ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Out-of-plane exchange bias and magnetic anisotropy in MnPd/Co multilayers N.H Dung a,Ã, N.P Thuy a,b, N.A Tuan a, N.T Long b, N.N Phuoc c a b c International Training Institute for Materials Science (ITIMS), Hanoi University of Technology, Dai Co Viet road, Hanoi, Vietnam Faculty of Electronics and Telecommunications, College of Technology, Vietnam National University, Hanoi, Vietnam Physics Department, National University of Singapore, Singapore a r t i c l e in f o a b s t r a c t Article history: Received April 2008 Received in revised form 18 June 2008 Available online 15 July 2008 Magnetic and structural properties in [MnPd/Co]10 multilayers deposited onto Si(111) substrates have been investigated The dependences of anisotropy and exchange bias on the thicknesses of both MnPd and Co layers have been studied In most of the samples, the out-of-plane magnetic anisotropy and both large out-of-plane and in-plane exchange biases have been observed at cryogenic temperature below the blocking temperature TBE240 K With appropriate MnPd and Co thicknesses, we have obtained samples with a large out-of-plane exchange bias along with a large out-of-plane magnetic anisotropy The origin of the out-of-plane magnetic anisotropy in the samples has been suggested to be due to the formation of CoPd interfacial alloys which have tensile in-plane strains, while the spin structure of the antiferromagnetic layer at the interface which is believed to be responsible for exchange bias may be the same as that of the bulk material Also, the present study shows that the interplay between the outof-plane magnetic anisotropy and exchange bias is evident in our multilayers and plays an important role in the out-of-plane exchange-bias mechanism & 2008 Elsevier B.V All rights reserved PACS: 75.70.Cn 75.70.Ài 75.25.+z 75.30.Gw Keywords: Out-of-plane exchange bias Out-of-plane magnetic anisotropy Magnetic thin film Multilayer Introduction The phenomenon of exchange bias between antiferromagnetic (AF) and ferromagnetic (FM) materials has been studied extensively, since its discovery in 1956 by Meiklejohn and Bean [1] However, most of the studies concentrate on the in-plane configuration (the so-called in-plane exchange bias) The investigations on out-of-plane exchange bias have recently received much attention because it is relevant in the quest for a better understanding of the microscopic origin of the exchange bias phenomenon and it might lead to wide applications in magnetic sensors, perpendicular recording media, perpendicular magnetic read heads and magnetic random access memories (MRAMs) So far, several groups [2–13] have observed out-of-plane exchange bias and magnetic anisotropy in multilayers but very few works [8] have indicated the significant contribution for out-of-plane magnetic anisotropy arising from the induced unidirectional anisotropy For the out-of-plane exchange bias mechanism, all the studies concentrate on the explanation for the difference in the exchange bias field (HE) in various directions based on the orientation of the uncompensated AF spins at the interface Some à Corresponding author Tel.: +84 8680787; fax: +84 8692963 E-mail address: nhdzung@gmail.com (N.H Dung) 0304-8853/$ - see front matter & 2008 Elsevier B.V All rights reserved doi:10.1016/j.jmmm.2008.07.007 authors [4,7] suggest that the spin structure at the interface is the same as that of AF bulk, while others [5,13] believe in some interfacial AF spin fluctuations Recently, our group has discovered a huge unidirectional anisotropy in exchange-biased MnPd/Co bilayer systems in the in-plane configuration [14] From the fundamental viewpoint, it will be interesting to extend our work from bilayers to multilayers to investigate the role of out-of-plane exchange bias and magnetic anisotropy for a better understanding of the physical origin of exchange bias and related phenomena In this paper, we therefore focus our study on exchange bias in both the out-of-plane and inplane directions and