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In most superconductors electrons form Cooper pairs in a spin-singlet state mediated by either phonons or by long-range interactions such as spin fluctuations. The superconductor UTe$_2$ is a rare material wherein electrons are believed to form pairs in a unique spin-triplet state with potential topological properties. While spin-triplet pairing may be mediated by ferromagnetic or antiferromagnetic fluctuations, experimentally, the magnetic properties of UTe$_2$ are unclear. By way of muon spin rotation/relaxation ($\mu$SR) measurements on independently grown UTe$_2$ single crystals we demonstrate the existence of magnetic clusters that gradually freeze into a disordered spin frozen state at low temperatures. Our findings suggest that inhomogeneous freezing of magnetic clusters is linked to the ubiquitous residual linear term in the temperature dependence of the specific heat ($C$) and the low-temperature upturn in $C/T$ versus $T$. The omnipresent magnetic inhomogeneity has potential implications for experiments aimed at establishing the intrinsic low-temperature properties of UTe$_2$., Comment: 33 pages, 9 figures

The $d$-wave superconductor ${\mathrm{CeCoIn}}_{5}$ has been proposed as a strong candidate for supporting the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state near the low-temperature boundary of its upper critical field. Neutron diffraction, however, finds spin-density-wave (SDW) order in this part of the phase diagram for field in the $a\text{\ensuremath{-}}b$ plane, and evidence for the SDW disappears as the applied field is rotated toward the tetragonal $c$ axis. It is important to understand the interplay between the SDW and a possible FFLO state in ${\mathrm{CeCoIn}}_{5}$, as the mere existence of an SDW does not necessarily exclude an FFLO state. Here, based on a model constructed on the basis of available experiments, we show that an FFLO state competes with an SDW phase. The SDW state in ${\mathrm{CeCoIn}}_{5}$ is stabilized when the field is directed close to the $a\text{\ensuremath{-}}b$ plane. When the field is rotated toward the $c$ axis, the FFLO state emerges, and the SDW phase disappears. In the FFLO state, the nodal planes with extra quasiparticles (where the superconducting order parameter is zero) are perpendicular to the field, and in the SDW phase, the quasiparticle density of states is reduced. We test this model prediction by measuring heat transported by normal quasiparticles in the superconducting state. As a function of field, we observe a reduction of thermal conductivity for field close to the $a\text{\ensuremath{-}}b$ plane and an enhancement of thermal conductivity when field is close to the $c$ axis, consistent with theoretical expectations. Our modeling and experiments, therefore, indicate the existence of the FFLO state when field is parallel to the $c$ axis.

Kitaev magnets are materials with bond-dependent Ising interactions between localized spins on a honeycomb lattice. Such interactions could lead to a quantum spin-liquid (QSL) ground state at zero temperature. Recent theoretical studies suggest two potential signatures of a QSL at finite temperatures, namely, a scaling behavior of thermodynamic quantities in the presence of quenched disorder, and a two-step release of the magnetic entropy. Here, we present both signatures in ${\mathrm{Ag}}_{3}{\mathrm{LiIr}}_{2}{\mathrm{O}}_{6}$ which is synthesized from $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ by replacing the interlayer Li atoms with Ag atoms. In addition, the dc susceptibility data confirm the absence of a long-range order, and the ac susceptibility data rule out a spin-glass transition. These observations suggest a closer proximity to the QSL in ${\mathrm{Ag}}_{3}{\mathrm{LiIr}}_{2}{\mathrm{O}}_{6}$ compared to its parent compound $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ that orders at 15 K. We discuss an enhanced spin-orbit coupling due to a mixing between silver $d$ and oxygen $p$ orbitals as a potential underlying mechanism.

