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elemental cerium is stark example of the complicating effects of magnetism in metals . in principle a simple system , cerium at room temperature and ambient pressure presents a monatomic bravais lattice ( the face - centered - cubic @xmath3 phase ) . however , under the application of modest pressures , cerium undergoes a spectacular first - order transition to a low temperature @xmath4 phase . both @xmath4 and @xmath3 are isostructural f.c.c . phases , but differ by @xmath5 in volume , and have markedly different magnetic susceptibilities and resistivities.@xcite there are competing explanations for the transition , which variously invoke a `` kondo volume collapse''@xcite mechanism , a `` mott transition'',@xcite or some entropic mechanism@xcite . in all cases however , it is generally agreed that the large volume @xmath3 phase contains relatively larger localized magnetic moments ( evinced by the higher susceptibility ) and relatively less itinerant electrons ( evinced by the higher resistivity ) . beyond that , the nature of the transisiton remains contentious . one of the main complications in the study of cerium is that although the @xmath2 transition occurs on cooling over a wide range of pressures , it is avoided at ambient pressure . in that case , an intervening dhcp phase forms from the @xmath3 phase , and transforms into the @xmath4 phase only at lower temperature.@xcite there are commonly two methods used to resolve this problem . measurements are either performed under pressure on pure cerium , or else the cerium is alloyed with other elements known to suppress the dhcp phase ( typically thorium ) . results from these two avenues of investigation are not always consistent - for example , it has been claimed that the phonon entropy plays little role in the @xmath2 transition in a ce@xmath6th@xmath1 alloy,@xcite while studies on pure cerium under pressure have returned the opposite result.@xcite nevertheless , the alloying of cerium has generated a family of related compounds , in which the order of the transition , the magnitude of the volume collapse , and the transition temperature can be smoothly varied.@xcite    one such alloy , ce@xmath0la@xmath1th@xmath1 , is of particular interest in regards to spin - lattice coupling at the phase transition . alloying with thorium suppresses the dhcp phase , while alloying with lanthanum causes the transition to become continuous and supresses the critical temperature.@xcite it has been reported that cooling ce@xmath0la@xmath1th@xmath1 in high magnetic fields can suppress the resistivity change associated with the volume collapse to lower temperature , and that the application of pulsed magnetic fields can induce a large moment below the critical temperature.@xcite these measurements map out a phase boundary for the @xmath2 transition as a function of magnetic field , and suggest that the volume collapse can be fully suppressed by @xmath7 tesla . here we report a direct study of the structure of ce@xmath0la@xmath1th@xmath1 , using synchrotron x - ray powder diffraction in pulsed magnetic fields as high as 28 tesla . lattice parameter and structural correlation length are extracted throughout the @xmath8 phase diagram . samples of ce@xmath0la@xmath1th@xmath1 were prepared at los alamos by arc - melting elemental cerium , lanthanum and thorium in a zirconium gettered argon atmosphere . the button was melted and flipped 15 times to ensure mixing . the final melt was cooled in a round - bottomed trough , which was 5 mm wide . the resulting @xmath9 25 mm long sample was unidirectionally rolled @xmath9 10 times to achieve a finished thickness of 50 microns . a section of the as - rolled material was heat treated at 450@xmath10c for 1 hour to remove the rolling texture before a final sample , 2 mm in diameter , was cut from the sheet with a razor blade . the sample was subsequently mounted inside a blind hole in a sapphire bracket , and sealed with a sapphire cap and stycast epoxy , to ensure good thermal contact and prevent oxidization . the sapphire bracket was anchored to the cold finger of the double - funnel solenoid pulsed magnet at the advanced photon source ( aps ) , which facilitates diffraction at up to 22@xmath11 of scattering angle , to temperatures as low as @xmath12 k and in magnetic fields as high as @xmath9 30 tesla.