scholarly journals Time effects in the magnetic cooling method─I

1936 ◽  
Vol 155 (886) ◽  
pp. 629-639 ◽  
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Initial Temperature ◽  
Magnetic Method ◽  
Time Effects ◽  
Magnetic Cooling ◽  
Cooling Method ◽  
Degree Of Orientation ◽  
Paramagnetic Salt ◽  
The Magnetic Field

The recent progress in attaining extremely low temperatures was made possible by the magnetic method of cooling. This method is based on the following principle: Supposing we have a paramagnetic salt, the ions of which carry a magnetic moment (spin) μ. We assume that the interaction of these spins with the lattice and with one another is so small that the spins can be considered as relatively free. These properties are realized in some salts of the rare earths and of the iron group. In the absence of a magnetic field the spins are distributed at random. The crystal has then a comparatively large entropy due to the exchange of spin directions. If we now switch on a magnetic field H isothermally , the spins will be orientated in the direction of the field. The degree of orientation will depend upon the ratio Hμ/ k T i , where T i is the initial temperature. The entropy will decrease according to the degree of orientation produced by the magnetic field. The decrease in entropy is a certain function of Hμ/ k T i .

Time effects in the magnetic cooling method

1939 ◽  
Vol 35 (2) ◽  
pp. 256-264 ◽  
Author(s):  
H. N. V. Temperley
Keyword(s):  
Exchange Interactions ◽  
Time Effects ◽  
Magnetic Cooling ◽  
Cooling Method ◽  
Mechanism Of Interaction ◽  
Iron Alum ◽  
Paramagnetic Salt ◽  
Simultaneous Transition ◽  
Theory And Experiment

In consequence of the magnetic and exchange interactions between the ions of a paramagnetic salt, a new mechanism of interaction between ion and lattice is possible, involving the simultaneous transition of two or more ions with the emission or absorption of only one elastic quantum. This new mechanism seems to be capable of removing the discrepancy between theory and experiment for iron alum, and considerably reduces the discrepancy for caesium titanium alum.

scholarly journals Time effects in the magnetic cooling method II—the conductivity of heat

1936 ◽  
Vol 155 (886) ◽  
pp. 640-652 ◽  
Keyword(s):  
Magnetic Field ◽  
Critical Temperature ◽  
Spin System ◽  
Magnetic Energy ◽  
Preceding Paper ◽  
Lattice Vibrations ◽  
Magnetic Cooling ◽  
Cooling Method ◽  
Paramagnetic Salt ◽  
Time Required

In the preceding paper (which we shall refer to as I) Teller and one of us (H.) have discussed some characteristic effects occurring at the low temperatures which can be attained by the magnetic cooling method. In this method a paramagnetic salt is used, the spins of which can be freely, or almost freely, orientated in an external magnetic field. It is essential, however, that (at least at the initial temperature T i ) the magnetic energy H of the spins can be transferred to the lattice vibrations. For this purpose the interaction between the spins and the lattice vibrations is essential. Now it has been shown in I that this interaction is in general very small. It depends upon the temperature and the magnetic field H applied and is practically interrupted when the lattice vibrations have reached a critical temperature T c given by I equations (14) and (13). Under usual conditions (H∽ 15,000 gauss) T c is of the order of 0·1° abs. The crystal can then be considered as consisting of two practically independent systems, the spins of the paramagnetic ions and the lattice vibrations. If a temperature lower than this critical temperature T c is measured, the temperature refers to the spin system only, but not to the lattice vibrations. When the field is switched off again the thermal equilibrium between the spin system and the lattice will be restored very slowly, the time required being of the order of an hour at 0·2° abs ( cf . I, equation (15)).

Simple Systems

2017 ◽  
Author(s):  
Jochen Rau
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
General Framework ◽  
Gibbs State ◽  
Macroscopic System ◽  
Basic Model ◽  
System A ◽  
Paramagnetic Salt ◽  
High And Low Temperatures ◽  
Simple Systems

Even though the general framework of statistical mechanics is ultimately targeted at the description of macroscopic systems, it is illustrative to apply it first to some simple systems: a harmonic oscillator, a rotor, and a spin in a magnetic field. These applications serve to illustrate how a key function associated with the Gibbs state, the so-called partition function, is calculated in practice, how the entropy function is obtained via a Legendre transformation, and how such systems behave in the limits of high and low temperatures. After discussing these simple systems, this chapter considers a first example where multiple constituents are assembled into a macroscopic system: a basic model of a paramagnetic salt. It also investigates the size of energy fluctuations and how—in the case of the paramagnet—these fluctuations scale with the number of constituents.

