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Showing papers on "Antiferromagnetism published in 1995"


Journal ArticleDOI
15 Jun 1995-Nature
TL;DR: In this article, the authors examined the possibility that this effect is related to dynamical two-dimensional spin correlations, incommensurate with the crystal lattice, that have been observed in La2-SrxCuO4 by neutron scattering.
Abstract: ONE of the long-standing mysteries associated with the high-temperature copper oxide superconductors concerns the anomalous suppression1 of superconductivity in La2-xBaxCuO4 (and certain related compounds) when the hole concentration x is near . Here we examine the possibility that this effect is related to dynamical two-dimensional spin correlations, incommensurate with the crystal lattice, that have been observed in La2-xSrxCuO4 by neutron scattering2–4. A possible explanation for the incommensurability involves a coupled, dynamical modulation of spin and charge in which antiferromagnetic 'stripes' of copper spins are separated by periodically spaced domain walls to which the holes segregate5–9. An ordered stripe phase of this type has recently been observed in hole-doped La2NiO4 (refs 10–12). We present evidence from neutron diffraction that in the copper oxide material La1.6-xNd0.4SrxCuO4, with x = 0.12, a static analogue of the dynamical stripe phase is present, and is associated with an anomalous suppression of superconductivity13,14. Our results thus provide an explanation of the ' ' conundrum, and also support the suggestion15 that spatial modulations of spin and charge density are related to superconductivity in the copper oxides.

2,449 citations


Journal ArticleDOI
TL;DR: In this paper, a phenomenological view of spin fluctuations in heavy electron systems around their antiferromagnetic instability is discussed by using a sum rule for the dynamical susceptibility valid in the strong correlation limit.
Abstract: Spin fluctuations in heavy electron systems around their antiferromagnetic instability are discussed from a phenomenological point of view by using a sum rule for the dynamical susceptibility valid in the strong correlation limit. As a result the dynamical susceptibility takes the same form as in the standard spin fluctuation theory of weak itinerant antiferromagnetism, although the values for the parameters are substantially different from those in d-metals. The expression for the Neel temperature given in terms of the staggered magnetization at 0 K and the spin fluctuation parameters are successfully compared with experiment. Anomalous (non-Fermi liquid) behaviors reported for the specific heat and electrical resistivity in some heavy electron systems around their magnetic instabilities are explained in terms of this theory.

586 citations


Journal ArticleDOI
TL;DR: A two-cluster drifting state with zero magnetization forms spontaneously at very small temperatures; at larger temperatures an initial density modulation produces this state, which relaxes very slowly, which suggests the possibility of exciting magnetized states in a mean-field antiferromagnetic system.
Abstract: We study the dynamics of a fully coupled network of N classical rotators, which can also be viewed as a mean-field XY Heisenberg (HMF) model, in the attractive (ferromagnetic) and repulsive (antiferromagnetic) cases. The exact free energy and the spectral properties of a Vlasov-Poisson equation give hints on the values of dynamical observables and on time relaxation properties. At high energy (high temperature T) the system relaxes to Maxwellian equilibrium with vanishing magnetization, but the relaxation time to the equilibrium momentum distribution diverges with N as ${\mathit{NT}}^{2}$ in the ferromagnetic case and as ${\mathit{NT}}^{3/2}$ in the antiferromagnetic case. The N dependence of the relaxation time is suggested by an analogy of the HMF model with gravitational and charged sheets dynamics in one dimension and is verified in numerical simulations. Below the critical temperature the ferromagnetic HMF mode shows a collective phenomenon where the rotators form a drifting cluster; we argue that the drifting speed vanishes as ${\mathit{N}}^{\mathrm{\ensuremath{-}}1/2}$ but increases as one approaches the critical point (a manifestation of critical slowing down). For the antiferromagnetic HMF model a two-cluster drifting state with zero magnetization forms spontaneously at very small temperatures; at larger temperatures an initial density modulation produces this state, which relaxes very slowly. This suggests the possibility of exciting magnetized states in a mean-field antiferromagnetic system.