out-of-plane magnetic anisotropy in [MnPd/Co]10 multilayers Experimental Samples with the structure of Si(111)/[MnPd/Co]10 were deposited at ambient temperature using the RF sputtering system The deposition was carried out in pure Ar gas with the pressure of  10À3 mbar No external field was applied during the deposition The atomic composition analyses using both the energy dispersive X-ray spectrometer (EDS) and the wavelength dispersive X-ray spectrometer (WDS) pointed out Mn:Pd ¼ 11:89 Crystal structure was determined by X-ray diffraction (XRD) with ARTICLE IN PRESS N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 Cu Ka radiation (l ¼ 1.54056 A˚) and small incident angle (11) The vibrating sample magnetometer (VSM) was used to characterize the magnetic properties of the samples For the exchange bias study, all samples had to undergo the so-called field cooling (FC) process First, MnPd/Co multilayers deposited onto Si(111) substrates were heated to 590 K and kept at that condition for min, and then cooled down to room temperature in the presence of a magnetic field of kOe applied either in the film plane (in-plane direction) or normal to the plane (out-of-plane direction) This process was realized in a vacuum chamber with the pressure better than 10À5 mbar The annealing at such high temperature will stabilize the structure of the sample The samples were then cooled in a field of kOe between the two poles of the VSM system from room temperature down to measurement temperature In the present study, the hysteresis loops were measured in a magnetic field up to 13.5 kOe at cryogenic temperature in both the in-plane and out-of-plane directions It should be noted that the applied field direction in the magnetization measurements is in the same direction as the cooling field, except for some cases of additional experiments that will be described in a later section Results (220) (200) Intensity (a.u) (111) Fig shows XRD patterns for [MnPd/Co]10 multilayers It is observed that MnPd is polycrystalline with fcc phase Meanwhile, almost no peak for Co is found It is likely caused by the less crystallinity formation of Co layers As a result, the average saturation magnetization of these samples is only 320 emu/cm3, much lower than that of Co bulk (about 1400 emu/cm3) Another possibility is that the thickness of Co layer is not thick enough for the detection of the diffraction peaks by XRD Hysteresis loops at 120 K for the sample series in which the Co thickness (tCo) is varied from 2.5 to 10 nm while the MnPd thickness (tMnPd) is fixed at 10 nm are shown in Fig The negative shifts of the hysteresis loops show that exchange bias effect exists in [MnPd/Co]10 multilayers in both the in-plane and out-of-plane directions Also, one can see the out-of-plane orientation of the Co layer magnetization in the samples with tCo o10 nm However, the sample with tCo ¼ 10 nm exhibits an inplane magnetic anisotropy (the last graph in Fig 2) This behavior unambiguously demonstrates that the easy axis of Co layer changes from the out-of-plane direction to the in-plane one with increasing the Co thickness x = 4.5 nm x = 3.5 nm x = 2.5 nm 25 30 35 40 45 50 2θ θ (deg.) 55 60 65 70 Fig X-ray diffraction patterns for [MnPd(10 nm)/Co(x nm)]10 (x ¼ 2.5, 3.5, 4.5 nm) multilayers with small incident angle (11) 3335 Shown in Fig are the hysteresis loops at 120 K for the sample series in which tMnPd is varied from 3.5 to 30 nm while keeping tCo at 3.5 nm The negative shifts of the hysteresis loops in both the in-plane and out-of-plane directions are also observable Concerning the preferential orientation of the Co layer magnetization, it is interesting to note that the easy axis of Co layer switches from the in-plane direction (in the sample with the smallest tMnPd, 3.5 nm, as seen in the first graph in Fig 3) to the out-of-plane one as tMnPd increases In order to know better about the preferential orientation of the Co layer magnetization at temperature higher than TB, hysteresis loops were measured at room temperature for the as-deposited