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Mestre Suassuna | |
|---|---|
 Suassuna Capoeriando 2004 | |
| Background information | |
| Birth name | Reinaldo Ramos Suassuna |
| Origin | Ilhéus, Bahia, Brazil |
| Genres | Capoeira Brazilian Folklore |
| Occupation(s) | Head of Cordão de Ouro, Musician, Educator |
| Instrument(s) | Berimbau, Atabaque, Pandeiro |
| Years active | 1975 - Present |
| Labels | Wea International |
| Website | [1] |
Reinaldo Ramos Suassuna also known as Mestre Suassuna (IPA: ['mɛ:stɾɛ suɑ'su:nɑ]), born 1938 in Ilhéus, Bahia, Brazil is the founder and head of the international capoeira organization Cordão de Ouro.[1]
Early life
He was raised in Itabuna and started to practice capoeira, an Afro-Brazilian martial art developed initially by African slaves in Brazil, in the beginning of the 1950s, against his will.[2]Due to a physical handicap in his legs, the doctor recommended that he should involve himself in a sport that was not soccer. Under the influence of two friends that had begun capoeira and his medications, Suassuna started to practice this Brazilian art.
Suassuna states that in the beginning he had not liked capoeira at all because he had difficulty learning the ginga and its unique sway and he lacked rhythm to sing, but with time he started to enjoy the taste of capoeira so much that he began to take his training seriously and at this point his mother thought he was sick or ill.
When Suassuna started capoeira he did not fixate himself to a group, but rather, he learned to love capoeira as a whole, independent of whether it was Angola or Regional. He met people from the Academies of Mestre Bimba and Mestre Pastinha. He participated in presentations in Salvador, Brazil with Canjiquinha, Gato, Caicara … and all of this has served as an excellent base for developing his work and arriving to where he is today: international recognition.
Professional career
At the beginning of the 1960s, Suassuna excelled in Bahia with his capoeira presentations and consequently many invitations from other states and from abroad were offered. In 1965, after two of his friends kept on insisting for him to come to São Paulo, he left Bahia and went to the land of the rain with the intention of opening an academy and succeeding in life with capoeira. His mission was to develop capoeira as folklore and as a sport. At the beginning it was very hard; he was far from his friends, he worked at various jobs, went through financial difficulties. After a lot of struggle, he met some people from Itabuna that took him to Ze Freita’s Academy, in São Paulo, Brazil. That is where he met Brasilia. On 1 September 1967, together with Brasilia, he founded the “Associacao de capoeira Cordão de Ouro”.
Today, Suassuna is dearly liked and respected. He is proud to see that his group’s work is well structured and full of creativity, with members found all over the world. His many doings include various presentations, the recording of four compact discs, the directing of the Show Group of Cordão de Ouro, the creation and development of the “Miudinho Game” and the conducting of workshops and seminars in several states in Brazil and around the world.
References
The anisotropic magnetoresistance (AMR)(also known as spontaneous magnetoresistance anisotropy (SMA) or the ferromagneticresistivity anisotropy) describes the change in electrical resistivity of a material depending on the direction of the material's magnetization with respect to the current.
History
About 150 years ago the AMR was discoveredby William Thomson in 1857.[1]About a century later systematicresearch was carried out on this topic and theoretical and experimental workwas done by R.M. Bozorth,[2] J.L. Snoek [3], J. Smit,[3] H.C. vanElst [5],L. Berger [6], R.I.Potter [7], T.R. McGuire [8], J.W.F. Dorlijn [9], O. Jaoul, I.A. Campbell, J. Fert[4], and many more. First technical use of this phenomenonwas made with magnetic bubble memory in the late 1960s. Todaysensors for magnetic fields based on the AMR are built for the automobileindustry[5] where robustness and heat resistance are needed.
