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based on low temperature resistivity and heat capacity measurements in applied magnetic fields ybagge was recently classified as a new heavy fermion material with long range , possibly small moment , magnetic order below 1 k @xcite that shows magnetic field induced non - fermi - liquid ( nfl ) behavior @xcite . the critical field required to drive ybagge to the field - induced quantum critical point ( qcp ) is anisotropic ( @xmath3 45 koe , @xmath4 80 koe ) and conveniently accessible by many experimental groups @xcite . ybagge is one of the _ rarae aves _ of intermetallics ( apparently only second , after the extensively studied ybrh@xmath5si@xmath5 @xcite ) a _ stoichiometric _ , yb - based , heavy fermion ( hf ) that shows magnetic field induced nfl behavior and as such is suitable to serve as a testing ground for experimental and theoretical constructions relevant for qcp physics . among the surfeit of detailed descriptions developed for a material near the antiferromagnetic qcp we will refer to the outcomes @xcite of two more general , competing , pictures : in one viewpoint the qcp is a spin density wave ( sdw ) instability @xcite of the fermi surface ; within the second picture that originates in the description of heavy fermions as a kondo lattice of local moments @xcite , heavy electrons are composite bound states formed between local moments and conduction electrons and the qcp is associated with the breakdown of this composite nature . it was suggested @xcite that hall effect measurements can help distinguish which of these two mechanisms may be relevant for a particular material near a qcp . in the sdw scenario the hall coefficient is expected to vary continuously through the quantum phase transition , whereas in the composite hf scenario the hall coefficient is anticipated to change discontinuously at the qcp . perhaps more importantly , in both scenarios a clear and sharp change in the field dependent hall effect ( for the field - induced qcp ) is anticipated to occur at low temperatures , near the critical field value . although hall effect measurements appear to be a very attractive method of gaining insight into the nature of the qcp , one has to keep in mind that an understanding of the different contributions to the measured hall coefficient , in particular in magnetic or strongly correlated materials , is almost inevitably difficult and potentially evasive @xcite . therefore measurements on samples well characterized by other techniques @xcite as well as comparison with non - magnetic as well as non - hf members of the same series can be beneficial . in this work we present temperature- and field- dependent hall effect measurements on ybagge single crystals . the non - magnetic member of the same ragge ( r = rare earth ) series , luagge , and the magnetic , essentially non - hybridizing , tmagge were used for  common sense  checks , or calipers , of the ybagge measurements . ybagge , luagge and tmagge single crystals in the form of clean , hexagonal - cross - section rods of several mm length and up to 1 mm@xmath6 cross section were grown from high temperature ternary solutions rich in ag and ge ( see @xcite for details of the samples growth ) . their structure and the absence of impurity phases were confirmed by powder x - ray diffraction . temperature and field dependent hall resistivity , @xmath7 , and auxiliary high field magnetization measurements were performed down to 1.9 k , in an applied magnetic field of up to 140 koe in a quantum design ppms-14 instrument . for ybagge hall measurements were extended down to 0.4 k using the he-3 option of the ppms-14 . a four probe , ac technique ( @xmath8 = 16 hz , @xmath9 = 1 - 0.1 ma ) , was used for the hall measurements . samples were polished down to a plate - like shape with thicknesses of 0.3 - 0.4 mm . pt leads were attached to the sample with epotek h20e silver epoxy so that the current was flowing along the crystallographic @xmath10 axis . for the @xmath11 case hall resistivity ( @xmath12 ) was measured in the hexagonal crystallographic plane ( approximately along @xmath13 $ ] direction ) with the magnetic field applied perpendicular to both the current and the hall voltage directions ( approximately along @xmath14 $ ] direction ) ( see the lower inset to figure [ rhlutm ] ) . in the @xmath2 case , current was flowing in the hexagonal plane , approximately in @xmath13 $ ] direction , the hall voltage was measured along @xmath14 $ ] direction . due to rod - like morphology of the crystals , samples that were cut and polished for @xmath2 measurements were smaller and the error bars in the absolute values ( due to geometry and position of the contacts ) are larger than for the @xmath11 data sets . to eliminate the effect of inevitable ( small ) misalignment of the voltage contacts , the hall measurements were taken for two opposite directions of the applied field , @xmath15 and @xmath16 , and the odd component , @xmath17 was taken as the hall resistivity . to determine the hall resistivity in the limit of low field , linear fits of the initial ( linear ) parts of the @xmath18 data in both quadrants were used . he-4 hall measurements for ybagge and luagge were performed on two samples of each material , the results were the same within the error bars in sample dimensions and contact position measurements . during the measurements particular care was taken to avoid rotation and/or misplacement of the tmagge sample due to its magnetic anisotropy . the field - dependent hall resistivity for luagge for @xmath11 is shown in the upper inset to fig . [ rhlutm](a ) for several temperatures . @xmath12 is only slightly non - linear in field over the whole temperature range . this minor non - linearity causes some difference in the @xmath19 _ vs. _ @xmath20 data obtained in different applied fields ( fig . [ rhlutm](a ) ) . the hall coefficient , @xmath21 , is measured to be negative . the overall temperature dependence is monotonic , slow and featureless with approximately a factor of two increase in the absolute value of @xmath19 from room temperature to low temperatures . this temperature - dependency of the hall coefficient of the non - magnetic material possibly reflects some details of its electronic structure ( for example , comparable factor of 2 changes in @xmath22 were recently observed in latin@xmath23 , t = rh , ir , co , @xcite ) . overall the temperature- and field - dependence of the hall coefficient for tmagge ( fig . [ rhlutm](b ) ) is similar to that of luagge with two main differences : ( i)the long range order and metamagnetism of tmagge @xcite is reflected in hall measurements as a low temperature decrease in @xmath24 and as anomalies in @xmath25 for @xmath26 2 k that are consistent with the fields of the metamagnetic transitions ; ( ii)the absolute values of the @xmath27 data for tmagge are a factor of 3 - 4 smaller than for luagge .      the temperature dependent hall coefficient and the dc susceptibility data for ybagge with the same orientation of the magnetic field with respect to the crystallographic axis are shown in fig . [ rhmtyb ] . the susceptibility , @xmath28 , is field - independent above  50 k ( _ i.e. _ @xmath29 is linear below 140 koe in this temperature range ) and is similar to the data reported in @xcite . the hall coefficient , @xmath22 , is field - independent above approximately 25 k. the temperature dependencies of the susceptibility and the hall coefficient at high temperatures closely resemble each other . at low temperatures a field - dependent maximum in @xmath22 ( see inset to fig . [ rhmtyb ] ) is observed . qualitatively the temperature dependence of the hall coefficient is consistent with the picture presented in @xcite ( see also @xcite for a comprehensive review ) . within this picture the temperature dependence of the hall coefficient in heavy fermion materials is a result of two contributions : a residual hall coefficient , @xmath30 , and a hall coefficient due to the intrinsic skew scattering , @xmath31 . the residual hall coefficient is ascribed to a combination of the ordinary hall effect and residual skew scattering by defects and impurities and , to the first approximation , is considered to be temperature - independent , although , realistically , both the ordinary hall effect and the residual skew scattering may have weak temperature dependence . the temperature - dependent , intrinsic skew scattering contribution ( @xmath32 ) at high temperatures ( @xmath33 , where @xmath34 is the kondo temperature ) increases as the temperature is lowered in a manner that is mainly due to the increasing magnetic susceptibility . at lower temperatures @xmath32 passes through a crossover regime , then has a peak at a temperature on the order of the coherence temperature , @xmath35 , and finally , on further cooling rapidly decreases ( in the coherent regime of skew scattering by fluctuations ) to zero ( _ i.e. _ @xmath22 ultimately levels off to the @xmath36 value at very low temperatures @xcite ) . in the high temperature ( @xmath33 ) limit we can ( very roughly , within an order of magnitude ) separate these two contributions to the observed temperature - dependent hall coefficient using a phenomenological expression @xmath37 @xcite with the temperature - dependent skew scattering contribution written as @xmath38 where @xmath39 , @xmath40 is the curie constant , and @xmath41 is the weiss temperature . using @xmath42 = -15.1 k from @xcite we can plot @xmath43 _ vs. _ @xmath44 ( fig . [ rht ] ) and from the linear part of the curve we can estimate @xmath45 0.02 n@xmath46 cm / oe and @xmath47 -0.17 n@xmath46 cm it seems peculiar that our estimate of @xmath48 for ybagge differs noticeably from the hall coefficient measurements for luagge and tmagge ( see fig . [ rhlutm ] ) . regarding this discrepancy it should be mentioned that besides possible experimental ( mainly geometrical ) errors these three materials may have different residual skew scattering and , additionally , as indicated by the preliminary results of band structure calculations @xcite , the density of states at the fermi level can be considerably different for all three compounds under consideration . although the magnetic susceptibility , @xmath49 of tmagge above the nel temperature has a clear curie - weiss behavior @xcite , in contrast to the case of ybagge , the temperature dependence of the hall coefficient for tmagge ( fig . [ rhlutm](b ) ) does not have a similar functional form . the reason for this difference is apparently the very small skew scattering contribution ( @xmath50 ) to the hall coefficient in tmagge . similarly small couplings of local moment magnetism with the hall effect has been seen in other rare earth intermetallics , _ e.g. _ rni@xmath5b@xmath5c ( r = rare earth ) borocarbides @xcite . in order to further explore the low temperature behavior of the hall coefficient , measurements down to 0.4 k were performed . the results ( on a semi -_log _ scale ) are shown in fig . [ rhltyb ] . the data taken in applied fields of 75 koe and higher show the expected levelling off of the @xmath24 as @xmath51 . it is noteworthy that the measured value of @xmath52 is close to the aforementioned estimate of the residual hall coefficient . this agreement suggests that at the lowest temperatures the hall coefficient is dominated by @xmath48 and , barring the residual skew scattering contribution , can probe the concentration of the electronic carriers .    whereas the higher field values of the hall coefficient vary smoothly with temperature ( fig . [ rhltyb ] ) , the low field data , below @xmath53 3 k , show large variations . although the signal to noise ratio in the low field measurements is inherently lower , these variations appear to be above the noise level ( fig . [ rhltyb ] , inset ) and the peaks slightly above 0.6 k and 1.0 k are understood as the signatures of the magnetic transitions in ybagge @xcite that are suppressed ( in this orientation ) when a 75 koe , or higher , magnetic field is applied .    to further study the field - induced qcp in ybagge , field dependent hall resistance measurements were performed at different temperatures ( fig . [ rhhyb ] ) . although the theoretical constructions are usually formulated in terms of the hall _ coefficient _ , not hall _ resistivity _ , in the case of ybagge the magnetic field itself is a control parameter for the qcp that makes the proper definition of the hall coefficient ambiguous . we will continue presenting our data as hall resistivity , since it is a quantity unambiguously extracted from the measurements , and leave the discussion on the suitable definition of the hall coefficient for the appendix .    