The thermal conductivity measurement in a rotating magnetic field is a powerful probe of the structure of the superconducting energy gap. We present high-precision measurements of the low-temperature thermal conductivity in the unconventional heavy-fermion superconductor CeCoIn_{5}, with the heat current J along the nodal [110] direction of its d_{x^{2}-y^{2}} order parameter and the magnetic field up to 7 T rotating in the ab plane. In contrast to the smooth oscillations found previously for J∥[100], we observe a sharp resonancelike peak in the thermal conductivity when the magnetic field is also in the [110] direction, parallel to the heat current. We explain this peak qualitatively via a model of the heat transport in a d-wave superconductor. In addition, we observe two smaller but also very sharp peaks in the thermal conductivity for the field directions at angles Θ≈±33° with respect to J. The origin of the observed resonances at Θ≈±33° at present defies theoretical explanation. The challenge of uncovering their source will dictate exploring theoretically more complex models, which might include, e.g., fine details of the Fermi surface, Andreev bound vortex core states, a secondary superconducting order parameter, and the existence of gaps in spin and charge excitations.

A substance with controllable properties is valuable in many industrial applications. Scientists show how one such material---CeCoIn${}_{5}$---exists with three different superconducting and magnetic states intertwined together.

International audience; The interplay of magnetic and charge fluctuations can lead to quantum phases with exceptional electronic properties. A case in point is magnetically-driven superconductivity1,2, where magnetic correlations fundamentally affect the underlying symmetry and generate new physical properties. The superconducting wavefunction in most known magnetic superconductors does not break translational symmetry. However, it has been predicted that modulated triplet p-wave superconductivity occurs in singlet d-wave superconductors with spin-density-wave (SDW) order3,4. Here we report evidence for the presence of a spatially inhomogeneous p-wave Cooper pair-density wave in CeCoIn5. We show that the SDW domains can be switched completely by a tiny change of the magnetic field direction, which is naturally explained by the presence of triplet superconductivity. Further, the Q-phase emerges in a common magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus represents an example where spatially modulated superconductivity is associated with SDW order.

We present specific heat and thermal conductivity of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical fieldH c2, measured with magnetic field in the plane of this quasi-2D compound and at temperatures down to 50 mK. The superconducting phase diagram and the first order nature of the superconducting phase transition at high fields close to a critical fieldH c2 indicate the importance of the Pauli limiting effect in CeCoIn5. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state, and interpret it as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. In addition, the thermal conductivity data as a function of field display a kink at a fieldH k below the superconducting critical field, which closely coincides with the low temperature anomaly in specific heat tentatively identified with the appearance of the FFLO superconducting state. The enhancement of thermal conductivity within the FFLO state calls for further theoretical investigations of the real space structure of the order parameter (and in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.

Low temperature specific heat and thermal conductivity measurements on the ambient pressure heavy fermion superconductors CeIrIn5 and CeCoIn5 reveal power law temperature dependences of these quantities below T(c). The low temperature specific heat in both CeIrIn5 and CeCoIn5 includes T2 terms, consistent with the presence of nodes in the superconducting energy gap. The thermal conductivity data present a T-linear term consistent with the universal limit (CeIrIn5), and a low temperature T3 variation in the clean limit (CeCoIn5), also in accord with prediction for an unconventional superconductor with lines of nodes.

The low temperature spin dynamics of the geometrically frustrated antiferromagnet Gd 3Ga 5O (12) (GGG) have been investigated using muon spin relaxation. No evidence for static order is seen down to a temperature of 25 mK or a few percent of the Curie-Weiss temperature. Instead there is a linear decrease in the Gd spin fluctuation rate below 1 K which extrapolates to a small but finite value of 2 GHz at zero temperature. In terms of the spin fluctuations the system appears essentially to remain dynamic at low temperatures (T>0.02 K) and magnetic fields up to 1.8 T.

