 across spin reorientation transition (SRT) temperature. A strong change in magnetic anisotropy due to the substitution of the Sm3+was observed, which is reflected as a change in spin reorientation transition (SRT) temperature. The SRT temperature of Tm0.5Sm0.5FeO3is found to be around 200–230 K, which is relatively high in comparison to TmFeO3. A sudden decrease in the value of coercivity has been observed in the SRT region for both the sample. The lattice dynamics of TmFeO3 and Tm0.5Sm0.5FeO3were investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. We observed unusual contractions in the lattice parameter at low temperatures due to complex exchange interaction between RE3+ and Fe3+ ions sub-lattice. Anomalous behavior in lattice parameters was observed in the vicinity of SRT, which confirms the system’s spontaneous magnetostriction.The strong anomaly was observed in line width and phonon frequency of Raman modes of around SRT, which established the spin-lattice coupling in TmFeO3 and Tm0.5Sm0.5FeO3 nanoparticles. Observation of spin-lattice coupling utilizing Raman scattering substantiates our magnetic and structural correlation and supports its candidature for magneto-elastic applications.

Doping tuned spin reorientation and spin switching in praseodymium–samarium orthoferrite single crystals

We investigate the detailed analysis of the magnetic properties in a series of Pr1–x Sm x FeO3 single crystals from x = 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperature T SR Γ4 (G x , A y , F z ) to Γ2 (F x , C y , G z ) covers a wide temperature range including room temperature. A ‘butterfly’-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points in x = 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3 single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+–Fe3+ and Sm3+–Fe3+ exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

Critical sample aspect ratio and magnetic field dependence for antiskyrmion formation in Mn1.4PtSn single crystals

Mn1.4PtSn is the first material in which antiskyrmions have been observed in ultra-thin single crystalline specimens. While bulk crystals exhibit fractal patterns of purely ferromagnetic domain ordering at room temperature, ultra-thin Mn1.4PtSn lamellae clearly show antiskyrmion lattices with lattice spacings up to several $\mu$m. In the work presented here, we systematically investigate the thickness region from 400 nm to 10 $\mu$m using 100 $\times$ 100 $\mu$m$^2$ -wide Mn1.4PtSn plates, and identify the critical thickness-to-width aspect ratio $\alpha_0 = 0.044$ for the ferromagnetic fractal domain to the non-collinear texture phase transition. Additionally, we also explore these non-collinear magnetic textures below the critical aspect ratio $\alpha_0$ above and below the spin-reorientation transition temperature $T_{SR}$ while applying variable external magnetic fields. What we find is a strong hysteresis for the occurrence of an antiskyrmion lattice, since the antiskyrmions preferentially nucleate by pinching them off from helical stripes in the transition to the field polarized state.

Growth and characterization of Dy1-xYxMnO3 single crystals by optical floating zone technique: A combined X-ray diffraction and DC magnetization study

Large size single crystals of DyMnO3, YMnO3 and their solid solutions, Dy1-xYxMnO3, have been grown by the optical floating zone technique. It is shown that pristine DyMnO3 crystals grown in air atmosphere correspond to the orthorhombic phase in the Pnma space group symmetry while growth in the argon atmosphere leads to the hexagonal phase in the P63cm space group symmetry. The crystals grown in air atmosphere for the composition range 0.10 ≤ x ≤ 0.50 show coexistence of orthorhombic and hexagonal phases with increasing hexagonal phase fraction until at x ~ 0.60, the orthorhombic phase completely transforms to the hexagonal phase even in the air atmosphere. On the other hand, all the crystals grown in argon atmosphere correspond to the hexagonal phase only. Our Rietveld refinements using X-ray powder diffraction data on powders obtained after crushing the crystals further confirm the hexagonal structure in the P63cm space group symmetry for all crystals grown in argon atmosphere. The unit cell volume and the lattice parameters obtained by Rietveld refinement are shown to decrease with increasing Y3+ substitution at the Dy3+ site in DyMnO3. DC magnetisation measurements on h-Dy1-xYxMnO3 single crystals reveal that Y3+ substitution marginally increases the antiferromagnetic ordering temperature (TN) from 67 K for h-DyMnO3 to 72 K for h-YMnO3. However, the first spin reorientation (SR) transition temperature (TSR1) of Mn3+ decreases with increasing Y3+ substitutions as per TSR1 ~ k(x-xc)0.3, where k is a proportionality constant and xc is the critical composition for which this transition temperature goes to 0 K. The remaining two magnetic transition temperatures related to Dy3+ reordering (TDy3+)/spin-glass transition (TSG) and second spin reorientation transition (TSR2) show very weak dependence on Y3+ substitution before going to 0 K around x = xc ~ 0.90 composition. A magnetic phase diagram of h-Dy1-xYxMnO3 showing stability field regions in respect of different magnetic phases is also presented.

