1
|
Metaxas PJ, Jamet JP, Mougin A, Cormier M, Ferré J, Baltz V, Rodmacq B, Dieny B, Stamps RL. Creep and flow regimes of magnetic domain-wall motion in ultrathin Pt/Co/Pt films with perpendicular anisotropy. Phys Rev Lett 2007; 99:217208. [PMID: 18233251 DOI: 10.1103/physrevlett.99.217208] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2007] [Indexed: 05/25/2023]
Abstract
We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, alpha.
Collapse
Affiliation(s)
- P J Metaxas
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France.
| | | | | | | | | | | | | | | | | |
Collapse
|
2
|
Kleemann W, Rhensius J, Petracic O, Ferré J, Jamet JP, Bernas H. Modes of periodic domain wall motion in ultrathin ferromagnetic layers. Phys Rev Lett 2007; 99:097203. [PMID: 17931031 DOI: 10.1103/physrevlett.99.097203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Indexed: 05/25/2023]
Abstract
Magnetization reversal in a periodic magnetic field is studied on an ultrathin, ultrasoft ferromagnetic Pt/Co(0.5 nm)/Pt trilayer exhibiting weak random domain wall (DW) pinning. The DW motion is imaged by polar magneto-optic Kerr effect microscopy and monitored by superconducting quantum interference device susceptometry. In close agreement with model predictions, the complex linear ac susceptibility corroborates the dynamic DW modes segmental relaxation, creep, slide, and switching.
Collapse
Affiliation(s)
- W Kleemann
- Angewandte Physik, Universität Duisburg-Essen, D-47048 Duisburg, Germany.
| | | | | | | | | | | |
Collapse
|
3
|
van der Beek D, Petukhov AV, Davidson P, Ferré J, Jamet JP, Wensink HH, Vroege GJ, Bras W, Lekkerkerker HNW. Magnetic-field-induced orientational order in the isotropic phase of hard colloidal platelets. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 73:041402. [PMID: 16711795 DOI: 10.1103/physreve.73.041402] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2005] [Indexed: 05/09/2023]
Abstract
The magnetic-field-induced orientational order in the isotropic phase of colloidal gibbsite [Al(OH)3] platelets is studied by means of optical birefringence and small-angle x-ray scattering (SAXS) techniques. The suspensions display field-induced ordering at moderate field strengths (a few Tesla), which increases with increasing particle concentration. The gibbsite particles align their normals perpendicular to the magnetic field and hence possess a negative anisotropy of their diamagnetic susceptibility Delta(chi). The results can be described following a simple, Onsager-like approach. A simplified model is derived that allows one to obtain the orientational distribution function directly from the scattering data. However, it leads to an underestimate of the diamagnetic susceptibility anisotropy Delta(chi). This accounts for the difference between the Delta(chi) values provided by the two experimental techniques (SAXS and magneto-optics). The order of magnitude Delta(chi) approximately 10(-22) J/T(2) lies in between that of goethite suspensions and that of suspensions of organic particles.
Collapse
Affiliation(s)
- D van der Beek
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
| | | | | | | | | | | | | | | | | |
Collapse
|
4
|
Bauer M, Mougin A, Jamet JP, Repain V, Ferré J, Stamps RL, Bernas H, Chappert C. Deroughening of domain wall pairs by dipolar repulsion. Phys Rev Lett 2005; 94:207211. [PMID: 16090287 DOI: 10.1103/physrevlett.94.207211] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Indexed: 05/03/2023]
Abstract
As a magnetic domain wall propagates under small fields through a random potential, it roughens as a result of weak collective pinning, known as creep. Using Kerr microscopy, we report experimental evidence of a surprising deroughening of wall pairs in the creep regime, in a 0.5 nm thick Co layer with perpendicular anisotropy. A bound state is found in cases where two rough domains nucleated far away from one another and first growing under the action of a magnetic field eventually do not merge. The two domains remain separated by a strip of unreversed magnetization, characterized by flat edges and stabilized by dipolar fields. A creep theory that includes dipolar interactions between domains successfully accounts for (i) the domain wall deroughening as the width of the strip decreases and (ii) the quasistatic and dynamic field dependence of the strip width s.