The non-Fermi-liquid (NFL) behavior observed in the low temperature specific heat $C(T)$ and magnetic susceptibility $\ensuremath{\chi}(T)$ of many chemically substituted $f$-electron systems is analyzed within the context of a recently developed theory based on Griffiths' singularities. Measurements of $C(T)$ and $\ensuremath{\chi}(T)$ in the systems ${\mathrm{Th}}_{1\ensuremath{-}x}{\mathrm{U}}_{x}{\mathrm{Pd}}_{2}{\mathrm{Al}}_{3}$, ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{U}}_{x}{\mathrm{Pd}}_{3}$, and ${\mathrm{UCu}}_{5\ensuremath{-}\mathrm{x}}{\mathrm{M}}_{x}$ ( $M\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{Pd},\mathrm{Pt}$) are found to be consistent with $C(T)/T\ensuremath{\propto}\ensuremath{\chi}(T)\ensuremath{\propto}{T}^{\ensuremath{-}1+\ensuremath{\lambda}}$ predicted by this model with $\ensuremath{\lambda}l1$ in the NFL regime. These results suggest that the NFL properties observed in a wide variety of disordered $f$-electron systems can be described within the context of a common physical picture.

We report the discovery of a low-temperature anomaly in thermal conductivity of Bi{sub 2}Sr{sub 2}Ca(Cu{sub 1{minus}x}Ni{sub x}){sub 2}O{sub 8} high-temperature superconductor. This anomaly manifests itself as a sharp reduction of the thermal conductivity of the samples at a temperature T{sup {asterisk}}{sub c}{approx}200 mK. The temperature dependence of the thermal conductivity changes dramatically from T{sup {alpha}} with {alpha} between 1.6 and 1.75 above T{sup {asterisk}}{sub c} to T -linear behavior below it. Application of a small magnetic field suppresses the low-temperature anomaly. We propose that such behavior is consistent with a phase transition into a second bulk low-temperature superconducting state at T{sup {asterisk}}{sub c}. The presence of a second superconducting state would constitute direct evidence for unconventional superconductivity in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} . Within the suggested scenario, time-reversal symmetry is likely to be violated in the low-temperature phase. {copyright} {ital 1998} {ital The American Physical Society}

A zero-temperature magnetic-nonmagnetic phase boundary is accessed in CeR${\mathrm{h}}_{2}$S${\mathrm{i}}_{2}$ by application of pressure and in ${\mathrm{CeRh}}_{2\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{Si}}_{2}$ at ambient pressure for $x\ensuremath{\approx}1.0$. A comparison of specific heat and resistivity measurements in the two cases emphasizes the importance of disorder in producing non-Fermi-liquid-like behavior in these as well as in other Ce-based systems.

Magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2 from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10−7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to a Hall voltage independent of the spin-orbit coupling within the material--a geometrical Hall effect. We show that the highly-correlated metal UCu5 possesses an unusually large controllable geometrical Hall effect at T, article and supplemental information

We report resistivity measurements on the cubic heavy-fermion compound YbBiPt at ambient and hydrostatic pressures to [approx]6 kbar and in magnetic fields to 1 T. Resistivity anisotropy sets in below the phase-transition temperature [ital T][sub [ital c]]=0.4 K. We interpret a rise of resistivity below 0.4 K as due to partial gapping of the Fermi surface with the weak coupling energy gap of [Delta][sub 0]/[ital k][sub [ital B]][ital T][sub [ital c]]=1.65[plus minus]0.15. Effects of hydrostatic pressure and magnetic field on the phase transition and heat capacity data are consistent with a spin density wave formation in a very heavy electron band at [ital T]=0.4 K.

We have studied the magnetic order inside the superconducting phase of ${\mathrm{CeCoIn}}_{5}$ for fields along the $[1\text{ }0\text{ }0]$ crystallographic direction using neutron diffraction. We find a spin-density wave order with an incommensurate modulation $\mathbf{Q}=(q,q,1/2)$ and $q=0.45(1)$, which within our experimental uncertainty is indistinguishable from the spin-density wave found for fields applied along $[1\text{ }\ensuremath{-}1\text{ }0]$. The magnetic order is thus modulated along the lines of nodes of the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ superconducting order parameter, suggesting that it is driven by the electron nesting along the superconducting line nodes. We postulate that the onset of magnetic order leads to reconstruction of the superconducting gap function and a magnetically induced pair density wave.

