Temperature Dependence Of Magnetic Properties Research Articles

Dependence of the Structural and Magnetic Properties on the Growth Sequence in Heterostructures Designed by YbFeO3 and BaFe12O19.

The structure and the chemical composition of individual layers as well as of interfaces belonging to the two heterostructures M1 (BaFe12O19/YbFeO3/YSZ) and M2 (YbFeO3/BaFe12O19/YSZ) grown by pulsed laser deposition on yttria-stabilized zirconia (YSZ) substrates are deeply characterized by using a combination of methods such as high-resolution X-ray diffraction, transmission electron microscopy (TEM), and atomic-resolution scanning TEM with energy-dispersive X-ray spectroscopy. The temperature-dependent magnetic properties demonstrate two distinct heterostructures with different coercivity, anisotropy fields, and first anisotropy constants, which are related to the defect concentrations within the individual layers and to the degree of intermixing at the interface. The heterostructure with the stacking order BaFe12O19/YbFeO3, i.e., M1, exhibits a distinctive interface without any chemical intermixture, while an Fe-rich crystalline phase is observed in M2 both in atomic-resolution EDX maps and in mass density profiles. Additionally, M1 shows high c-axis orientation, which induces a higher anisotropy constant K1 as well as a larger coercivity due to a high number of phase boundaries. Despite the existence of a canted antiferromagnetic/ferromagnetic combination (T < 140 K), both heterostructures M1 and M2 do not reveal any detectable exchange bias at T = 50 K. Additionally, compressive residual strain on the BaM layer is found to be suppressing the ferromagnetism, thus reducing the Curie temperature (Tc) in the case of M1. These findings suggest that M1 (BaFe12O19/YbFeO3/YSZ) is suitable for magnetic storage applications.

Annealing temperature dependence of magnetic properties in FeCo ordered alloy thin films fabricated using the nitrogen surfactant effect

L10-FeCo has attracted attention as a new, rare-metal-free magnetic material due to its large uniaxial magnetic anisotropy. However, the low stability of the L10 phase hampers its practical application. We here intend to prepare FeCo alloy thin films by utilizing the nitrogen surfactant effect. The enhancement of the out-of-plane magnetization of this thin film was observed by stacking cobalt single atomic layer on bilayer iron nitride and subsequent annealing at 470 K. This study provides an insight into the relationship between structural changes and magnetic properties of the FeCo interface on the atomic scale, and paves the way for the development of rare metal-free magnetic materials.

Finite temperature properties of rare earth free Fe4CoSi permanent magnet

Developing rare-earth free permanent magnet is attracting extensive research efforts for several device applications and other issues. Here, we investigate the temperature-dependent magnetic properties of the Fe4CoSi alloy. The Fe4CoSi alloy shows a high critical temperature of 980 K with perpendicular magnetic anisotropy. At room temperature, it exhibits a magnetization of 1.44 T, anisotropy constant of 0.8 MJ/m3, and a magnetic hardness parameter of 0.75. We obtain the (BH)max of 554 kJ/m3 at 0 K, 410 kJ/m3 at 300 K, and 215 kJ/m3 at 600 K without demagnetization effect. Even with a demagnetization factor of 0.3, the Fe4CoSi alloy still possesses the (BH)max of 268 kJ/m3 at room temperature. The Fe4CoSi exhibits better permanent magnetic properties compared with ferrites and SmCo5. This may imply that the Fe4CoSi alloy can be a potential Fe-based gap permanent magnet between ferrite and Nd-Fe-B (or Sm–Co) at room temperature.

Synthesis of lithium doped magnesium ferrites and their vibrational and magnetic properties: Correlation of experimental and density functional theory