Collapse
Affiliation(s)
- M Bauer
- Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris Sud, 91405 Orsay, France
| | | | | | | | | | | | | | | |
Collapse
|
5
|
Lemaire BJ, Davidson P, Ferré J, Jamet JP, Petermann D, Panine P, Dozov I, Stoenescu D, Jovilet JP. The complex phase behaviour of suspensions of goethite (α-FeOOH) nanorods in a magnetic field. Faraday Discuss 2005; 128:271-83. [PMID: 15658779 DOI: 10.1039/b403074e] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In 1902, Majorana reported the magneto-optical properties of aqueous colloidal suspensions of mixed iron oxides. Oddly enough, the magnetic-field induced birefringence displayed a non-monotonic dependence upon field intensity. This behaviour was later interpreted as due to the existence in these sols of at least two different chemical species. During the course of our studies of mineral liquid crystals, we have revisited this problem by examining aqueous suspensions of pure goethite (alpha-FeOOH) nanorods. Although they are comprised of a single chemical species, these suspensions show the same odd behaviour reported by Majorana. Moreover, we show that, as the volume fraction increases, the suspensions have an isotropic liquid/nematic/rectangular columnar phase sequence, with first-order transitions between these phases. The non-monotonic dependence of the field-induced birefringence can be explained by the existence of a remanent magnetic moment of the nanorods and the negative anisotropy of their magnetic susceptibility. Therefore, the nanorods align parallel to a weak field but realign perpendicular to the field beyond Bc approximately 375 mT. In addition, other interesting phenomena appear upon application of a magnetic field: the disordered (i.e. isotropic in zero-field) phase becomes highly anisotropic and difficult to distinguish from the nematic phase. Both phases then acquire not only quadrupolar order but also dipolar order. The rectangular columnar phase is strongly stabilised versus the nematic one. Our experimental observations raise new theoretical questions about the phase diagram of these suspensions with respect to volume fraction and magnetic field intensity.
Collapse
Affiliation(s)
- Bruno J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Bâtiment 510 Université Paris-Sud, Orsay, France
| | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Attané JP, Samson Y, Marty A, Toussaint JC, Dubois G, Mougin A, Jamet JP. Magnetic domain wall propagation unto the percolation threshold across a pseudorectangular disordered lattice. Phys Rev Lett 2004; 93:257203. [PMID: 15697933 DOI: 10.1103/physrevlett.93.257203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2004] [Indexed: 05/24/2023]
Abstract
The reversal process of thin FePt/Pt(001) layers with perpendicular magnetization was observed by magnetic imaging techniques. Reversal occurs through domain wall propagation across a strongly disordered rectangular lattice of linear anisotropy defects. Micromagnetic simulations of domain wall pinning allowed deriving an analytical model of the reversal process unto percolation threshold. Quantitative agreement is found between the calculated and experimental fractal dimension of the reversed domain.
Collapse
Affiliation(s)
- J P Attané
- DRFMC/CEA Grenoble, 17 avenue des Martyrs, 38054 Grenoble Cedex 9, France
| | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
The dynamics of a 1D domain wall (DW) in magnetic wires patterned in 2D ultrathin Co films is studied as a function of the wire width w0. The DW velocity v(H) is hugely reduced when w0 is decreased, and its field dependence is consistent with a creep process with a critical exponent micro=1/4. The effective critical field scales as (1/w0). Measurements of v(H) in wires with controlled artificial defects show that this arises from the edge roughness introduced by patterning. We show that the creep law can be renormalized by introducing a topologically induced critical field proportional to (1/w0).
Collapse
Affiliation(s)
- F Cayssol
- Institut d'Electronique Fondamentale, UMR CNRS 8622, Université Paris Sud, 91405 Orsay, France
| | | | | | | | | |
Collapse
|
8
|
Lemaire BJ, Davidson P, Ferré J, Jamet JP, Petermann D, Panine P, Dozov I, Jolivet JP. Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part I: In the isotropic phase. Eur Phys J E Soft Matter 2004; 13:291-308. [PMID: 15103523 DOI: 10.1140/epje/i2003-10078-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Depending on volume fraction, aqueous suspensions of goethite (alpha-FeOOH) nanorods form a liquid-crystalline nematic phase (above 8.5%) or an isotropic liquid phase (below 5.5%). In this article, we investigate by small-angle X-ray scattering, magneto-optics, and magnetometry the influence of a magnetic field on the isotropic phase. After a brief description of the synthesis and characterisation of the goethite nanorod suspensions, we show that the disordered phase becomes very anisotropic under a magnetic field that aligns the particles. Moreover, we observe that the nanorods align parallel to a small field (< 350 mT), but realign perpendicular to a large enough field (> 350 mT). This phenomenon is interpreted as due to the competition between the influence of the nanorod permanent magnetic moment and a negative anisotropy of magnetic susceptibility. Our interpretation is supported by the behaviour of the suspensions in an alternating magnetic field. Finally, we propose a model that explains all experimental observations in a consistent way.