Experimental and theoretical study of magnetization and magnetocaloric effect in Nd1−xSmxFeO3

We have experimentally and theoretically investigated the magnetic properties and magnetocaloric effect in doped orthoferrite series Nd1−xSmxFeO3 (x = 0, 0.1, and 0.4). Our magnetization measurements reveal that the spin-reorientation transition temperatures of the Fe3+ moments increase as a function of Sm doping. Our measurements on the magnetocaloric effect indicate that the effect [measured by the maximum change in magnetic entropy (−ΔSM)] reduces with Sm doping. Non-collinear calculations including the effect of Coulomb correlation (U) and spin–orbit interaction (SO) were performed within the GGA + U + SO approximation using the first-principles density functional theory (DFT) to establish the magnetic structure above and below the spin-reorientation transition. Calculations of the exchange interaction strengths using DFT reveal a higher strength of Sm–Fe exchange interaction than that of Nd–Fe interaction, which explains the higher spin-reorientation transition temperatures observed in the doped compounds. Using Monte Carlo calculations on the Ising model with large moments of Nd/Sm, we have extracted the effective nearest neighbor exchange interaction values between rare-earth moments, which provide good agreement with the corresponding experimental results on −ΔSM around and below the transition temperature.

Spin induced exchange bias and lattice modulation in Nd1−x Eu x CrO3

We report the evolution of coupled phonons and exchange bias (EB) in perovskite-type Nd1−x Eu x CrO3 (x = 0.0, 0.05, and 0.10) samples by means of temperature-dependent Raman spectroscopy and dc magnetization measurements. We observed a non-monotonic behavior of the EB field around the temperature T *, which lies between the antiferromagnetic ordering temperature (T N) and spin-reorientation transition temperature (T SR). The temperature dependence of phonon modes related to antistretching and bending of CrO6 octahedra and Nd3+/Eu3+ ion vibration below T N confirms the strong spin–phonon coupling. The T * found from the non-monotonicity of the EB is imprinted with the additional anomaly observed in the low-temperature spin–phonon behavior. The phonon modes and phonon anomaly are also verified using the density functional theory-based calculations.

Features of magnetostriction behavior of the intermetallic compound Sm0.2Y0.8Fe2 near the spin reorientation transitions

The structural and magnetic properties of Sm0.2Y0.8Fe2 intermetallic compound are investigated using X-ray diffraction and magnetic measurements and compared with the properties of the SmFe2 compound. It is established that the partial substitution of Y for Sm in SmFe2 leads to the decrease in both the Curie temperature TC and the two spin-reorientation transition temperatures TSR1 and TSR2. The complex behavior of the field and temperature dependencies of the longitudinal, transversal, anisotropic and volume magnetostriction in a wide temperature range (including the spin-reorientation region) is discussed in terms of the single-ion anisotropy and magnetostriction theory. The influence of other factors, such as peculiarities of the state of Sm3+ ions and competition between contributions to magnetostriction from the iron and samarium sublattices, is also considered.

Enhanced refrigeration capacity in Ho1-xDyxB2 compounds around liquid hydrogen temperature

In this study, the crystal structure, magnetic properties, and magnetocaloric effect of Ho1-xDyxB2 compounds were investigated. It was found that nearly single-phase (Ho,Dy)B2 compounds with the AlB2-type structure directly form in the as-arc melted alloys and have two successive magnetic transitions. With the increase of Dy concentration x from 0 to 0.8, the spin reorientation transition temperature remains at about 13 K, while the Curie temperature significantly increases from 16 to 43 K. As a result, the full-width at half-maximum of the magnetic entropy change versus temperature curve increases from 19.9 to 48.2 K. Also, these Ho1-xDyxB2 compounds exhibit a large refrigeration capacity of 523–635 J kg−1 under a magnetic field change of 5 T, although the maximum magnetic entropy change decreases from 34.3 to 17.2 J kg−1 K−1. In addition, Dy-containing compounds exhibit a table-like magnetocaloric effect compared with the HoB2 compound. Our results indicate that Ho1-xDyxB2 compounds are a promising candidate for cryogenic magnetic refrigeration around liquid hydrogen temperature.