High ... Q magnetostatic surface wave planar yttrium iron garnet resonator

Exp.erim.entaI results on the magnetostatic surface wave resonance characteristics of planar yttnu~ Iron garnet resona.tors are given. Single-mode resonance with wide tunability range and hIgh Q have been achIeved. Q as high as 3500 and insertion loss as low as 13 dB with offresonance rejection as high as 15 dB have been achieved at 6 GHz. A microwave oscillator built with the resonators and a laboratory-made hybrid amplifier provided oscillations in the range 3-:-5.3 GHz with phase noise of - 105 dBc/Hz at 10 KHz offset/rom the carrier frequency

EPR and optical studies in pseudotetrahedral tetramethyl ammonium copper {II) bromide

EPR studies of single crystal copper tetramethyl ammonium bromide, T2CuBr4(T = (CH3~4N] in the temperature range 77-300 K indicate the largest covalency in this compound compared to similar halogenated pseudotetrahedral copper compounds. The angle cos _,r between the c axis and the ionic g 11 axis is 12' and 65' at 250 and 220 K, respectively. The change is continuous down to 200 K. The g shift between 300 and 200 K indicates an increase in the strength of the ligand field with lowering of temperature. The magnetic susceptibility ellipsoid and the g -tensor ellipsoid do not coincide in this material. Optical spectra in T2(Cu:Zn)Br4 have been assigned. The nonobservation of an EPR signal in T,(Cu:Zn)Br4 and Cs2CuBr4 indicates that ligand field properties in these pseudotetrahedral compounds are quite different from that of T2CuBr4

First Observation of Orthorhombic Jahn-Teller EPR Spectra in Cu(II) doped (NH4)2Cd2(SO4)3 (ACS) Single Crystals. Paper I

Since the first experimental confirmation of axial Jahn-Teller effect in Cu(II) doped ZnSiF6.6H2O in 1950, the Orthorhombic Jahn-Teller Effect (OJTE) in solids has not been clearly observed experimentally even though a lot of conjectures have been made. This is the first report of experimental observation of orthorhombic Jahn-Teller EPR spectra 2E Cu(II) ion in cadmium ammonium sulphate crystal providing the direct confirmation of the OJTE. The spectra correspond to all the three Jahn-Teller potential well minima being non-equivalent in energy. The detailed theoretical analysis (not reported here) of the spectra led to evaluation of many spectroscopic parameters and their temperature dependence, suggesting potential applications of such systems

Theoretical investigation of estimation of steady and pulsatile blood flow and blood vessel cross section by cw NMR excitationt

In this paper we show theoretically that when a magnetised blood bolus enters a cw NMR excitor coil of length Le at resonance and the signal from the T2-decaying, precessing transverse magnetisation of the flowing blood spins is subsequently detected by a detector coil of length L separated from the excitor coil by a distance !ll, then by recording cw NMR signals at three positions such as !ll = 0, 0.5 and 1.0 em one can eliminate the static tissue signal and measure non-invasively the steady component V0 as well as the total vessel cross section, {3 accurately. The time dependent part of the cw NMR signal which depends on Vpul,e(1), is also dependent on V0 non-linearly unless both Land Le are greater than 50 em and !ll is zero. Finally, methods of obtaining true Vpu,,e(l) from the cw NMR signal after applying proper correction due to the steady flow are discussed

Jahn-Teller impurity dependence of the transition· . I 1 tetnper~ture Tcu· criticai exponent and pseudo~JahtiTeller p~tenthd -well splitting in ZoTiF6 • 6H20

