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The variation with temperature of the magnetizations of single crystals of Ni, Fe, and Fe+3 wt % Si are studied. New data for Fe and Fe(Si) is presented along with previously reported measurements for Ni. These data were obtained by means of the pyromagnetic effect at various applied fields and in the temperature range 4.2-140, 30, and 120°K for the Fe, Fe(Si), and Ni crystals, respectively. The observed departures from T 3/2 behavior are well described by spin-wave theory. Attempts to ascribe some of the measured variation of the magnetization to Stoner-type excitations or to variation of the moment per atom due to lattice expansion are mainly unsuccessful. The coefficients of the JT 3/2 term appropriate for zero spin-wave energy gap are C=7.5=t=0.2, 3.4=1=0.2, and 4.4±0.2X10-6 deg~3/ 2 for Ni, Fe, and Fe(Si), respectively. The coefficients of the T 6/2 term for zero gap are determined only for the Ni and Fe crystals as Z>= (1.5=1=0.2) X10~8 deg~6 /2 and (1±1)X10~9 deg~6 /2 , respectively. The measured variation of the spin-wave energy gap with applied field is consistent with the known g values of 2.19 and 2.09 for Ni and Fe. The magnitude of the gap at zero field is fully explained by the effects of magnetocrystalline anisotropy and magnetic-dipolar coupling. The values of the C and D coefficients are compared with results from independent experiments and are discussed in relation to theories of ferromagnetism in metals. OF FERROMETALS:Ni, Fe, AND Fe + 3% Si 2053 ARGYLE, CHARAP, AND PUGH

The first use of linear magnetic birefringence (optical Cotton-Mouton effect) to observe a magnetic resonance is reported. This allows us to make the first direct observation of resonant motion of a ferromagnetic vortex. This vortex is present in an easy-plane garnet film at the intersection of two 90° Neel walls. Agreement between the resonant frequencies and our theory confirms a previously proposed equation of vortex motion. PACS numbers: 76.90. + d, 75.40.Dy, 78.20.Ls We present here the first conclusive evidence for a Magnus-type force acting on a simple, topologically quantized vortex in a ferromagnetic medium. The existence of such forces which act orthogonally to the velocity of quantized superfluid and superconducting vortices is well known. A similar force, based on the classical Landau-Lifshitz equation that describes ferromagnetic-spin precessions, is expected to act on vortices occurring in a ferromagnet. 1 It illustrates a general law stating that the effective force component orthogonal to the velocity V of a micromagnetic structure (soliton) MO? -V/) is proportional to the product of V and the spherical angle mapped by the structure's distribution in M space. 2 This force is dominant whenever pseudoinertial effects can be neglected. 3 Recent unpublished work provides evidence of a resonance provisionally attributed to the motion of a magnetic vortex present within a Bloch line in a 180° Neel wall found in a garnet film of 0.8 /xm thickness. 4 This configuration was complicated by the absence of a well-defined restoring force for the wall due to the presence of permeable closure domains at its ends. However, these results did give some support to the equation of vortex motion employed in a statistical theory of two-dimensional ferromagnetism. 1 We have now investigated the dynamics of a magnetic vortex which forms at the intersection of two 90° Neel walls separating well defined in-plane domains stabilized by a "Swiss cross" geometry ( Fig. 1). In this geometry, fixing the four-ends of the walls to the inner corners defines the restoring force. Moreover, the walls do not touch closure domains. Thus the present configuration is suitable for a conclusive comparison of experiment with theory. Figure 2(a) shows a magneto-optic photomicrograph of two static 90° Neel walls intersecting at right angles. The bright or dark contrast of the walls is obtained by means of the Cotton-Mouton effect, a linear birefringence, Arc = n\\ -n L , for the two eigenmodes of linearly polarized light, parallel and perpendicular to the magnetization. (The circular birefringence or Faraday effect is absent because the in-plane magnetization is orthogonal to the normally incident laser illumination.) Intensity contrast between regions of different orientations of M^ becomes visible when an optical compensator and an analyzer are suitably adjusted. (We utilize an adjustable Ehringhaus compensator with its axes fixed at 45° with respect to the crossed polarizer and analyzer axes.) For incident ^-polarized light E=*E y y, t...

A variety of relatively transparent materials containing Eu+ + have become available, thus enabling a study to be made of the magneto-optical properties of the Eu+ + ion in widely different environments. The following materials are reviewed: Eu2SiO4 (orthorhombic structure with a ferromagnetic Curie temperature Tc of 7°K), dilute Eu+ + in CaF2 (fluorite structure), EuF2 (fluorite structure, Tc≈0), EuO−Al2O3−B2O3 glasses (Tc=0), EuSe (NaCl structure, Tc=7°K), and EuO (NaCl structure, Tc=69°K). We discuss the magneto-optical properties of the ``nonmagnetic'' materials (CaF2: Eu+ +, EuF2, Eu glasses) in terms of an intra-atomic 4f7→4f65d transition. Using this transition, calculation of the Faraday and Cotton-Mouton birefringence in EuF2 gives reasonable agreement with experiment. The magneto-optical properties of the ``magnetic materials'' (Eu chalcogenides) are discussed in terms of an interatomic (4f7) (4f7) → (4f6) (4f75d) transition. This transition gives reasonable agreement with the observed magnitudes of the magnetic absorption edge shifts in EuSe and EuO.