@xcite this system features a resistive magnet coil ( of tohoku design ) in a liquid nitrogen bath , connected to a 40 kj capacitor bank . the bank is capable of discharging a 3 kv charge through the coil in a @xmath13 ms half - sine wave pulse , generating a peak current of @xmath14 ka and a peak magnetic field of @xmath15 tesla . the heat generated in the resistive coil during a pulse must be allowed to dissipate before the system can be pulsed again . at peak field values , this requires a wait time @xmath16 8 minutes between pulses . the sample to be studied is both thermally and vibrationally isolated from the coil . this new instrument offers a complementary measurement geometry to the aps split - pair pulsed magnet developed previously.@xcite     14.9 tesla , integrated over @xmath17 0.5 tesla for the exposure . middle : raw data collected on the image plate for a single 1 ms exposure . bottom : the same data , radially integrated and converted to @xmath18.,width=306 ]    experiments were performed at the 6id - b station at the aps . 30 kev photons were selected using a si(111 ) monochromator , with the mirror removed to provide an unfocused beam . the monochromator was detuned so as to reduce higher harmonic contamination . the incident beam size was defined by slits , with an illuminated area on sample of 0.2 mm x 1.0 mm . a @xmath19 ms pulse of x - rays was defined using a pair of fast platinum shutters , and the arrival of this pulse at the sample was synchronized with the peak of the magnetic field pulse . scattered x - rays were recorded on a two - dimensional image plate detector . in this configuration , our system is similar to the pulsed magnet instrument in operation at the european synchrotron radiation facility ( esrf).@xcite to calibrate our instrument , we repeated the measurements@xcite of detlefs _ et al . _ on polycrystalline tbvo@xmath20 in pulsed magnetic fields , as previously measured by the esrf instrument.@xcite we reproduced the reported high field peak splitting in the tetragonal phase of tbvo@xmath20,@xcite validating our measurement scheme.@xcite we performed our measurements of ce@xmath0la@xmath1th@xmath1 with the axis of the solenoid coincident with the incident beam , and the detector positioned so as to capture the majority of the solenoid exit window . in this way , at 30 kev the first two powder rings ( corresponding to the @xmath21111@xmath22 and @xmath21200@xmath22 peaks ) are completely captured by the detector , allowing a full radial integration and excellent counting statistics even for a single 1 ms exposure . the current through the solenoid and the x - ray flux incident on the sample were monitored as a function of time by tracing the output of a high - resolution current monitor and an air - filled ion chamber on a digital storage oscilloscope . a typical trace is shown in fig . 1 , along with data from a single exposure on the image plate . in order to extract the correlation length and lattice parameter from these diffraction patterns , each of the two lowest lying peaks was fit individually , generating two independent sets of data , which were subsequently compared . in all cases , the properties extracted from the two peaks aggreed within the errorbars of the measurement , and the quantities quoted in the following are the average of the two powder diffraction patterns at room temperature show a single phase material , with symmetry and lattice constant consistent with the @xmath3 phase of ce@xmath0la@xmath1th@xmath1 . on cooling , we observe the first two bragg peaks to shift to higher @xmath18 , while also broadening by a factor of @xmath23 and exhibiting a reduction in peak intensity ( see fig . this is consistent with a collapse in volume , accompanied by a striking reduction in the structural correlation length . it is interesting to note that we observe a single phase at all temperatures , in contrast to recent neutron diffraction measurements on ce@xmath6th@xmath1 which reported a coexistence of both the @xmath4 and @xmath3 phases over a wide range of temperatures.@xcite our sample was initially cooled directly to 8k to characterize the magnitude of the volume collapse , then warmed to 250 k while collecting data . the volume was observed to approach the @xmath3 phase value quite gradually . next we cooled slowly and measured the lattice parameters with a fine point density . the resulting continuous but hysteretic volume collapse curves are plotted in fig . surprisingly , on our second cooling we found that the absolute size of the volume collpase was diminished - thermal cycling of the sample is detrimental to the phase transition . 