Temperature-induced Spin Reorientation 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.

Real-space observation of magnetic transitions in RMn6Sn6 (R = Ho, Dy) kagome magnets

Rare-earth RMn6Sn6 magnets reattract the attention due to their recently discovered topological properties in a strong correlation with a kagome magnetic lattice and different rare-earth magnetic elements. To understand the microscopic mechanism and discover topological spin textures, we report here the real-space observation of temperature-induced spin reorientation transition in RMn6Sn6 (R = Ho, Dy) magnets. The magnetic domain evolution corresponding to the magnetization deviation from the ab-plane into a cone state is in situ demonstrated by using Lorenz transmission electron microscopy and, moreover, individual biskyrmions are generated at room temperature under an external magnetic field in DyMn6Sn6.

Spontaneous Topological States and Their Mutual Transformations in a Rare-Earth Ferrimagnet.

Nontrivial chiral spin textures with nanometric sizes and novel characteristics (e.g., magnetic skyrmions) are promising for encoding information bits in future energy-efficient and high-density spintronic devices. Because of antiferromagnetic exchange coupling, skyrmions in ferrimagnetic materials exhibit many advantages in terms of size and efficient manipulation, which allow them to overcome the limitations of ferromagnetic skyrmions. Despite recent progress, ferrimagnetic skyrmions have been observed only in few films in the presence of external fields, while those in ferrimagnetic bulks remain elusive. This study reports on spontaneously generated zero-field ground-state magnetic skyrmions and their subsequent transformation into traditional magnetic bubbles via intermediate states of (bi-)target bubbles during a magnetic anisotropy change in the rare-earth ferrimagnetic crystal DyFe11 Ti. Spontaneous reversible topological transformation driven by a temperature-induced spin reorientation transition is directly distinguished using Lorentz transmission electron microscopy. The spontaneous generation of magnetic skyrmions and successive topological transformations in ferrimagnetic DyFe11 Ti are expected to advance the design of topological spin textures with versatile properties and potential applications in rare-earth magnets.

Field-free topological behavior in the magnetic domain wall of ferrimagnetic GdFeCo

Exploring and controlling topological textures such as merons and skyrmions has attracted enormous interests from the perspective of fundamental research and spintronic applications. It has been predicted theoretically and proved experimentally that the lattice form of topological meron-skyrmion transformation can be realized with the requirement of external magnetic fields in chiral ferromagnets. However, such topological transition behavior has yet to be verified in other materials. Here, we report real-space observation of magnetic topology transformation between meron pairs and skyrmions in the localized domain wall of ferrimagnetic GdFeCo films without the need of magnetic fields. The topological transformation in the domain wall of ferrimagnet is introduced by temperature-induced spin reorientation transition (SRT) and the underlying mechanism is revealed by micromagnetic simulations. The convenient electric-controlling topology transformation and driving motion along the confined domain wall is further anticipated, which will enable advanced application in magnetic devices.

Magnetic domains in a uniaxial magnet Dy3Al2

The rare-earth intermetallic Dy3Al2 is a low-temperature permanent magnet with temperature-induced spin reorientation transition. In this work, we report the observation of magnetic domains in lamellae of Dy3Al2 using Liquid-Nitrogen cryo-Lorentz transmission electronic microscopy (cryo-LTEM) above TSR (70 K). We studied the magnetic field dependence of domain evolution from stripe domains at zero magnetic field to the saturation state. When the easy axis lies within the lamella plane, stripe domains gradually narrow and disappear as the applied field increases. The saturation field decreases with the increasing temperature. In the presence of misalignment between the easy axis and external field, stripe domains evolve into type-II magnetic bubbles (as small as 50–60 nm). The spin configuration was further verified by utilizing differential phase contrast scanning transmission microscopy and micromagnetic simulations.

Demagnetization of an ultrathin Co/NiO bilayer with creation of submicrometer domains controlled by temperature-induced changes of magnetic anisotropy

We have investigated the magnetization in a ferromagnetic/antiferromagnetic Co/NiO bilayer from room temperature (RT) to 200 °C. Using polar magneto-optical Kerr effect (PMOKE) based magnetometry, we observe the temperature-induced spin reorientation transition of the Co layer at 150 °C (from out-of-plane to in-plane state). Zero field cooling (ZFC) down to RT leads to the appearance of a micrometer size domain structure and demagnetization of the sample. The remanence magnetization after the ZFC process strongly depends on the temperature from which the cooling process starts (onset temperature). The domain structure and its evolution under the external out-of-plane magnetic field were studied with magnetic force and PMOKE microscopies.

