Magnetization Reversal Phenomena Research Articles

Magnetic hysteresis mechanism in Lu0.9Sr0.1Cr0.5Fe0.5O3 studied by Monte Carlo simulations

In this work we report magnetic properties of the orthorhombic perovskite Lu0.9Sr0.1Cr0.5Fe0.5O3 synthesized by a wet chemical method. As in LuCr0.5Fe0.5O3 the compound with Sr shows the magnetization reversal phenomenon, but the magnetic order and the compensation temperature occur at higher temperatures. Interestingly, in M vs H curves a hysteresis loop is observed when Cr4+ and Cr3+ ions coexist as a consequence of the aliovalent substitution of Lu3+ by Sr2+ in the B sites of the perovskite. To explain this behavior, we performed numerical simulations with a magnetic model for Lu1−x Sr x Cr0.5Fe0.5O3 perovskites with x= 0 and x = 0.1. We found that the ferromagnetic coupling of Fe3+ and Cr4+ through superexchange interactions (according the empiric Goodenough–Kanamori–Anderson rules) increases the magnetization at high fields and that the presence of ferromagnetic clusters explains the hysteretic behavior found in simulations.

Magnetization reversal phenomenon of higher-order lump and mixed interaction structures on periodic background in the (2+1)-dimensional Heisenberg ferromagnet spin equation

This paper mainly researches a useful model that can describe the rapid magnetization reversal process, namely the (2+1)-dimensional Heisenberg ferromagnet spin equation. Based on its Lax pair, we construct the iterative generalized (r,N−r)-fold Darboux transformation (DT), and obtain new position-controllable higher-order lump, periodic wave and rich mixed lump–breather interaction structures on periodic background. In particular, with the increase of N in the iterative generalized (r,N−r)-fold DT, we find that the structure of the lump and periodic wave can flip over with respect to the background. Moreover, we also find a bright lump structure with two peaks and two valleys, which does not flip with the increase of N. We study the magnetization trajectory and magnetization on the Bloch sphere, from which we discover that the magnetization is distributed in an incomplete unit sphere for the flipped case, while the magnetization is distributed in a complete unit sphere for the non-flipped case. These magnetization reversal phenomena are expected to have potential applications in understanding the rapid magnetization reversal process.

Significant role of thermal effects in current-induced exchange bias field switching at antiferromagnet/ferromagnet interface

The current-induced switching of in-plane exchange bias field (<i>H</i><sub>eb</sub>) has many advantages, such as switching without assistance of external magnetic field, excellent immunity to magnetic field, and robust magnetic anisotropy. However, the blocking temperature of the nanoscale antiferromagnet/ferromagnet (AFM/FM) heterostructure is relatively low and susceptible to thermal effects. Therefore, the Joule heating theoretically plays a substantial role in the switching of <i>H</i><sub>eb</sub> driven by current, but its underlying mechanism requires further investigation and verification. We prepare a series of Pt/IrMn/Py heterostructures with varying antiferromagnet IrMn thicknesses and systematically investigate the role of thermal effects in current-driven <i>H</i><sub>eb</sub> switching. These results demonstrate that under millisecond-level current pulses, Joule heating heats the device above the blocking temperature, leading to the decoupling of exchange coupling at AFM/FM interface. Simultaneously, the Oersted field and spin-orbit torque field generated by the current switch the ferromagnetic moments, and then a new <i>H</i><sub>eb</sub> will be induced along the direction of the ferromagnetic moments in the cooling process. Furthermore,in the switching process of <i>H</i><sub>eb</sub>, the anisotropic magnetoresistance curve of the AFM/FM heterostructure exhibits a temperature-dependent two-step magnetization reversal phenomenon. Theoretical analysis indicates that this phenomenon arises from the competitive relationship between exchange bias coupling at AFM/FM interface and direct exchange coupling between the ferromagnetic moments. The findings of this study elucidate the crucial role of thermal effects in the current-driven switching of <i>H</i><sub>eb</sub>, thereby contributing to the advancement of spintronic devices based on electrically controlled <i>H</i><sub>eb</sub>.

