Temperature Dependence Of Magnetization Research Articles

Temperature variation of surface magnetization in antiferromagnetic six lines ferrihydrite nanoparticles

Six lines ferrihydrite nanoparticles are synthesized following a chemical route. The sample is characterized using x-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Average crystallite size is 5 nm. The sample exhibits superparamagnetic behavior. Magnetization versus magnetic field data in the superparamagnetic region are analyzed considering a distribution in particle size. Temperature dependence of saturation magnetization originating from surface spins and antiferromagnetic susceptibility of particle cores are studied.

Phonon frequency and its modification by magnon–phonon coupling from all-temperature theory of magnon

The all-temperature magnon (ATM) theory [Datta and A. Panda, J. Phys. Condens. Matter 21, 336003 (2009)] has been used to analyze the temperature dependence of magnetization and internal energy components of a mono-domain ferromagnetic solid. One impact of the ATM formulation is that calculated critical exponents are in better agreement with experiments than their counterparts from mean-field and critical phenomenon theories. These exponents can vary from one ferromagnet to another of similar symmetry and dimensionality but differing in spin and can be field-dependent. The ATM finding is that exponent β depends on spin and increases as T approaches TC, whereas the exponent γ is weakly dependent on spin and the applied field but relies on crystal symmetry. The main thrust of the present work has been to derive the thermally averaged spin-center force constants in terms of the baseline related (solid) and exchange-cum-field mediated (magnetic) components and to formulate phonon frequencies and their modifications by magnon–phonon coupling. The derived expressions are suitable for correct quantum chemical evaluation. A detailed calculation on different spin configurations at varying geometries is still hardly possible and beyond the scope of the present work that emphasizes the correctness of formulas and has the significance of explaining properties. The phonon frequency shift due to lattice expansion is always negative. It is also clarified that frequency modification by the magnon–phonon interaction is negative for certain phonon branches near TC, and the ratio of frequency modification and phonon frequency is approximately proportional to the ratio of curvatures of involved energy surfaces.

Observation of itinerant ferromagnetic behaviour in equiatomic medium entropy AlNiCo alloy

A medium entropy AlNiCo alloy has been synthesized by vacuum arc melting, which shows single phase B2 structure. Atom probe tomography analysis showed that the elements are homogeneously and randomly distributed in AlNiCo alloy without any clustering tendency. A detailed analysis of temperature and field dependent magnetization data suggests an itinerant ferromagnetic ground state of AlNiCo alloy. The magneto crystalline anisotropy is evaluated to be 1.03 × 105 ergs/cm3 at 5 K. A broad maximum at low temperature in zero-field-cooled (ZFC) magnetization, as well as irreversibility of ZFC and field-cooled (FC) curves indicated a glassy behavior. This observation is supported by the memory effects observed at low temperature. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions. To the best of our knowledge, this is the first report on microstructure and magnetic properties of an equiatomic ternary AlNiCo alloy.

Magnetocrystalline anisotropy of interstitially and substitutionally Sn-doped MnBi for high temperature permanent magnet applications

First-principles calculations were performed to calculate the electronic structures of low temperature phase (LTP) MnBi (Mn50Bi50) and substitutionally and interstitially Sn-doped MnBi [Mn50Bi25Sn25, (Mn0.5Bi0.5)66.7Sn33.3]. Brillouin function predicts the temperature dependence of saturation magnetization M(T). Sn substitution for Bi in MnBi (Mn50Bi25Sn25) changes the magnetocrystalline anisotropy constant (Ku) from −0.202 MJ/m3 (the in-plane magnetization) for LTP MnBi to 1.711 MJ/m3 (the out-of-plane magnetization). In comparison, the Ku remains negative but slightly decreases to −0.043 MJ/m3 when Sn is interstitially doped in MnBi [(Mn0.5Bi0.5)66.7Sn33.3]. The Curie temperature (TC) decreases from 716 K for LTP Mn50Bi50 to 445 K for Mn50Bi25Sn25 and 285 K for (Mn0.5Bi0.5)66.7Sn33.3. Mn50Bi25Sn25 has a lower magnetic moment of 5.034 μB/f.u. but a higher saturation magnetization of 64.2 emu/g than (Mn0.5Bi0.5)66.7Sn33.3 with a magnetic moment of 6.609 μB/f.u. and a saturation magnetization of 48.2 emu/g because the weight and volume of the substitutionally Sn-doped MnBi are smaller than the interstitially Sn-doped MnBi. The low Curie temperature and magnetization for Sn-doped MnBi are attributed to the high concentration of Sn. Thus, future study needs to focus on low Sn-concentrated MnBi.