475 citations


Journal ArticleDOI
TL;DR: The magnetism of an insulator, located near the 10 K superconducting phase in the BEDT-TTF family, has been studied by NMR for the first time.
Abstract: The magnetism of an insulator, $\ensuremath{\kappa}$-(BEDT-TTF${)}_{2}$Cu[N(CN${)}_{2}$]Cl, situated near the 10 K superconducting phase in $\ensuremath{\kappa}$-type BEDT-TTF family, has been studied by ${}^{1}$H NMR for the first time. A commensurate antiferromagnetic ordering with a moment of (0.4--1.0) ${\ensuremath{\mu}}_{B}$/dimer was found below 26--27 K. The features, quite different from the conventional spin density wave, suggest that the magnetic order is driven by strong electron correlation rather than by nesting of the Fermi surface, and that the present salt is a Mott insulator. Magnetization measurements show spin canting parallel to the conducting layer below 23 K at low fields.

203 citations


Journal ArticleDOI
07 Apr 1995-Science
TL;DR: At high magnetic fields, a spin flop transition with a strong dependence on orientation was seen in the natural ferritin, providing evidence of antiferromagnetism in this system.
Abstract: Artificial ferritin has been synthesized with control of both the magnetic state (antiferromagnetic or ferrimagnetic) and the particle size over an ofer of magnitude in the number of iron atoms. The magnetic properties of the artificial ferritin were compared with those of natural horse spleen ferritin in a range of temperatures (20 millikelvin to 300 kelvin) and fields (1 nanotesla to 27 tesla). In the classical regime, the blocking temperature was found to correlate with the average particle size. A correlation was also observed in the quantum regime between the resonance frequency of macroscopic quantum tunneling of the Neel vector and the particle size. At high magnetic fields (to 27 tesla), a spin flop transition with a strong dependence on orientation was seen in the natural ferritin, providing evidence of antiferromagnetism in this system.

197 citations


Journal ArticleDOI
TL;DR: The structural analysis of the 5 \ifmmode\times\else\texttimes\fi{} 1 phase finds an increased atomic volume in combination with a complex reconstruction pattern with sinusoidal shifts and vertical buckling that points towards a structural instability of the ferromagnetic fcc phase.
Abstract: Ultrathin fcc Fe films on Cu(100) up to 5 monolayers (ML) show a peculiar structural arrangement that is intimately linked with the ferromagnetic coupling within the film. Our structural analysis of the 5 \ifmmode\times\else\texttimes\fi{} 1 phase finds an increased atomic volume in combination with a complex reconstruction pattern with sinusoidal shifts and vertical buckling. The atomic configuration differs considerably from the bulklike structure of the interior of antiferromagnetic Fe films above 5 ML. This points towards a structural instability of the ferromagnetic fcc phase.

196 citations


Book
01 Jan 1995
TL;DR: In this paper, the growth and characterization of hematite theory magnetization and susceptibility phase transitions heat capacity and other thermodynamic quantities electrical transport and optical properties elastic and magneto-elastic interactions electron magnetic resonance hyperfine interactions small particles and thin films surface and rock magnetism domains magnetization processes doped hematites.
Abstract: Crystal growth and characterization of hematite theory magnetization and susceptibility phase transitions heat capacity and other thermodynamic quantities electrical transport and optical properties elastic and magneto-elastic interactions electron magnetic resonance hyperfine interactions small particles and thin films surface and rock magnetism domains magnetization processes doped hematite.

176 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic properties of perovskite-type manganese oxide were investigated for a single-crystal compound and the magnetic field-induced insulator-to-metal transition was shown to be irreversible.
Abstract: Magnetotransport properties were investigated for a crystal of perovskite-type manganese oxide, Pr 1- x Ca x MnO 3 ( x =0.3). The single-crystal compound is insulating and below 220 K shows the charge-ordering of Mn 3+ and Mn 4+ species. Application of a magnetic field (>20 kOe) changes a canted antiferromagnetic insulating state into a ferromagnetic metallic state accompanied by change of resistivity by several orders of magnitude. At low temperatures, e.g. , <50 K, the hysteresis of the transition field is pronounced and the field-induced insulator-to-metal transition becomes irreversible.

163 citations


Journal ArticleDOI
TL;DR: It is argued that competing exchange interactions are a general feature of organic charge transfer compounds, and that they increase the temperature at which a spin-Peierls transition takes place.
Abstract: The magnetic properties of CuGeO{sub 3}are shown to be well described by the one-dimensional Heisenberg {ital S}={ital cf};1;2 model with competing antiferromagnetic interactions. Provided that the competing exchange is moderately large but smaller than the critical value required to produce a gap in the excitation spectrum without lattice dimerization, the model agrees with a variety of experimental properties. It is argued that competing exchange interactions are a general feature of organic charge transfer compounds, and that they increase the temperature at which a spin-Peierls transition takes place.