Demonstration of Pavlov Associative Memory by Implementation of Rate Coding Using Magnetic Tunnel Junction Neurons

In this paper, a fully functioning Pavlov associative memory system, one of the most famous examples of the biological brain function, is implemented by a basis of rate coding. In order to create a neural signal which is capable of emulating the synaptic weight based on rate coding, a neural signal is constructed by utilizing telegraphic switching of the magnetic tunnel junction (MTJ), a random magnetization reversal phenomenon. Spike rate of the MTJ neuron is controllable by adjusting the STT current bias, creating signals with rate information that is capable of implementing rate coding scheme as a weight update method for the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> memristor synapse. The proposed neuron creates random spike signals containing rate information, which participates in emulating Pavlov associative memory characteristics such as learning and forgetting, as well as rate controlling characteristics. The suggested structure shows a coding scheme which both input and output neurons participate, which can be expanded to larger neuromorphic neural network applications.

Influence of Cr substitution on structural, optical, and magnetic properties of La2SrFe2O7: Their application as a photocatalyst for the degradation of Rhodamine B dye

A new n = 2 Ruddlesden-Popper (RP) series La2SrFe2-xCrxO7 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been prepared via Sol-gel Pechini method, and their structural, optical, and the magnetic characterization was done. Furthermore, we are for the first-time reporting on the photo-catalytic degradation of a dye by a complete n = 2, La2SrFe2-xCrxO7 RP series. Rietveld refinement analysis confirms the formation of single-phase compounds with tetragonal crystal symmetry and I4/mmm space group. The results indicate a steady decrease in unit cell parameters and cell volume with Cr3+ doping. Dominant anti-ferromagnetic (AFM) interactions were observed in all the phases and the appearance of weak ferromagnetic (FM) interactions takes place owing to the Fe3+―O―Cr3+ FM interaction with Cr3+ doping. The χM−FC curve for x = 0.8 phase shows the magnetization reversal (MR) phenomenon and becomes zero at Tcomp ∼127 K and the value becomes negative on further decreasing the temperature. The MR phenomenon is discussed in terms of the competing Fe3+―O―Fe3+, Fe3+―O―Cr3+, and Cr3+―O―Cr3+ super-exchange interactions. Enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) dye was obtained for x = 0.2 substituted phase, displaying a ∼99% degradation of dye in 30 min followed by ∼83%, ∼75%, ∼64% and ∼61% by x = 0.4, 0.0, 0.8 and 0.6 phases respectively in the same time interval. The results are explained in terms of crystallite size, the narrowing of band gap with Cr3+ substitution, and based on of recombination of charge carriers which, are in good agreement with the results of Photoluminescence (PL) emission intensity spectra.

Magnetization Reversal and Domain Structures in Perpendicular Synthetic Antiferromagnets Prepared on Rigid and Flexible Substrates

Ferromagnetic (FM) layers separated by nonmagnetic metallic spacer layers can exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, which may lead to a stable synthetic antiferromagnetic (SAF) phase. In this article, we have studied magnetization reversal by varying the number of bilayer stacks [Pt/Co] as well as thicknesses of Ir space layer t\(_{Ir}\) on rigid Si(100) and flexible polyimide substrates. The samples with t\(_{Ir}\) = 1.0 nm show a FM coupling, whereas samples with t\(_{Ir}\) = 1.5 nm show an antiferromagnetic (AFM) coupling between the FM layers. At t\(_{Ir}\) = 2.0 nm, it shows a bow-tie shaped hysteresis loop indicating a canting of magnetization at the reversal. Higher anisotropy energy compared to the interlayer exchange coupling (IEC) energy is an indication of the smaller relative angle between the magnetization of lower and upper FM layers. We have also demonstrated the strain-induced modification of IEC as well as magnetization reversal phenomena. The IEC shows a slight decrease upon application of compressive strain and increase upon application of tensile strain, which indicates the potential of SAFs in flexible spintronics.