Synthesis of Fluorous Ferrofluids and Effects of the Nanoparticle Coatings on Field- and Temperature-Dependent Magnetizations.

Ferrofluids have been extensively employed in industrial, environmental, and biomedical areas. Among them, fluorous ferrofluids are of particular interest because of the biorthogonal nature of perfluorocarbons (PFCs). However, the noninteracting nature of PFCs as well as challenges in functionalization of nanoparticle surfaces with fluorous ligands has limited their applications, especially in biomedicine. In particular, commercially available fluorous ferrofluids are stabilized using ionic surfactants with charged groups that physically interact with a wide range of charged biological molecules. In this paper, we developed a unique two-phase ligand attachment strategy to render stable fluorous ferrofluids using nonionic surfactants. The superparamagnetic Fe3O4 or MnFe2O4 core of the magnetic nanoparticles, the magnetic component of the ferrofluid, was coated with a silica shell containing abundant surface hydroxyl groups, thereby enabling the installation of fluorous ligands through stable covalent, neutral, siloxane bonds. We explored chemistry-material relationships between different ligands and PFC solvents and found that low-molecular-weight ligands can assist with the installation of high-molecular-weight ligands (4000-8000 g/mol), allowing us to systematically control the size and thickness of ligand functionalization on the nanoparticle surface. By zero-field-cooled magnetization measurements, we studied how the ligands affect magnetic dipole orientation forces and observed a curve flattening that is only associated with the ferrofluids. This work provided insight into ferrofluids' dependence on interparticle interactions and contributed a methodology to synthesize fluorous ferrofluids with nonionic surfactants that exhibit both magnetic and chemical stability. We believe that the doped MnFe2O4 fluorous ferrofluid has the highest combination of stability and magnetization reported to date.

Correlating structural and magnetic ground states of 3d-5d based double perovskites: Evidence of two magnetic phase transitions

We present a detailed study on both the structural and magnetic properties of the Sr2RuMn1-xIrxO6double perovskite oxides with four different concentrations (x = 0, 0.25, 0.5 and 0.75). The main objective of the work is to study the effect of Ir substitution for Mn on the high-temperature crystallographic and low-temperature magnetic phases of the compounds. Thephase purity was confirmed by the Rietveld analysis of the X-ray diffraction (XRD)pattern. The high temperature crystallographic information of the compounds was investigated by the help of high temperature X-ray diffraction and Raman spectroscopy. Signature of two structural phase transitions for x = 0.75 and one structural phase transition for x = 0 was seen. FESEM (Field emission scanning electron microscopy) with EDS (energy dispersive spectroscopy) of Ir-01 (x = 0.25) confirmed the presence of all the elements in the sample. The magnetic structure of all the samples have been studied at low temperature (5 K). The existence of two magnetic transitions for x = 0.5 and x = 0.75 are evident from the temperature dependent magnetization behavior.