162 citations


Journal ArticleDOI
TL;DR: The record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system.
Abstract: Record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system. At 125 K, the CMR of the La0.5Ca0.5MnO3 reaches nearly 1 000 000%. It increases exponentially to 100 000 000% at 57 K. While the ground state is primarily an antiferromagnet, application of a magnetic field induces a ferromagnetic alignment of spins that is highly beneficial to the electron conduction. Other ferromagnetic samples exhibit very sharp magnetic phase transitions, with which the magnetotransport is closely correlated.

157 citations


Journal ArticleDOI
01 Dec 1995-EPL
TL;DR: In this article, elastic and inelastic-neutron-scattering experiments were performed on a single crystal of the quasi-one-dimensional system CuGe0.993Si0.007O3.
Abstract: We have performed elastic- and inelastic-neutron-scattering experiments on a single crystal of the quasi-one-dimensional system CuGe0.993Si0.007O3. Our experimental data show unambiguously that both quasi-gapless antiferromagnetic fluctuations and gapped magnetic fluctuations, associated with a dimerized phase, coexist in this material below a spin-Peierls transition temperature TSP ≈ 9.2 K. When the temperature is lowered below TN ≈ 4 K, part of the system undergoes a new phase transition towards long-range antiferromagnetism, coexisting with the dimerized non-magnetic phase. We will describe the temperature and wave vector dependences of magnetic responses in these two phases, which can be understood as the superposition of two independent spectra.

Journal ArticleDOI
TL;DR: The magnetic properties of ThCr2Si2-type structure RMn2Ge2 (R = Ce, Pr, Nd) compounds have been investigated by the use of neutron diffraction experiments.

Journal ArticleDOI
TL;DR: In this paper, the thermal dependence of the Mn sublattice magnetic orderings within the RMn 2 X 2 (X = Si, Ge) compounds is proposed, and the occurrence of an in-plane antiferromagnetic Mn component (obviously correlated with a critical MnMn intralayer spacing value of ∼ 2.87 A ) over the whole ordered range leads to strongly revise the ferromagnetic ordering previously proposed to take place in such compounds.

Journal ArticleDOI
01 Sep 1995-Nature
TL;DR: In this paper, a hole-doped two-chain spin-ladder compound, La1a¤-xSrxCuO2.5, was synthesized.
Abstract: A SPIN-½ Heisenberg antiferromagnetic ladder is a model system comprising parallel chains of interacting elemental spins. Spin ladders having an even number of chains have been predicted1a¤-6 to exhibit interesting dynamics, including superconductivity, when unoccupied spin sites are introduced along the chain (that is, when the chains are doped with holes). Spin-ladder models thus provide a novel potential mechanism for high-temperature superconductivity in real materials. But unfortunately materials with spin-ladder structure are quite rare4a-10, and the few known compounds have not previously been doped successfully with holes. Here we report the high-pressure synthesis of a new hole-doped two-chain ladder compound, La1a¤-xSrxCuO2.5. We have observed a marked insulator-to-metal transition in this compound with increased doping, but no superconducting transition down to 5 K. The absence of superconductivity in this material must be reconciled with theoretical predictions based on ideal hole-doped spin-ladder models.

Journal ArticleDOI
TL;DR: In this article, dilute 57 Fe Mossbauer spectroscopy studies of RMn 2 X 2 (X = Si or Ge, R = La, Ce, Pr, Nd, Sm and Gd) at temperatures 4.2-650 K were conducted.

Journal ArticleDOI
TL;DR: It is suggested that the magnetic susceptibility, the temperature dependence of the spin gap, and the spin-Peierls transition temperature of this material can be reasonably described by including nearest and next-nearest-neighbor antiferromagnetic interactions along the chain.
Abstract: We study numerically, using a one-dimensional Heisenberg model coupled to the lattice in the adiabatic approximation, the spin-Peierls transition in the linear ${\mathrm{Cu}}^{2+}$ spin-1/2 chains in the inorganic compound ${\mathrm{CuGeO}}_{3}$, which has been recently observed experimentally. We suggest that the magnetic susceptibility, the temperature dependence of the spin gap, and the spin-Peierls transition temperature of this material can be reasonably described by including nearest and next-nearest-neighbor antiferromagnetic interactions along the chain. We estimate that the nearest-neighbor exchange parameter J is approximately 160 K, and that the next-nearest-neighbor exchange parameter is approximately 0.36J.