Recently, there has been an increased focus on investigating the possible use of ferrite nanoparticles as magnetic memory devices. In this study, we report on the structural, microstructural, Raman, density functional theory and magnetic characteristics of Mg1-xLixFe2O4 (x = 0, 0.15, 0.3, 0.45, 0.5 and 0.75). Samples were synthesized by solution combustion synthesis method. Samples were subjected to characterize X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman Spectra. XRD reveals that all synthesized samples show a single phase formation and unit cell volume, crystallite size varied with an increase in Lithium-ion concentration. SEM micrographs confirmed the porous nature increases with the rise of Li concentration. Particles are agglomeration and spherical type of nature was confirmed by TEM images. Further, Raman Spectra confirms the spinel cubic structure of MgFe2O4 nanoparticles belongs to the Fd3m space group. Despite the fact that the full unit cell has 56 atoms (Z = 8), the smallest Bravais cell consists of only 14 atoms (Z = 2). Consequently, in order to understand this effect, the electronic structure of pure and doped models was investigated through the Band Structure and Density of States (D.O.S.) profiles. First the crystalline structure of pure and Li-doped MgFe2O4 was analyzed based on the optimized lattice parameters and M − O (M = Mg, Li and Fe) bond distances. The band-gap was computed to be 2.54 eV being a direct transition between two points, in an excellent agreement with the experimental measurements. To investigate the temperature dependent magnetic properties, the M − H loops of Li doped MgFe2O4 nanoparticles traced at below and above room temperature over the applied magnetic field ±60 kOe. The M − H loops recorded at above and below room temperature demonstrated that the ferromagnetic nature of the sample. Further, the magnetic properties was investigated using temperature dependent FC and ZFC magnetization measurements. Above room temperature, the ZFC and FC curves show irreversibility and split at certain temperatures, as well as a broad maximum in ZFC curves at blocking temperature (TB). Saturation magnetization (Ms) values are higher at 15 K compared to 300 K, attributed to reduced thermal fluctuation. Our results suggest that synthesized materials are useful for room temperature magnetic memory device application.

Influence of Pt Ultrathin Interlayers on Magnetic Anisotropy in Ni/NiO Multilayers

Perpendicular magnetic anisotropy at transition metal/oxide interfaces plays a significant role in technological applications such as magnetic storage and spintronics. In this study, we investigate the effects of thermal annealing and Pt ultrathin interlayers on the magnetic anisotropy in Ni/NiO multilayers. Ni/NiO/Pt multilayers were fabricated via radiofrequency magnetron sputtering and natural oxidation. The static magnetic properties of the samples were studied using temperature-dependent SQUID magnetometry. We focus on a sample with a Nickel thickness of 6.7 nm in each multilayer period. This multilayer in Ni/NiO form showed the maximum enhancement of perpendicular magnetic anisotropy after mild thermal annealing in past work. In this work, we study the effects of ultrathin Pt interlayers on the magnetic properties of such a Ni/NiO multilayer before and after annealing. We have observed a further increase in perpendicular magnetic anisotropy, and we study the temperature-dependent magnetic properties of this system, which combines the favorable magnetic properties of Ni/Pt and Ni/NiO multilayers.

The Study of Temperature-Dependent Magnetic Properties Variation in CoCr2O4 Nanoparticles with (y = 0.8) and Without Coating Concentration of Non-Magnetic (SiO2)y

Abstract The present study investigates the temperature-dependent magnetic (MT) properties of CoCr2O4/(SiO2)y (y = 0 and 0.8) nanoparticles. Nanoparticles were synthesised by using the conventional sol–gel technique. The X-ray diffraction (XRD) method confirmed the normal spinel structure of CoCr2O4 nanoparticles. The main peak analysis of the XRD pattern using Debye–Scherrer’s formula probes the mean crystallite sizes for coated and uncoated nanoparticles, and the sizes based on which the probes have been carried out amount to 19 nm and 28 nm, respectively. The transmission electron microscopy (TEM) image showed the non-spherical shape of these nanoparticles. Field-cooled (FC) and zero field-cooled (ZFC) MT plots were taken by using a superconducting quantum interference device (SQUID) magnetometer. Pure CoCr2O4 nanoparticles showed the ferrimagnetic transition at Curie temperature (Tc = 99 K) on an applied field (H) of 50 Oe. Tc decreased up to 95 K with the increase in 80% SiO2 concentration in CoCr2O4 nanoparticles. For pure samples, conical spiral temperature (TS) and lock-in transition temperature (TL) remain unchanged with increasing magnetic field because of strong spin–lattice coupling. However, for 80% SiO2 impurity, the decrease in Tc was attributed to the reduction in surface disorder with a minor decline in TS and TL. The Ms declined with a decrease in temperature because of the existence of stiffed/strong conical spin-spiral and lock-in states in pure CoCr2O4 nanoparticles, while nanoparticles with 80% coating SiO2 concentration showed abnormal behavior. The coercivity increases with a decrease in temperature due to a decrease in thermal fluctuations at low temperatures for both samples. The fitting of coercivity (Hc) versus temperature plot by using Kneller’s law has given the values of coercivity constant (α) and coercivity at average blocking temperature (TB) for both samples, which are α = 0.54, TB = 75 K and α = 1.59, TB = 81 K, respectively. Hence, the increase in the concentration of SiO2 decreased nanoparticles size and surface disorder in CoCr2O4 nanoparticles while enhancing Ms below spin-spiral state ordering.