The 182.K (::.91.2 °C) trigohal-to-mouoclinic phase transition in ZnTiF6 • 6HP _ sin&Je CI1(Stal has been studied by EPR, for various concentrations of doped Jahn-Teller (JT) , .. - impar4ty Cu2+ ions and also for non-JT impurity NF+ ions. Tbe tr~nsition temperature Td which decreases with increase in impurity concentration, is more strongly affected by the JT impurity. The critical exponent {3 as well as the JT potential well splitting E0 have been determiqd from the temperature variation in EPR signal intensity in the immedi-ate neighbourhood ef Tc1 for the Cu2+ impurity. The critical exponent {3 and E0 are dependent strongly on the JTimpurity concentmtioP For two different concentrations of Cu2+ ions, i.e. : 0.043 wt% and 0.98 wt%, the values of p ,,;e().5 ± 0.05 and 0.12 ± 0.03, respectively, while the values of E0.are 140 ± 15 cm-J -and-97.:!; 1.1 cm-1, respectively. The valN.e of £ 0 for a deuteratcd crystal containing a low Cu2+ conccntrati~s 78 ± 10 cm-1• The dec.rease in E0 with incn:asing Cu2 t c.oncentration fur a hydrated crystal and also with deuteration (for n , low copper concentration) is in qualitative agreement with the corresponding gradual phase . transition observed in these material

SUPERCONDUCfiVE QUANTUM INTERFERENCE DEVICE FOR THE NON-DESTRUCTIVE EVALUATION OF METALS

High·Tc superconductor quantum interference devices (SQUIDs) for noise-free, accurate measurements of defects and flaws in metal shapes and forms by measuring changes in the secondary magnetic field intensity around any point which is excited by a primary excitation current or by measuring changes in the impedance of the exciting coils. These measured changes are corre-· lated to defects and flaws present in the metal

EPR studies of the effect of Zn2+ ion impurities in phase transition of CaCd(CH3C00) 4·6H20 crystals

The effect of Zn2+ ion impurities on the phase transition temperature of single crystals of calcium cadmium acetate hexahydrate (CCDAH) has been studied using the electron-paramagnetic-resonance technique. The lowering of the phase transition temperature as a function of increasing zn2+ impurity ion concentration in the crystals has been observed to be quite different from that found in our earlier studies of Cu2 + and Mn2 + ion doped crystals. Though the observed lowering of phase transition temperature with atomic fraction x of the Zn2+ impurity ion can be explained fairly well in terms of mean-field theory and a soft mode arising out of the harmonic vibration of the Ca-Cd(l-x)Znx-Ca chain along the c axis of the crystal, contrary to expectation, values of constants (such as the ratio of the square of the soft-mode frequency before transition, the mean-field constant, and the phase transition temperature, etc. of the pure crystal) are quite different from that obtained by fitting the phase transition temperatures in the Cu2+ ion only impurity doped crystals. The temperature variation of the spin-Hamiltonian parameters of the Cu2+ ion probe in the Zn2+ -doped crystal of CCDAH is somewhat different from that in the Cu2+ ion only doped crystal. Deviation from mean-field theory is then considered in the Zn2+ impurity driven modification of phase transition of the crystal and good agreement between the observed and computed values of phase transition temperature as a function of the Zn2+ atomic fraction has been obtained using the same values of the said constants as obtained for Cu2+ ion only impurity doped crystals

NMR/MRI Blood Flow Magnetization Equation in the Rotating Frame of Reference-Part I

This paper describes thoroughly the need and the method of deriving the first of its kind the NMR/MRI blood flow magnetization (y component) equation in the rotating frame when rf B1 field is applied along laboratory X direction. �� v ·� + � �t � 1 �B1�x� t� � v ·� + � �t + 1 T2 � + 1 �B1�x� t�T1 � v ·� + � �t + 1 T2 +�2B2 1�x� t�T1 �� My = Mo T1 where v ·� = vx � �x +vy � �y vx and vy are the components of blood flow velocity along the x and y directions of the rotating frame in an NMR experiment. The equation is expected to serve as the mother equation for accurate non invasive blood flow quantification through all NMR/MRI experiments. It is shown how Awojyogbe’s equation of blood flow magnetization can be obtained from above equation under assumption of constant B1 field and vy = 0. The method of deriving the equation can be applied to modify Bloch Torey Diffusion MRI equation to include relaxation times and flow and also to derive the NMR/MRI spin flow magnetization equation in the laboratory frame of reference. The derivation of the corresponding equation for magnetization of flowing blood spins in the laboratory frame of reference will be discussed in a separate paper