Phase stabilization of double perovskite Sm2FeMnO6 and the study on its Structural, magnetic and dielectric properties

Sm2FeMnO6 offers combined physical properties of two single perovskite compounds SmFeO3 and SmMnO3, making it a technologically feasible functional material. Sm2FeMnO6 crystallizes in a distorted orthorhombic Pbnm symmetry with lattice parameters a = 5.3805(2) Å, b = 5.6182(2) Å and c = 7.6434(3) Å. The Fe/Mn cation arrangement is found to be random in this symmetry. The phonon modes concurrent to the existence of (Fe/Mn)O6 octahedra and Jahn-Teller distortion due to Mn ions are found. Both Fe and Mn ions present at the B-octahedral sites have trivalent state. Temperature and field dependent magnetization measurements on Sm2FeMnO6 illustrate multiple transitions. A distinctive switching associated with a spontaneous spin-flip transition of Sm and Mn/Fe sublattices are observed at 201 K and 206 K in ZFC and FC curves respectively. The antiferromagnetic to paramagnetic transition occurred at a Neel temperature of 491 K. The transition temperatures are lowered compared to the reported single perovskite SmFeO3 indicating the influence of Mn ions on the magnetic exchange integral chains. Thermally activated dielectric relaxation processes are observed in the temperature range 300 K to 500 K and near 700 K. The anomaly is found to exist in the magnetic transition region, evidencing the coupling of magnetic order with electric order parameter. Thus, the collective effect of Fe and Mn ions at the B-site on various physical properties of Sm2FeMnO6 opens up new avenues in the field of magnetoelectric applications.

Trapped flux in pure and Mn-substituted CaKFe4As4 and MgB2 superconducting single crystals

Measurements of temperature dependent magnetization associated with trapped magnetic flux in single crystals of CaKFe4As4, CaK(Fe0.983Mn0.017)4As4 and MgB2 using zero-field-cooled and field-cooled protocols are presented. The results allow for the determination of the values of superconducting transition temperature, lower critical field and self-field critical current density. These are compared with the literature data. Possible experimental concerns are briefly outlined. Our results, on these known superconductors at ambient pressure, are qualitatively similar to those recently measured on superhydrides at megabar pressures (Minkov et al 2023 Nat. Phys. https://doi.org/10.1038/s41567-023-02089-1) and, as such, hopefully serve as a baseline for the interpretation of high pressure, trapped flux measurements.

Signature of filamentary superconductivity in centrosymmetric silicide LuScSi

Discovery of new superconductors with different crystal structure and exotic physics provides a great prospect for better understanding of superconducting mechanism. In this context, a detailed investigation of the structural, magnetic and electrical transport properties of a new superconducting alloy, LuScSi have been reported. Temperature (T) and magnetic field (H) dependent magnetisation (M) analysis reveals the onset of filamentary superconductivity below TC ∼ 4.2 K, which is among the highest value of TC that has been reported for LuTX (T = transition element, X = p block element) systems. This is corroborated with T and H dependent resistivity (ρ) and heat capacity (C) studies. Interestingly, in normal state, ρ exhibits a non-Fermi liquid behaviour (ρ (T) ∝ T2.38) in the range 5 < T < 50 K and Bloch-Gruneisen–type T dependence for 50 K < T < 250 K. The Kohler scaling is also employed on the magnetoresistance (MR) data indicating a single scattering rate across the Fermi surface in the normal state. Our studies reflect the conventional nature of moderately coupled superconducting state of this alloy.

Borderline first-order phase transition and large cryogenic magnetocaloric effect in PrNdIn

We report a large cryogenic magnetocaloric effect stemming from an unconventional borderline first-order magnetic phase transition with negligibly small thermomagnetic hysteresis in a rare-earth-based intermetallic compound PrNdIn. The sample exhibits maximum magnetic field-induced entropy change as large as −10 J/Kg K (for 20 kOe magnetic field change) near the boiling point of oxygen. Magnetocaloric properties of PrNdIn are comparable to those of other known potential magnetocaloric materials with operating temperatures ranging between 50 and 125 K. The magnetic properties of the present sample are qualitatively reminiscent of those of the binary Pr2In and Nd2In, including the emergence of a second low-temperature anomaly in the temperature dependence of magnetization.