Role of Y3+ on the temperature-dependent magnetic properties of Lu orthoferrite prepared by solution combustion method using a mixture of fuels

Role of Y3+ on the temperature-dependent magnetic properties of Lu orthoferrite prepared by solution combustion method using a mixture of fuels

Temperature dependent structural properties of Mn1.90M0.10O3 (M = Cr and Fe)

The polycrystalline samples of Mn1.90Cr0.10O3 (MCO) and Mn1.90Fe0.10O3 (MFO) have been investigated for their temperature dependent magnetic and structural properties. The Cr and Fe substitutions have significant effect on the magnetic and structural properties of Mn2O3. Like pristine Mn2O3, the Cr and Fe substituted samples MCO and MFO also exhibit two antiferromagnetic transitions; one at ∼77 K, ∼80 K, respectively and another at ∼40 K. Our room temperature synchrotron x-ray powder diffraction (SXRD) results confirm that both the MCO and MFO samples crystallize in cubic symmetry. The temperature dependent SXRD results demonstrate the cubic to orthorhombic structural transition for the studied samples. The pristine Mn2O3 shows cubic to orthorhombic transition around 310 K, whereas this structural transition shifted towards lower temperature side with these substitutions i.e. around 240 K for MCO and 260 K for MFO. Interestingly, the centrosymmetric Pcab to non-centrosymmetric Pca21 change in symmetry is also resolved at the ferroelectric ordering temperature for MCO.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Inclusion of CoFe2O4 ultrafine nanoparticles in 7CB liquid crystal: effects on temperature-dependent magnetic properties and insights for expanding the application of LC systems in hyperthermia treatments

ABSTRACT This work presents a comprehensive analysis of the magnetic properties of pristine and citric acid-coated cobalt ferrite ( CoF e 2 O 4 ) nanoparticles (NPs) dispersed in the host nematic 4 ′ -heptyl-4-biphenylcarbonnitrile (7CB) system. Our results shed light on the promising potential of combining liquid crystals (LC) with magnetic nanoparticles for cancer treatment. This opens up exciting avenues for further exploration and possible applications in the field of oncology. The study focuses on examining the magnetic behaviour of LC dispersed systems with two concentrations of magnetic nanoparticles (0.03 and 0.04 wt%). Notably, intriguing temperature-dependent magnetisation plots reveal a distinctive cusp, which can be attributed to the freezing phenomenon of the liquid crystal. This observation offers valuable insights into the system's magnetic properties and interactions, deepening our understanding of its behavior.

Ultra-thin 2D Fe3GaTe2 rare-earth free permanent magnet at finite temperatures

Despite extensive studies on permanent magnets (PMs) in bulk-type materials, the possibility of PMs in two-dimensional (2D) materials is barely explored so far. In this work, we systematically investigate temperature dependent magnetic properties of 2D trilayer and four-layer Fe3GaTe2 systems based on the first principle calculations. The calculated Curie temperature (T C) in both trilayer and four-layer structures are 340 K–352 K. Both systems have perpendicular magnetic anisotropy, and the uniaxial anisotropy constant is monotonically decreased with increasing temperature. At 300 K, the 2D Fe3GaTe2 has a coercive field of 0.34 T in the trilayer and it becomes 0.44 T in the four-layer. Besides, both systems have a magnetic hardness parameter κ larger than 1 even at 300 K. We also obtain a maximum energy product (BH)max of 24 kJ m−3 in the trilayer, and it is further increased to 26 kJ m−3 in the four-layer at 300 K. Nonetheless, these (BH)max are decreased by more than two times with including the demagnetization factor. Overall, we obtain that 2D Fe3GaTe2 at 2–3 nm (trilayer and four-layer) thickness possesses the same scale of coercive field and maximum energy product of well-known bulk ferrite PM. Our findings may indicate that the atomically thin 2D system can be a potential rare-earth-free PM for small-scale device applications.

