Uncompensated Metal Research Articles

3D Printed, Self-Temperature Compensated Microwave Cavity Notch Filters

Utilizing 3D printing to create custom microwave filters has promising aspects such as light weight and low cost, most importantly including the fact that complicated structures can be printed quickly and inexpensively. Some SLA resins have very high Coefficient of Thermal Expansion (CTE) compared to metal, so SLA 3D printed microwave filters can have frequency responses that are strongly dependent on temperature—a serious problem for narrow band filters. The presented technique overcomes this limitation, and in fact yields an SLA 3D printed filter with better temperature stability than an uncompensated metal 3D printed or a conventionally machined metal filter. Two 3D printed, temperature compensated microwave cavity notch filters have been fabricated using stereolithography (SLA) resins. Both use two different values of CTE for compensation. The 3D printed plastic parts are electroplated with copper. One filter consists of a resonant cavity with the TE011 mode coupled to a TE10 waveguide. The other is a TE101 resonant cavity coupled to TE10 waveguide. As temperature increases, the side walls of the cavities grow, lowering the resonant frequency. At the same time, for the TE011 cavity, an end-wall tuning plunger made of stereolithography resin with a higher CTE than the cavity walls expands at a faster rate. The end wall expansion increases the resonant frequency. In the case of the TE101 cavity, a metallic plunger expands much more slowly than the cavity and effectively withdraws as temperature increases, which increases the resonant frequency.

Charge Density Wave Transition in EuAl4

Charge Density Wave Transition in EuAl₄

Anomalous Electronic Behaviors in Ferromagnetic Kondo Lattice SmFe4P12

The electronic properties in SmFe 4 P 12 have been investigated by means of the de Haas–van Alphen effect, transverse magnetoresistance, Hall effect, and band structure calculation. We have found a markedly large anisotropy in the cyclotron effective mass of the 47th band Fermi surface despite its nearly spherical shape. Moreover, this mass enhancement in SmFe 4 P 12 is robust against magnetic field. The transverse magnetoresistance increases nearly quadratically with magnetic field for all field directions; this is unexpected for an ordinary uncompensated metal. The Hall coefficient is found to be 4-fold enhanced at low temperature compared with that at room temperature. These anomalies in transport properties are ascribed to the stronger enhancement of the cyclotron effective mass of the 48th band Fermi surface.

Electronic Band Structure and Fermi Surface of Heavy-Fermion Neptunium Superconductor NpPd5Al2

Electronic band structure calculations were carried out for a new neptunium superconductor NpPd 5 Al 2 using a relativistic linear-augmented plane wave method within a local density approximation. The Fermi energy in the band structure is found to be located just on the 5 f -bands of the j =5/2 state with the extremely narrow band width and therefore the theoretical electronic specific heat coefficient γ b is extremely large, being γ b = 74.0 mJ/(K 2 ·mol), which is compared to γ= 390 mJ/(K 2 ·mol) estimated experimentally. NpPd 5 Al 2 is an uncompensated metal. The main electron Fermi surface corresponds to a doughnut-like flat Fermi surface centered at the Γ point which is connected with cylindrical Fermi surfaces elongated along the X–W–P line.

High field magnetoresistance in heavy fermion superconductor PrOs 4Sb 12

We have measured the magnetoresistance (MR) in Pr-based heavy fermion superconductor PrOs 4Sb 12. We have found distinct anomalies in MR indicating the existence of field induced ordered phase above ∼4.5 T . The field dependences of transverse MR tend to saturate, indicating PrOs 4Sb 12 to be an uncompensated metal with no open orbit in the Fermi surface.

Magnetoresistance of quasi-two-dimensional purple bronzesAMo6O17(A=Na,K, and Tl)

Magnetoresistances (MR's) of quasi-two-dimensional purple bronzes $A{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ $(A=\mathrm{K},$ Tl, Na) are comparatively studied at 2 K for magnetic fields of $H\ensuremath{\parallel}c$ and $H\ensuremath{\perp}c,$ respectively, where c is the direction normal to the two-dimensional plane of the sample. Unusually huge positive MR's for $H\ensuremath{\parallel}c$ are analyzed quantitatively by a two-band carriers galvanomagnetic effect on the ungapped residual Fermi surfaces, in which the concentration of the carriers is modified by an applied magnetic field. The modified two-band model can explain the MR's well, and the resulting parameters suggest that the purple bronzes belong to an uncompensated metal.

De Haas–van Alphen Effect in Quasi-Two-Dimensional Material La2RhIn8

We have grown a single crystal of La 2 RhIn 8 with the tetragonal structure and have measured the de Haas–van Alphen (dHvA) effect and magnetoresistance in the 4 He temperature region up to 9 T. The two dHvA frequencies α=6220 T and β=400 T were observed for the field along the [001] direction. The corresponding cross-sectional areas of the Fermi surfaces of α and β are about 33 and 2% of the Brillouin zone base area, respectively. The cyclotron mass m c * for the α is about 0.7 m 0 , where m 0 is the free electron mass. The angular dependence of the dHvA frequencies suggests that the frequency α originates from a large cylindrical Fermi surface elongated the c -axis, and the frequency β corresponds to a small pocket. The result of the magnetoresistance suggests that La 2 RhIn 8 is an uncompensated metal.