We have performed low-temperature specific heat and thermal conductivity measurements of the Ni-based superconductor ${\mathrm{BaNi}}_{2}{\mathrm{As}}_{2}$ (${T}_{\mathrm{c}}=0.7\text{ }\text{ }\mathrm{K}$) in a magnetic field. In a zero field, thermal conductivity shows $T$-linear behavior in the normal state and exhibits a BCS-like exponential decrease below ${T}_{c}$. The field dependence of the residual thermal conductivity extrapolated to zero temperature is indicative of a fully gapped superconductor. This conclusion is supported by the analysis of the specific heat data, which are well fit by the BCS temperature dependence from ${T}_{c}$ down to the lowest temperature of 0.1 K.

We report Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a justaposed continuous films of permalloy and cobalt. Our studies demonstrate the capability of FMRFM to perform local spectroscopy of different ferromagnetic materials. Theoretical analysis of the uniform resonance mode near the edge of the film agrees quantitatively with experimental data. Our experiments demonstrate the micron scale lateral resolution in determining local magnetic properties in continuous ferromagnetic samples., Comment: 7 pages, 3 figures

We report nanoscale scanned probe ferromagnetic resonance force microscopy (FMRFM) imaging of individual ferromagnetic microstructures. This reveals the mechanism for high spatial resolution in FMRFM imaging: the strongly inhomogeneous local magnetic field of the cantilever mounted micromagnetic probe magnet used in FMRFM enables selective, local excitation of ferromagnetic resonance (FMR). This approach, demonstrated here in individual permalloy disks, is straightforwardly extended to excitation of localized FMR modes, and hence imaging in extended films.

We investigated the effect of Cd and Hg doping on the first order superconducting (SC) transition and the high field-low temperature SC state of CeCoIn$_5$ by measuring the specific heat of CeCo(In$_{\rm 1-x}$Cd$_{\rm x}$)$_5$ with x=0.0011, 0.0022 and 0.0033 and CeCo(In$_{\rm 1-x}$Hg$_{\rm x}$)$_5$ with x=0.00016, 0.00032, and 0.00048 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the cross-over temperature $T_{\rm 0}$, where the superconducting transition changes from second to first order, to $T$=0 K with x=0.0022 for $H\parallel$ [100], while it remains roughly constant up to x=0.0033 for $H\parallel$ [001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.00048, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the non-magnetic, possibly FFLO, origin of the high field - low temperature state in CeCoIn$_5$.

NaV2O4 crystals were grown under high pressure using a NaCl flux, and the crystals were characterized with x-ray diffraction, electrical resistivity, heat capacity, and magnetization. The structure of NaV2O4 consists of double chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic, with the resistivity perpendicular to the chains more than 20 times greater than that parallel to the chains. Magnetically, the intrachain interactions are ferromagnetic and the interchain interactions are antiferromagnetic; 3D antiferromagnetic order is established at 140 K. First-principles electronic structure calculations indicate that the chains are half-metallic. Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was found for half-metallic materials.

Measurements of specific heat and electrical resistivity in magnetic fields up to 9 T along [001] and temperatures down to 50 mK of Sn-substituted CeCoIn5 are reported. The maximal -ln(T) divergence of the specific heat at the upper critical field Hc2 down to the lowest temperature characteristic of non-Fermi-liquid systems at the quantum critical point (QCP), the universal scaling of the Sommerfeld coefficient, and agreement of the data with spin-fluctuation theory provide strong evidence for quantum criticality at Hc2 for all x< or =0.12 in CeCoIn5-xSnx. These results indicate the "accidental" coincidence of the QCP located near Hc2 in pure CeCoIn5, in actuality, constitute a novel quantum critical point associated with unconventional superconductivity.

