Magnetic Field Dependence of a Capacitance Temperature Sensor

The influence of a magnetic field on the capacitance of a glass-ceramic temperature sensor (Lake Shore CS-501GR) has been measured extensively at temperatures down to 0.09 K and magnetic fields up to 12 T. While the influence of a magnetic field is still negligible at 4 K, the sensor shows an increasing non-monotonic dependence on the magnetic field with falling temperature. The maximum relative change of capacitance with respect to the zero field value remains smaller than 5 · 10⁻⁴. However, with the given sensitivity of the sensor, this small magnetoeffect may not be ignored in the low temperature region.     

Temperature Dependence of Magnetic Parameters in FePt Nanoparticles

Here, particular focus is placed on the atomic alignment and the order–disorder phase transition of the FePt alloy with the aid of a model that can describe realistic phenomena. Here, we present a method to study the order–disorder phenomena of FePt alloys. We will discuss the increase in the coercivity of FePt nanoparticles by an increasing annealing temperature for annealed FePt nanoparticles. According to the experimental evidence, we will present a model for explaining spin-glass-like behavior of these particles during the annealing procedure. In the phase transition from disordered FCC to ordered FCT in FePt nano-particles can be treated by first-order phase transitions. So, the mean field approach can be used in order to model this kind of phase transition. In nanoparticles, which are synthetized by sol–gel methods, the short range parameter is predominant because in these kinds of preparations, the long range order takes a lot of time to happen. By using a short range parameter, we are able to use the mean field approach, which considers the diffusion of atoms to the near neighborhood sites. The effects of random exchange and random magnetocrystalline anisotropy are known as the main results of coercivity reduction in magnetic nanoparticles. These effects are strongly dependent to the annealing temperature of nanoparticles. During disorder–order transition, these two effects are max. As transition continues, these effects vanish and coercivity of nanoparticles increases. Here, we will add these two effects to the Hamiltonian of the FePt system. With increasing the annealing temperature, the fraction of the FePt nanoparticles with a FCC disordered phase vanishes, which leads to decrease in the amount of 〈j〉. During the annealing process, the $\frac{c}{a}$ ratio varies as a function of the annealing temperature. The relation between the $\frac{c}{a}$ ratio and the annealing temperature is derived. The derived $\frac{c}{a}$ ratio and coercivity formulas are compared with experimental results. The results are in a good agreement with experimental data.     

Temperature Dependence of the Magnetic Properties of Amorphous Fe-Me-Si-B Alloys

Alloying of amorphous Fe-Me-Si-B metallic compositions with nickel and molybdenum results in a decrease in the values of saturation magnetization in fields with a magnetic intensity of 0.72 MA/m. The same alloying additions decrease the temperature of formation of new magnetic Fe₃B-type phases, which are stable up to 873 ± 5 K.     

Toward the Temperature Dependence of the Young Modulus of Magnetic Materials

Journal of Engineering Physics and Thermophysics - Using the example of a ferromagnetic dielectric, an algorithm is proposed for calculating the Young modulus of elastically deformable solid bodies...     

Retardation of the Magnetic Relaxation in High-Temperature Superconductors Near a Ferromagnet

The creep of a magnetic flux trapped in a bulk high-temperature superconductor has been studied. It has been found that the magnetic relaxation is retarded when the superconductor is placed near a ferromagnet. The value of the retardation effect depends on the sequence of magnetization and the approach of the superconductor to a ferromagnet. The magnetic relaxation is fully suppressed when a superconducting sample first is magnetized and then is brought close to a ferromagnet. An interpretation of this effect has been discussed. Being magnetized, a ferromagnet produces its own magnetic field. While penetrating into a disk sample through its planes, the ferromagnet field induces screening currents, which circulate oppositely to the current that arises upon trapping of the magnetic flux. As a result, the stability of the magnetic structure is sharply improved since opposite driving forces can act on different sections of the vortices.     

Low Temperature and High Magnetic Field Dependence and Magnetic Properties of Nanocrystalline Cobalt Ferrite

The DC magnetic hysteresis loop measurements were carried out for temperatures varying from 5 to 300 K over a field range of ±10 T on nanocrystalline (～35 nm) cobalt ferrite samples (crystallized to \(Fd\bar {3} m\) space group with cubic symmetry) to validate the law of approach at low temperature for the nanocrystalline cobalt ferrite. A magnetocrystalline anisotropy constant and saturation magnetization have been obtained by analyzing the magnetization curve in saturation using the “law of approach (LA) to saturation.” The magnetocrystalline anisotropy constant is found to be almost constant in the temperature range of 5 to 150 K due to the freezing of spin at low temperature. Also, spin freezing leads to a decrease of coercivity with the increase in the temperature.     