Synthesis and magnetic properties of Ba2Fe14O22 Y-type hexaferrite

Using the solid state reaction method, Y-type hexaferrite Ba2Fe2+2Fe3+12O22 (Fe2Y) polycrystalline ceramics were fabricated by calcining and sintering in a nitrogen atmosphere, and their magnetic properties were systematically investigated. The kink occurs at around 130 K in the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves is independent of measuring frequencies, which is probably derived by the temperature-induced spin reorientation transitions of Fe2Y phase. While the kink at 50 K in the ZFC magnetization and the irreversibility between ZFC and FC curves were observed and ascribed to the spin-glass-like transition in the low temperature region. Both ac susceptibility and thermoremanent magnetization (TRM) measurements confirmed this assumption.

Terahertz spectroscopic characterization of spin mode and crystal-field transition in high-throughput grown <inline-formula><tex-math id="Z-20201027023844-1">\begin{document}$ {\bf Sm}_{ x}{\bf Pr}_{ 1– x}{\bf FeO_3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20200732_Z-20201027023844-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20200732_Z-20201027023844-1.png"/></alternatives></inline-formula> crystals

Terahertz (THz) transient has become an effective method to study the optical and electronic spin characteristics of the rare earth orthoferrites <i>R</i>FeO<sub>3</sub>. High-throughput grown crystal sample is sliced at different locations, then the continuously tunable rare earth elements co-doped single crystal Sm<sub><i>x</i></sub>Pr<sub>1–<i>x</i></sub>FeO<sub>3</sub> is studied with antiferromagnetic spin mode (qAFM) and crystal field transitions of rare earth ions under zero magnetic fields. Using THz time-domain spectroscopy, the qAFM resonance frequencies of Sm<sub>0.2</sub>Pr<sub>0.8</sub>FeO<sub>3</sub> and Sm<sub>0.4</sub>Pr<sub>0.6</sub>FeO<sub>3</sub> single crystals are located on the connection line of the qAFM frequencies of PrFeO<sub>3</sub> (0.57 THz) and SmFeO<sub>3</sub> (0.42 THz), therefore the frequency of qAFM increases linearly with doping concentration of Sm<sup>3+</sup> ion increasing. The Sm<sub>0.4</sub>Pr<sub>0.6</sub>FeO<sub>3</sub> crystal undergoes a temperature-induced spin reorientation phase transition at about 160 K. When the crystal temperature is lower than 80 K, a wide band absorption peak of about 0.5 THz appears in the absorption spectrum of Sm<sub>0.2</sub>Pr<sub>0.8</sub>FeO<sub>3</sub> due to the crystal field effect. Our results show that THz spectral data not only allow us to monitor the quality of rare earth orthoferrite crystals prepared by high throughput and analyze the rare earth elements of the sample, but also improve the ability to analyze the physical properties of the co-doped <i>R</i>FeO<sub>3</sub>.

Temperature induced interface roughness and spin reorientation transition in Co/Au multilayers thin films

Spin reorientation transition (SRT) due to high temperature has been studied in Co/Au multilayered thin films. The effect of temperature on structural and magnetic properties of the thin films has been investigated. Film thickness and interface roughness has been studied by measuring x-ray reflectivity. Multilayers are thermodynamically stable, and thickness of the layers and interface roughness remains unchanged over longer periods of time as well as up to a temperature of 300 °C. An increase in interface roughness at higher temperatures indicates intermixing of Co and Au into each other. Behavior of coercive field for both the samples is quite different. However, the spin reorientation transition occurred in both the samples around 350 °C. Here we are reporting our study on temperature induced spin reorientation transition in Co/Au multilayers. A spin reorientation transition is observed from out-of-plane to in-plane direction for 12 Å thick Co layer sample at 350 °C and a reverse transition is observed for 25 Å thick Co layer sample. Results were obtained using ex situ and in situ Magneto-Optic Kerr Effect (MOKE) measurements.

