scholarly journals A mechanism of magnetic hysteresis in heterogeneous alloys

1948 ◽  
Vol 240 (826) ◽  
pp. 599-642 ◽  
Keyword(s):  
Magnetic Anisotropy ◽  
Domain Boundary ◽  
Magnetic Hysteresis ◽  
Orientation Angle ◽  
Magnetization Vector ◽  
Prolate Spheroid ◽  
Shape Effect ◽  
Magnetization Curves ◽  
Easy Magnetization ◽  
Boundary Formation

The Becker-Kersten treatment of domain boundary movements is widely applicable in the interpretation of magnetization curves, but it does not account satisfactorily for the higher coercivities obtained, for example, in permanent magnet alloys. It is suggested that in many ferromagnetic materials there may occur ‘particles’ (this term including atomic segregates or ‘islands’ in alloys), distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector, I O . As the field changes continuously, the resolved magnetization, I H , may change discontinuously at critical values, H O , of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle, and on the orientation of ‘easy axes’ with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magneto-crystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution (§§ 2, 3, 4), and a less detailed treatment for the general ellipsoidal form (§ 5). For the first it is convenient to use the non-dimensional parameter such that h = H /(| N a - N b |) I O , N a and N b being the demagnetization coefficients along the polar and equatorial axes. The results are presented in tables and diagrams giving the variation with h of I H / I O . For the special limiting form of the oblate spheroid there is no hysteresis. For the prolate spheroid, as the orientation angle, θ , varies from 0 to 90°, the cyclic magnetization curves change from a rectangular form with | h O | = 1, to a linear non-hysteretic form, with an interesting sequence of intermediate forms. Exact expressions are obtained for the dependence of h θ on θ , and curves for random distribution are computed. All the numerical results are applicable when the anisotropy is due to longitudinal stress, when h = HI 0 /3λδ, where λ is the saturation magnetostriction coefficient, and δ the stress. The results also apply to magneto-crystalline anisotropy in the important and representative case in which there is a unique axis of easy magnetization as for hexagonal cobalt. Estimates are made of the magnitude of the effect of the various types of anisotropy. For iron the maximum coercivities, for the most favourable orientation, due to the magneto-crystalline and strain effects are about 400 and 600 respectively. These values are exceeded by those due to the shape effect in prolate spheroids if the dimensional ratio, m , is greater than 1·1; for m = 10, the corresponding value would be about 10,000 (§7). A fairly precise estimate is made of the lower limit for the equatorial diameter of a particle in the form of a prolate spheroid below which boundary formation cannot occur. As m varies from 1 (the sphere) to 10, this varies from 1·5 to 6·1 x 10 -6 for iron, and from 6·2 to 25 x 10 -6 for nickel (§ 6). A discussion is given (§ 7) of the application of these results to ( a ) non-ferromagnetic metals and alloys containing ferromagnetic ‘impurities’, ( b ) powder magnets, ( e ) high coeravity alloys of the dispersion hardening type. In connexion with ( c ) the possible bearing on the effects of cooling in a magnetic field is indicated.

Domain boundary formation on Au(110)

2002 ◽  
Vol 59 (4) ◽  
pp. 559-565 ◽  
Author(s):  
M. J Rost ◽  
S. B. van Albada ◽  
J. W. M Frenken
Keyword(s):  
Domain Boundary ◽  
Boundary Formation

scholarly journals The Process of Magnetizing FeNbYHfB Bulk Amorphous Alloys in Strong Magnetic Fields

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1367
Author(s):  
Bartłomiej Jeż ◽  
Jerzy Wysłocki ◽  
Simon Walters ◽  
Przemysław Postawa ◽  
Marcin Nabiałek
Keyword(s):  
Magnetic Fields ◽  
Amorphous Alloys ◽  
Magnetization Vector ◽  
Direct Methods ◽  
Structural Defects ◽  
Alloy Sample ◽  
Magnetization Curves ◽  
Magnetization Process ◽  
Strong Magnetic Fields ◽  
Antiferromagnetic Ordering

