Surface magneto-plasmons in magnetic multilayers - Walther ...

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38 Chapter 3 Excitation of surface plasmon polaritons As the inner part of the rotation stage has a diameter of ≈ 10 cm, the total length lFe of the yoke is lFe ∼ = 3 × 10 cm = 30 cm. Moreover, for the 5 mm prism, an air gap of 5...10 mm is mandatory. Thus, lFe = 0.3 m and gair = 0.01 m are determined by the setup, hence only the product nI is a free parameter. For B = 20 mT, Eq. (3.2) yields nI = 255. In this calculation losses due to stray fields are neglected. These losses can be approximated with the ratio of the air gap length (gair) to the iron yoke thickness (d) and are here ≈ 50 % (gair = 10 mm and dyoke = 20 mm) [68]. Further, a field µ0H > µ0HC is desired, which is arbitrarily chosen to be 30 mT. Thus Eq. (3.2) with B = 60 mT yields nI ≈ 820, with a current of I ∼ = 2 A roughly 410 turns are needed. Following this rough estimation, 500 turns with a 0.5 mm diameter copper wire, are used (Fig. 3.5(b)). To prevent the wire from Joule heating and allowing a continu- ous operation the VDE 0100 − 430 [72] recommends a maximum current density of 6 A/mm 2 for a copper wire with 1 mm diameter. With I = 2 A only 4 A/mm 2 are reached and thus even with 0.5 mm diameter copper wire there should not be any problem with Joule heating. The electromagnet yields a maximum field of about 55 mT at the yoke and about 30 mT in the middle of the gap (for I = 2 A). The inhomogeneity can be explained by the gap size. To achieve a homogeneous field in the gap, the gap should be much smaller than the thickness of the yoke (gair ≪ d). For the yoke a steel of 20 mm×20 mm thickness is used. This is about size of the air gap (gair = 10 mm). But for this thesis the homogeneity is acceptable. The magnet is driven by bipolar BOP 20 − 10 power supply from Kepco. The magnetic field is measured and controlled with a 475 DSP gaussmeter from Lakeshore. During measurements the hall probe is positioned behind the sample and is roughly adjusted on same height as the laser. Via an analog output the 475 DSP controls the output current of the BOP 20 − 10. Thus, the magnetic field desired is always indeed applied, and the magnetic hysteresis of the Fe yoke is "automatically" compensated. Table 3.1 summarises the most important specifications of the built electromagnet. Photo-detectors The photo-detectors used in this thesis are built according to a design which was developed by Reinhard Roßner during his student work a the WMI [73]. They consist of a photodiode (BP104S from Osram Opto Semiconductors) and an
Section 3.1 Experimental setup 39 l 1,Fe I l 2,Fe (a) 59 mm s d d l 3,Fe g air 100 mm 20 mm (b) 11.2 mm Figure 3.5: (a) Sketch of the electromagnet to estimate the number of turns. li,Fe are the lengths of the segments of the iron yoke and gair is the gap size and d = 20 mm is the lateral dimension of the quadratic iron yoke. The red curve depicts the integration path s. (b) Photograph of the electromagnet with 500 turns. length of the yoke lFe = l1,Fe + 2l2,Fe + 2l3,Fe 30.9 cm length of the gap gair 1.1 cm number of turns 500 maximum field at the yoke (I = 2 A) 55 mT maximum field in the middle (I = 2 A) 30 mT Table 3.1: Specifications of the electromagnet operational amplifier (OPA627B from Burr - Brown). Tables 3.2 and 3.3 give the relevant parameters of the photodiode and the operational amplifier. The photo-detector is driven in the low gain mode. This means that R2 = 1 MΩ is used (see the wiring diagram in [73]). Again the E3630A power supply from Agilent is used which also allows to supply the photo-detector with ±10 V, what should be the optimal voltage [73].
