摘要:

The properties of cylindrical domains in wafers of bulk single crystals of various magnetic oxides have been extensively studied and described in recent months. Mobile cylindrical domains have been produced in single‐crystal thin films of gallium‐substituted yttrium iron garnet. The deposits are formed by chemical vapor deposition onto nonmagnetic garnet substrates greater than 1 cm2in area. A model of magnetic anisotropy in epitaxial films is proposed and shown to be in good agreement with experimental domain observations. In a typical sample, a domain diameter of 8 &mgr; is observed in a 6‐&mgr;‐thick film at a bias field of 25 Oe. From the domain translational velocity of 5600 cm/sec, a cylindrical domain mobility of 1500 cm/sec Oe has been calculated. A fractional change in cylindrical domain diameter of −0.07%/°K has been measured at 300°K. Annealing at 1570°K for several hours did not alter the Ne´el temperature or the optical transmission spectrum.

ISSN:0021-8979    

DOI:10.1063/1.1660200

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Cylindrical magnetic domains in thin platelets of anisotropic single‐crystal materials have been detected using the Hall effect in silicon, the pseudo‐Hall effect in Permalloy, flux change, and Faraday rotation. The silicon detector, active area ≈400 &mgr;2, active thickness ≈1 &mgr;, input and output resistance ≈1.5 k&OHgr;, and 8‐mA rated current, delivered 0.5‐mV signals from orthoferrite domains. For 20‐mA input current the Permalloy detector, input and output resistance ≈15 &OHgr;, diameter ≈50 &mgr;, and thickness ≈0.03 &mgr;, yielded 0.9‐mV signals from 60‐&mgr;‐diam domains in Sm0.55Tb0.45FeO3orthoferrite. Domains in Y2.25Tb0.75Ga0.9Fe4.1O12, diameter ≈7 &mgr;, were read with a Permalloy detector approximately 7 &mgr; in diameter. The output was 0.2 mV at 2‐mA input current. An output of 1 mV &mgr;sec was obtained by detecting the flux change on collapse of a TmFeO3domain previously expanded 40 times in surface area. A Faraday‐rotation detection system consisting of a 5‐&mgr;W He&sngbnd;Ne laser, sheet polarizers, and an avalanche photodiode has operated at 106bits/sec with a 20‐dB signal‐to‐noise ratio. Among these detection methods, the Permalloy device appears most promising at this time. It offers the simultaneous advantages of relatively simple fabrication, small active area, small initial cost, and low power consumption. Additional experimental results relating to these detection methods are presented. Their relative merits and limitations are discussed and compared to those of the magnetoresistor and the magnetodiode. The problems associated with the detection of small domains at high speed are also considered.

ISSN:0021-8979    

DOI:10.1063/1.1660201

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Detailed inelastic neutron scattering measurements have yielded the behavior of the scattering functionS(q, &ohgr;) for both the transverse and the longitudinal fluctuations throughout the critical region of the uniaxial antiferromagnet MnF2. The results are discussed in the light of the theory of dynamic scaling. The results belowTNare discussed with reference to quasihydrodynamic theories of the spin fluctuations in the ordered state.

ISSN:0021-8979    

DOI:10.1063/1.1660202

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

We have carried out a detailed investigation of the linear chain antiferromagnet, (CD3)4N MnCl3using elastic and inelastic neutron scattering techniques. The MnCl3chains in this compound are found to exhibit purely one‐dimensional paramagnetic behavior down to at least 1.1°K, with no evidence for the onset of three‐dimensional order. The interactions between Mn2+ions along the chain are such that a molecular field theory would predict an ordering at 76°K. The quasielastic measurements, which yield∫d&ohgr;S(Q,&ohgr;)=1/N⟨S(−Q,0)S(Q,0)⟩showplanesof scattering intensity perpendicular to the chain axis. From the thermal evolution of the planar scattering, the temperature dependence of the correlation length has been obtained and is compared with the theory for the classical Heisenberg linear chain antiferromagnet with which it shows very good agreement. The inelastic measurements show that at 4.4°K forqand &ohgr;≠0,S(q, &ohgr;) may be described by long‐lived spin waves which accurately follow the dispersion relation ℏ&ohgr;=6.1 sinqzc/2 (meV) over the entire one‐dimensional Brillouin zone. As the temperature is increased these ``spin waves'' weaken in intensity and broaden asymmetrically, with the scattering increasing on the low‐energy side.