The structure of amorphous alloys still has not been described satisfactorily due to the lack of direct methods for observing structural defects. The magnetizing process of amorphous alloys is closely related to its disordered structure. The sensitivity of the magnetization vector to any heterogeneity allows indirect assessment of the structure of amorphous ferromagnetic alloys. In strong magnetic fields, the magnetization process involves the rotation of a magnetization vector around point and line defects. Based on analysis of primary magnetization curves, it is possible to identify the type of these defects. This paper presents the results of research into the magnetization process of amorphous alloys that are based on iron, in the areas called the approach to ferromagnetic saturation and the Holstein–Primakoff para-process. The structure of a range of specially produced materials was examined using X-ray diffraction. Primary magnetization curves were measured over the range of 0 to 2 T. The process of magnetizing all of the tested alloys was associated with the presence of linear defects, satisfying the relationship Ddi p < 1H. It was found that the addition of yttrium, at the expense of hafnium, impedes the magnetization process. The alloy with an atomic content of Y = 10% was characterized by the highest saturation magnetization value and the lowest value of the Dspf parameter, which may indicate the occurrence of antiferromagnetic ordering in certain regions of this alloy sample.

Rock Magnetic and Magnetostratigraphic Study of Chicxulub Crater Impact Breccias and Post-Impact Carbonates in the Yaxcopoil-1 and Santa Elena Boreholes

2020 ◽  
Author(s):  
Jaime Urrutia-Fucugauchi ◽  
Ligia Perez-Cruz ◽  
Elia Escobar-Sanchez ◽  
Miriam Velasco-Villarreal ◽  
Edgar Garcia-Garnica
Keyword(s):  
Oxygen Isotope ◽  
Carbonate Platform ◽  
Magnetic Hysteresis ◽  
Magnetization Vector ◽  
Carbonate Sediments ◽  
Carbon And Oxygen Isotope ◽  
Post Impact ◽  
Chicxulub Crater ◽  
The Impact ◽  
Santa Elena

&lt;p&gt;Chicxulub crater was formed ~66 Ma ago by an asteroid impact at the Cretaceous/Paleogene (K/Pg) boundary on the Yucatan carbonate platform in the southern Gulf of Mexico. The crater is the youngest and best preserved of the three large impact basins, with a ~200 km diameter and multi-ring and peak ring morphology. The crater, covered by post-impact carbonate sediments with thickness up to ~1.1 km, has been investigated by geophysical studies and drilling programs. Initial drilling in Yucatan was carried out by the Pemex oil company, followed by the National University UNAM Chicxulub program, the ICDP Yaxcopoil-1 project and the IODP-ICDP Expedition 364 marine drilling. Here, results of combined paleomagnetic, rock magnetic, petrographic and geochemical studies are used to characterize the sequence and constrain the unit&amp;#8217;s emplacement and crater formation. We analyze core samples of suevitic breccias and Paleogene carbonates from the Yaxcopoil-1 and Santa Elena boreholes drilled in the southern sector, inside and to the south of the crater rim marked by the ring of cenotes. &amp;#160;Magnetic hysteresis, low-field susceptibility and coercitivity analyses indicate that main carriers are titanomagnetites and magnetite. Mineralogical and magnetic properties indicate effects of hydrothermal alteration, associated with the high temperature system generated by the impact. Higher coercitivity minerals are also observed in some samples. In the carbonate sections, hydrothermal effects as marked by the geochemical logs decrease upwards from the breccia-carbonate contact. Alternating field and thermal demagnetization is used to investigate the magnetization vector composition and isolate the characteristic remanent components. Magnetic polarities defined from the inclination data show a sequence of reverse to normal, which correlate to polarity chrons 29r to 26r, with impact occurring within 29r chron.&amp;#160; The correlations of the magnetostratigraphy and stable isotopes indicate a hiatus at the basal Paleocene section. In Santa Elena cores, d&lt;sup&gt;13&lt;/sup&gt;C values range from 1.2 to 3.5%&lt;sub&gt;0 &lt;/sub&gt;and d&lt;sup&gt;18&lt;/sup&gt;O values range from -1.4 to -4.8%&lt;sub&gt;0, &lt;/sub&gt;with variation trends correlating with the marine carbon and oxygen isotope records for the late Maastrichtian and early Paleocene. The positive carbon isotopes indicate high productivity after the K/Pg extinction event, while the oxygen isotope values are more negative reflecting regional and local effects. Silica contents decrease from high in the suevites to low values in carbonates showing higher variability and then increased contents at the Paleocene-Eocene Thermal Maximum (PETM). The geochemical trends correlate in other elements including iron, titanium, potassium and aluminum that record impact-induced hydrothermal effects and possibly changing depositional conditions. Ca shows an opposite trend, with lower values in the upper suevitic breccias, higher values in the Paleocene carbonates and lower values in the PETM.&lt;/p&gt;