Appearance of the AMR
For many ferromagnetic metals and alloys such as iron, nickel, or a mixtureof those like permalloy (Ni80Fe20) the AMR changes the resistivity by a few percent. The size of the effect is strongly dependent on the material, the temperature, and the shape of the object, especially the thickness of a metallic film.[2]The AMR-ratio is usually defined as the normalized variation of the resistivity given in percent:
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Angular dependence
The resistivity
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Field strength dependence
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The resistivity
References
Raw text from my Diplomarbeit
appears as the change of few percent in electrical resistivity 
Figure 2.1: Electrical resistivity �(#) as a function of the angle
- = \(~j, ~M ) between the direction of the electrical current ~j(~r) and the
orientation of the samples magnetisation ~M (~r).2.1.1 Formalism of the AMRThe AMR ratio �AMR is defined as the normalized variation in resistivityand is a good measure for the size of the effect2. It can be obtained directly2In many publications the AMR ratio is also given as ��/�ave where �ave = 13�k + 23�?is the average value for truly demagnetized polycrystalline bulk material. In this case2.1. Anisotropic magnetoresistance 5from experiment by measuring the resistance parallel and perpendicular tothe magnetisation.�AMR =(Rk − R?)Rk=�RRk,=(�k − �?)�k=���k.(2.2)Taking the z-axis along the direction of magnetisation, the resistivity can bewritten in form of a tensor asˆ�ik = 0@�? −�H 0�H �? 00 0 �k1A. (2.3)With ~uM being the unit vector in the direction of the magnetisation, Ohm’slaw can be given in the form of~E= ˆ�ik~j= �?~j + �� (~uM ·~j)~uM + �H ~uM×~j(2.4)The diagonal elements are the resistivities along or perpendicular to the magnetisationwhile the off-diagonal elements ±�H represent the spontaneous oranomalous Hall effect, which is small for permalloy and shall not be discussedhere.2.1.2 Fundamentals of the AMRAn exhaustive quantum mechanical description of the effect is rather lengthly.Solely an overview on the microscopic origin of the anisotropic magnetoresistanceas well as a short introduction to the basic principles of ferromagnetismin iron and nickel will be given. This should give a qualitative understandingof the nature of the AMR (see also [11], [12] and [13]). A more extensivedescription can be found in [8].Ferromangetism in transition metalsExchange interaction In a model assuming localized electrons one can describethe interaction between the electron spins with the Hamiltonian introthemagnetisation of the domains is randomly orientated throughout the three dimensions.In thin films where the magnetisation is only in-plane the expression changes to�ave = 12�k + 12�?.6 2. THEORYduced by Heisenberg [14]:HHeisenberg = −2A �1�2. (2.5)For a positive exchange constant (A > 0) the two spins �1 and �2 willenergetically prefer a parallel orientation, which leads to a ferromagneticspin lattice. A negative exchange constant (A < 0) will cause the spins toorientate antiparallel and promote an antiferromagnetic spin lattice.This exchange interaction can issue from divers sources: either directlyfrom a relevant overlap of the electron orbits or indirectly via interaction withelectrons of diamagnetic atoms situated between the atoms of the (anti-) ferromagneticlattice. This is a good model for antiferromagnetic manganousoxide (Mn2+O2−). Additionally the conduction electrons can act as mediatorbetween the spins as proposed by M. A. Rudermann, C. Kittel, T. Kasuyaand K. Yosida. RKKY-interaction can play a relevant role in the ferromagnetismof rare earths [15].In transition metals the spins of the 3d-like electrons are responsible forthe ferromagnetism. In those materials these electrons cannot be consideredas localized since they hybridize with the 4s-like electrons and form a halffilled conduction band. Here the exchange interaction between the quasi freeelectrons lowers the energy of the majority electrons (") and rises that of theminority electrons (#) as shown in Fig. 2.2.a)10 20 30 10 20 30 0EF0.90.80.70.60.50.40.30.20.1Energy (Ry)D(E) [103/Ry]
- "
b)0.40.30.20.10.50.60.70.80.9Energy (Ry)0 10 20 30 10 20 30EFs,p-bandd-bandD(E) [103/Ry]
- "
Figure 2.2: Density of states in nickel divided into majority (") and minority(#) spin states according to J. Callaway and C. S. Wang [16]a) From self-consistent band structure calculationsb) Schematic illustration of the s,p- and d-bands2.1. Anisotropic magnetoresistance 7Domain patterns In a macroscopic ferromagnetic structure the magnetisationwill generally not point homogeneously in one direction, but divide intodomains in which the magnetisation is parallel, divided by domain walls,where the magnetisation changes direction. The average over many domainseventually sums up to zero, so that an iron nail may seem without magnetisation.This is due to a series of energy terms, that oppose and balance:Etotal = Eexchange + Estray-field + Eanisotropy + EZeeman + Eother. (2.6)The exchange energy, as described by the Heisenberg Hamiltonian, tends toparallelize the spins and therefore prefers a homogeneous magnetisation. Thisis in contradiction to the second term, that represents the energy of the strayfield, which would maximize for a homogeneous magnetisation. The thirdterm denotes the symmetry of the lattice, that makes certain directions ofmagnetisation more favourable than others. The face-centred cubic lattice ofnickel, for example, prefers magnetisations in one of the four [111] directions,i. e. the space diagonals. The Zeeman energy arises from the interactionwith the applied magnetic field and tends to align the magnetisation with~Bext. The last term contains other energies like the magnetostrictive energy,which can be neglegted here. As a result, a magnetic object may have amagnetisation as in Fig. 