The dependence of the spontaneous magnetization on the magnetic field at low temperatures

1955 ◽  
Vol 5 (2) ◽  
pp. 171-176 ◽  
Author(s):  
Luboš Valenta
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Spontaneous Magnetization ◽  
The Magnetic Field

scholarly journals A theoretical study of a possible model of paramagnetic alums at low temperatures

1940 ◽  
Vol 176 (965) ◽  
pp. 203-213 ◽  
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Theoretical Study ◽  
Spontaneous Magnetization ◽  
Critical Value ◽  
Transition Curve ◽  
Thin Specimen ◽  
First Order ◽  
Freely Suspended ◽  
Line Of Critical Points

An attempt is made to examine theoretically the properties of paramagnetic alums at low temperatures. The model taken is a lattice of freely suspended magnets, all interactions except purely magnetic being neglected. Even with this simplification it is impossible at present to make rigorous calculations of the partition function, either on classical or quantum lines. A simple model is proposed, which is really a generalization of the Bragg - Williams theory enabling one to take account of the effect of a magnetic field. The few configurations whose energies are known are used to fix arbitrary constants in the expression assumed for the energy. The theory predicts that the state of lowest energy is either a spontaneously magnetized, state for a long thin specimen, or a state in which alternate rows of magnets point in opposite directions for a sphere, spontaneous magnetization appearing in an ellipsoid with an eccentricity greater than a certain critical value. The transition curve bounding the region in which the antiparallel state is stable consists partly of a line of Curie points corresponding to transitions of the second, order, passing smoothly into a line of critical points corresponding to a transition of the first order. The effect of shape on the magnetic properties of the specimen seems to be experimentally verified, but the rough nature of the theory prevents it being more than qualitative.

On Damage Evaluation Method of the Ferromagnetic Material Based on Weak Magnetic Field Detection Technology

2006 ◽  
Vol 324-325 ◽  
pp. 331-334 ◽  
Author(s):  
Feng Yun Yu ◽  
Chuan Xu Zhang ◽  
Miao Wu
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Evaluation Method ◽  
Spontaneous Magnetization ◽  
Tensile Load ◽  
Ferromagnetic Material ◽  
Magnetic Intensity ◽  
Damage Level ◽  
Detection Technology ◽  
The Magnetic Field

The increase of magnetic field of ferromagnetic components under service load and geomagnetic field is induced by the residual magnetic induction and spontaneous magnetization. The stress concentration positions can be found by detecting the magnetic field and the fracture can be avoided. The variation of the residual magnetic intensity of bearing carriers under different damage conditions is studied in this paper; the statistical characteristic of the residual magnetic intensity of the specimens in different residual deformations is got, and a concept of residual magnetic intensity standard deviation is put forward with a lot of experiments and in-depth theoretic analysis. The results indicate that the curves of residual magnetic intensity standard deviation appear obvious turning points when the specimens reach the yield point in different original magnetic field conditions, and that the function between residual magnetic intensities standard deviation, tensile load and strain is established. Therefore, the plastic deformation can be judged by the variation of the magnetic field in their service process, and the damage level can be evaluated consequently, which gives a new reliable method to estimate the deformation of ferromagnetic material.

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 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 .

Onset Magnetic Field for Rearrangement of Martensite Variants in Ni2MnGa

2007 ◽  
Vol 561-565 ◽  
pp. 1109-1112
Author(s):  
Takashi Fukuda ◽  
Nariaki Okamoto ◽  
Tomoyuki Kakeshita
Keyword(s):  
Magnetic Field ◽  
Magnetocrystalline Anisotropy ◽  
Spontaneous Magnetization ◽  
Parent Phase ◽  
Anisotropy Constant ◽  
Ferromagnetic Shape Memory Alloy ◽  
Twinning Shear ◽  
Ferromagnetic Shape Memory ◽  
The Magnetic Field ◽  
Good Agreement