Synthesis, morphological, structural, and magnetic studies of Gd1-xPrxCrO3 nanoparticles

A series of nanocrystalline compounds, Gd1-xPrxCrO3 (where 0 ≤ x ≤ 1 and Gd: Gadolinium, Pr: Praseodymium, Cr: Chromium and O: oxygen), was synthesized by the auto-combustion route followed by annealing at 700 °C. XRD revealed that all samples in the series are perovskites with a distorted orthorhombic structure and crystallized into the Pbnm space group. The average particle size for the samples annealed at 700 °C for 4 h was in the range of (50–91) nm. There was an agreement between Rietveld fitting results and the TEM results for the average particle size. It is noted that with the rise in the Pr concentration due to the reduction of Gd concentration in the compounds, the magnetization for field cooling/zero-field cooling (FC/ZFC) modes decreases. The compounds in the series exhibit the magnetization reversal (MR) phenomenon at ZFC mode. In contrast, the parent compound displays negative magnetization behavior at FC mode with a minimum magnetization value at 14 K. The Néel transition temperature (TN) is found to increase linearly with increasing Pr concentration as well. Moreover, as the Pr concentration in the Gd1-xPrxCrO3 series increases, the compensation temperature (Tcomp2) increases while the spin flipping temperature (TSF) decreases. All samples under investigation showed magnetic switching, which makes them useful for magnetic switching applications. At different temperatures, the magnetization as a function of a magnetic field was measured. Weak ferromagnetism was observed just below (TN), and notable magnetic features at lower temperatures. Above (TN), the compounds are paramagnetic. The exchange bias (EB) phenomenon was studied for all the samples in the series without applying a cooling, magnetic field (ZFC-EB) and under different cooling, magnetic fields (FC-EB) at (1 T, 2 T, and 3 T). From the measurements of ZFC-EB, it is found that HEB increases by 600% with increasing the dopant concentration from x = 0 to x = 1 with a further increase by 200% with field cooling as small as 1 T. That means the compounds can be used in the applications of EB-based magnetic devices. It is observed that HEB, Mmax, and Hc of the compounds depend on the temperature at different applied cooling fields.

Magnetization reversal and tunable bipolar magnetization switching in Ni20Mn3B6 alloy

Magnetization reversal has attracted more and more interests due to its applications on spintronic devise and magnetic storage materials. However, the magnetization reversal is rarely studied in the non-rare earth intermetallic compounds. In this work, we have found that the Ni20Mn3B6 alloy exhibits the magnetization reversal phenomenon with the decreasing temperature at low applied fields (H ≤ 100 Oe), accompanying with two compensation temperatures. Further analysis showed that the first compensation temperatures is due to the competition between the two different interactions of Mn atoms that occupy two different positions. The second one is arising from the rotating of the moment on demand of Zeeman energy. Based on this phenomenon, a tunable bipolar switching of magnetization between positive and negative value has been found in the alloy between two compensation temperatures, which can be applied in the spintronic devices and magnetic storage materials.

Signs of superparamagnetic cluster formation in LuFe1−xCrxO3 perovskites evidenced by magnetization reversal and Monte Carlo simulations

In this paper, we study the magnetic properties of orthorhombic (Pbnm) perovskites $\mathrm{Lu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ with $x=0.25$, 0.45, 0.55, and 0.75 by magnetization vs temperature and neutron powder diffraction measurements at room temperature. The magnetic moments are oriented along the $x$ direction with a G-type antiferromagnetic (AFM) arrangement that corresponds to irreducible representation ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${G}_{x}{A}_{y}{F}_{z}$). Magnetization reversal (MR) is observed for $0.45\ensuremath{\le}x\ensuremath{\le}0.75$. The MR phenomenon was modeled using Monte Carlo simulations, modeling both homogeneous and inhomogeneous cation distributions. For $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$, the presence of MR could only be explained using an inhomogeneous distribution with well-defined magnetic clusters. Looking at the staggered magnetization of each cluster, we propose a superparamagnetic regime of ${\mathrm{Fe}}^{3+}$ clusters in a ${\mathrm{Cr}}^{3+}$-rich matrix for $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$. By calculating the specific heat, we found that, in $\mathrm{Lu}{\mathrm{Fe}}_{0.45}{\mathrm{Cr}}_{0.55}{\mathrm{O}}_{3}$ and $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$ the clusters order at nearly the same temperature ${T}_{N}^{\mathrm{Clus}}\ensuremath{\sim}535$ and 520 K, respectively, while the matrix orders at ${T}_{N}^{\mathrm{Mat}}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. There is considerable reduction in the cluster ordering temperature as compared with the bulk, as ${T}_{N}\ensuremath{\sim}628\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuFe}{\mathrm{O}}_{3}$, while the matrix orders at the expected temperature as ${T}_{N}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuCr}{\mathrm{O}}_{3}$.