Temperature Dependence of Magnetic Properties of SmCo/FeCo Multilayer Films

1. IntroductionIn addition to the magnetic properties of each individual particle, intergrain illteraction play a dominantrole during demagnetization processes[1'2]. These intergrain interactions are sensitively influenced by intergranular phases depending on the respective preparation methodl3'4]. A systematic improvement of permanent magnets is only possible by a deeper understanding of the relations between intergrain interaction, microstructural features, and magnetic properties.In this pa…     

A Change in the Debye Temperature of a Single-Component Substance upon Amorphization

Technical Physics Letters - A method for calculating the Debye temperature of a single-component substance in the amorphous state is proposed based on a nonlinear dependence of first coordination...     

Emergence of a Non-Van der Waals Magnetic Phase in a Van der Waals Ferromagnet

Manipulation of long-range order in 2D van der Waals (vdW) magnetic materials (e.g., CrI₃, CrSiTe₃ ,etc.), exfoliated in few-atomic layer, can be achieved via application of electric field, mechanical-constraint, interface engineering, or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition and hydrolysis in the presence of water/moisture causes degradation in magnetic nanosheets that, in turn, affects the nanoelectronic /spintronic device performance. Counterintuitively, the current study reveals that exposure to the air at ambient atmosphere results in advent of a stable nonlayered secondary ferromagnetic phase in the form of Cr₂Te₃ (T_C2 ≈160 K) in the parent vdW magnetic semiconductor Cr₂Ge₂Te₆ (T_C1 ≈69 K). The coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, and magneto-transport measurement. To capture the concurrence of the two ferromagnetic phases in a single material, Ginzburg-Landau theory with two independent order parameters (as magnetization) with a coupling term can be introduced. In contrast to the rather common poor environmental stability of the vdW magnets, the results open possibilities of finding air-stable novel materials having multiple magnetic phases.     

Thermodynamically Consistent Calculation of the Debye Temperature Using Thermophysical Data

Equations are obtained which must be satisfied by the temperature dependence of the Debye temperature ((T)) so that the thermodynamic functions calculated on its basis would satisfy both the third principle of thermodynamics and the law of equipartition of energy over degrees of freedom. A general expression for the function (T) is obtained, which satisfies these thermodynamic regularities.     

Magnetic Field Dependence of Blocking Temperature in Oleic Acid Functionalized Iron Oxide Nanoparticles

We report the synthesis of phase pure, mono-dispersed Fe₃O₄ nanoparticles of size ??10?nm via chemical co-precipitation of ferrous and ferric ions, under controlled pH and temperature. The nanoparticles are oleic acid functionalized and hence dispersible in organic medium. The structure and morphology of nanoparticles are determined by analyzing XRD pattern and TEM micrographs, confirming the formation of phase pure Fe₃O₄ nanoparticles. The magnetization studies reveal the superparamagnetic behavior of the nanoparticles at room temperature. The changes in blocking temperatures (T _B) of magnetic nanoparticles with applied magnetic fields (H _ap), noted from the cusp of the zero-field-cooled magnetization, the indicate effects of dipole interactions. A decrease in blocking temperature from 95?K to 15?K has been observed on varying the magnetic field from 50?Oe to 5000?Oe. T _B versus H relation follows the equation T _B(H)=T _o(1?(H/H _o)) ^m , i.e. the Néel?CBrown model of magnetic relaxation in nanoparticles.     

The Superconducting Ferromagnet UCoGe

The correlated metal UCoGe is a weak itinerant ferromagnet with a Curie temperature T _C=3 K and a superconductor with a transition temperature T _s=0.6 K. We review its basic thermal, magnetic—on the macro and microscopic scale—and transport properties, as well as the response to high pressure. The data unambiguously show that superconductivity and ferromagnetism coexist below T _s=0.6 K and are carried by the same 5f electrons. We present evidence that UCoGe is a p-wave superconductor and argue that superconductivity is mediated by critical ferromagnetic spin fluctuations.     