The magnetic field strength, Hs, at which rearrangement of martensite variants initiates has been investigated in Ni2MnGa ferromagnetic shape memory alloy by magnetization measurements in the [001]P direction ("P" stands for the parent phase). We have also calculated Hs from the magnetocrystalline anisotropy constant Ku, spontaneous magnetization Ms, twinning shear s and twinning stress τreq by considering the condition for the rearrangement of martensite variants reported previously [Int. J. Appl. Electromagnetics and Mechanics, 23 (2006) 45]. The calculated value of Hs is in good agreement with the experimental value for all the examined temperatures. The agreement confirms the applicability of the reported condition.

scholarly journals The theory of the magneto-resistance effects in metals

1947 ◽  
Vol 190 (1023) ◽  
pp. 435-455 ◽  
Keyword(s):  
Magnetic Field ◽  
Electrical Resistance ◽  
Low Temperatures ◽  
Lorenz Number ◽  
Strong Magnetic Fields ◽  
Pass Through ◽  
Set Up ◽  
Magneto Resistance ◽  
The Magnetic Field ◽  
Overlapping Bands

General formulae are obtained for the effect of a magnetic field on the electrical and thermal conductivities of a metal in which there are two overlapping bands of normal form. Simple formulae are set up which, though not strictly valid for all temperatures and fields, reduce to the correct expressions in the three limiting cases of high temperatures, low temperatures and very strong magnetic fields. The behaviour of the electrical resistance at low temperatures is discussed, and it is shown that in certain cases the resistance may pass through a minimum as the temperature is increased provided the magnetic field is large enough. It is also shown that in general the Lorenz number is increased by the presence of a magnetic field, but that the thermal conductivity of the lattice is unaffected by a magnetic field.

Synthesis and Magnetic Properties of β-Cu3Fe4(VO4)6 Single Crystals

2015 ◽  
Vol 233-234 ◽  
pp. 137-140
Author(s):  
Dmitry A. Balaev ◽  
Oleg A. Bayukov ◽  
Evgeniy V. Eremin ◽  
M.S. Molokeev ◽  
Anatoly I. Pankrats ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Single Crystal ◽  
Spin Glass ◽  
Single Crystals ◽  
Low Temperatures ◽  
Freezing Temperature ◽  
X Ray ◽  
Glass State ◽  
The Magnetic Field

β-Cu3Fe4(VO4)6 single crystals were synthesized. The X-ray, magnetic, Mössbauer, and EPR investigations of the crystals were fulfilled. It is established that single-crystal β-Cu3Fe4(VO4)6 is a spin glass at low temperatures. Freezing temperature varies considerably depending on the orientation of the magnetic field relative to the crystal axes. Spin-glass state is confirmed by the relaxation of the magnetization.

scholarly journals The change of resistance of gold crystals at very low temperatures in a magnetic field and supra-conductivity

1930 ◽  
Vol 126 (803) ◽  
pp. 683-695 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Low Temperatures ◽  
Crystalline State ◽  
Specific Resistance ◽  
Systematic Research ◽  
Continuous Curve ◽  
Strong Magnetic Fields ◽  
Relative Change ◽  
The Magnetic Field

In a paper published last year the author described a systematic research on the change of resistance which occurs in a number of metals in strong magnetic fields. As a result of these investigations the following formulæ expressing the relative change of resistance ∆R/R o with the field H were found to hold :— ∆R/R o = β' H 2 /3H k H ≼ H k , (1) and ∆R/R o = β' ( H-H k +H k 2 /3H) H ≽ H k , (2) where β' and H k are constant for a given sample of a metal and at a given temperature. These two expressions form a continuous curve, and it is evident that the formula (1) which holds for the weaker fields, shows that the resistance increases as the square of H, and formula (2) indicates that the change of resistance in strong fields approaches a linear law. These two formulæ have been obtained mathematically on the following assumption. It is known that in a metal which is not in a perfect crystalline state, and which contains even small traces of impurities, there exists a disturbance which increases its specific resistance. My hypothesis was that a magnetic field increases the specific resistance in a similar way to these imperfections, so that they are equivalent to an internal magnetic field H k , orientated at random. Then, if the metal is brought under the influence of an outside magnetic field H, the increase of resistance is such as would be produced by a combination of the two fields. Further, I assumed that the increase of resistance is proportional to the magnetic field, and this led to formulæ (1) and (2) which appear to fit all my experimental results very well. Several important consequences follow from this hypothesis.

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