111@xmath22 bragg reflection . the peak shifts to higher @xmath18 and broadens on cooling . the sample is a single phase at all temperatures . resolution limited peaks at high temperature are well described by gaussians , while a voigt shape at low temperature is consistent with an ornstein - zernike scattering function with a short correlation length ( solid lines).,width=321 ]    la@xmath1th@xmath1 . sample was warmed from 8 k to 250 k ( @xmath24 ) , then cooled back to 10 k ( @xmath25 ) . this thermal cycling lead to a reduction in the magnitude of the volume collapse , shown by the dashed lines . the inset shows the ornstein - zernike correlation length extracted from the cooling measurements ( see text ) . the correlated regions of the collapsed phase have average size of only @xmath26 nm.,width=321 ]    the observed peak broadening can be modelled phenomenologically , by assuming that the high temperature patterns show long - range ordered and resolution limited scattering , while the low temperature broadening arises from a reduction in the ornstein - zernike correlation length . our high temperature peaks are well described by gaussians , and we are assuming a lorentzian form for the scattering function ( see ref . [ ] for details ) . therefore , the measured scattering at low temperature should be well described by the convolution of a lorentzian and a gaussian - a voigt function . since the width of this voigt function is related to the width of the gaussian ( the resolution ) and the width of the lorentzian ( the inverse correlation length ) , the numerically extracted fullwidth of the bragg peaks can be converted to a resolution - deconvoluted correlation length . the solid lines in fig . 2 demontrate the degree of agreement between these lineshapes and the measured data , and the extracted correlation length is plotted in the inset of fig . our resolution limit is found to be on the order of a few microns , however , the low temperature collapsed phase exhibits correlation lengths which are roughly two orders of magnitude shorter than this . below @xmath9 30 k , the @xmath4 phase correlations are seen to extend over an average range of @xmath9 20 nm . since our alloy is @xmath9 80@xmath27 cerium , the mean distance between dopant atoms ( either lanthanum or thorium ) is on the order of 2 nm . thus , while the inclusion of lanthanum and thorium in the alloy does not completely hinder the formation of the @xmath4 phase , and each correlated region on average contains multiple dopant atoms , nevertheless these atoms act to strongly disorder the sample at the nanoscale within the @xmath4 phase . conversely , within the @xmath3 phase , individual grains are well correlated over micron - sized regions despite the same level of chemical disorder . motivated by the results of ref . [ ] , we next sought to characterize the effect of applied magnetic field on the volume collapse transition in ce@xmath0la@xmath1th@xmath1 . currently , the available capacitance at the aps limits our measurements to applied magnetic fields @xmath28 30 tesla , well below the 56 tesla estimated to fully suppress the @xmath2 transition to zero kelvin.@xcite however , inspection of the resistivity measurements of ref . [ ] reveals that our highest achievable magnetic fields should be sufficient to suppress the temperature of the volume collapse inflection point by @xmath9 8 k. we can maximize our sensitivity to this effect by cooling to the inflection point of the volume collapse ( @xmath9 35 k ) and pulsing to high magnetic field . the slope of @xmath29 is large at this temperature , and therefore an 8 k shift in the inflection point should cause a @xmath9 0.7 @xmath27 change in volume at 35 k , well within our resolution . however , as can be seen from fig . 4 , we failed to observe this effect . after cooling to 35 k , we collected five diffraction patterns at zero field , which served to define the zero field bragg peak positions to an accuracy better than @xmath30 . next , we collected ten patterns in pulsed field , with the average applied field over the x - ray exposure being @xmath31 tesla . we observed no measurable change in the bragg peak positions in any individual pattern . nor did we observe any cumulative effect from multiple high - field pulses . our measurements therefore constrain any volume changes at ( 35 k , 28 t ) to be less than @xmath9 0.07 @xmath27 , a full order of magnitude smaller than what would be expected.