A Room‐Temperature Ferroelectric Ferromagnet in a 1D Tetrahedral Chain Network

Ferroelectricity occurs in crystals with broken spatial inversion symmetry. In conventional perovskite oxides, concerted ionic displacements within a 3D network of transition‐metal–oxygen polyhedra (MO_x) manifest spontaneous polarization. Meanwhile, some 2D networks of MO_x foster geometric ferroelectricity with magnetism, owing to the distortion of the polyhedra. Because of the fundamentally different mechanism of ferroelectricity in a 2D network, one can further challenge an uncharted mechanism of ferroelectricity in a 1D channel of MO_x and estimate its feasibility. Here, ferroelectricity and coupled ferromagnetism in a 1D FeO₄ tetrahedral chain network of a brownmillerite SrFeO_2.5 epitaxial thin film are presented. The result provides a new paradigm for designing low‐dimensional MO_x networks, which is expected to benefit the realization of macroscopic ferro‐ordering materials including ferroelectric ferromagnets.     

Calculation of Magnetic Properties and Specific Heat for the Nuclear Enhanced Ferromagnet PrNi5

A general model hamiltonian for hyperfine enhanced magnetic materials is presented. The use of the model is not limited only to the nuclear regime, but the model treats also situations when the strength of the exchange interaction is close to and above the threshold value. The model is solved numerically for PrNi₅ and the results are compared with recent ultra-low temperature experiments. In particular, the behavior of magnetization, susceptibility, and specific heat of PrNi₅ is studied for two external field geometries and anisotropic properties are pointed out. The effect of the quadrupole interaction is examined in detail. The question of the correlations among interacting ions is also addressed.     

Temperature Dependence of Flexural Strength of a CF-SMC Composite

This paper presents the temperature dependence of predicting the flexural strength of a carbon fiber-reinforced sheet molding compound (CF-SMC). First, three-point flexural tests were performed to measure strength and elastic modulus at a variety of temperatures for CF-SMC specimens. Next, simple equations for predicting flexural strength were derived based on the fracture mechanics approach. The predicted flexural strength was in reasonably good agreement with the experiment results. The scatter of flexural strength was ascribed to the variation of location and size of the initial damage. In addition, the effect of temperature on flexural strength and delamination behavior was explained in association with the temperature dependence of the elastic modulus and fracture toughness.     

The Temperature Dependence of Elastic Nonlinearity in Metal-Matrix Composites

Abstract

Thermal stresses are very important in determining the strength of composites. In metal-matrix composites, these stresses are generated at the matrix-reinforcement interface as a result of the difference in thermal expansion coefficients of matrix and reinforcement during solidification. In order to evaluate these stresses, we studied the effect of temperature on the second- and third-order elastic constants in two metal-matrix composites consisting of the aluminum alloys 8091 and 7064 and silicon carbide particles up to 20% volume fraction. The elastic constants were determined at the temperatures 0, 25 and 55°C using measurements of absolute as well as changes of ultrasonic velocities as a function of applied stress. The values of these constants are used to calculate the acoustic nonlinearity parameters. In both composites, the acoustic nonlinearity parameters increase with the amount of reinforcement, which is opposite to that previously observed in aluminum alloys containing second-phase precipitates. Also, the temperature behavior of the nonlinearity parameters in the composites are opposite to those in the aluminum matrices. These differences in behavior are interpreted as due to the presence of thermal stresses at the matrix-reinforcement interface, and give promise to the possibility of using these parameters in the nondestructive evaluation of these stresses in metal-matrix composites.     

An Explicit Function Expression for dc Bias and Temperature Dependence of Magnetoresistances in Magnetic Tunnel Junctions

An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters.Two of these intrinsic parameters are the Curie temperature Tc and the density of state(DOS) for itinerant majority and minority electronsξ(ρM/ρm),which are the eigen parameters of ferromagnetic electrodes.Others are the spin-dependent matrix-element ratio(i.e.,|T^d)^2/{T^j}^2 )and the anisotropic-wavelength-cutoff energy Ec^γ of spin-wave spectrum in magnetic tunnel junction(MTj),which are the structure parameters of an MTj.These intrinsic parameters can be predetermined using the experimental measurement or,in principle,using the first-principle calculation method for an MTj with the three key layers of FM/1/FM.Furthermore,a series of experimental data for an MTj,for example,a spin-valve-type MTj of Ta(5nm)/Ni79Fe21(25nm)/Ir22Mn78(12nm)/Co75Fe25(4nm)/Al(0.8nm)-oxide/Co75Fe25(4nm)/Ni79Fe21(20nm)/Ta(5nm)in this work,can be self-consistently evaluated and explained using such explicit function formulations.