samples Besides, the samples annealed at 590 K for in vacuum were also used in these experiments The results indicated that the out-of-plane magnetic anisotropy is present in most of the cases Especially for the multilayer with tMnPd ¼ 10 nm and tCo ¼ 7.5 nm, the in-plane anisotropy in the as-deposited sample switched to the out-of-plane one after annealing (see Fig 4) We have also carried out some additional hysteresis loop measurements at cryogenic temperature in which the FC process is similar to that described in a previous section but the measurement field is applied both perpendicular and parallel to the FC direction A representative result depicted in Fig for the sample with tMnPd ¼ 10 nm and tCo ¼ 5.5 nm shows a double shift of the out-of-plane hysteresis loop after the in-plane FC However, no loop shift was observed in the case of the in-plane hysteresis loop after the out-of-plane FC Discussion It should be noted that the blocking temperature is quite narrow for our multilayers and its value is around 240 K for all the samples as can be seen in Fig for some representatives where the temperature dependence of the HE is derived from the hysteresis loops measured at various temperatures Therefore, the effect of variation of blocking temperature leading to variation in the exchange bias properties which is usually observed in the literature can be negligible in the present cases From the hysteresis loops in Fig 2, the HE, the unidirectional anisotropy energy or exchange bias coupling energy (JK), the coercive field (HC) and the remanence-to-saturation magnetization ratio (MR/MS) for both the in-plane and out-of-plane cases at 120 K have been derived and are shown in Fig as a function of the Co thickness Here, JK was calculated by J K ¼ 12  HE  MS  t Co, where HE is the exchange bias field, and tCo and MS are the thickness and saturation magnetization of Co layer, respectively The factor of 12 in the above equation is because each Co layer has two interfaces It is worthwhile to note that from this figure the maximum values of the HE are huge, up to 1650 and 950 Oe for the out-of-plane and in-plane cases, respectively, and much higher than those reported in the previous studies for FePt/FeMn multilayers [10,11] Another behavior of this sample series is that the out-of-plane JK is larger than the in-plane one and JK reaches the maximum values of 0.17 and 0.15 erg/cm2 for the out-of-plane and in-plane cases, respectively, at the largest tCo Shown in Fig is the variation of the HE, the JK, the HC and MR/MS with the tMnPd for both the in-plane and out-of-plane cases at 120 K derived from the experimental curves in Fig Of interest are the opposite trends of HE in these two configurations Specifically, the out-of-plane HE increases with tMnPd from 3.5 to 7.5 nm, approaching a maximum value of 1650 Oe, and decreases gradually with increasing tMnPd larger than 7.5 nm On the contrary, a decrease in HE for the in-plane case can be seen clearly with increasing tMnPd from 3.5 to 7.5 nm down to ARTICLE IN PRESS 3336 N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 1.0 Out-of-plane In-plane Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 1.0 tCo = 5.5 nm tCo = 2.5 nm Out-of-plane In-plane Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 tCo = 7.5 nm tCo = 3.5 nm Out-of-plane In-plane 1.0 Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 tCo = 4.5 nm -10 -5 H (kOe) 10 tCo = 10 nm -10 -5 H (kOe) 10 Fig Out-of-plane and in-plane hysteresis loops at 120 K for [MnPd(10 nm)/Co(x nm)]10 (x ¼ 2.5, 3.5, 4.5, 5.5, 7.5, 10 nm) multilayers The out-of-plane loops were measured with the field applied along the film normal, while the in-plane loops were measured with the field applied in the film plane The applied field direction is in the same direction as the cooling field a minimum value of 250 Oe, followed by an increase with tMnPd over 7.5 nm These are very different from the results reported by Phuoc and Suzuki for FePt/FeMn multilayer system [10,11] We note here that by choosing appropriate