for temperatures at and above @xmath5410 k , the @xmath25 behavior is monotonic and , at higher temperatures , eventually linear ( fig . [ rhhyb](b ) ) . this type of behavior has been observed in a number of different materials in the paramagnetic state @xcite . the low temperature evolution of the @xmath25 behavior is more curious ( fig . [ rhhyb](a ) ) and ought to be compared with the phase diagram obtained for ybagge ( @xmath11 ) in @xcite ( an augmented version of which is shown in fig . [ pd ] below ) . the lines in fig . [ rhhyb](a ) roughly connect the points according to the phase lines in @xcite ( see also fig . [ pd ] below ) . it can be seen that the lower @xmath55 magnetically ordered phase line possibly has ( despite the scattering of the points ) correspondent features in @xmath25 , and the coherence line in @xcite ( and fig . [ pd ] ) roughly corresponds to the beginning of the high field linear behavior in @xmath25 . on the other hand , the higher @xmath55 magnetically ordered phase line can not unambiguously be associated with any feature in @xmath25 curves . the most interesting feature shown in fig . [ rhhyb](a ) though is the presence of the pronounced peak , or local maximum , in @xmath25 that occurs at @xmath56 koe for the @xmath26 0.4 k curve and can be followed up to temperatures above long range magnetic order transition temperatures . for @xmath26 2.5 k a broad , local maximum in @xmath12 , centered at @xmath57 koe can just barely be discerned . as temperature is reduced this feature sharpens and moves down in field . for @xmath26 1 k the local maximum in @xmath12 is clearly located at @xmath58 koe and by @xmath59 k @xmath12 has sharpened almost to the point of becoming discontinuous with @xmath60 koe . the temperature dependence of @xmath61 is shown in fig . [ pd ] clearly demonstrating that as @xmath62 , @xmath63 for the qcp . independent of any theory these data clearly show that ( i ) @xmath12 is an extremely sensitive method of determining @xmath64 of qcp , ( ii ) @xmath61 has a clear temperature dependence , and ( iii ) the qcp influences @xmath12 up to @xmath65 k , a temperature significantly higher than the @xmath66 antiferromagnetic ordering temperature .    the new phase line ( shown as stars in fig . [ pd ] ) associated with @xmath12 maximum is distinct from the lines inferred from @xmath67 and @xmath68 data @xcite . as @xmath51 this line approaches @xmath64 , but for finite @xmath20 it is well separated from the coherence line that was determined by the onset of @xmath69 resistivity behavior . this new @xmath61 line rather clearly locates @xmath64 at @xmath70 koe , the field at which the long range antiferromagnetic order appears to be suppressed . since the response of ybagge to an applied magnetic field is anisotropic @xcite , it is apposite to repeat the hall measurements for the magnetic field applied parallel to the crystallographic @xmath10-axis . the temperature - dependent hall coefficient taken in different applied fields is presented in fig . [ rhltybc ] ( the low - field data were obtained as described above ) . the @xmath24 behavior for @xmath2 is qualitatively similar to that for @xmath11 with a broad maximum being shifted to @xmath71 k ( as compared to @xmath72 k for @xmath11 ) and being less sensitive to the applied field . the low temperature , field - dependent hall resistivity for @xmath2 is shown in fig . [ rhhybc ] . in many aspects the overall behavior is similar to that for @xmath11 : there are no apparent features associated with the phase lines derived from magnetoresistance and specific heat measurements @xcite ( shown as lines in fig . [ rhhybc ] ) , however there is the presence of a pronounced minimum in @xmath25 that occurs at @xmath73 koe for the @xmath26 0.4 k curve and can be followed up to the temperatures well above the zero - applied - field magnetic transition temperatures . for @xmath26 2 k a broad , local minimum in @xmath12 , centered at @xmath74 koe can still be recognized and at @xmath75 k a local minima occurs just at the edge of our field range . as temperature is reduced this feature sharpens and moves down in field . the temperature dependence of @xmath76 is shown in fig . [ pdc ] clearly demonstrating that , akin to the @xmath11 case , as @xmath51 , @xmath77 for the qcp . the @xmath25 behavior for this orientation is more complex , and there is an additional , broad maximum in lower fields ( @xmath58 koe at 0.4 k ) that fades out with increasing temperature . this highly non - monotonic in field behavior is the origin of the dissimilarities in the low temperature @xmath24 data ( fig . [ rhltybc ] ) taken in different applied fields . the high field minimum in @xmath25 ( fig . [ rhhybc ] ) defines a new phase line ( shown as stars in fig . [ pdc ] ) which is clearly different from the lines inferred from @xmath67 and @xmath68 data @xcite . as @xmath51 this line approaches @xmath64 , but for finite @xmath20 it is well separated from the coherence line that was determined by the onset of @xmath69 resistivity behavior . for this orientation of the applied field this new @xmath76 line rather clearly locates @xmath64 at @xmath78 koe , the field at which the long range antiferromagnetic order appears to be suppressed . it should be noted that the new lines in the @xmath55 phase diagrams were established from different types of extrema in @xmath25 , _ maximum _ for @xmath11 and _ minimum _ for @xmath2 . we neither consider this difference as a reason for particular discomfort nor do we necessarily view it as a potential clue to deeper understanding of the nature of the field - induced qcp in this material . the preliminary band structure calculations @xcite on luagge , the non - magnetic analogue of the title compound , suggest that the members of the ragge series have a complex fermi surface consisting of multiple sheets . in such a case a change in the fermi surface may possibly have different signatures in the hall measurements with different field orientation . in addition , existing qcp models appear not to be at the level of considering different shapes and topologies of the fermi surfaces . whereas these new , @xmath79 lines on the @xmath80 phase diagrams ( figs . [ pd ] and [ pdc ] ) appear to be closely related with the qcp their detailed nature and temperature dependencies will require further experimental and theoretical attention . the temperature- and field - dependent hall resistivity have been measured for ybagge single crystals with @xmath11 and @xmath2 orientation of the applied magnetic field . the temperature dependent hall coefficient of ybagge behaves similarly to other heavy fermion materials . low temperature , field - dependent measurements reveal a local maximum ( @xmath11 ) or minimum ( @xmath2 ) in @xmath25 for @xmath65 k that occurs at a value that approaches @xmath81 koe ( @xmath11 ) and @xmath82 koe ( @xmath2 ) as @xmath51 . these data indicate that ( i ) the hall resistivity is indeed a useful measurement for the study of qcp physics and ( ii ) the influence of the qcp extends to temperatures significantly higher than the @xmath66 antiferromagnetic ordering temperature . coleman _ et al . _ @xcite suggest that @xmath83 data ( where @xmath84 is a control parameter , _ i.e. _ @xmath15 in our case ) can be used to distinguish between two possible qcp scenarios : diffraction off of a critical spin density wave or a breakdown of the composite nature of the heavy electron , with the former manifesting a change of slope at @xmath85 and the latter manifesting a divergence in the slope of @xmath83 at @xmath85 . since in our case the magnetic field is itself the control parameter , it in not clear if @xmath21 , @xmath86 or just simply @xmath12 should be used for comparison with the theory . @xmath87 curves determined by two aforementioned ways are presented in fig . [ drhhyb ] ( @xmath11 ) and fig . [ drhhybc ] ( @xmath2 ) . for both definitions and both orientations the evolution of a clear feature in @xmath87 ( defined as a local extremum for @xmath19 and as a mid - point between two different field - dependent regimes for @xmath88 ) replicates ( albeit with slight @xmath15-shift ) the behavior of the hall resistivity ( figs . [ rhhyb](a ) , [ rhhybc ] ) . given that the new phase line in figs . [ pd ] and [ pdc ] is fairly insensitive to the data analysis we feel that the use of @xmath25 data is currently the least ambiguous data set to analyze . on the other hand , if the form of the anomaly near @xmath64 is to be analyzed in detail it will