@xcite    111@xmath22 bragg peak at t=35 k. there is no discernable change in the position or width of the peak . the expected curve is calculated based on the position and width change that would arise from an 8 k shift in the transition temperature , consistent with the results of ref . [ ] .,width=321 ]    ) and ornstein - zernike correlation length ( @xmath32 ) , comparing zero field cooled measurements and measurements where the system is repeatedly pulsed to 28 t on cooling . no field effect is seen.,width=321 ]    it is important to remember that the evidence for field induced suppression of the volume collapse in ce@xmath0la@xmath1th@xmath1 for magnetic fields below 30 tesla comes from resistivity curves , measured by cooling in constant applied magnetic fields . this is procedurally distinct from the zero - field - cooled pulsed measurements reported here . discrepancy between field - cooled and zero - field - cooled behaviour is a hallmark of spin glass materials , wherein chemical disorder and competing interactions collude to freeze in disordered ground states.@xcite we have already shown that chemical disorder in our alloy has a strong effect on the development of @xmath4-phase correlations ( see fig . it is therefore tempting to sugest that there may be some glassy behavior at play in ce@xmath0la@xmath1th@xmath1 . direct comparison between field cooled and zero field cooled measurements are therefore highly desirable , however , a truly field - cooled measurement is not achievable with pulsed magnets . we have attempted to approximate one by slow cooling , and pulsing in regular intervals . in order to minimize the obscuring effects of thermal cycling , we performed two identical cooling curves , one after the other , warming to 280 k once to reset the system . for each of these measurements , we cooled at a controlled rate of 1 k@xmath33min from 280 k. during the first of these cooldowns , we pulsed to 28 t at 10 min ( 10 k ) intervals . during the second cooldown , we collected zero - field data in the same manner , albeit more frequently since there was no need to wait for the coil to cool down . the results are plotted in fig . 5 . clearly , magnetic fields applied in this way are no more effective at suppressing the volume collapse than the zero - field - cooled methods shown in fig . 4 .    we are therefore forced to conclude that the available magnetic fields were insufficient to induce any structural effects in ce@xmath0la@xmath1th@xmath1 . if the @xmath2 transition were continuous for this alloy ( as claimed in ref . [ ] ) , and the magnetic field induced suppression occured as claimed in ref . [ ] , then we would have expected to see a clear shift in @xmath18 as denoted in fig . 4 for the zero - field - cooled measurements , and a clear suppression in temperature should have occurred for the repetitively pulsed measurements reported in fig . conversely , if the @xmath2 transition were first order for this alloy ( as claimed in ref . [ ] ) , then our measurements imply that the phase boundary was never crossed in our cooling curve . this would require a steeper increase of the critical field on lowering temperature than was reported in ref . [ . ] it is also possible that the alloy is dynamically inhibited on the timescale of the magnetic field pulse , which would be consistent with a glassy behavior . finally , it is possible that the effects reported in ref . [ ] were not intrinsic to ce@xmath0la@xmath1th@xmath1 . clearly , the issue of field induced suppression of the @xmath2 transition requires further investigation in elemental cerium and its alloys . as has been noted in the preceeding sections , we have observed a detrimental effect due to thermal cycling . our initial measurements on as - grown samples revealed well - correlated grains on the order of microns in size . on first cooling , the volume collapsed @xmath4 phase was seen to exhibit nanoscale disorder , and on second cooling the absolute size of the volume collapse had diminished ( see fig . 3 and discussion in section iii ) . over the course of our week - long experiment , we observed the @xmath4-phase volume to gradually increase with each thermal cycling , while the @xmath3-phase volume was seen to gradually decrease . in addition , while the @xmath4-phase consistently showed nanoscale disorder with correlation lengths of @xmath9 20 nm , the @xmath3 phase correlations were observed to shrink , from micron - sized grains in the as - grown sample to correlation lengths of only @xmath9 150 nm after 11 thermal cycles . zero - field cooling curves from the second , seventh , and eleventh cycle are plotted in fig . 