Tuning spin reorientation in Er1-xYxFeO3 single crystal family

A temperature-induced spin reorientation transition between Γ4 (Gx, Ay, Fz) and Γ2 (Fx, Cy, Gz) has been studied in the family of Er1-xYxFeO3 (x = 0, 0.25, 0.5, 0.75, 1) single crystals. By doping nonmagnetic Y3+, we tuned the spin reorientation temperature to low temperature with increasing x. Moreover, the typical compensation point and spin flip transition of ErFeO3 also decreases with doping, and disappears above x = 0:75. We also report the Rietveld refinements and Raman spectroscopy of Er1-xYxFeO3, where some Raman peaks are shifted to low frequency with increasing doping. Our results shed light on the understanding of the interaction between two magnetic sub-lattices of rare earth (R3+) and iron (Fe3+) ions, and will also contribute to the materials design and potential applications.

Site-Resolved Contributions to the Magnetic-Anisotropy Energy and Complex Spin Structure of Fe/MgO Sandwiches

Fe/MgO-based Magnetic Tunnel Junctions (MTJs) are among the most promising candidates for spintronic devices due to their high thermal stability and high tunneling magnetoresistance. Despite its apparent simplicity, the nature of the interactions between the Fe and MgO layers leads to complex finite size effects and temperature dependent magnetic properties which must be carefully controlled for practical applications. In this letter, we investigate the electronic, structural and magnetic properties of MgO/Fe/MgO sandwiches using first principles calculations and atomistic spin modeling based on a fully parameterized spin Hamiltonian. We find a large contribution to the effective interfacial magnetic anisotropy from the two-ion exchange energy. Minimization of the total energy using atomistic simulations shows a surprising spin spiral ground state structure at the interface owing to frustrated ferromagnetic and antiferromagnetic interactions, leading to a reduced Curie temperature and strong layer-wise temperature dependence of the magnetization. The different temperature dependences of the interface and bulk-like layers results in an unexpected non-monotonic temperature variation of the effective magnetic anisotropy energy and temperature-induced spin-reorientation transition to an in-plane magnetization at low temperatures. Our results demonstrate the intrinsic physical complexity of the pure Fe/MgO interface and the role of elevated temperatures providing new insight when interpreting experimental data of nanoscale MTJs.

Domain Structure and Spin Reorientation in TbCo5 and DyCo5 Intermetallics

In this paper, we study the spin-reorientation processes in DyCo5 and TbCo5 intermetallic compounds by direct observation of domain structure (DS) realignment during the easy plane—easy cone—easy axis phase transitions. In addition to the analysis of DS changes due to temperature induced spin reorientation, a description is given of a newly discovered effect of surface out-of-plane domain reorientation produced by abrasion and/or indentation of the surface of macroscopic samples with overall easy-plane magnetocrystalline anisotropy.

Temperature and field induced spin reorientation and dielectric properties in YCr0.88Fe0.12O3 single crystal

The structural, magnetic, and dielectric properties of the YCr0.88Fe0.12O3 single crystals were studied. Detailed magnetic studies demonstrate that the crystal is antiferromagnetic with weak canted ferromagnetism and experiences three sequential magnetic transitions around TN1 ∼ 127.3 K, TN2 ∼ 115.2 K, and TSR ∼ 99.0 K. Interestingly, a temperature induced spin reorientation (SR) near TSR and magnetic field induced SR below TSR were observed. The H–T phase diagram was revealed to be quite different from both parent compounds YFeO3 and YCrO3. A dielectric relaxation around TN1 was found to be associated with electron hopping. An intrinsic magnetoelectric effect was also observed at low temperatures. These results are helpful for understanding the exotic magnetic and magnetoelectric properties in the orthochromite and orthoferrite related systems.

Mössbauer and Magnetization study of polycrystalline multiferroic [formula omitted

The present work reports the preparation of polycrystalline SmFeO3 (SFO) and its characterization using bulk magnetization, 57Fe Mössbauer spectroscopy and ferroelectric polarization measurements. Temperature dependent bulk magnetization study shows crossover between zero-field cooled (ZFC) and field cooled (FC) curves at 4K and slope variation of ZFC curve in 200–300K region due to the spin switching transition which is found to be tunable with the applied magnetic field as observed in recent literature on single crystal SFO sample. From the temperature dependent Mössbauer measurements, transition from antiferromagnetic to paramagnetic state at about 708K and signatures of temperature induced spin reorientation of Fe3+ are observed in quadrupole shift (QS) and A23 hyperfine parameters in the temperature range 450–500K. The least square fitting to the temperature variation of Hint gives the critical exponent (β)≈0.327±0.001 suggesting the 3D Heisenberg magnet like behavior. The presence of ferroelectric ordering is shown from ferroelectric and PUND (Positive Up Negative Down) data measured at low temperatures (200K).