Electronic structure and Fermi surfaces of La 3Pd 20Ge 6

The dHvA effects measured in Ce 3Pd 20Ge 6 and La 3Pd 20Ge 6 show the similar angular dependence, indicating that the 4f electrons in Ce 3Pd 20Ge 6 are localised. However, larger dHvA frequencies have not been observed even in an uncompensated metal La 3Pd 20Ge 6. To clarify the Fermi surface property, an FLAPW band structure calculation has been performed for La 3Pd 20Ge 6.

Magnetoresistance and de Haas-van Alphen Effect in CeRu2Si2and LaRu2Si2

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in CeRu 2 Si 2 and LaRu 2 Si 2 . From the results of magnetoresistance, CeRu 2 Si 2 is concluded to be a compensated metal, possibly possessing an open orbit along the c -axis of the tetragonal structure. On the other hand, LaRu 2 Si 2 is an uncompensated metal, showing the saturated magnetoresistance. These results imply that the 4 f electrons in CeRu 2 Si 2 are itinerant. In the dHvA experiments of LaRu 2 Si 2 , we have found a large ellipsoidal Fermi surface which occupies roughly half of the Brillouin zone in volume. On the other hand, CeRu 2 Si 2 possesses multiply connected Fermi surfaces in part, although main Fermi surfaces are not observed yet.

High Field Magnetoresistance and de Haas-van Alphen Effect in LaSn3

We have measured the magnetoresistance and the de Haas-van Alphen (dHvA) effect in LaSn 3 . From the results of magnetoresistance, this substance has been confirmed to be an uncompensated metal with open orbits. About fifteen dHvA branches have been observed, which are well explained by the results of the recent band calculation done by Hasegawa and Yamagami.

High Field Magnetoresistance and de Haas-van Alphen Effect in CeSn3

The magnetoresistance and the de Haas-van Alphen (dHvA) effect in CeSn 3 have been measured in the field up to 150 kOe and at temperature down to 0.45 K. The magnetoresistance does not show a tendency to saturate in all field directions. This result claims that CeSn 3 is a compensated metal with an equal carrier concentration of electrons and holes, and electron and hole Fermi surfaces possess no open orbits. In contrast to an uncompensated metal LaSn 3 , the 4 f electrons in CeSn 3 become itinerant electrons. This is consistent with the dHvA data which are almost explained by the modified Fermi surface model based on the result of band calculation where the 4 f electrons are treated the same as the usual s , p , d conduction electrons.

Fermi surface in CeSn 3

We have measured the magnetoresistance and the de Haas-van Alphen (dHvA) effect in CeSn 3. The magnetoresistance increases in all field directions. This result claims that CeSn 3 is a compensated metal. Compared to an uncompensated metal LaSn 3, the 4f electrons in CeSn 3 become itinerant electrons. This is consistent with the dHvA data which are almost explained by the modified Fermi surface model based on the result of band calculation where the 4f electrons are treated the same as the usual s, p, d conduction electrons.

Transverse Magnetoresistance and Shubnikov-de Haas Effect in Intermetallic Compounds InBi and In2Bi

The transverse magnetoresistance of intermetallic compounds InBi and In 2 Bi have been studied at 4.2 K in magnetic fields up to 100 kOe. Shubnikov-de Haas oscillations of InBi were observed for the fields over 60 kOe. The results indicate that InBi is a compensated metal with all closed orbits. These are compared with a Fermi surface model proposed already by Schirber et al . In 2 Bi is an uncompensated metal with an open orbit along the direction. The present results are compared with the nearly free electron model which contains a multiply connected Fermi surface.

Magnetoresistance of UIr3 and UGe3 to 220 kG

Topological properties of the Fermi surfaces of UIr3 and UGe3 were investigated. UIr3 is an uncompensated metal with open orbits along 〈110〉. This is in agreement with a proposed model of Arko and Koelling, based on augmented-plane-wave (APW) calculations. UGe3 is a compensated metal, which showed nearly quadratic magnetoresistance behavior for all field directions studied. The results are compared with the APW model of Arko and Koelling, which contains a multiply connected sheet of Fermi surface. The model, or slight variations thereof, is consistent with the available data.

Transverse Magnetoresistance in hcp Cobalt

Measurements of transverse magnetoresistance in hep cobalt single crystals have been made at a temperature of 4.2 K in applied magnetic field up to 53 kOe. The transverse magnetoresistance ratio at high field is represented as a function of the magnetic induction B by Δ R / R = a + b B n . The value of exponent n is smaller than 1 for general field direction. A maximum value of n with valcano-like structure is observed around [11\bar20] and [10\bar10] field direction for J //[10\bar10] and J //[11\bar20], respectively. Also, maximums of n are observed in [10\bar10] and [11\bar20] field direction for J //[0001] and a minimum in [0001] field direction for J //[10\bar10] and J //[11\bar20], respectively. From these results, hep cobalt is an uncompensated metal. The maximum and minimum are interpreted as produced by the topological properties of the Fermi surface.