Page 1: TECHNISCHE UNIVERSITÄT MÜNCHEN WA
Page 4 and 5: II Contents 4.2 Reflectivity of mul
Page 6 and 7: 2 Chapter 1 Introduction via a grat
Page 8 and 9: 4 Chapter 1 Introduction
Page 10 and 11: 6 angular frequency, t the time, an
Page 12 and 13: 8 Chapter 2 Theory Here, µ (1) =
Page 14 and 15: 10 electron density. Chapter 2 Theo
Page 16 and 17: 12 Chapter 2 Theory [8]. In this co
Page 18 and 19: 14 2.3.1 Reflectivity of a single l
Page 20 and 21: 16 Chapter 2 Theory curve shown in
Page 22 and 23: 18 t 10 t 10 t 10 r 01 E 0 r 10 e i
Page 24 and 25: 20 Chapter 2 Theory Hereby, i = 1,
Page 26 and 27: 22 2.4 Simulation of the reflectivi
Page 28 and 29: 24 dopt = |ε ′(1) | − 1 4π |
Page 30 and 31: 26 p R 1 .0 0 .8 0 .6 0 .4 0 .2 0 .
Page 32 and 33: 28 2.5.1 Interaction of an external
Page 34 and 35: 30 ω |k x | Chapter 2 Theory Figur
Page 36 and 37: 32 Chapter 2 Theory enhancement wil
Page 38 and 39: 34 LASER lter beam splitter polaris
Page 40 and 41: 36 (a) εsubstrate εCo ε prism ε
Page 44 and 45: 40 Chapter 3 Excitation of surface
Page 46 and 47: 42 p h o to -d e te c to r s ig n a
Page 48 and 49: 44 9 0 8 5 8 0 7 5 7 0 6 5 6
Page 50 and 51: 46 5 V 0 V U out Chapter 3 Excitati
Page 52 and 53: 48 Chapter 3 Excitation of surface
Page 54 and 55: 50 U A-B (θ) [V] 0.00 -0.05 -0.10
Page 56 and 57: 52 U A -B (θ) [V ] U A (θ) [V ] U
Page 58 and 59: 54 will be discussed. 4.1.1.2 Deter
Page 60 and 61: 56 p R 1 .0 0 .8 0 .6 0 .4 0 .2 0 .
Page 62 and 63: 58 p R 0 .8 0 .4 0 .0 0 .8 0 .4
Page 64 and 65: 60 Chapter 4 Experimental study of
Page 70 and 71: 66 4.4 Summary Chapter 4 Experiment
Page 74 and 75: 70 Chapter 5 Surface plasmons in ma
Page 76 and 77: 72 U A -B , -1 5 m T (θ) [V ] 0 .0
Page 80 and 81: 76 Δ θ 0 2 0 1 5 1 0 5 0
Page 84 and 85: 80 ΔU θ = c o n s t (θ) [m V ]
Page 88 and 89: 84 p x 1 0 -4 p /δθ 1 /R δR 0 .5
Page 90 and 91: 86 δU /U (H ) x 1 0 -3 2 .5 2 .0 1
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88 Chapter 5 Surface plasmons in ma
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90 s M /M 1 .5 1 .0 0 .5 0 .0 -0 .5
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92 Chapter 5 Surface plasmons in ma
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94 Chapter 6 Conclusions and Outloo
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100 Chapter 6 Conclusions and Outlo
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102 (*Thickness of the layers in An
Page 108 and 109:
104 /Extract[Ms[lambda, theta], {1,
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106 40 mm 10 mm 130 mm Figure B.2:
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108 and d sin 45 = h/2 sin(90 + θ)
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110 Appendix C Prism correction
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112 Appendix D Code for SPP simulat
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114 (*MO Reflectivity*) Appendix D
Page 120 and 121:
116 Bibliography [12] J. Weeber, E.
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118 Bibliography [40] A. A. Maradud
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120 Bibliography [67] F. E. Luborsk
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122 Bibliography [93] T. Sidiropoul
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Robert Müller, Helmut Thies and hi
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