Room‐Temperature Ferromagnetic Materials Transparent in the Visible
01 Mar 1970-Journal of Applied Physics (American Institute of PhysicsAIP)-Vol. 41, Iss: 3, pp 1218-1224
TL;DR: The only known crystals which have spontaneous ferromagnetic moment at room temperature and are transparent well into the visible spectrum are ferric borate, FeBO3, and ferric fluoride, FeF3 as mentioned in this paper.
Abstract: The only known crystals which have a spontaneous ferromagnetic moment at room temperature and are transparent well into the visible spectrum are ferric borate, FeBO3, and ferric fluoride, FeF3. Each of these rhombohedral materials is a canted antiferromagnet with a small moment lying in the plane perpendicular to its unique axis. The Curie temperatures are 348° and 363°K and the room‐temperature moments are 115 and 40 G, respectively. Both materials contain ferric ions in a slightly distorted octahedral environment. Both are green with a series of absorption bands in the visible, a fundamental absorption edge in the violet (FeBO3) or ultraviolet (FeF3), and a large Faraday rotation per unit absorption at room temperature, as high as 14°/dB at 5250 A for FeBO3 and 16°/dB at 4050 A for FeF3. Recent measurements of the magnetic, optical, magneto‐optical, and microwave resonance properties of these materials are discussed. Potential applications of room temperature transparent ferromagnets include microwave magneto‐optical modulation of visible lasers with very low modulation power per unit bandwidth, optical deflection and isolation, magneto‐optic displays, and holograms. Each of these applications is discussed along with the limitations imposed by the optical absorption and birefringence of the available materials. Birefringence interferes with the Faraday effect in most noncubic crystals. Methods for minimizing this interference are described. Finally, requirements for useful transparent ferromagnets are defined and guidelines for finding new materials are suggested.
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TL;DR: The observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8% is reported, indicating the existence of ferromagnetic long-range ordering.
Abstract: Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images reveal a magnetic domain structure in the films, indicating the existence of ferromagnetic long-range ordering. The materials remain ferromagnetic above room temperature with a magnetic moment of 0.32 Bohr magnetons per cobalt atom. The film is conductive and exhibits a positive magnetoresistance of 60% at 2 kelvin.
2,302 citations
TL;DR: A new magnetic material with appreciable optical transmission in the visible region at room temperature has been isolated as a gamma-Fe(2)O(3)/polymer nanocomposite.
Abstract: A new magnetic material with appreciable optical transmission in the visible region at room temperature has been isolated as a gamma-Fe(2)O(3)/polymer nanocomposite. The synthesis is carried out in an ion-exchange resin at 60 degrees C. Magnetization and susceptibility data demonstrate loading-dependent saturation moments as high as 46 electromagnetic units per gram and superparamagnetism for lower loadings where particle sizes are less than 100 angstroms. Optical absorption studies show that the small-particle form of gamma-Fe(2)O(3) is considerably more transparent to visible light than the single-crystal form. The difference in absorption ranges from nearly an order of magnitude in the "red" spectral region to a factor of 3 at 5400 angstroms. The magnetization of the nanocomposite is greater by more than an order of magnitude than those of the strongest room-temperature transparent magnets, FeBO(3) and FeF(3).
805 citations
TL;DR: In this paper, a review of the progress achieved in the understanding of the origin of the large bismuth induced magnetooptic effects in iron garnets is made, and optical efficiencies are determined by the ratio of Faraday rotation (θ) to optical absorption (α).
Abstract: Using the results of the phenomenological and microscopic description of magnetooptically active transitions presented in the beginning of the article, a review is made of the progress achieved in the understanding of the origin of the large bismuth induced magnetooptic effects in iron garnets. For applications involving the Faraday configuration, optical efficiencies are determined by the ratio of Faraday rotation (θ) to optical absorption (α). The dependence of θ/α on such variables as bismuth concentration, 4\piM_{s} and impurity ions is discussed with its spectral behavior. Finally, the behavior of bismuth substituted iron garnets in devices previously devised using unsubstituted iron garnets is discussed, in conjunction with devices which have only become feasible as a consequence of improvements in the optical properties of such iron garnets.
190 citations
TL;DR: A method based on the interference of synchrotron X-ray radiation is now shown to enable the determination of the sign of the Dzyaloshinskii-Moriya interaction in the prototypical weak ferromagnet iron borate as mentioned in this paper.
Abstract: Oxygen-mediated superexchange (or Dzyaloshinskii–Moriya) interactions result in weak ferromagnetism in oxides. A method based on the interference of synchrotron X-ray radiation is now shown to enable the determination of the sign of the Dzyaloshinskii–Moriya interaction in the prototypical weak ferromagnet iron borate.
136 citations
TL;DR: In this paper, photo-reversible enhancement of magnetization was demonstrated with metal polycyanides, which are classified as molecule-based magnets, based on the photo-induced electron transfer between diamagnetic (or paramagnetic) states and their valence isomers exhibiting ferrimagnetism.
Abstract: This article deals with novel opto-magnetic and magneto-optical phenomena These phenomena are demonstrated with metal polycyanides, which are classified as molecule-based magnets Cobalt hexacyanoferrate and copper octacyanomolybdate solids exhibit a photo-reversible enhancement of magnetization These photo-magnetic phenomena are based on the photo-induced electron transfer between diamagnetic (or paramagnetic) state and their valence isomers exhibiting ferrimagnetism (or ferromagnetism) By a combination of photo-magnetism and mixed ferro-ferrimagnetism, a novel photo-induced magnetic pole inversion is demonstrated with an iron–manganese hexyacyanochromate Each of these photo-magnetic phenomenon is the first known example in the whole field of magnetically ordered materials Furthermore, Faraday spectra of molecule-based magnets were observed for the first time with electrochemically synthesized vanadium hexacyanochromate films This Faraday effect originates from the intervalence charge-transfer band between vanadium and chromium ions in the visible region
130 citations
References
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TL;DR: The spin reorientation process has been established to occur over a finite temperature range as a fourth-order anisotropy, generally small, comes to dominate the orientational behavior as discussed by the authors.