Synthesis, structural, impedance, optical, Mössbauer characterizations and magnetic studies of Pb-containing germanate compounds

The orthorhombic antiferromagnetic germanate minerals Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9 have been prepared via solid state reaction procedure. An extensive study of structural, dielectric, optical and magnetic properties of both the germanates have been investigated by employing different measurements such as X-ray diffraction, FTIR, SEM, impedance, UV–Vis–NIR & Mössbauer spectroscopic and magnetometary. Rietveld refinement of room temperature XRD patterns revealed that both the compounds crystallize in the orthorhombic space group Pbcn. FTIR spectrum exhibits the presence of M−O & Ge–O bonds which confirms strong chemical bonding. Morphological analysis through SEM showed good crystallinity of both the samples. The variation of dielectric constant, loss tangent and impedance with frequency have been studied and it has been established that both the germanates are semiconducting at 300K (RT) which may be attributed to the stacking of ions at grain boundaries. The optical band gaps estimated by UV–Vis–NIR spectroscopic measurements further confirms the semiconducting nature of the prepared germanates. 57Fe Mössbauer spectroscopic measurement on synthesized Pb2Fe2Ge2O9 sample was carried out at RT. The obtained values of IS and QS showed that iron is in Fe3+ high spin state (t2g3eg2,s=5/2) and occupy two different sites, Fe1 and Fe2. The field dependent magnetization measurements show that both the compounds display dominant paramagnetic nature at 300K. The temperature dependent magnetization data reveal very sharp first order type AFM to PM transition at TN ∼50K and TN ∼8K for Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9, respectively, and weak FM nature below Neel temperature. The field dependent properties of both the compounds have been analyzed by drawing the M versus H plots at low and room temperatures. The values of calculated effective magnetic moment 6.07μB and 3.95μB for Fe3+ and Mn3+ ions are in the high spin states (t2g3eg2,s=5/2 and )t2g3eg1,s=2.

Structural and magnetic properties of nanoparticles of La3Ni2NbO9 double perovskite

The nanoparticles of La3Ni2NbO9 (LNNO) have been produced via the glycine-nitrate combustion technique followed by a process of calcination with an average crystallite size of ∼ 25 nm. The powder X-ray diffraction (XRD) pattern was analyzed for structure analysis by Rietveld structure refinement. Study on the XRD pattern reveals that LNNO crystallizes in the single phase of monoclinic crystal structure with P21/n space group. Analysis of temperature-dependent magnetization reveals that nanoparticles of LNNO undergo paramagnetic to antiferromagnetic phase transition at Neel temperature TN ∼ 43 K and antiferromagnetic to spin glass transition at Tg ∼ 31.45 K. Analysis of magnetic ac-susceptibility reveals that the LNNO nanoparticles follow Vogel-Fulcher and dynamic scaling power laws in the low-temperature region.

Temperature dependent magnetic properties of crystallographically amorphous TbCo: An atomistic simulation study

Due to interesting properties such as perpendicular magnetic anisotropy (PMA), ferrimagnetism, etc., rare earth-transition metal(RE-TM) alloys attract considerable attention in ultrafast and terahertz spintronics applications. The magnetic properties of RE-TM alloys strongly depend on their composition and vary with temperature. Here, we model crystallographically amorphous ferrimagnetic TbCo using atomistic spin dynamics(ASD) simulations to study their temperature dependence on magnetic properties by varying the compositions. In this study, we investigate the temperature dependence of magnetisation, uniaxial anisotropy, and coercivity values of amorphous TbxCo100−x for the composition range Tb18Co82 to Tb36Co64. The monte carlo method is used to calculate the temperature dependence of magnetisation and calculate the magnetisation compensation temperature(TM) and curie temperature(Tc) values for different compositions. The temperature dependence of uniaxial anisotropy is calculated from the angular dependence of free energy curves calculated at different temperatures using constrained monte carlo methods. Further, we evaluate the temperature dependence of coercivity values by calculating the magnetic hysteresis at different temperatures using the LLG Heun method. The results show the magnetic properties of amorphous TbCo can be easily tuned by varying their composition and have a strong temperature dependence. These highly tunable magnetic properties make them promising candidates for spintronics applications.