Journal ArticleDOI
TL;DR: In this article, powder neutron diffraction was used to determine the underlying antiferromagnetic component of the structure of the M"O6 octahedra and showed that they are weakly ferromagnetic.
Abstract: N&MI1P04*H20 (MI1 = Mn, Fe, Co, Ni) and KM"PO4qH20 (MI1 = Mn, Co, Ni) have been prepared and characterized by X-ray powder diffraction and bulk magnetometry, and the corresponding deuterio compounds, by neutron powder diffraction. They are isomorphous (space group Pmn21). The divalent metal ions form approximately square-planar layers of comer-sharing octahedra, the layers being bound by hydrogen bonds in the ammonium compounds and by electrostatic interactions in the potassium ones. In all cases, the M"O6 octahedra are severely distorted, the point symmetry being C2". Bulk susceptibility measurements on NH4FeP04eH20, N&MnP04aH20, and KMnP04*H2O show they are weakly ferromagnetic, with Nee1 temperatures of TN = 24.0(2), 17.5(3), and 18.0(3) K, respectively. Powder neutron diffraction was used to determine the underlying antiferromagnetic component of the structures. All three materials have simple two-sublattice structures, with the antiferromagnetic moments along &[OlO], perpendicular to the plane of the metal-containing layers. Analysis using the irreducible representations of the space group shows that the ferromagnetic moments are parallel to [OOl].

Journal ArticleDOI
TL;DR: In this paper, the static structure factor in the two-dimensional spinS = 1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2 was investigated.
Abstract: We have carried out a neutron scattering investigation of the static structure factorS(q 2D ) (q 2D is the in-plane wave vector) in the two-dimensional spinS=1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2. For the spin correlation length ξ we find quantitative agreement with Monte Carlo results over a wide range of temperature. The combined Sr2CuO2Cl2-Monte Carlo data, which cover the length scale from ≈1 to 200 lattice constants, are predicted without adjustable parameteres by renormalized classical theory for the quantum nonlinear sigma model. For the structure factor peakS(0), on the other hand, we findS(0)∼ξ 2 for the reduced temperature range 0.16

Journal ArticleDOI
TL;DR: The magnetoresistance of the FeRh alloy has been measured in the temperature range 200-300 K using high pulsed magnetic fields up to 36 T as mentioned in this paper, where the magnetic transition from the antiferromagnetic (AF) low temperature state to the ferromagnetic high temperature state at TAF −F =405 K was shown to be accompanied by a giant magnetoregressive effect (ΔR/R≊50%).
Abstract: The magnetoresistance of the FeRh alloy has been measured in the temperature range 200–300 K using high pulsed magnetic fields up to 36 T. This compound shows a first‐order magnetic transition from the antiferromagnetic (AF) low‐temperature state to the ferromagnetic (F) high‐temperature state at TAF–F=405 K. The F state is very close in energy to the AF state and can be reached by applying a magnetic field. The measurements made within the AF state show that the AF–F transition is accompanied by a giant magnetoresistance effect (ΔR/R≊50%).

Journal ArticleDOI
TL;DR: In this article, the magnetic phase diagrams for (Fe 1− x Ni x )Rh and for Fe(Rh 1 − x Pd x ) are determined for modified FeRh compounds with iron atoms partly substituted for nickel and with rhodium atoms substituted for palladium and iridium.

Journal ArticleDOI
TL;DR: The perovskite-like antiferromagnetic compound YBaCuFeO{sub 5} was studied by powder neutron diffraction, magnetic susceptibility measurements, and Moessbauer spectroscopy.