We measured the specific heat and resistivity of heavy fermion $\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}{\mathrm{n}}_{\mathrm{5}}$ between the superconducting critical field ${H}_{c2}=5\text{ }\mathrm{T}$ and 9 T, with the field in the [001] direction, and at temperatures down to 50 mK. At 5 T the data show a non-Fermi liquid (NFL) behavior down to the lowest temperatures. At the field above 8 T the data exhibit a crossover from the Fermi liquid to a non-Fermi liquid behavior. We analyzed the scaling properties of the specific heat and compared both the resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AFM) in $\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}{\mathrm{n}}_{\mathrm{5}}$ with the quantum critical point in the vicinity of ${H}_{c2}$. Below ${H}_{c2}$ the AFM phase which competes with the paramagnetic ground state is superseded by the superconducting transition.

We report specific heat measurements of the heavy fermion superconductor ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_{5}$ in the vicinity of the superconducting critical field ${H}_{c2}$, with magnetic fields in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first order for fields above 10 T for $H\ensuremath{\parallel}[110]$ and $H\ensuremath{\parallel}[100]$. In the same range of magnetic fields, we observe a second specific heat anomaly within the superconducting state. We interpret this anomaly as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for $H\ensuremath{\parallel}[001]$, with the FFLO state occupying a smaller part of the phase diagram.

We report low-temperature thermal expansion measurements on the tetragonal heavy-fermion superconductors $\mathrm{C}\mathrm{e}M{\mathrm{I}\mathrm{n}}_{5}$ ($M=\mathrm{I}\mathrm{r},\mathrm{C}\mathrm{o}$) in magnetic fields up to 8 T which allow for the analysis of the uniaxial pressure effects on both normal-state and superconducting properties. Our study reveals that ${T}_{c}$ is strongly affected by at least two factors, the lattice anisotropy and the $4f$-conduction-electron hybridization strength which is most sensitive to $c$-axis lattice distortions. Non-Fermi-liquid behavior caused by quantum-critical fluctuations is observed for both systems, most pronounced for ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_{5}$.

The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K in zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c). The change from second order at lower fields is reflected in strong sharpening of both specific heat and thermal expansion anomalies associated with the phase transition, a strong magnetocaloric effect, and a steplike change in the sample volume. This effect is due to Pauli limiting in a type-II superconductor, and was predicted theoretically in the mid-1960s.

The compound YbBiPt exhibits an extremely large low‐temperature C/T (γ∼8 J K−2 mol−1/Yb) which, if due solely to a renormalized effective mass, would make this material the heaviest correlated electron system known to date. In the Kondo model, the very large γ corresponds to a small characteristic energy scale that is expected to be pressure dependent. We have studied the effect of chemical pressure on YbBiPt single crystals by heat‐capacity measurements on Y and Lu‐doped samples. We have also made preliminary low‐temperature measurements under hydrostatic pressure of the heat capacity (300 mK≤T≤2 K, up to 8 kbar) and resistance (30 mK≤T≤1 K, at 16 kbar).

CeIrIn5 is a member of a new family of heavy-fermion compounds and has a Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk, thermodynamic transition to a superconducting state at Tc=0.40 K, below which the specific heat decreases as T2 to a small residual T-linear value. Surprisingly, the electrical resistivity drops below instrumental resolution at a much higher temperature T0=1.2 K. These behaviors are highly reproducible and field-dependent studies indicate that T0 and Tc arise from the same underlying electronic structure. The layered crystal structure of CeIrIn5 suggests a possible analogy to the cuprates in which spin/charge pair correlations develop well above Tc.

Muon spin rotation ( $\ensuremath{\mu}\mathrm{SR}$) measurements of the temperature dependence of the ${\ensuremath{\mu}}^{+}$ Knight shift in single crystals of ${\mathrm{U}}_{0.965}{\mathrm{Th}}_{0.035}{\mathrm{Be}}_{13}$ have been used to study the static spin susceptibility ${\ensuremath{\chi}}_{s}$ below the transition temperatures ${T}_{c1}$ and ${T}_{c2}$. While an abrupt reduction of ${\ensuremath{\chi}}_{s}$ with decreasing temperature is observed below ${T}_{c1}$, ${\ensuremath{\chi}}_{s}$ does not change below ${T}_{c2}$ and remains at a value below the normal-state susceptibility ${\ensuremath{\chi}}_{n}$. In the normal state we find an anomalous anisotropic temperature dependence of the transferred hyperfine coupling between the ${\ensuremath{\mu}}^{+}$ spin and the U $5f$ electrons.