6 , to illustrate the effect . it is likely that the strains associated with the large volume change and spatial variations in doping,@xcite which are manifest in the @xmath4-phase disorder , act to introduce new domain boundaries at low temperature , which thereafter persist as defects . this effect is insidious , since the suppression by thermal cycling we observe here could easily be mistaken for suppression by an external perturbation , if that perturbation was varied monotonically during the course of an experiment . hypothetically , had we measured cooling curves through the volume collapse in dc magnetic fields which were monotomically increased during the course of our measurements , we may easily have misinterpreted the gradual buildup of thermal cycling damage as a magnetic field induced effect . therefore , it is important to take extra care when mapping out phase diagrams in cerium alloys . more generally , these measurements highlight the need for careful consideration of strain driven effects in all materials studies , which can often obfuscate results .     transition . the effects are clear in both the magnitude of the volume collapse ( @xmath34 ) and the ornstein - zernike correlation length ( @xmath32 ) . all data was collected on cooling in zero magnetic field . the three data sets represent the second ( @xmath25 ) , seventh ( @xmath24 ) , and eleventh ( @xmath35 ) thermal cycle.,width=321 ] in this article , we have reported a synchrotron x - ray diffraction study of the volume collapse transition in ce@xmath0la@xmath1th@xmath1 , as a function of temperature and pulsed magnetic field . in this alloy , the @xmath2 transition is smooth but hysteretic , characterized by a @xmath36 volume change and a dramatic reduction in structural correlation length . the collapsed @xmath4 phase is shown to be unaffected by pulsed magnetic fields @xmath28 28 tesla , both in zero - field cooled conditions and under repetitive pulsing on cooling . it is suggested that a deviation between truly field cooled and zero field cooled behavior in ce@xmath0la@xmath1th@xmath1 may account for the disagreement between our measurements and previous bulk studies.@xcite this implies a glassy character to the low temperature phase . we have also shown that repeated thermal cycling through the @xmath2 transition acts to disorder the sample on nanometer length scales , while suppressing the magnitude of the volume collapse transition . these measurements may constitute a microscopic measure of what has been generally refered to as `` sluggish dynamics '' in cerium alloys.@xcite    it is our hope that these results will advance understanding of the exotic @xmath2 transition in elemental cerium and its alloys . specifically , we believe the data presented here highlights the strong effects of disorder in these systems . we gratefully acknowledge fruitful discussions with j. lashley and b. toby . use of the advanced photon source is supported by the doe , office of science , under contract no . de - ac02 - 06ch11357 . pulsed magnet collaborations between argonne and tohoku university are supported by the icc - imr . hn acknowledges kakenhi no . 23224009 from mext . jpcr aknowledges the support of nserc of canada . f. drymiotis , j. singleton , n. harrison , j.c . lashley , a. bangura , c.h . mielke , l. balicas , z. fisk , a. migliori and j.l . `` suppression of the @xmath37 structural phase transition in ce@xmath0la@xmath1th@xmath1 by large magnetic fields '' . condens . matter _ * 17 * l77-l83 ( 2005 )    m.e . manley , r.j . mcqueeney , b. fultz , t. swan - wood , o. delaire , e.a . goremychkin , j.c . cooley , w.l . hults , j.c . lashley , r. osborn , and j.l . `` no role for phonon entropy in the fcc - fcc volume collapse transition in ce@xmath6th@xmath1 at ambient pressure '' _ phys . rev . _ b * 67 * , 014103 ( 2003 )    i .- k . jeong , t.w . darling , r.h . heffner , a. llobet and j.c . . `` neutron diffraction study on the @xmath37 phase transition in ce@xmath6th@xmath1 alloy '' _ philosophical magazine letters _ vol * 88 * , no . * 8 * , 607 - 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we report synchrotron x - ray powder diffraction measurements of ce@xmath0la@xmath1th@xmath1 subject to pulsed magnetic fields as high as 28 tesla . 
 this alloy is known to exhibit a continuous volume collapse on cooling at ambient pressure , which is a modification of the @xmath2 transition in elemental cerium . 
 recently , it has been suggested on the basis of field - cooled resistivity and pulsed field magnetization measurements that the volume collapse in this alloy can be suppressed by the application of magnetic fields . 
 conversely , our direct diffraction measurements show a robust collapsed phase , which persists in magnetic fields as high as 28 tesla . 
 we also observe nanoscale disorder in the collapsed phase , which increasingly contaminates the high temperature phase on thermal cycling .