Symmetry Origin of the Dzyaloshinskii-Moriya Interaction and Magnetization Reversal in YVO3.

We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-resolution neutron powder diffraction toward understanding the phenomenon of magnetization reversal. Contrary to earlier reports, our study reveals that both C-type and G-type antiferromagnetic ordering, corresponding to G-type and C-type orbital ordered phases, respectively, occur at the same temperature (TN = 115 K) with the G-type antiferromagnetic phase growing at the expense of the C-type one on cooling. These processes cease at TS ∼ 77 K; however, a minor (∼4%) untransformed C-type phase remains unchanged down to 1.7 K. The symmetry analysis indicates different symmetry origins of the Dzyaloshinskii-Moriya interaction in each phase, which can explain the magnetization reversal observed between TN and TS. We discuss that magnetic phase separation and associated weak ferromagnetism may be the common mechanism underlying the magnetization reversal phenomenon observed in other RVO3 systems (R = rare earth).

Magnetic properties and ferrimagnetic structures of Mn self-doped perovskite solid solutions (Ho1−xMnx)MnO3

A high-pressure synthesis method was employed to prepare (Ho1-xMnx)MnO3 solid solutions with x = 0.2 and 0.3 (at about 6 GPa and 1,670 K) and magnetic properties and structures were investigated by magnetic, dielectric and neutron diffraction measurements. Both samples crystallize in the GdFeO3-type Pnma perovskite structure, and both samples show magnetization reversal behavior below the compensation temperature of about 35 K (at H = 100 Oe). The magnetization reversal phenomena are originated from a ferrimagnetic (FiM) structure which takes place below TC = 76 K (x = 0.2) and 102 K (x = 0.3) and is built from ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site which are antiferromagnetically (AFM) coupled with Ho3+ and Mn2+ cations at the A site. The magnetic moment of Ho3+ cations increases significantly with deceasing temperature, and it overcomes the saturated magnetic moment of Mn3+ and Mn4+ cations at the B site. Field-induced first-order transitions were found in both compounds below about 35 K. Neutron diffraction measurements on the x = 0.2 sample found a collinear FiM structure between 76 K and 40 K, and the development of spin canting at the A site below 40 K. The coexistence of Ho3+ and Mn2+ at the A-site gives rise to additional short-range magnetic ordering of Ho3+ and to strain effects along the a-direction which are stronger than in (R1−xMnx)MnO3 materials with heavier and smaller rare-earths cations.