Shape effect on the magnetic anisotropy of an array of epitaxial (10·0) Co dots

1999 ◽  
Vol 35 (5) ◽  
pp. 3472-3474 ◽  
Author(s):  
T. Kohda ◽  
Y. Otani ◽  
V. Novosad ◽  
K. Fukamichi ◽  
S. Yuasa ◽  
...  
Keyword(s):  
Magnetic Anisotropy ◽  
Shape Effect

Determination of the Constants of Magnetocrystalline Anisotropy in Sintered Magnets with Uniaxial Texture

2005 ◽  
Vol 498-499 ◽  
pp. 134-140 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Rare Earth ◽  
Single Crystal ◽  
Pole Figure ◽  
High Energy ◽  
Anisotropy Constant ◽  
Magnetization Curves ◽  
Easy Magnetization ◽  
Initial Magnetization ◽  
Usual Process

The usual process for producing the high energy magnets based on rare-earth-transition metals as for example NdFeB, SmCo5 or Sm(CoFeCuZr)z involves powder metallurgy. In many cases, it is necessary the determination of anisotropy constants (K1 – first order and K2 second order) from polycrystalline samples. This is not the ideal situation because for more accurate determinations a single crystal is necessary. Nevertheless, in many cases it is very difficult, or not possible, obtaining a single crystal. Then, for these situations, the anisotropy constants can be evaluated from polycrystalline samples with uniaxial texture. In this study, the methodology for making such determination is described. It includes the measurement of Schulz Pole figure by X-Ray diffraction in a surface perpendicular to the c-axis, the axis of easy magnetization. The measured Pole figure can be adjusted with a Gaussian distribution f(q)=exp(-q2/2s2) or with a distribution of type f(q) = cosn q. A model to evaluate the remanence from quantitative metallography is also described. From these distributions, and using the microstructural model, it is possible to estimate the initial magnetization curves for polycrystalline samples, including the effect of the 2nd order anisotropy constant (K2) which produces a curvature in initial magnetization curve. With all these data it is finally possible to estimate the initial magnetization curves for single crystal samples (theoretical), and the anisotropy constants K1 and K2. The inadequacy of Sucksmith-Thompson plots for determination of anisotropy constants from polycrystalline samples is also commented. The described method can be used either for rare-earth transition magnets or for Barium or Strontium ferrites.

scholarly journals Влияние дисперсии магнитной анизотропии кластеров Ge-=SUB=-3-=/SUB=-Mn-=SUB=-5-=/SUB=- на температурные зависимости намагниченности тонких пленок Ge:Mn

2019 ◽  
Vol 45 (2) ◽  
pp. 36
Author(s):  
А.И. Дмитриев ◽  
М.С. Дмитриева ◽  
Г.Г. Зиборов
Keyword(s):  
Magnetic Field ◽  
Magnetic Anisotropy ◽  
Lognormal Distribution ◽  
Anisotropy Constant ◽  
Zero Field ◽  
Magnetization Curves ◽  
Magnetic Anisotropy Energy ◽  
Size Dependent ◽  
Magnetic Anisotropy Constant ◽  
Temperature Dependences