Abstract: The rare‐earth orthoferrites are a family of canted antiferromagnets which show an unusual variety of magnetic properties. This article begins with a brief review of the ``allowed'' spin configurations compatible with the crystallographic symmetry of the orthoferrite structure and a summary of the experimentally observed spin configurations, spin reorientation temperatures, compensation temperatures, etc. We then review recent research on these materials, grouping most of the recent work into four major categories; studies of the spin reorientation transition, studies of the rare‐earth spin ordering, spectroscopic studies directed at determining magnetic interaction parameters, and studies of magnetic domains and domain walls. The spin reorientation process has been established to occur over a finite temperature range as a fourth‐order anisotropy, generally small, comes to dominate the orientational behavior in the temperature region where the usually domainant second‐order anisotropy passes through zero and changes sign. The spin reorientation has been monitored in a number of RE orthoferrites by several techniques; magnetic torque, microwave absorption, neutron diffraction, and optical spectroscopy. A few of the rare‐earth orthoferrites show RE‐RE interaction strong enough to cause an ordering of the rare‐earth ions at temperatures on the order of 2°–6°K; this ordering process has been documented by all the above techniques plus Mossbauer‐effect and magnetic‐susceptibility measurements. Spectroscopic measurements, showing the increase in RE ground‐state exchange splittings for the configurations stable at the lower temperatures, give a qualitative understanding of the mechanisms causing the spin reorientation and spin ordering processes, and promise detailed quantiative understanding of the unique magnetic behaviors seen in the orthoferrites. The low moment and high anisotropy of the orthoferrites make possible the fabrication of thin plates magnetized normal to the plate. Such plates are semitransparent, and the Faraday rotation through them can be used to study domain structures or can be used as a readout mechanism for memory and logic devices utilizing single small stable domains as the active element. Recent studies of such domains and of domain wall energy and mobility in the orthoferrites are accordingly reviewed. Finally, several investigations are summarized which utilize the orthoferrites as a vehicle for examining general properties of magnetic systems, such as critical‐point phenomena.
684 citations
TL;DR: In this paper, the authors discuss the properties of orthoferrites that make them suitable for magnetic device applications and consider magnetostatic problems relevant to domain structures found to be useful.
Abstract: It has been shown that isolated magnetic domains in thin platelets (≍2 mils thick) of orthoferrites can be manipulated to perform memory, logic, and transmission functions. The purpose of this paper is to discuss the properties of orthoferrites that make them suitable for magnetic device applications and consider magnetostatic problems relevant to domain structures found to be useful. Included is a brief indication of how memory, logic, and transmission can be accomplished; however, the details will be reserved for a later paper. The stability conditions of a cylindrical domain are discussed in detail and data is reported to support the conclusions. Of particular interest are the sizes of cylindrical domains available in the various orthoferrites. Such data has been taken on five of the fourteen possible orthoferrites and it is found that the thulium orthoferrite, TmFeO 3 , gives the smallest stable domain diameter (2.3 mils) and LuFeO 3 the largest. The stability results lead to a direct method for obtaining σ W , the domain wall energy density. For TmFeO 3 , as an example, σ W = 2.8 ergs/cm2. It is concluded that the orthoferrites are well suited indeed for device applications. Experimentally, 3 mil diameter domains have been manipulated and there is every reason to believe that operation of sub-mil domains will soon be realized.
275 citations
TL;DR: In this paper, a matrix equation is developed which relates the amplitude and relative phase of the electric vectors between any two points along the propagation direction, and it is shown that the presence of birefringence can drastically affect the behavior of wave propagation and that it is considerably different from pure Faraday rotation.
Abstract: Electromagnetic wave propagation through materials that possess both Faraday rotation and birefringence is analyzed A matrix equation is developed which relates the amplitude and relative phase of the electric vectors between any two points along the propagation direction It is shown that the presence of birefringence can drastically affect the behavior of wave propagation and that it is considerably different from pure Faraday rotation Methods of measuring the material parameters are also described Criteria for viewing domains in this type of material are established It is shown that the thickness of the sample plays a great role in determining the contrast between domains and at some thicknesses no contrast at all can be obtained It is also shown that the method using elliptical analyzers gives greater contrast over the plane analyzers Photographs of domain patterns in a wedge of ytterbium orthoferrite are presented and they verify the calculated results
223 citations
160 citations
TL;DR: In this article, an experimental study of natural and synthetic single crystals of hematite containing small quantities of impurities was made to establish what effect impurities had on a variety of magnetic properties.
Abstract: An experimental study of natural and synthetic single crystals of hematite containing small quantities of impurities was made to establish what effect impurities had on a variety of magnetic properties. In both types of crystals the average values for the weak magnetic moment were comparable regardless of the impurity. A triaxial anisotropy was observed in the basal plane of many natural crystals and for the samples with the largest anisotropy the major impurity was found to be Sn; this was also the only impurity which induced a triaxial anisotropy in the synthetic crystals. The coercive force was also much larger in the natural and synthetic crystals containing Sn. The transition temperature was found to be progressively lowered by increasing the amounts of certain impurities but the values for this temperature in synthetic and natural crystals containing the same impurities were often different. For the synthetic crystals, small additions of Sn depressed the transition temperature to a greater ...
113 citations