tCo and tMnPd we can obtain samples with the out-of-plane anisotropy which have a nearly ‘‘pure’’ out-of-plane exchange bias, i.e the in-plane exchange bias is almost suppressed in the sample with the strong out-of-plane anisotropy The sample with tCo ¼ 3.5 nm and tMnPd ¼ 7.5 nm as mentioned above is a good example (see Figs and 8) This behavior is again rather unusual comparing with other works, e.g in [FeMn/FePt]10 multilayers [10] where both outof-plane and in-plane exchange biases are always coexistent As can be seen in Figs and 8, HC for the samples depends on both tCo and tMnPd Especially for the multilayers with large tCo and also small tMnPd, the opposite behavior of out-of-plane and inplane HC with tCo and also tMnPd reflects the modification of the anisotropy property in these samples Meanwhile, the values of the MR/MS which are obtained after recentering the loops for the HE also vary with tCo and tMnPd in response to the change of the anisotropy property The ratio of MR/MS obtained from the out-ofplane hysteresis loops for the samples with the out-of-plane anisotropy is rather high, up to 0.9 when the tMnPd is over 15 nm as shown in Fig Regarding the origin of the out-of-plane magnetic anisotropy, based on the fact that the out-of-plane magnetic anisotropy is already existent at room temperature and can be obtained in the case of the multilayer with tMnPd ¼ 10 nm and tCo ¼ 7.5 nm after annealing as mentioned above (Fig 4), we suggest that the out-ofplane magnetic anisotropy observed in most of our samples most likely comes from the formation of CoPd alloys at the interface between Co and MnPd layers This assumption is consistent with the previous studies on out-of-plane magnetic anisotropy in Co/Pd multilayers [15,16] These alloys are known to have extremely large negative magnetostriction constants and can experience significant tensile in-plane strains due to the lattice mismatch with MnPd layers in the multilayers leading to the out-of-plane orientation of the FM magnetization The existence of the in-plane anisotropy in the multilayer with the smallest tMnPd in the sample series with varying tMnPd (see Fig 3) may originate from the reduction of the tensile in-plane strains of CoPd alloys In other words, the spin switching between the in-plane and outof-plane directions in this sample series can be reversibly controlled by strain modulation through the inverse magnetostrictive effect [17] From the area enclosed between the in-plane and out-of-plane magnetization curves, the effective magnetic anisotropy (Keff) can be readily obtained A positive (or negative) Keff describes the case of a preferential direction of the FM magnetization along the out-of-plane (or in-plane) direction It is well established that the Keff could be phenomenologically separated into a volume contribution (KV) and a contribution from the interfaces (KS), and approximately described by Keff ¼ KV+2KS/tCo ARTICLE IN PRESS N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 1.0 3337 Out-of-plane In-plane Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 1.0 tMnPd = 10 nm tMnPd = 3.5 nm Out-of-plane In-plane Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 1.0 tMnPd = 5.5 nm tMnPd = 15.5 nm Out-of-plane In-plane Out-of-plane In-plane M/MS 0.5 0.0 -0.5 -1.0 tMnPd = 7.5 nm -10 -5 H (kOe) 10 tMnPd = 30 nm -10 -5 H (kOe) 10 Fig Out-of-plane and in-plane hysteresis loops at 120 K for [MnPd(y nm)/Co(3.5 nm)]10 (y ¼ 3.5, 5.5, 7.5, 10, 15.5, 30 nm) multilayers The applied field direction is in the same direction as the cooling field or KefftCo ¼ KVtCo+2KS [18] By combining this equation with the linear fit of the plot of the product Keff tCo versus tCo, one can readily deduce KV from the slope of the fit line and 2KS from the vertical axis intercept (see Fig 9) The value of KS obtained by this way for the sample series with varying tCo is about 0.6 erg/cm2, which is close to that reported by Engel et al [19] for Co/Pd multilayers (0.63 erg/cm3), while |KV| is in the order of 106 erg/cm3, which is much lower