scholarly journals The orientation of iron–sulphur clusters in membrane multilayers prepared from aerobically-grown Escherichia coli K12 and a cytochrome-deficient mutant

1980 ◽  
Vol 190 (2) ◽  
pp. 385-393 ◽  
Author(s):  
Haywood Blum ◽  
Robert K. Poole ◽  
Tomoko Ohnishi
Keyword(s):  
Magnetic Field ◽  
Escherichia Coli ◽  
Cytoplasmic Membrane ◽  
Deficient Mutant ◽  
E Coli ◽  
Membrane Particles ◽  
Degree Of Orientation ◽  
High Degree ◽  
Cytochrome Content ◽  
The Magnetic Field

1. Membrane particles prepared from ultrasonically-disrupted, aerobically-grown Escherichia coli were centrifuged on to a plastic film that was supported perpendicular to the centrifugal field to yield oriented membrane multilayers. In such preparations, there is a high degree of orientation of the planes of the membranes such that they lie parallel to each other and to the supporting film. 2. When dithionite- or succinate-reduced multilayers are rotated in the magnetic field of an e.p.r. spectrometer, about an axis lying in the membrane plane, angular-dependent signals from an iron–sulphur cluster at gx=1.92, gy=1.93 and gz=2.02 are seen. The g=1.93 signal has maximal amplitude when the plane of the multilayer is perpendicular to the magnetic field. Conversely, the g=2.02 signal is maximal when the plane of the multilayer is parallel with the magnetic field. 3. Computer simulations of the experimental data show that the cluster lies in the cytoplasmic membrane with the gy axis perpendicular to the membrane plane and with the gx and gz axes lying in the membrane plane. 4. In partially-oxidized multilayers, a signal resembling the mitochondrial high-potential iron–sulphur protein (Hipip) is seen whose gz=2.02 axis may be deduced as lying perpendicular to the membrane plane. 5. Appropriate choice of sample temperature and receiver gain reveals two further signals in partially-reduced multilayers: a g=2.09 signal arises from a cluster with its gz axis in the membrane plane, whereas a g=2.04 signal is from a cluster with the gz axis lying along the membrane normal. 6. Membrane particles from a glucose-grown, haem-deficient mutant contain dramatically-lowered levels of cytochromes and exhibit, in addition to the iron–sulphur clusters seen in the parental strain, a major signal at g=1.90. 7. Only the latter may be demonstrated to be oriented in multilayer preparations from the mutant. 8. Comparisons are drawn between the orientations of the iron–sulphur proteins in the cytoplasmic membrane of E. coli and those in mitochondrial membranes. The effects of diminished cytochrome content on the properties of the iron–sulphur proteins are discussed.

Effect of Processing Variables on The Magnetic Field Orientation of Liquid Crystalline Thermosets

1999 ◽  
Vol 559 ◽  
Author(s):  
Derek M. Lincoln ◽  
Elliot P. Douglas
Keyword(s):  
Magnetic Field ◽  
Liquid Crystalline ◽  
Fractional Factorial Design ◽  
Fractional Factorial ◽  
Field Orientation ◽  
Magnetic Field Orientation ◽  
Liquid Crystalline Epoxy ◽  
Processing Variables ◽  
Degree Of Orientation ◽  
The Magnetic Field

ABSTRACTWe have investigated the effect of various processing variables on the magnetic field orientation of a liquid crystalline epoxy. By using a modified fractional factorial design, we created an empirical model which can be used to predict the degree of orientation as a function of these variables. The model predicts the correct qualitative trends, namely that orientation increases with increasing magnetic field strength, increases with increasing time in the field, and decreases with increasing B-staging. The model also reveals some surprising effects of B-staging on the degree of orientation.

TUNING OF THE MAGNETIC FIELD INDUCED SHARP BAND-EDGE OPTICAL ABSORPTION IN EUROPIUM CHALCOGENIDES

2004 ◽  
Vol 18 (27n29) ◽  
pp. 3813-3816 ◽  
Author(s):  
A. B. HENRIQUES ◽  
L. K. HANAMOTO ◽  
E. TER HAAR ◽  
E. ABRAMOF ◽  
A. Y. UETA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Optical Absorption ◽  
Low Temperatures ◽  
Optical Transition ◽  
Band Edge ◽  
Near Band Edge ◽  
High Magnetic Fields ◽  
Sharp Band ◽  
The Magnetic Field

The near band-edge polarized optical optical absortion spectra of EuTe at low temperatures and high magnetic fields were investigated. The samples were grown by MBE on BaF 2 substrates, and the thickness varied in the 0.18-2.0 μm range. At high magnetic fields, the well-known 4f7→4f65d(t2g) optical transition splits into two well resolved lines at σ+ and two lines for σ-. These lines can be described by localized transitions tunable by the d-f exchange interaction, with a quadratic dependence on the intensity of the external magnetic field. Comparative measurements of the magnetization and the optical absorption as a function temperature provides a further test of the model of a localized excitation extending over a few lattice sites.