AbstractThe temperature dependences of magnetization M ( T ) of thin ion-implanted Ge:Mn (4 at % Mn) films containing Ge_3Mn_5 clusters were measured on samples cooled in the absence of magnetic field (zero field cooled, ZFC) and in a magnetic field of 10 kOe (field-cooled, FC). It has been established that the shape of ZFC–FC differential M ( T ) curves is determined by lognormal distribution of the size-dependent magnetic anisotropy energy of Ge_3Mn_5 clusters. Analysis of the observed ZFC–FC magnetization curves allowed the magnetic anisotropy dispersion (variance) and magnetic anisotropy constant to be estimated.

scholarly journals Low-field Magnetic Anisotropy of Sr2IrO4

2022 ◽  
Author(s):  
Muhammad Nauman ◽  
Tayyaba Hussain ◽  
Joonyoung Choi ◽  
Nara Lee ◽  
Young Jai Choi ◽  
...  
Keyword(s):  
Magnetic Anisotropy ◽  
Exchange Interaction ◽  
Exchange Interactions ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Easy Magnetization ◽  
Magnetic Exchange ◽  
Crystal Field Effect ◽  
Out Of Plane

Abstract Magnetic anisotropy in strontium iridate (Sr2IrO4) is essential because of its strong spin–orbit coupling and crystal field effect. In this paper, we present a detailed mapping of the out-of-plane (OOP) magnetic anisotropy in Sr2IrO4 for different sample orientations using torque magnetometry measurements in the low-magnetic-field region before the isospins are completely ordered. Dominant in-plane anisotropy was identified at low fields, confirming the b axis as an easy magnetization axis. Based on the fitting analysis of the strong uniaxial magnetic anisotropy, we observed that the main anisotropic effect arises from a spin–orbit-coupled magnetic exchange interaction affecting the OOP interaction. The effect of interlayer exchange interaction results in additional anisotropic terms owing to the tilting of the isospins. The results are relevant for understanding OOP magnetic anisotropy and provide a new way to analyze the effects of spin–orbit-coupling and interlayer magnetic exchange interactions. This study provides insight into the understanding of bulk magnetic, magnetotransport, and spintronic behavior on Sr2IrO4 for future studies.

scholarly journals Слоевые нанопроволоки --- матричный синтез, структура и магнитные свойства

2019 ◽  
Vol 61 (9) ◽  
pp. 1682
Author(s):  
Д.Л. Загорский ◽  
И.М. Долуденко ◽  
Д.А. Черкасов ◽  
О.М. Жигалина ◽  
Д.Н. Хмеленин ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Magnetic Force Microscopy ◽  
Magnetic Force ◽  
Residual Magnetization ◽  
Magnetization Curves ◽  
Easy Magnetization ◽  
Force Microscopy ◽  
Shell Nanostructures ◽  
Magnetization Axis ◽  
Out Of Plane

AbstractNanowires (NWs) consisting of Ni/Cu and Co/Cu alternating layers with a diameter of 100 nm and layer thicknesses varying between 10 and 500 nm are prepared by template synthesis in pores of polymer track-etched membranes. Bath compositions and different regimes for pulsed electrodeposition of NWs are explored. A procedure for electrodeposition of NWs using pulses of equal charge is developed. By diminishing the amount of charge per pulse, initially we manage to lower the layer thickness to 10–15 nm, but further diminishing of charge in pulses leads to the blending of elemental composition of adjacent layers and/or formation of rod–shell nanostructures within the NWs. The coercive force (15–30 mT) and residual magnetization of our layered NWs are determined from magnetization measurements. For NWs with a layer thickness of 50–100 nm, the magnetization curves recorded in the out-of-plane and in-plane geometries are similar in shape and have similar parameters. For NWs with thicker layers (250 and 500 nm), magnetization curves are markedly different due to magnetic anisotropy (an easy magnetization axis emerges longitudinally to NWs) and interference between neighboring NWs. Magnetic force microscopy of isolated NWs identifies that the NWs comprise magnetic regions extending over ~100–150 nm. The NW can be partially remagnetized by applying an external magnetic field (+16 mT) longitudinally.

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