The resistance and magnetoresistance of lithium tetra-ammine

Resistance and magnetoresistance measurements are presented for specimens of Li(NH3)4 with mole ratios of 4:1, NH3:Li. Measurements were made using a probeless, mutual inductance technique from 1.5 to 4.2 K and from 10 to 100 K. The low-temperature resistivity has a largely quadratic temperature dependence, ρ=ρ(0)+BT2. The coefficient B has only a small temperature variation from 1.5 to 25 K and is independent of the residual resistivity. Near 69 K there is a local minimum in the electrical resistivity. Thermal hysteresis is observed in this region as well. We suggest that these features are characteristic of the compound Li (NH3)4 and may be due to a magnetic transition near 70 K. The magnetoresistivity was determined from 0 to 100 kG at both 1.66 and 4.2 K. It is large, with a marked decrease in field dependence above 50 kG. Our results indicate that lithium tetra-ammine is probably an uncompensated metal with a high proportion of open-orbit carriers.

Electrical transport properties and preparation of the metal-ammonia compound lithium tetraammine

On specimens of the compound lithium tetraammine, Li(NH 3) 4, the resistance from 10 to 100°K and the magnetoresistance at 4.2 and 1.66 K have been measured. Measurements were made using a probeless, mutual inductance technique. Specimen preparation and aspects of the measurement technique used in preparing well mixed, homogeneous specimens are described. The resistivity shows several anomalies in the solid phase, one of which has also been observed in thermal measurements and is associated with a transition from an fcc to an hcp structure. The second, near 69 K, has not been observed in thermal measurements. It is suggested that this anomaly is characteristic of the compound Li(NH 3) 4 and may be a Martensitic or magnetic transition. The magnetoresistance is large with a marked decrease in slope above 50 kG. These results are compared with standard galvanomagnetic theory for compensated and uncompensated metals. In conjunction with arguments based on a free electron construction of the Fermi surface, it is concluded that lithium tetraammine is probably an uncompensated metal with a high proportion of carriers in open orbits.

De Haas-van Alphen Effect in Iridium

Measurements of the de Haas-van Alphen (dHvA) extremal areas have been performed in three main symmetry planes of an Ir single crystal using magnetic fields up to 120 kG. A newly designed modulation-technique magnetometer was used in modulation and sample-rotation experiments; some measurements used the torque technique. Large torque or magnetization oscillations were observed from all four closed sheets of the Fermi surface predicted by the band-structure calculations of Andersen and Mackintosh. The measured cross-sectional areas of two hole sheets centered at $X$ in the Brillouin zone and called $X3$ and $X4$ were found to be, respectively, 30% smaller and 6% larger than the calculated ones. The observed areas of two electron sheets centered at $\ensuremath{\Gamma}$ were larger than the calculated ones by not more than 0.5%. The results agree with magnetoresistance data, confirming that Ir is an uncompensated metal and that its Fermi surface does not support open orbits. A few effective-mass values were determined from torque and modulation measurements of the temperature dependence of the amplitude of dHvA oscillations in magnetic fields up to 21 kG. A simulataneous determination of effective masses associated with two dHvA frequencies beating with each other was obtained. A spin-splitting zero was observed in the $\ensuremath{\Gamma}6$ sheet in the (111) plane. The Dingle temperature was determined from the magnetic field dependence of the amplitude of torque oscillations. A generalized formula describing the magnetoresistance of an uncompensated metal was used to calibrate a copper-wire magnetoresistor for magnetic field measurements.

Onset of linear field dependence of the transverse magnetoresistance in a polycrystalline metal

The linear field dependence of the transverse magnetoresistance of a polycrystalline uncompensated metal with an open Fermi surface is said to arise from a contrast between extended and truly open orbits. We show that in the intermediate-field regime this is incorrect for Cu at least, where the linear dependence is initiated by the transition to the high-field condition of electrons in closed orbits.

Induced galvanomagnetic effects in copper

The galvanomagnetic properties of copper were studied by observing the torque induced in single-crystal copper by a slowly rotating magnetic field at 1.4 °K. The induced torque varied linearly with the speed of magnet rotation and quadratically with magnetic field. There was large induced torque in high-purity samples from the open orbits in both one-dimensional and two-dimensional regions. In a sample with low ωcτ, there was also a background torque. The induced torque is described by Falicov's solution of the boundary value problem for a sample sphere with a resistivity tensor. The open-orbit torque in an uncompensated metal such as copper is approximately proportional to the transverse resistivity component ρ11. The anisotropy of the open-orbit torques for the (100) and (110) planes of copper is in agreement with that calculated for the magnetoresistance from the Fermi surface of copper. There is anisotropy in the background torque with minima in the region of symmetry directions and for a rotation in a (100) plane.