Thermal conductivity of type-Ib HPHT synthetic diamond irradiated with electrons

The effect of irradiation with 3 MeV electrons and subsequent high-temperature annealing on the thermal conductivity κT of synthetic HPHT diamond containing impurity nitrogen at a concentration of about 100 ppm was studied at temperatures from 5 to 410 K. At each stage of the experiment, the optical absorption and photoluminescence spectra, magnetization and thermal conductivity were measured on two plates from the same diamond single crystal. Color centers and their concentration in different locations in the samples were determined from the optical spectra. The concentration of paramagnetic impurities in the samples was determined from the temperature and field dependencies of the paramagnetic magnetization. Thermal conductivity is suppressed by two orders of magnitude at temperatures from 35 to 50 K after irradiation to a fluence of 5×1018 cm−2. Annealing at a temperature of 1800° C restored the thermal conductivity of diamond at moderate and high temperatures, but not at temperatures below 120 K. The measured data on thermal conductivity were analyzed within the framework of the phenomenological Callaway model in order to understand the role of various phonon scattering processes and how it changes during irradiation and annealing.

Magnetic features of hybrid transition metal-rare earth nanoparticles: Monte Carlo simulations

Magnetic features of transition metal (TM)-Rare earth (RE) heterostructures were studied using atomistic simulations. The ferromagnetic ordering temperature of pure Cobalt (Co) and Dysprosium (Dy) nanoparticles were reproduced, then hybrid structures of Co and Dy were simulated following the same approach, where the emphasis is mainly laid on the influence of exchange energy which plays a key role in the magnetic ordering of materials. In the framework of Heisenberg spin Hamiltonian, we study the effect of interfacial exchange coupling on the Temperature-dependent magnetization of Co@Dy, Dy@Co, and Co@Dy@Co hybrid nanoparticles using Monte-Carlo (MC) simulations. The hybrid nanostructures created reveal interesting magnetization-temperature features. The effect of the sign of interfacial coupling constant, chemical arrangement, and the thickness of the spacer (Dy in the case of multi-shell Co@Dy@Co) is investigated. The transition of nanoparticles to a paramagnetic state & the associated spin structures display an intriguing pattern. Antiferromagnetic (AFM) coupled nanoparticles (NPs) display a compensation temperature in their M–T plot that is a characteristic of Ferrimagnetic (FI) NPs.

Large energy product of rare earth free Fe3MnC2 alloy permanent magnet

Due to the importance for device applications and also other subtle issues, study on rare-earth free permanent is becoming more and more important subject. Here, we investigate the temperature dependent magnetic characteristics of the Fe3MnC2 structure. We find that the Fe3MnC2 alloy exhibits a critical temperature of 640 K with perpendicular magnetic anisotropy. With increasing temperatures, both the coercive field and the magnetic anisotropy constant monotonically decrease. From temperature dependent magnetization and coercive field, the (BH)max of the Fe3MnC2 system obtained is 396 kJ/m3 at zero Kelvin. The (BH)max suppressed with increasing temperature. Nonetheless, we find the (BH)max of 253 kJ/m3 is at 300 K. Compared with the (BH)max of ferrites and SmCo5, the Fe3MnC2 alloy structure exhibits better permanent magnetic properties. Therefore, we suggest that the Fe3MnC2 could be a suitable candidate for a Fe-based gap permanent magnet between ferrite and Nd-Fe-B (or Sm-Co) at room temperature.

Monte-Carlo simulation of phase transition in 2D and 3D ising model

In this work, Markov Chain-Monte Carlo technique was used to study the phase transition in two and three dimensional Ising Model (IM) in a square and cubic lattice. The study of temperature dependence of average magnetization and specific heat in different magnetic fields has been carried out in the 3x3 and 3x3x3 lattice with periodic boundary. Critical temperature point kBTc / J for 2D and 3D Ising Model has been observed at around 2.2 and 4.3 respectively at zero field. Our work satisfies Onsager’s critical value in 2D IM. The simulation suggests bifurcation in average magnetization below critical temperature Tc. Temperature plays the role of increasing randomness of spins. We found that Ising Model in small lattice size still retains interesting features like spontaneous magnetization and symmetry breaking below Tc at B = 0. At a non-zero field, the likelihood of spins to prefer certain alignment depends on the direction of the external field and magnitude of magnetization depends on magnitude of field ±B. Specific heat Cv, which gives us fluctuation of energy at particular temperature, has been found to attain maximum value at critical regions.