ISSN:0021-8979    

DOI:10.1063/1.1660203

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Propagation circuits for circular magnetic domains using only a single electric current conductor are described. A circuit which in addition uses Permalloy dots for domain stability and for determining the direction of propagation has been operated at 475 kHz with a 100‐mA amplitude current.

ISSN:0021-8979    

DOI:10.1063/1.1660204

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

This paper describes a simple Permalloy magnetoresistive readout transducer for detecting magnetic bubble domains. The advantages over inductive detection are a large increase in signal and an independence of bubble velocity. The advantages over Hall effect detection are simpler fabrication and higher efficiency. The detector is a strip of thin Permalloy film with two contacts, both of which can be deposited onto the same overlay used for bubble propagation. As an example, a 250 Å×38 &mgr;× 138‐&mgr; device (52 &OHgr;) was used with a measuring current of 7 mA to give a 2.3‐mV signal when detecting 138‐&mgr; diameter bubbles in TmFeO3. The response was constant up to the maximum data rate allowed by the bubble domain, in this case, 106bits/sec in DyFeO3. The detector itself can switch in less than 10−8sec. It can be used when conducting strip lines are used for bubble propagation, and also when a rotating field and Permalloy overlay are used. Optimum device placement and shape, as well as ultimate limitations, are discussed in terms of the stray field contours of the bubbles.

ISSN:0021-8979    

DOI:10.1063/1.1660205

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A new type of domain structure, a hollow bubble or ring domain, has been studied. Calculations with zero Bloch‐wall pinning force show that these ring domains can exist in platelets of uniaxial materials within a narrow region of the magnetic field normal to the platelet. Within this region the dimensions of the ring change enormously; they can be changed by a factor 2 by a field variation, which is about 100 times less than the variation needed to change the bubble radius by the same amount. We observed that the presence of a pinning force strongly influences the field region for stable ring domains and their behavior under a varying magnetic field. For a high‐coercivity sample an experiment is reported, in which each cycleH1‐H2‐H1of a varying magnetic field normal to the platelet diminishes the size of a ring. This experiment is in some sense the microscopic analogy to the ``bascule'' and ``reptation'' described by L. Ne´el.

ISSN:0021-8979    

DOI:10.1063/1.1660206

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A simple method is described for measuring wall mobility in materials which support cylindrical domains. The mobility is determined from the initial velocity with which a domain wall responds to a field step. A sample, which is demagnetized into the stripe domain state, is subjected repetitively to a fast rise‐time pulsed field. The displacement of the stripe domain walls is observed optically as the domains adjust to the new equilibrium configuration. In the particular case of viscous damping and negligible wall mass, for a field stepH0which results in an equilibrium displacementx0, the instantaneous displacement isx=x0[1‐exp(‐&ohgr;ct)], where &ohgr;cis the ratio of the restoring force constant to the damping constant. The mobility &mgr;=x0&ohgr;c/H0. The time‐dependent displacement can be displayed graphically in a few minutes by a sampling technique. Measurements on TmFeO3yield results in good agreement with previous data. The mobility for DyFeO3is found to be 330 cm (sec Oe)−1.

ISSN:0021-8979    

DOI:10.1063/1.1660207

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An instrumental technique has been devised for mapping crystalline imperfections which prevent the reliable operation of bubble‐domain devices. A special polarizing microscope permits the crystal to be automatically scanned through the field of view in a raster‐like manner. Photoelectrically detected distortions induced in a test domain by imperfections are plotted on anx‐youtput of the scan. This sensitive method easily locates imperfections found with difficulty by other methods and has been used to locate crystals which have later been used successfully in devices.

ISSN:0021-8979    

DOI:10.1063/1.1660208

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The wall‐motion fieldHcin an as‐polished orthoferrite platelet is generally too large (Hc>0.5 Oe) for use in domain propagation devices without further treatment. Very low values ofHcdown to less than 0.02 Oe have previously been reported by Heinlein and Pierce1using a 1500°C anneal in a highly purified atmosphere. We find that a simple anneal at 1200°C for one hour in ambient atmosphere produces samples havingHcof 0.25–0.50 Oe, but this is sufficiently low to demonstrate device operation. The annealing treatment was successful with samples mechanically polished by various methods including samples which were also etched in 250°C phosphoric acid. Temperatures lower than 1200°C do not lowerHcsufficiently, and somewhat higher annealing temperatures lead to no further improvement. Annealing times longer than an hour do not lead to improvement inHcand may cause surface damage. This simple technique has proven useful in obtaining samples for initial studies on domain propagation and device design.

ISSN:0021-8979    

DOI:10.1063/1.1660210

出版商:AIP    

年代:1971

数据来源: AIP