than that found in the literature [18] It should be noted that in the above calculations we have ignored the influence of the induced unidirectional anisotropy on the FM anisotropy, which is not simply the loop shifts The plot in Fig also indicates that the easy axis of Co layer transforms from the out-of-plane direction into the in-plane one as tCo passes a critical value of about nm Of interest is that this value is much larger than that in previous studies [18] as a result of the reduction of the Co layer magnetization which leads to a decrease in demagnetizing field, an opponent of the out-of-plane anisotropy Since MS is slightly different over the tCo range from 2.5 to 10 nm, the low saturation magnetization is not directly related to the low magnetization of CoPd interfacial alloys It is likely because the large entropy for these interfacial layers would disorder the Co layers, thus lowering its magnetization This magnetization disordering mechanism is similar to that observed in Co/Re multilayers [20] Another possibility is that the strains may give rise to the less crystallinity for Co layers Since MnPd layers are polycrystalline and not textured as determined from XRD, we assume that isotropic crystallographic orientation is present for these AF layers Upon the FC process, the interfacial AF spins are presumed to be frozen into the preferential bulk spin anisotropy axes which are closest to the orientation of the interfacial FM spins due to the bilinear exchange interaction between the FM spins and AF spins at the interface The reorientation of the interfacial AF spins or repopulation of the AF domains with the magnetic easy axes leading to uncompensated spins or net moments at the interface and forming AF regions locally oriented in various directions can induce a unidirectional anisotropy at the interface and give rise to exchange bias These AF regions are not necessarily AF domains in the strict thermodynamic sense, but rather are areas where the properties of the AF, most likely the orientation of the uncompensated AF spins at the interface, are modified due to the presence of the FM [21] Here, the FM domains are expected to be much larger than the AF regions so that each FM domain will feel the average effect of several of these AF regions and can be essentially treated as a separate sample [22] Then the uncompensated spins of various AF regions are distributed in a cone with a limited half-apex angle and the averaged direction of the uncompensated AF spins is along the direction of the FM spins Naturally, one may expect that the FM spins at the interface favor to align in the FC direction However in some cases, they are canted with the FC direction because our cooling field is not enough to entirely saturate the magnetization along the hard axis of the FM layer, especially for the samples with the strong out-ofplane magnetic anisotropy field cooled in the in-plane direction ARTICLE IN PRESS 3338 N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 Out-of-plane 1.0 1.2 In-plane 0.9 HE (kOe) M/MS 0.5 0.0 Out-of-plane 0.6 0.3 In-plane -0.5 0.0 -1.0 As-deposited 1.2 Out-of-plane 0.9 In-plane HE (kOe) 1.0 M/MS 0.5 Out-of-plane 0.6 In-plane 0.3 0.0 0.0 -0.5 120 -1.0 After annealing -10 -5 H (kOe) 10 Fig Out-of-plane and in-plane hysteresis loops at room temperature for [MnPd(10 nm)/Co(7.5 nm)]10 as-deposited and after-annealing multilayers 1.0 Out-of-plane M/MS 0.5 0.0 -0.5 HFC ⊥ Plane HFC // Plane -1.0 -10 -5 H (kOe) 10 Fig Out-of-plane hysteresis loops at 120 K for [MnPd(10 nm)/Co(5.5 nm)]10 multilayers field cooled in the out-of-plane and in-plane directions (see Fig 10) In these cases, with the out-of-plane FM easy axis, larger net moment components can be induced along the out-ofplane cooling field than those along the in-plane cooling field, leading to the higher out-of-plane HE than the in-plane one, and vice versa These arguments explain why the in-plane HE seems to 140 160 180 200 T (K) 220 240 260 Fig Temperature dependence of in-plane and out-of-plane exchange bias fields (HE) for (a) [MnPd(10 nm)/Co(4.5 nm)]10 and (b) [MnPd(10 nm)/Co(10 nm)]10 multilayers be suppressed in the sample with the strong out-of-plane magnetic anisotropy as mentioned above They are also in good agreement with the experimental results in most of the present cases, except for the case of [MnPd(30 nm)/Co(3.5 nm)]10 multilayer In this exception, the sample with the out-of-plane magnetic anisotropy, however, exhibits the smaller out-of-plane HE than the in-plane one (see Figs and 8) The orientation of the interfacial AF spins may not be strongly influenced by the orientation of the FM anisotropy as a result of the strong anisotropy of the thick AF layer [7] Moreover, some demagnetizing effects will tend to keep them in the film plane giving rise to smaller net moment components induced along the out-of-plane FC direction than those along the in-plane FC direction Based on the above reasons, the opposite trends of HE in the in-plane and out-of-plane configurations in the sample series with changing tMnPd as shown in Fig can be clarified As for [MnPd(10 nm)/Co(10 nm)]10 multilayer, since the FM anisotropy is expected to be very small, the cooling field is sufficient to completely saturate the FM magnetization in both the in-plane and out-of-plane directions leading to that the interfacial FM spins is along the FC direction Therefore, the fact that the inplane HE is nearly equal to the out-of-plane one as seen in Figs and 6b again confirms the bulk spin structure of the AF layers In order to explain the behavior of exchange bias in the sample series with varying tCo (see Fig 7), it should be noticed that the interfacial FM spins align in the FC direction when the cooling field is applied along the film normal The HE is usually expected to be inversely proportional to tCo above a certain Co thickness Thus, with tCo larger than 5.5 nm the out-of-plane HE decreases, indicating that this is an interfacial effect This is confirmed by the fact that JK for the out-of-plane case is only slightly different over ARTICLE IN PRESS N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 2.0 2.0 1.5 Out-of-plane HE (kOe) HE (kOe) 1.5 1.0 In-plane Out-of-plane 1.0 0.5 In-plane 0.5 0.0 0.12 0.0 Out-of-plane JK (erg/cm2) 0.15 JK (kOe) 3339 0.10 0.09 Out-of-plane 0.06 0.03 In-plane In-plane 0.05 0.00 4 Out-of-plane HC (kOe) HC (kOe) 0.00 Out-of-plane 2 1 In-plane 1.0 In-plane Out-of-plane 0.8 MR/MS 1.0 Out-of-plane 0.8 0.6 MR/MS 0.4 0.6 0.2 In-plane 0.4 0.0 0.2 In-plane 0.0 10 10 15 20 tMnPd (nm) 25 30 Fig MnPd thickness dependence of exchange bias field (HE), exchange bias coupling energy (JK), coercive field (HC) and remanence-to-saturation magnetization ratio (MR/MS) at 120 K for [MnPd/Co]10 multilayers tCo (nm) Fig Co thickness dependence of exchange bias field (HE), exchange bias coupling energy (JK), coercive field (HC) and remanence-to-saturation magnetization ratio (MR/MS) at 120 K for [MnPd/Co]10 multilayers this tCo range An increase in the out-of-plane HE with tCo below 5.5 nm may be related to the formation of CoPd interfacial alloys depending on the FM thickness in this range Meanwhile, an increase in the in-plane JK with tCo is obviously affected by the strong out-of-plane FM anisotropy and a tendency toward the inplane FM anisotropy with increasing tCo The discrepant behavior of the hysteresis loops as shown in Fig affirms that the FM anisotropy is clearly affected by the induced unidirectional anisotropy, i.e the competition between the FM and unidirectional anisotropies in the case of the in-plane FC and/or the enhanced out-of-plane magnetic anisotropy in the case of the out-of-plane FC These features may originate from the strong JK in our samples and they are rather unique compared ARTICLE IN PRESS 3340 N.H Dung et al / Journal of Magnetism and Magnetic Materials 320 (2008) 3334–3340 Keff (106 erg/cm3) 1.5 2KS KefftCo (erg/cm2) 1.0 sample and the sign for the net exchange bias for each of these domains is set by the direction of the magnetization of the FM domain, the FM spin canting results in