Journal ArticleDOI
TL;DR: The f-electrons in rare earth and actinide intermetallic compounds are responsible for a rich variety of novel superconducting and magnetic states that have been discovered during the past two decades.
Abstract: The f-electrons in rare earth and actinide intermetallic compounds are responsible for a rich variety of novel superconducting and magnetic states that have been discovered during the past two decades. In this paper, we briefly review these remarkable superconducting and magnetic states, how they are believed to originate, and the f-electron materials in which they are found. Examples of phenomena that are produced by superconducting-magnetic interactions in certain ternary and quaternary rare earth compounds include the coexistence of superconductivity and antiferromagnetism, the destruction of superconductivity by the onset of ferromagnetism at a second critical temperature Tc2 below the superconducting critical temperature Tc1, accompanied by a new sinusoidally modulated magnetic state that coexists with superconductivity in a narrow temperature interval above Tc2, and the induction of superconductivity by the application of high magnetic fields. Multiple superconducting phases have been discovered in several U “heavy fermion” compounds, f-electron materials in which the electrons have enormous effective masses as high as several hundred times the mass of the free electron. The multiple superconducting phases are apparently the result of the interaction of an unconventional superconducting state with a coexisting weakly antiferromagnetic state. This unconventional superconducting state is presumed to involve electrons that are paired in states with angular momentum greater than zero via antiferromagnetic spin fluctuations, and is similar to the superconducting state that is believed by many (but not all!) researchers to be responsible for high-Tc superconductivity in the cuprates.


Journal ArticleDOI
10 Jun 1995-EPL
TL;DR: In this article, the authors investigated Haldane's conjecture for the S = 2 antiferromagnetic quantum spin chain with nearest-neighbour exchange and showed that the ground state has hidden topological order.
Abstract: We have investigated Haldane's conjecture for the S = 2 antiferromagnetic quantum spin chain with nearest-neighbour exchange J Using a density matrix renormalization group algorithm for chains up to L = 350 spins, we show that the ground state has hidden topological order: the physics of the S = 2 chain can be captured by a valence bond solid description We also observe effective free spin-1 states at the ends of an open S = 2 chain We find in the thermodynamic limit a gap Δ = 0085(5) J and a spin correlation length ξ = 49(1) lattice spacings in the isotropic case We give the phase diagram in the presence of single-ion and exchange anisotropy, showing how the Haldane phase is squeezed out when the spin S increases

Journal ArticleDOI
TL;DR: In this article, the authors investigated Haldane's conjecture for the S = 2 isotropic antiferromagnetic quantum spin chain with nearest-neighbor exchange J and showed that the ground state has a hidden topological order that is revealed in a nonlocal string correlation function.
Abstract: We have investigated Haldane's conjecture for the S=2 isotropic antiferromagnetic quantum spin chain with nearest-neighbor exchange J. Using a density matrix renormalization group algorithm for chains up to L=350 spins, we find in the thermodynamic limit a finite spin gap of Delta = 0.085(5)J and a finite spin-spin correlation length xi = 49(1) lattice spacings. We establish the ground state energy per bond to be E_0=-4.761248(1)J. We show that the ground state has a hidden topological order that is revealed in a nonlocal string correlation function. This means that the physics of the S=2 chain can be captured by a valence-bond solid description. We also observe effective free spin-1 states at the ends of an open S=2 chain.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the magnetic susceptibility χ and the 59 Co Knight shift 59 K in a single ion model with the low-spin 1 A 1 ground state above which the high-spin 5 T 2 state is located was analyzed.
Abstract: 59 Co and 139 La NMR measurements have been performed to study the microscopic magnetic properties closely related with the spin state of a trivalent cobalt ion in LaCoO 3 . The temperature-independent 59 Co and 139 La Knight shifts below ∼ 30 K clearly revealed the presence of a nonmagnetic ground state at low temperatures. We calculated the temperature dependence of the magnetic susceptibility χ and the 59 Co Knight shift 59 K in a single ion model with the low-spin 1 A 1 ground state above which the high-spin 5 T 2 state is located. Then, both the trigonal crystal-field and spin-orbit interactions are taken into account. From this analysis, we infer the presence of an antiferromagnetic exchange interaction between the high-spin states. The characteristic temperature dependence of the 59 Co hyperfine coupling constant is also discussed.