Temperature-induced spin reorientation and magnetization jump of rare-earth orthoferrite Ho0.5Pr0.5FeO3 single crystal

We report temperature-induced spin reorientation and magnetization jump effects in the rare earth (RE) orthoferrite Ho0.5Pr0.5FeO3 single crystal. The single crystal of about 6 mm in diameter and 50 mm in length was successfully grown by optical floating zone method. Both X-ray diffraction and Laue photograph confirmed the homogeneity and high quality of the crystal. Magnetic properties of Ho0.5Pr0.5FeO3 single crystal are studied over a wide temperature range from 2 to 300 K. Spin reorientation transition from Γ2 to Γ4 phase is observed in the temperature range of 75–90 K. At lower temperature, the Ho0.5Pr0.5FeO3 shows an abrupt jump of magnetization along the a-axis, which occurs only in the field-cooling process, and is sensitive to external applied magnetic field. By analyzing the jump temperature and magnitude of the magnetization, we conclude that it is caused by the spin reversal of the rare earth ions. The isothermal magnetization versus field hysteresis loop measurements along a axis explain the spin configuration variation from 3K to 60 K.

Effects of Dzyaloshinskii–Moriya interaction on magnetic stripe domains

Recently, the domain walls of stripe domain in Fe/Ni bilayer system are found to have Néel-type domain wall with a definite chirality. We investigated how Dzyaloshinskii–Moriya (DM) interaction modifies the properties of magnetic stripe domains generated by long-range dipole interaction at spin reorientation transitions using a theoretical model calculation and a computational simulation. The chirality of the domain wall magnetism and the size of stripe domains are affected by DM interaction, and the modification depends on the direction of the DM vector. We analyzed the amount of modification and obtained a formulation with the ratio between the strengths of the DMI and dipolar interaction. It is studied how DMI affects the temperature induced spin reorientation transition.

Dynamical spin reorientation transition in NdFeO3 single crystal observed with polarized terahertz time domain spectroscopy

Temperature-induced spin reorientation transition in NdFeO3 single crystal is studied by terahertz time-domain spectroscopy in the temperature range from 50 K to 290 K. Following the resonant excitation of quasi-antiferromagnetic (AF) mode, the nature of temperature dependence of emission from AF-mode is investigated systematically in the spin reorientation temperature interval. The emission frequency is observed at 0.485 THz for both Γ4 and Γ24 phases, and it shifts abruptly to 0.456 THz (around 110 K) corresponding to Γ2 phase. The evolution of vector G is obtained from the temperature-dependent polarization changes of the AF-mode excitation. Our results demonstrate that the polarized terahertz time-domain spectroscopy is a sensitive tool to explore the dynamical spin reorientation transition in RFeO3 crystals, and the terahertz magnetic pulse shows potential application for non-thermally manipulating ultrafast spin reorientation.

Temperature-induced spin reorientation in TbMn6Sn6−xGax

The spin reorientation process in TbMn6Sn6−xGax has been investigated using Sn119 Mössbauer spectroscopy. The Sn site hosting the substituting Ga atoms is identified as Sn-2d. The reorientation is confirmed to be a 90° rotation of the Mn moments from ab plane to c axis upon cooling through Tsr. The reorientation temperature Tsr is observed to decrease with increasing Ga doping at 255±18K∕Ga. Finally, we evaluate the anisotropic contributions to the hyperfine field at the Sn sites as seen through the spin reorientation.

Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins inNi81Fe19∕α‐Fe2O3

We report studies of exchange bias and coercivity in ferromagnetic Ni$_{81}$Fe$_{19}$ layers coupled to antiferromagnetic (AF) (0001), (11$\bar{2}$0), and (11$\bar{0}$2) $\alpha$-Fe$_2$O$_3$ layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show for the first time that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.

Temperature-induced phase transitions in Co-doped YIG films

The garnet YIG:Co films have been investigated within the temperature range 10–300 K. Torque magnetometry study showed the temperature-induced spin-reorientation phase transitions. Using the Faraday effect, magnetic domain structures were visualized by optical microscope and analyzed by digital image processing technique. Temperature- and magnetic-field-induced transitions between phases with in-plane and out-of-plane magnetization were studied by the magneto-optical technique.