Field-driven spin reorientation in SmMnO3 polycrystalline powders

The SmMnO3 perovskite system shows interesting magnetic properties and making them an attractive material for specific technological application. However, these materials on nanosized dimension display properties that can be significantly different from their bulk dimension. In this regard, using the sol-gel method, the successful synthesis of SmMnO3 polycrystalline powders is herein reported. The structure, morphology, vibrational and magnetic properties of the as-produced sample have been investigated. X-ray diffraction pattern shows a single-perovskite SmMnO3 crystalline phase structure, with a crystalline size of ∼70 nm. The room temperature Raman spectrum confirms the formation of the perovskite SmMnO3 crystalline structure observed by XRD. DC magnetic measurements show an antiferromagnetic-like transition at 60 K (TN ≈ 60 K), attributed to the antiferromagnetic ordering of the Mn3+ spins, magnetic measurements also reveal a temperature-induced magnetization reversal phenomenon characterized by the magnetic compensation temperature (Tcomp ≈ 6 K), attributed to antiparallel orientation of weak ferromagnetic Mn3+- and Sm3+-ion magnetic moments induced by Sm3+-Mn3+ exchange interaction. Magnetization loops, recorded from the as-synthesized SmMnO3 sample contain some singularity compared to previous studies of SmMnO3, which are assigned to small particle size and single domain character of the particles, which are characterized by two well-defined anomalies, both connected with the spin inversion phenomena: one at low fields showing increasing and decreasing branches intersecting each other; another at high fields revealing sudden jumps. The study of a Schottky anomaly in the specific heat measurements recorded at low temperatures (below 10 K) under DC magnetic fields (in the range 5–14 T), is consistent with the presence of a field-driven spin reorientation, from antiferromagnetic to a net ferromagnetic order.

Room-temperature magnetization reversal and magnetocaloric switching in Fe substituted GdMnO3

Room-temperature tunable bipolar magnetization switching and magnetically switchable magnetocaloric phenomena having numerous application potentials are reported in $\mathrm{GdM}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{F}{\mathrm{e}}_{x}{\mathrm{O}}_{3}$ ($x=0.55$ and 0.60) polycrystalline samples. Substitution of Fe in antiferromagnetic $\mathrm{GdMn}{\mathrm{O}}_{3}$ induces a first-order spin-reorientation transition $({T}_{SR})$, which along with antiferromagnetic ordering transition $({T}_{\mathrm{N}})$ gives rise to anomalies in dielectric spectra, a signature of magnetodielectric effect. Temperature-dependent Raman spectra confirm the spin-phonon coupling which could be the origin of the magnetodielectric effect in the system. Notably, low-field magnetically tunable magnetization reversal is found to appear between ${T}_{\mathrm{SR}}$ and ${T}_{\mathrm{N}}$ in these compounds owing to the competition between single-ion magnetic anisotropy and antisymmetric Dzyaloshinsky-Moriya interaction. Additionally, the $\mathrm{GdM}{\mathrm{n}}_{0.40}\mathrm{F}{\mathrm{e}}_{0.60}{\mathrm{O}}_{3}$ sample reveals the coexistence of magnetically switchable conventional and inverse magnetocaloric effect at 250 and 310 K. The tailoring of these coexisting room-temperature magnetization reversal and magnetocaloric phenomena in a single-phase system suggests a route to design the material suitable for potential applications in electromagnetic and memory devices.

Origin of negative magnetization phenomena in (Tm1−xMnx)MnO3 : A neutron diffraction study