be vital to have a more detailed theoretical treatment of magneto - transport in field - induced qcp materials . it is tempting to say that for the case of applied field as a control parameter the quantity @xmath89 ( rather than @xmath90 ) serves the role of the low - field hall coefficient and should be compared with the prediction of the models . if this point of view is accepted , then for @xmath11 the shape and evolution of the @xmath89 curves ( fig . [ drhhyb](b ) ) suggest that possibly the composite fermion model of the qcp is more relevant to the case of ybagge , although for @xmath2 the shape and evolution of the @xmath89 curves ( fig . [ drhhybc](b ) ) are at variance with the simple theoretical views . the lack of the @xmath91 k data and an absence of more detailed , realistic - fermi - surface - tailored , model do not allow us to choose the physical picture of the field - induced qcp in ybagge unambiguously . ames laboratory is operated for the u.s . department of energy by iowa state university under contract no . this work was supported by the director for energy research , office of basic energy sciences . we thank h. b. rhee for assistance in growing some of the additional crystals needed for this work . , of luagge measured in different applied fields ( @xmath11 ) . upper inset : field - dependent hall resistivity of luagge measured at different temperatures . lower inset : the sample , current and applied field geometry used during the measurements . ( b ) similar data for tmagge.,title="fig:",width=377 ] , of luagge measured in different applied fields ( @xmath11 ) . upper inset : field - dependent hall resistivity of luagge measured at different temperatures . lower inset : the sample , current and applied field geometry used during the measurements . ( b ) similar data for tmagge.,title="fig:",width=377 ]    , of ybagge measured in different applied fields ( @xmath11 ) . inset : enlarged , low temperature part of the data . lower panel : dc susceptibility of ybagge ( @xmath15 along @xmath14 $ ] direction ) . the  low h  label in the legend refers to the low field hall resistivity ( see experimental section ) and for susceptibility measured in @xmath15 = 1 koe.,width=453 ]      ) measured in different applied fields down to 0.4 k. open symbols - he-4 measurements ( 2 - 300 k ) , filled symbols - measurements using he-3 option ( 0.4 - 10 k ) . inset : enlarged low temperature part of the low field data with the estimated error bars.,width=453 ]    ) measured at different temperatures : ( a)low temperature data : the curves , except for @xmath20 = 0.4 k , are shifted by @xmath93 cm increments for clarity ; the lines represent the phase lines from the phase diagram in fig . 10(a ) of the ref . 2 ; the triangles mark the position of the local maximum in @xmath25 ; ( b)intermediate and high temperature data . note : @xmath94 k data is shown in both plots for reference and is un - shifted in ( b ) . , title="fig:",width=340 ] ) measured at different temperatures : ( a)low temperature data : the curves , except for @xmath20 = 0.4 k , are shifted by @xmath93 cm increments for clarity ; the lines represent the phase lines from the phase diagram in fig . 10(a ) of the ref . 2 ; the triangles mark the position of the local maximum in @xmath25 ; ( b)intermediate and high temperature data . note : @xmath94 k data is shown in both plots for reference and is un - shifted in ( b ) . , title="fig:",width=340 ]     phase diagram for @xmath95 . long range magnetic order ( lrmo ) and the coherence temperature lines marked on the phase diagram are taken from ref . 2 . filled stars and corresponding dashed line as a guide to the eye are defined from the maximum in the @xmath25 curves.,width=453 ]      ) ; the curves , except for @xmath20 = 0.4 k , are shifted by @xmath93 cm increments for clarity ; the lines represent the phase lines from the phase diagram in fig . 10(b ) of the ref . 