Growth rate and substrate temperature dependent magnetic and magneto-microstructural properties of sputtered Fe-Co-Al thin films

This work reports the effect of growth rate and substrate temperature on the structural, magnetic and magneto-microstructural properties of Fe-Co-Al alloy thin films. 75 nm thick Fe-Co-Al films were deposited on Si 〈100〉 substrates at room temperature by high power impulse magnetron sputtering at different growth rates viz., 0.67–1.6 Å/s. All the films exhibited a uniform composition of about Fe60Co25Al15 irrespective of growth rates. In addition to this, all the films crystallized in single phase with bcc type structure. Growth rate was found to have a considerable impact on the magnetic properties of Fe-Co-Al thin films. Film grown at 1.3 Å/s exhibited an in-plane magnetic anisotropy with large saturation magnetization combined with low coercivity when compared with other films. To improve the magnetic properties further, Fe-Co-Al films were also processed at different substrate temperatures (Ts) viz., 300, 400 and 500 °C. Substrate temperature of about 300 °C was found to have beneficial effect on the soft magnetic characteristics of Fe-Co-Al films. While the crystal structure did not show any perceptible change with processing conditions, magnetic microstructures traced from magneto optic Kerr microscopy displayed substantial change. Upon increase in substrate temperature, during magnetization reversal process, magnetic domain images traced along the easy magnetization direction magnetization showed transformation from branched band domains (as-deposited) → wide band domains (Ts = 300 °C) → less periodic branched band domains (Ts = 400 °C) → ripple domains (Ts = 500 °C). Attempts were made to correlate the achieved magnetic properties in Fe-Co-Al with magnetic microstructures.

Te doping effects on the ferromagnetic performance of the MnGe/Si quantum dots grown by ion beam sputtering deposition

Dilute magnetic MnGe quantum dots (QDs) have been a popular research topic due to their great potential application on spintronics and their natural compatibility with today's highly developed silicon-based complementary metal oxide semiconductor (CMOS) technology. However, the relatively low Curie temperature impedes their ability to maintain the ferromagnetic phase and creates difficulty for their practical application in spintronics at room temperature. Here, we report the first preparation of the Te-doped dilute-magnetic Mn0.064Ge0.895Te0.041/Si QDs by using the ion beam composite target sputtering technique. Growth temperature and deposition thickness dependent QDs density and magnetic properties were investigated systematically. The experimental results indicate that the QD density of Mn0.064Ge0.895Te0.041/Si sample increases first and then reduces with the deposited thickness, while the QDs' diameters increase monotonously from 10.18 ± 0.21–33.6 ± 0.34 nm. Curie temperature of 369 K observed in Mn0.064Ge0.895Te0.041 QDs is higher than that of 295 K observed in Mn0.061Ge0.939 counterparts grown at the same conditions. Correspondingly, the saturation and residual magnetization in the former are much higher than in the latter. The ferromagnetic enhancement can be attributed to that the nonpolar Mn0.064Ge0.936 QDs transform into Rashba polar Mn0.064Ge0.895Te0.041 QDs with the doping of Te ions, which obviously promotes the exchange coupling between holes and Mn atoms. Our work provides a practical approach for improving the ferromagnetism and Curie temperature of silicon-based diluted magnetic semiconductor QDs.