EFFECT OF A MAGNETIC FIELD ON THE BROKEN ELECTROWEAK SYMMETRY

2002 ◽  
Vol 17 (04) ◽  
pp. 561-573 ◽  
Author(s):  
E. RODRÍGUEZ QUERTS ◽  
A. MARTÍN CRUZ ◽  
H. PÉREZ ROJAS
Keyword(s):  
Magnetic Field ◽  
Symmetry Breaking ◽  
Strong Magnetic Field ◽  
Low Temperatures ◽  
Strong Field ◽  
Electroweak Symmetry ◽  
Rest Energy ◽  
Vector Bosons ◽  
Breaking Parameter ◽  
The Magnetic Field

We discuss the effect of a strong magnetic field in the behavior of the symmetry of an electrically neutral electroweak plasma. We analyze the case of a strong field and low temperatures as compared with the W rest energy. If the magnetic field is large enough, it is self-consistently maintained. It is shown that the charged vector bosons play the most important role, leading only to a decrease of the symmetry breaking parameter, the symmetry restoration not being possible.

scholarly journals Магнитокалорический эффект в сплаве Fe-=SUB=-49-=/SUB=-Rh-=SUB=-51-=/SUB=- в импульсных магнитных полях до 50 T

2020 ◽  
Vol 62 (1) ◽  
pp. 117
Author(s):  
А.П. Каманцев ◽  
А.А. Амиров ◽  
Ю.С. Кошкидько ◽  
К. Салазар Мехиа ◽  
А.В. Маширов ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Temperature Change ◽  
Initial Temperature ◽  
Adiabatic Temperature ◽  
Ferromagnetic Phase ◽  
Pulsed Magnetic Fields ◽  
Absolute Value ◽  
Adiabatic Temperature Change ◽  
The Absolute ◽  
The Magnetic Field

The direct magnetocaloric effect (MCE) was measured in pulsed magnetic fields up to 50 T in the Fe49Rh51 alloy. At different initial temperatures in the metamagnetic phase transition with an increase in the field up to 20 T, a reverse MCE ∆T ≈ -8 K is observed, while a further increase in the field to 50 T results in a decrease in the absolute value of the adiabatic temperature change by ~ 1 K, which is connected with direct MCE and indicates a complete transition of the sample into the ferromagnetic phase. The maximum of the absolute value of the adiabatic temperature change |∆Т| = 9.8 K with a decrease in the magnetic field of 6 T on initial temperature of 310 K was observed.

scholarly journals Identifikasi Jalur Sesar Opak Berdasarkan Analisis Data Anomali Medan Magnet dan Geologi Regional Yogyakarta

2017 ◽  
Vol 4 (02) ◽  
pp. 192
Author(s):  
Ira Maya Fathonah ◽  
Nugroho Budi Wibowo ◽  
Yoshaphat Sumardi
Keyword(s):  
Magnetic Field ◽  
Surface Structure ◽  
Normal Fault ◽  
Magnetic Method ◽  
The West ◽  
Geomagnetic Data ◽  
Anomaly Pattern ◽  
Anomaly Analysis ◽  
Result Interpretation ◽  
The Magnetic Field

<p>This research was aimed to know the magnetic field anomaly pattern upon Opak’s fault, to identify the direction of Opak’s fault and the structure of Opak’s fault based on Geomagnetic data. It was conducted in the vicinity of Opak’s fault in Pundong sub-district, Yogyakarta. It used magnetic method which is based on rocks magnetic susceptibility. The data were taken by G-856AX Proton Precision Magnetometer (PPM) using looping method. Data analysis was done using diurnal variation and IGRF correction, reduction to pole, upward continuation and under surface structure modelling. From magnetic field anomaly analysis, it was discovered that magnetic field anomaly on Opak’s fault has -50 nT negative closure in the East, and 100 nT positive closure in the West. According to the result interpretation of 2.5D model on two slices using Mag2DC software, it can be obtained that the under surface structure of Opak’s fault consist of Young Alluvial formation, Nglanggran formation, Semilir formation, Kebo Butak formation, and Wungkal Gamping with various thickness. The location of this Opak’s fault is almost the same with the location of Opak’s fault in Yogyakarta geology map. Opak’s fault around Pundong sub-district is a normal fault directed to N 35º E. The eastern part of the fault has a relatively constant movement, while the western part is relatively moving down.</p>

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