Facile Synthesis of Chromium-Doped Fe1.1Mn1.9O4 Nanoparticles and the Effect of Cr Content on Their Magnetic and Structural Properties.

In the present study, Fe1.1(CrxMn1-x)1.9O4 nanoparticles (0 ≤ x ≤ 0.5) were successfully synthesized by a combustion method, and the influence of Cr substitution on the structural and magnetic properties of the obtained nanoparticles was studied by various methods. The structural analysis revealed that the sample with x = 0 has a tetragonal structure, while all Cr-doped samples crystallize into a cubic structure. Additionally, the results of TEM show that doping with chromium leads to an increase in particle size. The magnetic hysteresis loops demonstrate the behavior typical for soft magnetic materials with low coercivity and remanence magnetization. The magnetic measurements revealed that the saturation magnetization of the obtained nanoparticles demonstrates a decreasing trend with increasing Cr content. The influence of chromium doping on the observation change in saturation magnetization is discussed. Based on the results of temperature-dependent magnetization measurements, it was found that the temperature of a magnetic transition in synthesized nanoparticles depends on Cr content.

Magnetic Field and Temperature-Dependent Brillouin Light Scattering Spectra of Magnons in Yttrium Iron Garnet.

Knowledge of the magnon responses to an external magnetic field and temperature is significant for spintronics applications. Herein, exploiting Brillouin light scattering (BLS) spectroscopy, we investigate the magnetic field and temperature dependence of the magnon frequency, line width, and intensity in yttrium iron garnet (YIG). The applied magnetic field here can effectively change the magnon frequency while maintaining the lifetime of the magnon. Specifically, we determine the temperature dependence of magnon frequency and the linear relationship between magneto-optic effects-related terms (|A(+)|2/|A(-)|2) and temperature below room temperature (RT), which can serve as a temperature sensor. Our results open an avenue to sense the temperature and the external magnetic field, including the effective magnetic field induced by the magnetic proximity effect. Furthermore, our results provide a route toward designing the operating frequency and loss of the devices, facilitating future research in spin-related applications, including magnon-based logic, memory, sensing, and thermospin devices.

Investigation on various properties of Dy0.7Ca0.3MnO3:TiO2 based nano-micro composites

In the present research work, manganite metal oxide nano-micro composites have been synthesized successfully wherein, chemically grown Dy0.7Ca0.3MnO3 was combined in different weight ratio composition of micron sized TiO2 (i.e., 0 %, 10 %, 20 %, 30 %, 40 % and 100 %). Prepared nano-micro DCMO:TiO2 has been characterized further wherein, structural aspects have been carried out using X-ray diffraction and W-H plot measurements which provides information regarding crystalline size, lattice strain and crystallinity. FESEM and HRTEM has been characterized for the assessment of the crystallinity and granular morphology. The elemental composition with desired stoichiometric quantities has been verified using EDAX. SAED patterns gives detailed information about intereticular distance and angles between crystallographic planes. Different frequency dependent electrical properties (i.e., dielectric constant (ε’), a.c. conductivity (σac) and impedance (Z)) carried out in the frequency range of 20 Hz to 2 MHz. The observed modified electrical properties have been understood using different theoretical models, mechanisms and different aspects (role of grain and crystalline size). Temperature dependent magnetization (M-T) measurements have been carried out to evaluate the magnetic phase shifting of the sample which has been understood using ZFC and FCC protocols. These phase shifting has been verified using M-H loop at different temperatures of 5 K and 300 K. The adaptation in magnetic properties have been discussed using different magnetic aspects.