Electrodeposition of Platinum-Transition Metal Alloys for Magnetic Thermometry

The present work seeks to develop materials and structures with temperature-dependent magnetic properties providing optimal sensitivity for near-room temperature thermometry. Studies of the electrodeposition of Pt1-xMx (M=Ni,Co) alloys will be presented. The effects of boric acid and deposition potential on the deposition process and magnetic properties of Pt1-xNix and Pt1-xCox films will be compared. For Pt1-xNix, it was found that the presence of boric acid during deposition was accompanied by decreased Coulombic efficiency at more reducing deposition potentials, increased oxygen incorporation, and decreased magnetization relative to films deposited in the absence of boric acid.[1] Preliminary results for the Pt1-xCox system indicate its behavior is not simply analogous to the Pt1-xNix system.[1] Rus, E. D.; L. Corrêa, E.; Groopman, E.; Williamson, T.; Hijazi, H.; Kasaei, L.; Dennis, C. L.; Moffat, T. P., Magnetic Characterization of Electrodeposited Pt1−xNix Alloy Films: Influence of Deposition Potential and the Presence of Boric Acid, J. Electrochem. Soc. 2022, 169 (9), 10.1149/1945-7111/ac8ad1.

Spring exchange mechanism and temperature dependent magnetic properties of BaFe12O19/CoFe2O4 nanocomposites

Bare BaFe12O19, CoFe2O4, and their nanocomposites with concentration percentage 30–70, 50–50 and 70–30 were synthesized by sol–gel approach. The average crystallite size < D > of bare BaFe12O19 nanoparticles (NPs) was 35 nm which gets reduced with the addition of CoFe2O4 phase and found minimum for bare CoFe2O4 nanoparticles, i.e. 12 nm. Transmission electron microscopy (TEM) image showed the agglomeration of nanocomposites and mean particle size was observed to be 44 nm as estimated from normal size distribution. The ZFC/FC curves exhibited that the blocking temperature TB of all samples lies above room temperature. However, a small broad peak at ∼ 75 K in pure BaFe12O19 NPs is attributed to the surface freezing peak (Tf). The flatness in FC curve at low temperature with the addition of CoFe2O4 phase revealed the strong inter-particle interactions. From M−H loops, the value of saturation magnetization (MS) for Ba70/Co30 was found to be maximum (100.82 emu/g) than their corresponding bare nanoparticles. The higher value of MS showed the presence of exchange spring mechanism in these samples. The coercivity of BaFe12O19 sample was observed to be 4262 Oe which get increased with the addition of CoFe2O4 phase and found maximum for CoFe2O4 (7349 Oe), which shows the hard magnetic nature of CoFe2O4 NPs. However, the smaller value of Bloch’s constant “B” for BaFe12O19 phase (4.8 x10−6K-3/2) showed the strong intra-particle interactions in the core of BaFe12O19 NPs. The dM/dH vs. H curves showed the well-established exchange coupling of both hard and soft magnetic phases for 50% concentration of both phases and may be beneficial for high density recording devices.

Temperature dependence of semi-hard iron silicide rare-earth free magnet

Searching for rare-earth free permanent magnet attracts extensive research interests due to diverse technological applications and other subtle issues. Here, the temperature dependent magnetic properties of Fe5SiC structure are explored. The Fe5SiC has a critical temperature of 710 K with perpendicular magnetic anisotropy. The magnetic anisotropy constant and coercive field are monotonically decreased with increasing temperature. For instance, the magnetic anisotropy constant is 0.42 MJ m−3 at zero Kelvin and reduced to 0.24 MJ m−3 and 0.06 MJ m−3 at 300 K and 600 K. The coercive field becomes 0.7 T at 0 K. With increasing the temperatures, it is suppressed to 0.42 T and 0.20 T at 300 K and 600 K, respectively. Overall, the Fe5SiC system has a (BH)max of 417 kJ m−3 at zero Kelvin. The (BH)max is decreased at high temperature. Nonetheless, we obtain the (BH)max of 234 kJ m−3 at 300 K. Since the Fe5SiC shows better permanent magnetic (PM) property than the conventional ferrites and also CeCo5. This finding may indicate that the Fe5SiC can be a potential candidate as a Fe-based gap PM between ferrite and Nd–Fe–B (or Sm–Co) at room temperature.

Dual Charge Transfer Generated from Stable Mixed-Valence Radical Crystals for Boosting Solar-to-Thermal Conversion.