2 ; the triangles mark the position of the peak in @xmath25 . , width=453 ]     phase diagram for @xmath96 . long range magnetic order ( lrmo ) and the coherence temperature lines marked on the phase diagram are taken from ref . filled stars are defined from the minimum in the @xmath25 curves . dashed lines are guides to the eye.,width=453 ]    ) , defined as ( a ) @xmath21 and ( b ) @xmath97 , measured at different temperatures . the curves , except for @xmath20 = 0.4 k , are shifted by ( a ) 0.02 n@xmath46 cm and ( b ) 0.2 n@xmath46 cm increments for clarity ; the triangles mark the position of the feature in @xmath87 : a local maximum in @xmath19 and a mid - point of the transition between two different field - dependent regimes ( see _ e.g. _ 0.8 k curve)in @xmath88 . curves in the ( b ) panel were obtained by differentiation of the 5-adjacent - points - smoothed @xmath25 data . small downturn at @xmath98 koe in some @xmath88 curves ( panel ( b ) ) is most likely an artifact of using digital smoothing and differentiation.,title="fig:",width=283 ] ) , defined as ( a ) @xmath21 and ( b ) @xmath97 , measured at different temperatures . the curves , except for @xmath20 = 0.4 k , are shifted by ( a ) 0.02 n@xmath46 cm and ( b ) 0.2 n@xmath46 cm increments for clarity ; the triangles mark the position of the feature in @xmath87 : a local maximum in @xmath19 and a mid - point of the transition between two different field - dependent regimes ( see _ e.g. _ 0.8 k curve)in @xmath88 . curves in the ( b ) panel were obtained by differentiation of the 5-adjacent - points - smoothed @xmath25 data . small downturn at @xmath98 koe in some @xmath88 curves ( panel ( b ) ) is most likely an artifact of using digital smoothing and differentiation.,title="fig:",width=283 ]    ) , defined as ( a ) @xmath21 and ( b ) @xmath97 , measured at different temperatures . the curves , except for @xmath20 = 0.4 k , are shifted by ( a ) 0.02 n@xmath46 cm and ( b ) 0.1 n@xmath46 cm increments for clarity ; the triangles mark the position of the feature in @xmath87 : a local minimum in @xmath19 and a mid - point of the transition between two different field - dependent regimes ( see _ e.g. _ 0.8 k curve)in @xmath88 . curves in the ( b ) panel were obtained by differentiation of the 5-adjacent - points - smoothed @xmath25 data . small downturn at @xmath98 koe in some @xmath88 curves ( panel ( b ) ) is most likely an artifact of using digital smoothing and differentiation.,title="fig:",width=283 ] ) , defined as ( a ) @xmath21 and ( b ) @xmath97 , measured at different temperatures . the curves , except for @xmath20 = 0.4 k , are shifted by ( a ) 0.02 n@xmath46 cm and ( b ) 0.1 n@xmath46 cm increments for clarity ; the triangles mark the position of the feature in @xmath87 : a local minimum in @xmath19 and a mid - point of the transition between two different field - dependent regimes ( see _ e.g. _ 0.8 k curve)in @xmath88 . curves in the ( b ) panel were obtained by differentiation of the 5-adjacent - points - smoothed @xmath25 data . small downturn at @xmath98 koe in some @xmath88 curves ( panel ( b ) ) is most likely an artifact of using digital smoothing and differentiation.,title="fig:",width=283 ]
temperature- and field - dependent hall effect measurements are reported for ybagge , a heavy fermion compound exhibiting a field - induced quantum phase transition , and for two other closely related members of the ragge series : a non - magnetic analogue , luagge and a representative ,  good local moment  , magnetic material , tmagge . whereas the temperature dependent 
 hall coefficient of ybagge shows behavior similar to what has been observed in a number of heavy fermion compounds , the low temperature , field - dependent measurements reveal well defined , sudden changes with applied field ; in specific for @xmath0 a clear local maximum that sharpens as temperature is reduced below 2 k and that approaches a value of 45 koe - a value that has been proposed as the @xmath1 quantum critical point . 
 similar behavior was observed for @xmath2 where a clear minimum in the field - dependent hall resistivity was observed at low temperatures . 
 although at our base temperatures it is difficult to distinguish between the field - dependent behavior predicted for ( i ) diffraction off a critical spin density wave or ( ii ) breakdown in the composite nature of the heavy electron , for both field directions there is a distinct temperature dependence of a feature that can clearly be associated with a field - induced quantum critical point at @xmath1 persisting up to at least 2 k.