Journal ArticleDOI
TL;DR: In this paper, the structural rearrangements of the (111) surface in the system Cr2O3(111)/Cr(110) as a function of temperature were investigated by means of low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS).
Abstract: Structural rearrangements of the (111) surface in the system Cr2O3(111)/Cr(110) as a function of temperature were investigated by means of low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS). At room temperature, one observes a simple (1*1) LEED pattern of the clean (111) surface. If the temperature was lowered to 150 K a ( square root (3)* square root (3))R30 degrees superstructure was observed. The structure reached its maximum intensity at about 150 K substrate temperature. Below 150 K the superstructure vanished again and the simple (1*1) LEED pattern of the (111) surface was recovered at 90-100 K. Parallel to this, a considerable change in the electron energy loss spectra with varying temperature was observed. With the help of quantum-chemical cluster calculations the low-energy excitations in the range between 0.8 and 2.5 eV were assigned to local d-d excitations of Cr3+ ions at the Cr2O3(111) surface. Some of these peaks were quenched upon adsorption of gases such as CO, NO or CO2. We propose a model of two successive phase transitions the first of which is a disorder-to-order transition above 150 K whereas the second is an order-to-order transition below 150 K. The transitions may be driven by antiferromagnetic coupling of the surface chromium ions to those in the second layer.

Journal ArticleDOI
10 Jun 1995-EPL
TL;DR: In this paper, a qualitative interpretation of the phase diagram (T, x) is given, where the Si doping has a drastic effect on the spin-Peierls temperature TSP which decreases at TSP (x)/TSP (0) 1-50x at low Si concentrations.
Abstract: We have performed magnetic-susceptibility measurements and Cu nuclear-magnetic-resonance studies on single crystals of the quasi-one-dimensional antiferromagnet CuGe1-xSixO3, with 0 ≤ x ≤ 0.1. The Si doping has a drastic effect on the spin-Peierls temperature TSP which decreases at TSP (x)/TSP (0) 1-50x at low Si concentrations. For x ≥ 0.005, three-dimensional antiferromagnetic order with an easy axis along the Cu chains takes place below a well-defined Neel temperature TN. A qualitative interpretation of the phase diagram (T, x) is given.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of new Heusler alloys Ru 2 MnZ (Z  Si, Ge, Sn and Sb) were calculated to examine magnetic properties and it was shown that an antiferromagnetic state is stable for these alloys.
Abstract: Electronic structures of new Heusler alloys Ru 2 MnZ (Z  Si, Ge, Sn and Sb) were calculated to examine the magnetic properties. In this paper, it will be shown that an antiferromagnetic state is stable for these alloys, where the Mn magnetic moments are aligned ferromagnetically in the (111) plane and antiparallel along the [111] direction. It will also be shown that the alloys Ru 2 MnZ (Z  Si, Sb) can be half-metallic in a ferromagnetic phase.

Patent
Stuart S. P. Parkin1
15 May 1995
TL;DR: In this paper, the magnetic moments of the magnetic layers can lie only parallel or antiparallel to a single axis and each layer has its magnetic moment responsive to an external magnetic field strength that is different from the magnetic field strengths at which the other ferromagnetic layers are responsive.
Abstract: A magnetoresistive (MR) sensor based on the giant magnetoresistance (GMR) effect provides a digital output signal. The multilayer stack of alternating ferromagnetic layers and nonferromagnetic metal spacer layers in the GMR sensor has an essentially single crystalline structure so that each of the ferromagnetic layers exhibits uniaxial magnetic anisotropy, i.e. the magnetic moments of the ferromagnetic layers can lie only parallel or antiparallel to a single axis. Unlike GMR multilayers where all of the magnetic moments are affected simultaneously by the external magnetic field, in the present GMR sensor each ferromagnetic layer has its magnetic moment responsive to an external magnetic field strength that is different from the magnetic field strengths at which the magnetic moments of the other ferromagnetic layers are responsive. This allows each ferromagnetic layer to switch its magnetization direction from parallel to antiparallel, or vice versa, independently of the other ferromagnetic layers. This unique property of each ferromagnetic layer is accomplished by either selecting each ferromagnetic layer to have a different uniaxial magnetic anisotropy energy, such as by varying the strain during crystalline growth, or by subjecting each ferromagnetic layer to a different value of antiferromagnetic exchange coupling energy, such as by varying the thicknesses of the nonferromagnetic metal spacer layers. As a result, the resistance of the GMR sensor changes in stepped increments as the external magnetic field is varied, thereby providing a digital signal output. The digital GMR sensor can be used as a read head in a multiple data layer magnetic recording data storage system. In one disk drive embodiment, the magnetic recording disk has two magnetically isolated and decoupled magnetic data layers. The digital GMR sensor reads the written data bits from both data layers simultaneously, and it's digital output signal is then decoded by conventional logic circuitry to provide the separate data recorded in each of the data layers.