The temperature dependent magnetic susceptibility, specific heat, and electrical resistivity were measured on PrInA${\mathrm{g}}_{2}$. A broad peak, which is identified as a Kondo anomaly, is observed in the specific heat at $\ensuremath{\sim}0.4\mathrm{K}$ with a strongly enhanced linear contribution at lower temperatures. PrInA${\mathrm{g}}_{2}$ is a Pr-based heavy-fermion compound and has one of the largest known Sommerfeld coefficients of $\ensuremath{\sim}6.5\mathrm{J}/\mathrm{mol}{\mathrm{K}}^{2}$. A new type of nonmagnetic interaction between the conduction electrons and the non-Kramers doublet ground state of the ${\mathrm{Pr}}^{3+}$ ion may be responsible for this behavior. Related features are also observed in the susceptibility and resistivity.

Resistivity measurements are reported on the cubic heavy‐fermion compound YbBiPt at ambient and hydrostatic pressures to ≊19 kbar and in magnetic fields to 1 T. The phase transition at Tc=0.4 K is identified by a sharp rise in resistivity. That feature is used to build low‐temperature H‐T and P‐T phase diagrams. The phase boundary in the H‐T plane follows the weak‐coupling BCS expression remarkably well from Tc to Tc/4, while small hydrostatic pressure of ≊1 kbar suppresses the low‐temperature phase entirely. These effects of hydrostatic pressure and magnetic field on the phase transition are consistent with an spin‐density‐wave (SDW) formation in a very heavy electron band at T=0.4 K. Outside of the SDW phase at low temperature, hydrostatic pressure increases the T2 coefficient of resistivity, signaling an increase in heavy‐fermion correlations with hydrostatic pressure. The residual resistivity decreases with pressure, contrary to trends in other Yb heavy‐fermion compounds.

The effect of dilute La substitution in Ce 1- x La x RhIn 5 (0 ≤ x ≤0.07) has been investigated macroscopically by specific heat measurement and microscopically by nuclear magnetic/quadrupole resonance (NMR/NQR). The Neel temperature decreases gradually by dilute La substitutions from 3.8 K ( x =0) to 2.9 K ( x =0.07). The specific heat for Ce 1- x La x RhIn 5 exhibits nuclear Schottky contributions below 1 K, which are compatible with the microscopic parameters obtained by NMR/NQR. Below the Neel temperature, the residual Sommerfeld coefficient of ∼50 mJ K -2 /mol is nearly independent of increasing La substitution, while the entropy in the ordered state is slightly enhanced. Microscopically, 1/ T 1 in the AF ordered state can be explained by spin-wave term of 4 f moments, spin fluctuation term by uncompensated localized Ce moments near the La ions, and a small Korringa contribution by non-4 f electrons, which suggests a localized 4 f nature in CeRhIn 5 .

From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field and temperature dependence of the FLL form factor (FF), which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work (Bianchi et al 2008 Science 319 177) to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the FF with field. Near Hc2 the FF decreases again, and our results indicate that this fall-off extends outside the proposed Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover toward more conventional mixed state behavior is observed., New Journal of Physics, 12, ISSN:1367-2630

We used magnetic resonance force microscopy (MRFM) to study a 50nm thick continuous Permalloy film. We mechanically measured the ferromagnetic resonance signal in the temperature range between 10 and 70K in the presence of a static magnetic field applied normal to the surface of the film. The measurements show a decrease of the ferromagnetic resonance field with increasing temperature. We attribute this behavior to the temperature-dependent changes of the saturation magnetization. Our experiments demonstrate the potential of MRFM to perform quantitative ferromagnetic resonance measurements as a function of temperature.