$(\mathrm{T}{\mathrm{m}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x})\mathrm{Mn}{\mathrm{O}}_{3}$ solid solutions were synthesized at a high pressure of 6 GPa and a high temperature of about 1570--1670 K for 2 h for $x=0$, 0.1, 0.2, and 0.3. Magnetic, dielectric, and neutron diffraction measurements revealed that the introduction of magnetic ${\mathrm{Mn}}^{2+}$ cations into the A site leads to an incommensurate spin structure for $x=0.1$ and to a ferrimagnetic structure for $x\ensuremath{\ge}0.2$. Commensurate magnetic structures have a much larger correlation length $(\ensuremath{\sim}400\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0,\ensuremath{\sim}600\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0.3)$ than the incommensurate magnetic structure $(\ensuremath{\sim}12\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0.1)$. The presence of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ (with different sizes) at the A site causes significant microstrain effects along the $a$ direction which are absent for $x=0$ and get stronger with increasing $x$. Magnetic ordering occurs at the N\'eel temperature ${T}_{N}=37\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.1)$ and at the ferrimagnetic Curie temperatures ${T}_{C}=75\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.2)$ and ${T}_{C}=104\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.3)$. Ordering of magnetic Mn moments triggers short-range order (for $x=0.1)$ and long-range order (for $x\ensuremath{\ge}0.2)$ of the ${\mathrm{Tm}}^{3+}$ cations at the same temperature---an unusual situation in perovskite materials with a simple ${\mathrm{GdFeO}}_{3}$-type $Pnma$ structure. For $x=0.1$, long-range IC magnetic order [with propagation vector $\mathbf{k}=({k}_{0},0,0)$ and ${k}_{0}\ensuremath{\approx}0.40]$ of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ cations at the B site coexists with short-range order of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ moments at the A site. Short-range order is induced at the N\'eel temperature ${T}_{N}=37\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, increases towards an additional specific heat anomaly at $T=4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, and remains at lower temperature. The ferrimagnetic structure [with propagation vector $\mathbf{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}0)]$ consists of ferromagnetically ordered ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ cations at the B site which are coupled antiferromagnetically with ordered ${\mathrm{Mn}}^{2+}$ moments at the A site. ${\mathrm{Tm}}^{3+}$ moments adopt a zigzag magnetic structure which contains a macroscopic ferromagnetic moment that aligns with the direction of the ordered ${\mathrm{Mn}}^{2+}$ moments. Towards low temperature, the ordered ${\mathrm{Tm}}^{3+}$ moments strongly increase and overcome the saturated magnetic Mn moments at the B site, and this behavior results in the observation of magnetization reversal or negative magnetization phenomena with a compensation temperature of about 15 K at small magnetic fields in the $x=0.2$ and 0.3 samples. This is a classical mechanism of the magnetization reversal effects for ferrimagnets.

Ferromagnetic layer thickness dependence of the misalignment between anisotropy axes in Co/IrMn bilayers

In this work, exchange-biased Co/IrMn bilayers were fabricated by dc magnetron sputtering at room temperature. We investigated the misalignment angle between uniaxial and unidirectional anisotropies by measuring in-plane angular dependent ferromagnetic resonance. We found that the misalignment angle decreases with the ferromagnetic-layer (Co) thickness increasing. An asymmetric magnetization reversal phenomenon was also observed due to the misalignment anisotropy. By rotating the sample to a certain angle which respond to the direction of effective easy axis of uniaxial and unidirectional anisotropies, the asymmetry magnetization reversal can be effectively eliminated.

Thermally Activated Magnetic Switching Mode for Various Thicknesses of Perpendicularly Ferromagnetic Nano-dot

Background:Even applying thermal pulse has been succeeded to reduce the coercivity through randomization the magnetization in such a way stimulate the magnetic reversion, the efficiency of magnetic switching field consumption in writing process still turns out to be an exciting research field to implement the HAMR technology. One of the remarkable geometric properties of HAMR storage media that can be correlated to the writing field reduction issue is the nano-dot thickness. Furthermore, thermal fluctuation causes the magnetization switching process to be probabilistic. This magnetic switching probability determines the magnitude of the writing field. This paper aims to investigate the impact of changes in media thickness on the magnetization process in particular at high temperatures numerically.Methods:Nano-dot was modeled as a parallelepiped with uniaxial anisotropy which was regarded as a magnetically isolated system where no disturbance field of neighboring nano-dots. Simulation arrangements were implemented to evaluate the two viewpoints in the current heat-assisted magnetic recording, either coercivity, as well as writing field consume. Coercivity was gauged by inducing a magnetic field which linearly increased up to 2 Tesla for 2.5 ns at thermal equilibrium to the surrounding. In evaluating writing field consume, thermal field pulse which just below the Curie temperature was generated while the magnetic field inducing the nano-dot. These schemes investigations were based on the Landau-Lifshift- Gilbert equation which accommodates the fluctuation-dissipation theorem in calculating thermal fluctuation effect. Also, temperature dependent material parameters such as magnetic saturation, magnetic anisotropy, and exchange interaction, were taken into account.Results:At room temperature, the coercive and nucleation fields are highly sensitive to the nano-dot thickness. Under thermal assistance, the writing field for 10 nm and 100 nm of the chosen thicknesses are 0.110 T and 0.125 T respectively. These writing grades are significantly lower than the coercivity of the media. For both thicknesses, zero field magnetization reversal phenomena are observed as indicated by the existences of the switching probabilities at H = 0.Conclusion:This numerical study showed that using the heating assistance close to the Curie point, nanodots with the chosen thicknesses and magnetic parameters were probably to be magnetized even no driven magnetic field. Along with this result, magnetic field induction which required to utterly magnetizing was only in the sub-Tesla - about a tenth of the coercive field. During magnetization processes under thermal assistance, randomization of magnetic moments initiated the switching dynamic before the domain wall was nucleated and propagated to reach a single magnetized domain.

Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.

Mild Hydrothermal Crystallization of Heavy Rare-Earth Chromite RECrO3 (RE = Er, Tm, Yb, Lu) Perovskites and Magnetic Properties.

Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especially true for the small metal cations at the A-site with large distortion angle of CrO6 octahedral and small Goldschmidt tolerance factors. Here, we performed a progressive dehydration crystallization strategy to synthesize four RECrO3 with the smallest radii of rare earth elements (Er, Tm, Yb, Lu) in mild hydrothermal conditions. Profile refinement of the high-resolution powder X-ray diffraction results indicated slightly longer unit cell parameters of a and c in our samples with a higher distorted angle of CrO6 octahedral units along ⟨010⟩ direction. All of the samples show rounded rectangle plate morphology with uniform distribution of particle sizes. These four RECrO3 crystals can only form in a very narrow mineralization temperature range, i.e., 260-280 °C and 4.45-6.24 M of KOH. HRTEM results indicated that the normal crystallographic direction is ⟨001⟩, and the lattice of steps at the edge of elliptic rounded crystal is consistent with the bulk, which demonstrated single crystalline nature of the as-obtained crystals. Room-temperature Raman and FT-IR spectra reveal a continuous symmetry mode shift-dependent on the radii of A-site rare-earth cations. Temperature-dependent magnetization curves of RECrO3 show typical antiferromagnetism to paramagnetism transition with Néel temperature of 93, 90, 86, and 83 K for ErCrO3, TmCrO3, YbCrO3, and LuCrO3, respectively. Samples of YbCrO3 and LuCrO3 show clear magnetization reversal and exchange bias phenomena below their Néel points. This paper indicates that the coupling of magnetic exchange in perovskite structure oxides could be tailorable in mild hydrothermal condition, towards the exploration of new magnetic and other physical properties.

하지층의 스퍼터링 압력을 달리하여 제작한 Cr/CoSm/Cr 자성막의 자기상호작용과 자화역전 현상

하지층의 스퍼터링 압력을 달리하여 제작한 Cr/CoSm/Cr 자성막의 자기상호작용과 자화역전 현상

Low temperature magnetic and magnetocaloric studies in YCr0.85Mn0.15O3 ceramic

We have investigated low temperature magnetic and magnetocaloric properties of manganese (Mn) doped YCr0.85Mn0.15O3 (YCMO) polycrystalline compound, synthesized via solid state reaction route. The lattice volume was found to increase in comparison to that of pristine YCrO3 (YCO) compound. On the other hand, the paramagnetic-antiferromagnetic Néel temperature (TN ∼ 132 K) was found to be lower than that for YCO ceramic. On cooling below TN, under field cooled (FC) mode with an applied magnetic field of 0.02 T, magnetization flipped the polarity from positive to negative at Tcomp = 62 K. Furthermore, the magnetization switching temperature, defined as compensation temperature, exhibited field dependency and decreased with increasing field. Besides, the magnetization reversal phenomenon disappeared under higher applied magnetic field values. For the first time, the magnetocaloric effect for this compound was measured near 36 K through the parameters like magnetic entropy change (−ΔS) = ∼0.186 J kg−1 K−1 and the relative cooling power (RCP) ∼ 6.65 J kg−1, under an applied field of 5 T.