2.3, where the stray field is minimized and sevendomains result with a near zero average magnetisation.a) b) c)Figure 2.3: Possible domain pattern in a 2×4 µm2 permalloy element of25 nm thickness:a) Measured magnetisation with a magnetic force microscope (MFM).b) Calcutated MFM image from simulation.c) Micromagnetic computer simulation of the magnetisation.8 2. THEORYOrigin of the AMRSpin-orbit coupling The dependence of the resistivity on the angle betweenthe magnetisation and the current as illustrated in Fig. 2.4 is due to electronscattering from the 4s,p-band to the 3d-band connected by a spin flip. Thisadditional scattering channel is opened by the spin-orbit interaction whichcontributes to the Hamiltonian in the form ofHspin-orbit = K L S = K Lz Sz + K2L+ S− + K2L− S+. (2.7)Here the generators and annihilators L± = Lx ± iLy and S± = Sx ± iSy,if applied to an electron wave function, can increase or decrease the orbitalquantum number or flip the spin. The operator product L+ S− turns a majorityspin p"-electron wave function into that of a d#-electron.Unlike the rather isotropically widely spread s,p-states, the more localizedd-states have a strong orbital anisotropy. This accounts for an anisotropicscattering cross section for interband scattering with spin flip, that is biggerfor s,p-electrons with a momentum parallel to the orbit of the empty3d-state and therefore, due to spin-orbit coupling, bigger if parallel to themagnetisation [4].a) b)Figure 2.4: Illustration of the origin of the anisotropic magnetoresistance.The direction of the sample’s magnetisation is connected to the spin ofthe 3d-electrons. The anisotropic 3d-orbits have a bigger cross section foran electron current in the direction of the magnetisation.a) If the magnetisation is perpendicular to the current direction( ~M ?~j), then the resistivity is low.b) For parallel orientation (Mk~j) the resistivity is higher.Since the s,p-band has a few times higher group velocityvg(EFermi) = 1~@E(k)@k and a smaller effective mass m? = ~2( @2E(k)@k2 )−1 atthe Fermi energy than the d-band, as one can see from band structure2.1. Anisotropic magnetoresistance 9calculations and photoelectron spectroscopy [18, 16, 19], mostly s,p-likeelectrons contribute to the conductivity in permalloy. It is assumed, thatthe high density of states D#d(EFermi) of the minority spin d-electrons at theFermi energy is responsible for the short mean free path of the minoritys,p-conduction electrons, which results in a high resistivity for the minoritys,p-subband. Thus mostly majority spin s,p-electrons contribute to theconductivity and therefore the spin-orbit interaction plays a relevant role,since it scatters the main conduction electrons into the biggest reservoir ofempty states at the Fermi energy.r (B)r^r | || |^Bext[mT]Figure 2.5: Resistivity of a multi-domain ferromagnetic structure in dependenceof an applied magnetic field ~Bext. The red curve shows thebehaviour with the magnetic field in the direction of the current (k). Theblue curve corresponds to the perpendicular case (?).Applying magnetic fields As described above, a macroscopic ferromagneticstructure consists of domains with different directions of magnetisation.These domains can be aligned by an applied magnetic field ~Bext. The strengthof the magnetic field ~Bsat, that is needed to saturate the alignment varieswith material, form, direction, and temperature of the ferromagnetic structure.Although the alignment of the domains is not brought about by simultaneouslyrotating the magnetisation in each domain, a quasi continuousalignment process of the magnetisation of the sample is possible. The domainwalls are shifting in such a way, that the domains with a magnetisation indirection of ~Bext grow on cost of those pointing in other directions.10 2. THEORYA typical AMR signature is depicted in Fig. 2.5. Starting from a demagnetizedmulti-domain state at zero field, the magnetisation becomes alignedas the field strength rises. An external magnetic field ~Bext either parallelor perpendicular to the current results in a rise or fall of the resistance,respectively.In ferromagnetic microstructures certain domain configurations like thatin Fig. 2.3 are energetically favourable. In these cases, the domain configurationcan switch from one state to another, so that the magnetisation processis a series of quasi continuous (reversible) domain-wall movements separatedby (irreversible) configuration changes. The shape of the ferromagnetic microstructurecan induce hard and easy axes of magnetisation, e.g. directionsin which the structure can easily be saturated and othes in which the magneticfield strength for saturation Bsat is much higher. In cases of extremeshape anisotropy quasi single-domain microstructures can be produced. Inthin permalloy films with a thickness of about or less than t . 100 nm themagnetisation is preferably in-plane and the domain walls are N´eel walls,where the magnetisation between the domains is rotating in the plane ofmagnetisation.2.1.3 Magnitude of the AMRa)1234560 70 80 90 50Concentration ofnickel in iron x [%]b)1234540 60 80 20Film thickness t [nm]c)2100 200468Temperature T [K]Figure 2.6: Magnitude of the AMR-Ratio in NixFe1−x alloys:a) Depending on the concentration x of nickel at room temperature[2].b) Depending on the film thickness in Ni80Fe20 at 4 K [20].c) Depending on the temperature in Ni80Fe20 [4].The size of the effect usually given in percent as �AMR = �RR changeswith material, temperature, shape, and many other parameters. Especially2.2. Magnetic-force microscopy 11in thin films the resistance R is influenced by grain size, surface quality, andfilm thickness and therefore varies with deposition rate, groth temperature,heat treatment, and vacuum quality. In Fig. 2.6 the variation with threemain parameters is shown. For room temperature measurements Ni80Fe20permalloy films with a thickness of t & 20 nm still show a reasonable effect.