both the negative and positive HE forming the double-shifted loop In a similar way, this argument also indicates why no shifted loop could be seen in the in-plane measurements after the out-of-plane FC 2 0.5 tCo (nm) 10 Conclusions KV 0.0 T = 120 K -0.5 tCo (nm) 10 Fig The plot of the product KefftCo versus tCo at 120 K for [MnPd(10 nm)/ Co(x nm)]10 (x ¼ 2.5, 3.5, 4.5, 5.5, 7.5, 10 nm) multilayers The sketches are taken from Johnson et al [18] The inset indicates the dependence of Keff on the Co thickness In summary, we have systematically examined both in-plane and out-of-plane exchange biases of the multilayers of [MnPd/Co]10 as a function of the thicknesses of MnPd and Co layers The results show a strong out-of-plane magnetic anisotropy originating from the interface anisotropy of MnPd/Co multilayers and also from the induced unidirectional anisotropy, and exchange bias coming from the spin structure at the interface which may be similar to that of the AF bulk In return, this strong out-of-plane anisotropy plays a vital role in the behavior of in-plane and out-of-plane exchange biases, and vice versa, suggesting that one must take into account the interplay between out-of-plane magnetic anisotropy and exchange bias when studying out-of-plane exchange biased systems FM domain Acknowledgement This work was supported by the State Program on Fundamental Research of Vietnam in the periods 2006–2007 (Grants 4.049.06 and 4.105.06) and 2008–2009 FM AF HFC References AF region HFC Direction of uncompensatedAF spins Averaged direction of uncompensated AF spins FM AF Fig 10 Sketch of the magnetic configurations at the interface in the multilayers with the out-of-plane anisotropy field cooled along the out-of-plane (a) and inplane (b) directions, and the corresponding configurations (c) and (d) simplified for explanation of exchange bias with previously published studies on out-of-plane anisotropy and exchange bias The existence of the double-shifted loop as seen in Fig 5, which rather looks like a symmetric double-shifted loop reported by Bruăck et al [21], is a further proof of the FM spin canting After the out-of-plane FC, the projection of the uncompensated AF spins to the out-of-plane direction is along the ‘up’ direction, leading to a single-shifted loop (see Fig 10a,c), while the small projection of the uncompensated AF spins to the out-ofplane direction is equally spread along the ‘up’ and ‘down’ directions due to the FM spin canting after the in-plane FC, giving rise to both the negative and positive HE (see Fig 10b,d) In other words, since each FM domain can be regarded as a separate [1] W.H Meiklejohn, C.P Bean, Phys Rev 102 (1956) 1413 [2] B Kagerer, Ch Binek, W Kleemann, J Magn Magn Mater 217 (2000) 139 [3] Ch Binek, B Kagerer, S Kainz, W Kleemann, J Magn Magn Mater 226–230 (2001) 1814 [4] S Matt, K Takano, S.S.P Parkin, E.E Fullerton, Phys Rev Lett 87 (2001) 087202 [5] C.H Marrows, Phys Rev B 68 (2003) 012405 [6] F Garcia, J Sort, B Rodmacq, S Auffret, B Dieny, Appl Phys Lett 83 (2003) 3537 [7] Z.Y Liu, J Magn Magn Mater 281 (2004) 247 ˜ ach, [8] J Sort, F Garcia, S Auffret, B Rodmacq, B Dieny, V Langlais, S Surin ˜ oz, M.D Baro´, J Nogue´s, Appl Phys Lett 87 (2005) 242504 J.S Mun [9] L Sun, P.C 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V Baltz, S Surin Adv Mater 17 (2005) 2978 [22] I.V Roshchin, O Petracic, R Morales, Z.-P Li, X Batlle, I.K Schuller, Europhys Lett 71 (2005) 297 ... of in- plane and out-of-plane exchange biases, and vice versa, suggesting that one must take into account the interplay between out-of-plane magnetic anisotropy and exchange bias when studying out-of-plane. .. of MnPd and Co layers The results show a strong out-of-plane magnetic anisotropy originating from the interface anisotropy of MnPd/ Co multilayers and also from the induced unidirectional anisotropy, ... coupling energy (JK), coercive field (HC) and remanence-to-saturation magnetization ratio (MR/MS) at 120 K for [MnPd/ Co] 10 multilayers this tCo range An increase in the out-of-plane HE with tCo