Realizing dual charge transfer (CT) based on stable organic radicals in one system is a long-sought goal, however, remains challenging. In this work, a stable mixed-valence radical crystal is designed via a surfactant-assisted method, namely TTF-(TTF+• )2 -RC (where TTF = tetrathiafulvalene), containing dual CT interactions. The solubilization of surfactants enables successful co-crystallization of mixed-valence TTF molecules with different polarity in aqueous solutions. Short intermolecular distances between adjacent TTF moieties within TTF-(TTF+• )2 -RC facilitate both inter-valence CT (IVCT) between neutral TTF and TTF+• , and inter-radical CT (IRCT) between two TTF+• in radical π-dimer, which are confirmed by single-crystal X-ray diffraction, solid-state absorption, electron spin resonance measurements, and DFT calculations. Moreover, TTF-(TTF+• )2 -RC reveals an open-shell singlet diradical ground state with the antiferromagnetic coupling of 2J = -657 cm-1 and an unprecedented temperature-dependent magnetic property, manifesting the main monoradical characters of IVCT at 113-203 K while the spin-spin interactions in radical dimers of IRCT are predominant at 263-353 K. Notably, dual CT characters endow TTF-(TTF+• )2 -RC with strong light absorption over the full solar spectrum and outstanding stability. As a result, TTF-(TTF+• )2 -RC exhibits significantly enhanced photothermal property, an increase of 46.6°C within 180 s upon one-sun illumination.

Growth temperature dependent magnetic properties of Fe film on BaTiO3

We report on the growth temperature effect on magnetic coercivity (HC) and saturation magnetization (MS) of epitaxial Fe films grown on BaTiO3 (BTO). A tensile strain is observed in Fe films grown on tetragonal BTO below the growth temperature of 120 °C, whereas a compressive strain is induced in Fe films grown on cubic BTO above the growth temperature of 120 °C. Combining the lattice mismatch compressive strain and tensile thermal strain, the strongest tensile strain in Fe30 and the compressive strain in Fe400 are opposite trend to the expectation, which may be due to the FeOx interface layer with larger lattice constant. The HC grew from 14.6 to 66.6 Oe as the growth temperature increased from 30 to 400 °C, while the MS reduced from 2129 to 1244 emu/cm3.

Atomistic Simulation of Temperature Dependent Magnetic Properties of Hole Doped 2H-VSe₂ Bilayer

Density functional theory calculations provide very accurate physical quantities at zero Kelvin. Nonetheless, it is necessary to understand how the physical quantities are changed at finite temperatures for real device application purposes. Here, we investigate the finite temperature dependent magnetic properties of hole doped 2H-VSe₂ bilayer structure using atomistic simulation. We find that the Curie temperature of 600 K at the hole concentration of 2.27×10SUP20/SUP cmSUP-3/SUP, and this is enhanced to 620 K at the hole concentration of 3.01×10SUP20/SUP cmSUP-3/SUP. We fit the temperature dependent magnetization curve (M(T)) using both Curie-Bloch and Kuz’min equations. We also calculate temperature dependent magnetic anisotropy energy. We find that the magnetic anisotropy energy is almost linearly decreased with increasing temperature. Besides, we obtain that the normalized temperature dependent anisotropy constant [K(T)/K(0)] shows the relation to the temperature dependent magnetization curve of [M(T)/M(0)] SUP2.9/SUP, and this is well converged with the exponent of 2.9 in the Callen-Callen theory.

Hard ferrite magnetic insulators revealing giant coercivity and sub-terahertz natural ferromagnetic resonance at 5-300 K.

The temperature behavior of the magnetic properties is crucial for the application of magnetic materials. Recently, giant room temperature coercivities (20-36 kOe) and sub-terahertz natural ferromagnetic resonance (NFMR) frequencies (160-250 GHz) were observed for single-domain M-type hexaferrites with high aluminum substitution. Herein, the temperature dependences of the magnetic properties and natural ferromagnetic resonance are studied at 5-300 K for single-domain Sr1-x/12Cax/12Fe12-xAlxO19 (x = 1.5-5.5) particles. It is shown that the samples maintain their magnetic hardness over the whole temperature range. The coercivity and NFMR frequencies have a maximum shifting to the low-temperature region with a rise in aluminum concentration. The highest coercivity of 42 kOe and the maximum NFMR frequency of 297 GHz are observed for x = 5.5 at 180 K.