Collapse
Affiliation(s)
- B J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405, Orsay, France
| | | | | | | | | | | | | | | |
Collapse
|
9
|
Lemaire BJ, Davidson P, Ferré J, Jamet JP, Panine P, Dozov I, Jolivet JP. Outstanding magnetic properties of nematic suspensions of goethite (alpha-FeOOH) nanorods. Phys Rev Lett 2002; 88:125507. [PMID: 11909477 DOI: 10.1103/physrevlett.88.125507] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2001] [Indexed: 05/23/2023]
Abstract
Aqueous suspensions of goethite (alpha-FeOOH) nanorods form a mineral lyotropic nematic phase that aligns in a very low magnetic field (20 mT for samples 20 microm thick). The particles orient along the field direction at intensities smaller than 350 mT, but they reorient perpendicular to the field beyond 350 mT. This outstanding behavior is also observed in the isotropic phase which has a very strong magnetic-field induced birefringence that could be interesting for applications. We interpret these magnetic effects as resulting from a competition between a nanorod remanent magnetic moment and a negative anisotropy of its magnetic susceptibility.
Collapse
Affiliation(s)
- B J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Bâtiment 510, Université Paris-Sud, 91405 Orsay, France
| | | | | | | | | | | | | |
Collapse
|
10
|
Andrés R, Brissard M, Gruselle M, Train C, Vaissermann J, Malézieux B, Jamet JP, Verdaguer M. Rational design of three-dimensional (3D) optically active molecule-based magnets: synthesis, structure, optical and magnetic properties of ([Ru(bpy)3](2+), ClO4(-), [Mn(II) Cr(III)(ox)3](-))n and ([Ru(bpy)2ppy](+), [M(II)Cr(III)(ox)3](-))n, with M(II) = Mn(II), Ni(II). X-ray structure of ([deltaRu(bpy)3](2+), ClO4(-), [deltaMn(II)DeltaCr(III)(ox)3](-))n and ([lambdaRu(bpy)2ppy)](+), [lambdaMn(II)lambdaCr(III)(ox)3](-))n. Inorg Chem 2001; 40:4633-40. [PMID: 11511209 DOI: 10.1021/ic010363f] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To elucidate the relation between structural and magnetic properties, we have synthesized molecular materials having both Cotton effects and a ferromagnetic long range order. Such optically active 3D molecule-based magnets were rationally designed using the enantioselective template effect of optically active cations, namely Delta or Lambda [Ru(bpy)3, ClO4](+) or Delta or Lambda [Ru(bpy)3ppy](+) (bpy = bipyridine; ppy = phenylpyridine). Such cations are able to template the formation of optically active 3D anionic networks in which transition metal ions (Cr-Mn) and (Cr-Ni) are connected by oxalate ligands (ox). Following this strategy, we described the synthesis of ([Ru(bpy)3](2+), ClO4(-), [Mn(II)Cr(III)(ox)3](-))n and ([Ru(bpy)2ppy](+), [M(II)Cr(III)(ox)3](-))n with M(II) = Mn(II), Ni(II) in their optically active forms. In these 3D networks, all of the metallic centers have the same configuration, Delta or Lambda, as the template cation. We have determined the structure of ([DeltaRu(bpy)3][ClO4][DeltaMnDeltaCr(ox)3])n and ([LambdaRu(bpy)2ppy](+), [LambdaMn(II)LambdaCr(III)(ox)3](-))n by X-ray diffraction studies. These optically active networks show the Cotton effect and long-range ferromagnetic order at low temperatures. The magnetic circular dichroism of ([Ru(bpy)3](2+), ClO4(-), [Mn(II)Cr(III)(ox)3](-))n at 2 K is reported.
Collapse
Affiliation(s)
- R Andrés
- Laboratoire de Chimie Inorganique et Matériaux Moléculaires, CIM(2) Unité CNRS 7071, Université Pierre et Marie Curie, 4 place Jussieu, case 42, 75252 Paris Cedex 05, France
| | | | | | | | | | | | | | | |
Collapse
|
11
|
Aigouy L, Grésillon S, Lahrech A, Boccara AC, Rivoal JC, Mathet V, Chappert C, Jamet JP, Ferré J. Apertureless scanning near-field magneto-optical microscopy of magnetic multilayers. J Microsc 1999; 194:295-8. [PMID: 11388254 DOI: 10.1046/j.1365-2818.1999.00499.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We imaged magnetic domains in Pt/Co/Pt multilayers using an apertureless scanning near-field optical microscope operating in reflection mode. As the magneto-optical effects are weak for this kind of structure, a polarization modulation technique with a photoelastic modulator was used to reveal the contrast between magnetic domains. In the case of a Pt/Co/Pt trilayer structure, a strong improvement in lateral resolution is observed compared with far-field magneto-optical images and good sensitivity is achieved. In the case of a Pt/[Co/Pt]Pt multilayer structure, stripe domains of 200 nm width could be resolved, in good agreement with images obtained by magnetic force microscopy on the same structure.
Collapse
Affiliation(s)
- L Aigouy
- Laboratoire d'Optique Physique de l'E.S.P.C.I., Paris, France
| | | | | | | | | | | | | | | | | |
Collapse
|